chapter 1 - universidad autónoma...
TRANSCRIPT
CHAPTER 1. AQUEOUS PROCESSING SYSTEMS
1.1. Introduction.................................................................................................. 1
1.2 Aqueous Processing Technologies.................................................................... 21.2.1 Fields of Application and Academic Homes.................................... 21.2.2 Mineral Processing........................................................................... 41.2.3 Hydrometallurgical Extraction......................................................... 121.2.4 Ceramic Aqueous Processing........................................................... 221.2.5 Catalyst Preparation.......................................................................... 291.2.6 Emulsion-based Photographic Technology...................................... 311.2.7 Surface Finishing ............................................................................. 341.2.8 Semiconductor Device Microfabrication.......................................... 411.2.9 Cement Technology.......................................................................... 481.2.10 Battery Technology.......................................................................... 491.2.11 Solar Energy Conversion and Photoelectrochemical Processing..... 511.2.12 Waste Treatment and Control........................................................... 52
1.3 Common Denominators in Aqueous Processing............................................. 55
1.3.1 Integrated Processing...................................................................... 551.3.2 Reagents, Solutions, and Materials................................................. 561.3.3 Unit Processes................................................................................. 561.3.4 Physicochemical Processes............................................................. 57
______________________________________________________________________________1.1 Introduction
Our physical well-being depends, in part, on our ability to take raw materials from the earth and transform them into technologically useful materials. The raw materials include naturally occurring minerals (commercially useful mixtures of which are called ores), coal and crude oil (sources of energy and chemicals), and water (the premier solvent and transport medium). By processing, we refer to the various physical and chemical steps that connect ores to refined metals and to engineered materials. And in Aqueous Processing, in particular, our focus is on water-based chemical process technologies.
Water is the most abundant solvent, and it has some unique properties, which facilitate the dissolution of solids, while at the same time leaving room (under changed conditions) for the reverse process of solid formation from solution (crystallization and precipitation) to occur. Water is also a convenient vehicle for the solubilization and transport of ions and molecules, as well as for the suspension and transport of fine particles. The unique properties of water that make these processes feasible include: (a) a relatively high dielectric constant, which stabilizes ionic species, (b) the ability to donate and to receive protons (H+), which enables it to interact with a wide variety of chemical species, (c) the relatively high chemical and physical stability under ordinary conditions of temperature and pressure.
1.2 Aqueous Processing Technologies1.2.1 Fields of Application and Academic Homes
Aqueous processing is practiced in a wide variety of technological fields, as demonstrated in the non-exhaustive list provided in Figure 1.1. Traditionally, there has been a tendency to organize the different fields of application into different academic disciplines or majors. For example, aqueous processing applications in mineral processing are taught in departments and sub-departments with names such as: Mineral Processing, Mineral Engineering, and Metallurgical Engineering. Ceramic applications of aqueous processing are confined to departments of Ceramic Science and Engineering and departments of Materials Science and Engineering. Aqueous chemical aspects of cement technology are taught in Ceramic Science and in Civil Engineering programs, catalyst preparation is taught in Chemical Engineering, and waste treatment in departments of Environmental Engineering. Wet chemical processing in semiconductor device microfabrication is found in departments of Electronic and Electrical Engineering.
Figure 1.1 Aqueous processing technologies
One advantage of the established situation is that the student is exposed to aqueous processing in context, i.e., there can be immediate connection with the student's chosen field. Unfortunately, however, this approach to technical education is not without some disadvantages. First of all, many aqueous-oriented students may be completely unaware that in other academic departments (sometimes, housed literally next door) fellow students are tackling problems that are quite similar to theirs. The similarity may be in terms of materials, reagents, equipment, or process chemistry. So what happens then? Someone loses, who might otherwise benefit from the insights of the other group. There is unnecessary reinvention of the wheel; progress is slowed, while the answer to our problem lies idle next door; we congratulate ourselves for achievements, which are really no breakthroughs. Secondly, university educators have to come to grips with the fact that we are not just educating for today but for tomorrow. What kind of tomorrows do we see? In the future that is before us, an increasingly important requirement is flexibility; that is, a student's education should make him/her flexible in approaching problems. Part of this flexibility is acquired by gaining an early appreciation for the variety in the kinds of problems that a particular tool can tackle, and the variety in the tools (i.e., alternative tools/concepts/strategies/technologies) that can be brought to bear on a particular problem. We become acquainted with this variety, in part, by learning to look over our shoulders at our colleagues in other, but related majors. As we move towards the 21st century we have to consider the real possibility that the needs of the future may require that we reconfigure the traditional majors of technical education. The need for realignment, of course, is not a new phenomenon, and neither is it, at present, confined only to what one might call the applied fields. The pure sciences are confronted with a similar situation; for example, the traditional distinctions between solid-state chemistry and solid-state physics are becoming increasingly diffuse:
For many years the study of the electronic structure and properties of solids has been regarded as thepreserve of physicists. Chemists, who spend a good deal of time and effort looking at electronic structuresof molecules, have tended to avoid these aspects of solids. The situation is changing, however, and therehas recently been an upsurge of interest in those aspects of solid-state chemistry that have to do withelectronic properties and their relation to chemical bonding. In part, this change is due to the discovery of new classes of solids with unusual and surprising properties. Many of these investigations have beencarried out by teams of chemists and physicists working together, and such collaboration is slowly helpingto break down the traditional barriers between these two disciplines. (Cox, 1987, p.v).
Thirdly, and on a more pragmatic level, we should also be concerned about the employability of the students that pass through our educational factories. In the U.S., companies lay off their employees when the economic situation gets tough. When you are laid off, can you dust off your resume and repackage it attractively and solidly for a new prospective employer? That is, are you aware of the variety in the kinds of problems that your tools can tackle?
AQUEOUS PROCESSING
MAT. SCI & ENG.
MINERAL PROCESS.
HYDRO- MET
CERAMIC AQUEOUS PROCESS.
ENVIRON- MENTAL ENG.
CHEM. ENG.
CIVIL ENG.
ELECTRON. ENG.
Figure 1.2 The many mansions of aqueous processing.
This book is an invitation to join in breaking down the walls of our academic ghettos. Jesus said: In God's house there are many mansions. They are all yours: enter by the main gate above and all the rooms will be open before you (see Figure 1.2). Insist on entering by the individual doors below, and you are in danger of being boxed in by your major.
1.2.2 Mineral ProcessingIn mineral processing technology (Figure 1.3), the overall objective is to use physical and chemical
techniques to separate a solids feed of ores into a concentrate (which contains the minerals of commercial value) and the gangue (which is a collection of the waste solids of little immediate commercial value). Typically, no bulk chemical changes are effected, so that any chemical transformations that occur tend to be confined to the solid surfaces. Three processes used in mineral processing, and which fall within the scope of our present discussion of aqueous processing are flotation, flocculation, and dispersion (Table 1.1). All three may be viewed as involving interfacial or adsorptive processing.
Flotation is a particulate separation method in which particles with appropriately prepared surfaces attach themselves to gas bubbles, and are thereby parachuted upwards (floated) from the aqueous phase. Three main types of reagents are used: collectors, frothers, and regulators. Collectors and frothers are members of a class of molecules called surfactants. Table 1.2 shows the structures of selected flotation surfactants. The molecular structure of a surfactant is characterized by the simultaneous presence of both a nonpolar (i.e., hydrophobic or water-hating) group and a polar (i.e., hydrophilic or water-loving) group (e.g., -NH2, -SO3). By adsorbing at the solid/aqueous interface, a collector imparts an oil-like
character (hydrophobicity) to the surface
COMMINUTION
CLASSIFICATION
CONDITIONING
FLOTATION
ORE
CONCENTRATE
GANGUE
REGULATORS, COLLECTORS, DISPERSANTS
SOLID/LIQ. SEP'N
SOLID/LIQ. SEP'N
FROTHERS, AIR
FLOCCULANT
Figure 1.3 A schematic flowsheet for mineral processing
Table 1.1 Unit processes in aqueous processing systems
Mineral Processing Flotation Semiconductor Processing Polishing, Wet ChemicalFlocculation Cleaning, Etching,Dispersion Chemical-MechanicalConditioning Planarization
Hydrometallurgy Leaching Surface Finishing Alkaline CleaningFlocculation Emulsion CleaningPrecipitation ElectropolishingCrystallization ElectroplatingAdsorption Chemical (Electroless) PlatingIon Exchange AnodizationSolvent Extraction Pickling, PhosphatizingElectrowinning ChromatizingElectrorefining
Ceramic Processing Precipitation Environmental Eng. Soil WashingDispersion Precipitation, Ion ExchangeFlocculation Coagulation, FlocculationCoagulation LeachingSlip CastingGel Casting Battery Technology Synthesis of Cathode/AnodeTape Casting MaterialsLeaching Discharging, Recharging
Catalyst Preparation Precipitation Photographic Technology Precipitation of Silver HalidesAdsorption Fixing, DevelopingInfiltration
and this facilitates the removal of collector-coated particles from the aqueous phase (Figure 1.4). The
contact angle at the solid/water/air boundary provides a measure of the hydrophobicity/hydrophilicity of
a surface (Figure 1.4). Frothers adsorb at the gas/aqueous interface and thereby exercise a major
influence on the rate of particle-bubble attachment. Table 1.3 (Leja, p.225) provides a collection of
common flotation reagents, with corresponding applications. As indicated in Table 1.3, regulators tend
to be inorganic reagents, although some organics, such as starch and tannic acid are also utilized.
Regulators are used for a variety purposes, e.g., to control pH, modify the solid/aqueous interfacial
charge, alter oxidation states of surface or aqueous phase atoms, and alter concentrations via
precipitation or complexation. Regulators are called activators if they enhance collector adsorption and
depressants if they have the opposite effect.
Table 1.2 Structures of typical flotation surfactants
Solid particles in water usually carry surface charges. These charges are acquired through the ionization of surface groups or adsorption of charged species. For example, in the case of a metal oxide surface (-MO), the surface charging process involves the following steps: (a) surface hydration, resulting in the formation of surface hydroxyl groups -MOH(s) (Equation 1.1), (b) surface deprotonation, resulting in the formation of negatively charged surface groups (Equation 1.2), and surface protonation, giving positively charged surface groups (Equation 1.3):
Figure 1.4
-MO(s) + H2O = -M(OH)2(s) (1.1)-MOH(s) = -MO-(s) + H+(aq) (1.2)-MOH(s) + H+(aq) = -MOH2
+(s) (1.3)
When a suspension of particles is allowed to stand, the larger particles tend to settle out, under the influence of gravitational forces. However, the particles of colloidal dimensions (~ 1m) will remain suspended. It is then said that we have a stable dispersion (Figure 1.5). Also, dispersants, compounds which promote particle dispersion (by increasing surface charge or by providing adsorbed films which act as steric barriers) may be added. A dispersion may be destabilized by introducing coagulants, typically inorganic salts or flocculants, long-chain organic molecules with molecular weights in the range of 104-107. These molecules have repeat units which carry functional groups that are capable of adsorbing on particle surfaces. The multiple attachments produce particle aggregates which settle out of the liquid phase. Table 1.4 presents a classification of some of the common flocculants and Table 1.5 shows structures of some flocculants.
Table 1.3 Typical flotation reagents and their applications (Leja, 1982)
Type Classification and Composition
Usual form of additions Typical Applications and Some Properties
Collectors Xanthates
1. Ethyl-NaEthyl-K
10% solution }10% solution
For selective flotation of Cu-Zn, Cu-Pb-Zn sulfide ores
2. Isopropyl-NaIsopropyl-K
10% solution }10% solution
More powerful collector than ethyl for Cu, Pb, and Zn ores, Au, Ag, Co, Ni, and FeS2
3. Amyl-K secondaryAmyl-K
10% solution }10% solution
Most active collector but not very selective; used for tarnished sulfides (with Na2S), Co-Ni sulfides
Dithiophosphates, Aerofloats
1. Diethyl-Na 5-10% solution For the Cu and Zn (but not Pb) sulfide ores; selective, nonfrothing
2. Dicresyl, 15% P2S5Dicresyl, 25% P2S5Dicresyl, 31% P2S5
UndilutedUndilutedUndiluted
Ag-Cu-Pb-Zn sulfides, selective, frothsAg-Cu-Pb-Zn sulfides, selective, frothsMainly used for PbS and Ag2S ores
3. Di-sec-butyl-Na 5-10% solution Au-Ag-Cu-Zn sulfides; not good for Pb
Thionocarbamate, ethylisopropyl (Z-200)
Liquid emulsion Selective collector for Cu sulfides (or Cu-activated ZnS) in the presence of FeS2
Mercaptobenzothiazole Solid Floats FeS2 in acid circuits (pH 4-5)
Fatty acids
1. Tall oil (mainly oleic acid)
Collectors for fluorspar, iron ore, chromite, scheelite, CaCO3, MgCO3,
2. Refined oleic acid apatite, ilmenite; readily precipitated by3. Na soap of fatty acids "hard" waters (Ca2+ and Mg2+)Alkyl sulfates and sulfonates C12-C16 (dodecyl to cetyl)
5-20% solution Collectors for iron ores, garnet, chromite, barite, copper carbonates, CaCO3, CaF2, BaSO4, CaWO4
Cationic reagents
1. Primary andsecondary amines
2. Amine acetates3. Quaternary
ammonium salts
In kerosene
5-10% solution5-10% solution
Used to separate KCl from NaCl and to float SiO2Used to float quartz, silicates, chalcopyriteUsed to float quartz, silicates, chalcopyrite
Frothers Pine oil (-terpineol) Undiluted Provides most viscous stable froth
Cresylic "acid" (cresols) Undiluted Less viscous but stable froth; some collector action
Polypropylene glycols
MW ~ 200 (D-200) Solutions in H2O Fine, fragile froth; inert to rubber
MW ~ 250 (D-250) Solutions in H2O Slightly more stable froth than with D-200
MW ~ 450 (D-450) Solutions in H2O Slightly more stable froth than with D-250
Polyoxyethylene(nonyl phenol)
Undiluted Used as calcite dispersant in apatite flotation
Aliphatic alcohols: e.g., MIBC, 2-ethyl hexanol
Undiluted Fine textured froth; used frequently with ores containing slimes
Ethers (TEB, etc.) Undiluted
Regulators Lime (CaO) or slaked lime Ca(OH)2
Slurry pH regulator; depresses FeS2 and pyrrhotite
Soda Ash, Na2CO3 Dry pH regulator; disperses gangue slimes
Caustic soda, NaOH 5-10% solution pH regulator; disperses gangue slimes
Sulfuric acid, H2SO4 10% solution pH regulator
Cu2+ (CuSO4 · 5H2O) Sat. solution Activates ZnS, FeAsS, Fe1-xS, Sb2S3
Pb2+ (Pb acetate or nitrate) 5-10% solution Activates Sb2S3
Zn2+ (ZnSO4) 10% solution Depresses ZnS
S2- or HS- (Na2S or NaHS) 5% solution In sulfidization, activates tarnished (oxidized) sulfide minerals and carbonates
CN- [NaCN or Ca(CN)2] 5% solution Depresses ZnS, FeS2, and when used in excess, Cu, Sb, and Ni-S
Cr2O72-, CrO42- 10% solution Depresses PbS
SiO2 (Na2SiO3) 5-10% solution Disperses siliceous gangue slimes; embrittles froth
Starch, dextrin 5-10% solution Disperses clay slimes, talc, carbon
Quebracho, tannic acid 5% solution Depresses CaCO3, (CaMg)CO3
SO2 3% solution Depresses ZnS and Fe1-xS and, with
CN-, depresses Cu sulfides
_____________________________________________________________________________________________
Negatively charged particles
------
-----
---
-------
-----
- ------
- -
------
-
++ +
++
+
++ +
++
+
++ +
++
+
++ +
++
+
++ +
++
+
++ +
++
+
Positively charged particles
(a) Stable dispersions
++ +
++
++
+ +++
++
+ +++
+
++ +
++
+
------
-
-------
------
-----
---
------
-
Oppositely charged particles Neutral charge particles
(b) Unstable dispersions: Coagulation
--
-
--
A polymer chain with anionic functional groups
++ +
++
+ ++ +
++
++
+ +++
+
++ +
++
+
++ +
++
+
--
-
--
++ +
++
+
++ +
++
+
++ +
++
+
++ +
++
+
Multiple particle attachments
(c) Flocculation by polymer bridging
Figure 1.5 Coagulation and flocculation processes.
Table 1.4 Classification of some flocculants*
Origin Non-ionic Anionic Cationic Amphoteric Natural products Gum guar; starch Gelatine; albumen
Derivatives of natural products
Dextrin Sodium alginate; phosphated starch; sodium carboxy methyl cellulose
Cross-linked gelatin; aminated tannin
Synthetic polymers Polyacrylamide; Polyethylene oxide; Polyvinylalcohol
Hydrolyzed polyacrylamide
Polyethylenimine; vinyl pyridine-acrylamide copolymers
*J. A. Kitchener, "Principle of Action of Polymeric Flocculants", Br. Polym. J., 4, 217-229 (1972).
Table 1.5 Structures of typical synthetic flocculants
1.2.3 Hydrometallurgical ExtractionThe main technologies available for converting ores and concentrates into refined metals and metal
compounds are pyrometallurgy which exploits high temperature nonaqueous chemistry (e.g., gas/solid reactions, molten salt reactions, and liquid metal reactions), and hydrometallurgy, which is a water-based chemical technology. Table 1.6 presents a collection of the main metals which are extracted hydrometallurgically.
SOLIDS PREPARATION
LEACHING
LEACH RESIDUES
LIXIVIANTS
FEED SOLIDS
WASTE SOLIDS
SOLUTION PURIFICATION
METAL PRODUCTION
METAL/METAL COMPOUND
REAGENTS
REAGENTS AQUEOUS SOLUTION
IMPURITIES
SOLID/LIQUID SEPARATIONREAGENTS
Figure 1.6 Hydrometallurgical extraction
A hydrometallurgical plant typically is organized around subunits which provide the following five main functions: (a) solids preparation, (b) leaching, (c) solid/liquid separation, (d) solution purification, and (e) metal production, as illustrated in Figure 1.6. Solids preparation may involve physical operations such as grinding and magnetic separation, interfacial separation processes such as flotation, and pyrometallurgical processses such as roasting (a gas-solid reaction, such as the conversion of a sulfide to an oxide: MS(s) + 3/2O2(g) = MO(s) + SO2(g)). Leaching is a dissolution process in
which the prepared solids are treated with reagents called lixiviants or leachants. Table 1.7 presents a listing of selected hydrometallurgical reagents. Lixiviants include acids, such as sulfuric acid or hydrochloric acid, and bases, such as caustic soda and ammonium hydroxide. The acid provides hydrogen ions (H+) which react with the solid, causing its decomposition and the release of metal ions into the aqueous solution:
MO (s) + 2H+ (aq) = M2+ (aq) + H2O (1.4)
On the other hand, a base provides hydroxide ions (OH-) which effect dissolution by binding with metal ions to form water-soluble complexes:
M(OH)2 (s) + OH- (aq) = M(OH)3- (aq) (1.5)
A complexant binds chemically to a metal ion, thereby enhancing its aqueous solubility:
Cu2+ (aq) + 4NH3 (aq) = Cu(NH3)42+ (aq) (1.6)
Ag+ (aq) + 2CN- (aq) = Ag(CN)2- (aq) (1.7)
The leaching stage produces a metal-containing aqueous solution called the pregnant solution and unreacted solids, i.e., leach residues. The purpose of the solid/liquid separation step is to separate the pregnant solution from the leach residues. Frequently, flocculants are used as settling or filtration aids. Typically the pregnant solution contains a wide variety of metal ions. The solution purification step uses techniques such as precipitation, ion-exchange, adsorption, and solvent extraction to eliminate metallic impurities from the aqueous liquor and to concentrate the metal values in solution. Precipitation reagents include bases, acids (e.g., H2S), nonmetallic reducing agents (e.g., H2), and metals
such as zinc and iron:
Fe3+ + 3OH- = Fe(OH)3(s) (1.8)
Ni2+ + H2S = NiS (s) + 2H+ (1.9)
Co2+ + H2 (g) = Co (s) + 2H+ (1.10)
Au(CN)2- + Zn (s) + CN- = Au (s) + Zn(CN)3- (1.11)
Cu2+ + Fe (s) = Cu (s) + Fe2+ (1.12)
Precipitation reactions which use elemental metals as precipitants (e.g., Equations 1.11 and 1.12) are
called cementation or contact reduction processes.
Table 1.6 Aqueous Processing in Metal Extraction and End-Use of Extracted Metals and Metal Compounds
Metal Hydrometallurgical Extraction Technologies
Refined Products
Uses of Refined Products (2) Wastewater Treatment Technologies
Aluminum (Al)** Leaching of Al from bauxite ores; production of alumina trihydrate
Alumina trihydrate, Al2O3-3H2OCalcined alumina (Al2O3)
Al2O3 consumed by Primary Al smelters (84%); chemical, abrasive, refractory, advanced ceramic and other industries (16%)
Chemical Precipitation
Beryllium (Be)** Leaching of Be from bertrandite and beryl ores; precipitation
Be(OH)2, BeSO4 · 4H2O, BeO
BeO consumed in production of Be metal;Be-Cu alloys (0.5-2.0% Be); BeO oxide ceramics.
Boron (B)** Solvent extraction of B from natural brines containing dissolved borax (i.e., sodium tetraborate, Na2B4O7 · 10H2O); production of boric acid (H3BO3)
Boric acid (H3BO3);Boric oxide, B2O3
Synthesis of boron metal from B2O3; Synthesis of borates, used in glass fibers;Borosilicate glass; Cleaning and bleaching; Metallurgical: fluxes, electroplating baths, alloys; Neodymium-iron-boron magnets.
Cadmium (Cd)** Leaching, precipitation, electrowinning
Cd metal Batteries (32%), coatings and plating (29%), pigments (15%), plastic stabilizers (15%), alloys and other uses (9%)
Chemical precipitation; evaporation ion-exchange
Cobalt (Co)* Leaching of oxide, and sulfide ores, solution purification, electrowinning, electrorefining
Co metal, oxides Super alloys, cutting and wear-resistant materials, magnetic alloys, chemicals and ceramics.
Copper (Cu)* Leaching and precipitation; byproduct recovery from Al and Zn extraction
GaOH3, Ga2O3 Mainly consumed as GaAs for opto/electronic applications Chemical precipitation, ion-exchange, evaporation, electrolysis
Germanium (Ge)** Leaching, precipitation, solvent extraction
Infrared systems (65%); fiber optics (10%); gamma-ray, X-ray, and i.r. detectors (6%); semiconductors (5%); other (14%)
Gold (Au)** Leaching, separation with carbon, cementation on zinc, electrowinning, electrorefining, precipitation
Au metal Aerospace and electronics industries; jewelry.
Hafnium (Hf)** Coproduct Zr-Hf extraction by leaching of zircon concentrates; precipitation; solvent extraction
Hf metal Major metallurgical applications in nuclear industry.
Lithium (Li)** Leaching from spodumene (LiAlSi2O6) ores and concentrates; precipitation of hydroxide and salts
Lithium hydroxide monohydrate (LiOH·H2O), lithium carbonate (Li2CO3)
Synthesis of Li metal by fused salt electrolysis; Al industry: Li2CO3 used to synthesize LiF in cryolite bath; ceramic and glass manufacturing industries; chemicals, e.g., Li-based greases; Al-Li alloys.
Table 1.6 Aqueous Processing in Metal Extraction and End-Use of Extracted Metals and Metal Compounds
Metal Hydrometallurgical ExtractionTechnologies
Refined Products
Uses of Refined Products Wastewater TreatmentTechnologies
Magnesium (Mg) Precipitation, dissolution, evaporation, crystallization of Mg salts from seawater, and well and lake brines
MgCl2 Synthesis of Mg metal by fused salt electrolysis; applications of Mg metal in metallurgical industry; Al-Mg alloys, wrought foundry products, castings; applications of magnesia: refractories, animal feed, chemicals, pulp and paper, ceramics.
Nickel (Ni)* Leaching of oxide and sulfide ores; solution purification, electrowinning, precipitation, electrorefining
Forms of primary Ni consumed: Ni cathodes and pellets (56%), Ni briquets and powders (20%), ferronickel (13%), nickel oxide (8%), nickel salts (2%), other forms (2%); end-use consumption: stainless and heat-resisting steel (42%), non-ferrous alloys (excluding super alloys) (17%), electroplating (17%), super alloys (14%), other (10%).
Chemical precipitation (hydroxide, carbonate, sulfide), ion-exchange, evaporation, reverse osmosis
Niobium (Nb)** Leaching of niobite-tantalite ores; precipitation; solvent extraction
Nb metal; Nb2O5 Steel and alloys.
Platinum Group**Metals (Pt, Pd, Ir, Os, Rh, Ru)
Leaching of metallurgical byproducts and scrap; solution treatment
Automotive, catalyst for emission control (42.6%); electrical (21%); dental and medical (18.2%); chemical (5.3%); petroleum (3.4%); jewelry and decorative (1.1%); glass (0.6%); miscellaneous (7.9%).
Rare earths**(La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Vb, Lu)
Leaching of monazite and bastanasite ores and concentrates; solvent extraction; precipitation
Oxide salts Catalysts (53%); metallurgical (22%); ceramics and glass (18%); miscellaneous (7%).
Scandium (Sc)** Byproduct recovery from tungsten concentrates, fluorite tailings, uranium solutions; leaching, precipitation
Sc oxide Major use as laser crystals of gandolinium-scandium gallium garnets (GSGG); other, e.g., high-intensity mercury vapor lights.
Selenium (Se)** Byproduct of Cu electrorefining Electronic and photocopier components (43%); pigments and chemicals (20%), glass manufacturing (20%); other, e.g., agriculture and metallurgy (17%)
Chemical precipitation, activated carbon, ion-exchange, reverse osmosis, coagulation/coprecipitation
Silver (Ag)** Leaching of ores, concentrates, metallurgical intermediate products and scrip, adsorption, electrowinning, electrorefining
Ag metal Photographic materials (46%); electrical and electronic products (19.4%); coinage (11.3%); electroplated ware, sterlingware, jewelry (8.6%); brazing alloys and solders; coins, medallions, commemorative objects catalysis; dental and medical supplies; miscellaneous
Precipitation, ion-exchange, electrodeposition, electrodialysis, reverse osmosis
Table 1.6 Aqueous Processing in Metal Extraction and End-Use of Extracted Metals and Metal Compounds
Metal Hydrometallurgical Extraction Technologies
Refined Products
Uses of Refined Products (2) Wastewater Treatment Technologies
Sodium (Na)** Glass (50%); chemicals (21.2%); soaps and detergents (9.1%); flue gas desulfurization (4.4%); water treatment (3.6%); pulp and paper (2.9%)
Strontium (Sr)** Leaching of celestite ores; precipitation
Sr salts (e.g., carbonate, chloride, chromate)
TV picture tubes (63%); pyrotechnics and signals (13%); ferrite ceramic magnets (11%); electrolytic production of zinc (5%); pigments and fillers (5%); other (3%)
Tantalum (Ta)** Leaching of niobite-tantalite ores; precipitation; solvent extraction
Ta metal; Ta2O5 Alloys.
Tellurium (Te)** Byproduct of Cu electrorefining Iron and steel (58%); nonferrous metals (20%); chemicals and rubber (15%); other, e.g., xerographic and electronic applications (7%)
Thorium (Th)** Leaching of monazite ores and concentrates; solvent extraction; precipitation
Th metal, oxide, nitrate
Refractory application (57%); lamp mantles (18%); aerospace alloys (15%); welding electrodes (5%); miscellaneous, e.g., ceramics, lighting (5%)
Tungsten (W)** Leaching of scheelite and wolframite ores; solvent extraction, ion-exchange; precipitation
Oxide, tungsten metal
Tungsten carbide powder (54%); tungsten metal powder (28.7%); ferrotungsten (3.5%); other.
Uranium (U) Leaching, precipitation, solvent extraction, ion-exchange
Nuclear industry
Vanadium (V)** Leaching, byproduct of uranium ore processing; precipitation; solvent extraction
V metal; oxide Steel (85%); other (e.g., super alloys, chemicals, ceramics, catalysts).
Zinc (Zn)** Leaching of ores, concentrates and roasted concentrates; solvent extraction; electrowinning; electrorefining
Zn metal; oxide; Zinc sulfate
Zn metal: construction industry (43%); transportation (22%); machinery (10%); electrical (10%); chemical and other (15%). ZnO powder: rubber industry (58%); chemicals, paint, ceramics, photocopying. ZnSO4 powder: agriculture (83%).
Chemical precipitation; ion-exchange evaporation
Zirconium (Zr)** Leaching of zircon concentrates; solvent extraction; precipitation
Zr metal; oxide Zr metal: major use in nuclear power industry; chemical industry (corrosion resistant alloys); other (e.g., electronic industry). Zr oxide: ceramics, abrasives, chemical manufacture.
**Primary extraction via hydrometallurgy
Table 1.7 Typical hydrometallurgical reagents
Reagent Type Name Chemical Formula
Acid Sulfuric acid H2SO4Hydrochloric acid HClNitric acid HNO3Hydrofluoric acid HF
Base Caustic Soda (Sodium hydroxide) NaOHAmmonium hydroxide NH4OH
Complexant Ammonium hydroxide NH4OHSodium cyanide NaCNSodium Hydroxide NaOHHydrogen chloride HClHydrogen fluoride HF
Oxidant Oxygen O2Hydrogen peroxide H2O2Sodium hypochlorite NaOClFerric sulfate Fe2(SO4)3
Reductant Hydrogen H2Sulfur dioxide SO2Ferrous sulfate FeSO4Metallic zinc Zn
Metallic iron Fe____________________
Adsorption, ion-exchange, and solvent extraction are two-phase separation processes which remove
dissolved species from the bulk aqueous phase in the form of ions, complexes, or molecular species. In
all three processes, the aqueous solution constitutes one of the two phases. In the case of adsorption
separations, the second phase is a particulate solid material (the adsorbent) which possesses surface
functional groups that can interact with aqueous species. The solid material may be organic or
inorganic. In hydrometallurgy the most common adsorbent is activated carbon. Activated carbons are
high surface area carbon-containing materials prepared by the thermochemical decomposition of natural
(e.g., wood and vegetable matter) or synthetic (e.g., organic polymers) carbonaceous solids. Table 1.8
provides examples of the surface functional groups that are carried by activated carbons.
Organic ion-exchange materials are solid polyelectrolytes which are characterized by the presence of
three main constituents; (a) an insoluble skeleton or matrix, which is a hydrophobic three-dimensional
network of hydrocarbon chains, (b) the fixed ionic groups, which are inorganic hydrophilic functional
groups attached to the hydrocarbon matrix, and (c) the counterions, which are absorbed into the ion-
exchange material in order to establish electroneutrality with the fixed charges. Table 1.9 presents
typical functional groups encountered in organic polymer-based ion-exchange systems.
Solvent extraction is based on organic (oil)/aqueous systems. The main components of the organic
phase are: (a) an extractant, which is the chemical reagent which carries the functional groups that bind
(extract) aqueous species, and (b) a diluent, the organic solvent in which the extractant and the extracted
complex are retained as soluble species. Sometimes a third component, termed a modifier, is added to
enhance the organic phase stability. Table 1.10 presents a collection of selected solvent extraction
reagents. For an acidic extractant RH, the extraction of a metal ion into the organic phase may be
represented as:
RH(org) + Mz+(aq) = MRz(org) + zH+ (1.13)
With solution purification accomplished, the metal-containing solution can be further processed to give a final product of elemental metal (e.g., Au, Ni, Cu, Zn) or metal compound (e.g., Al(OH)3(s)).
The techniques used in the metal/metal compound production stage include electrowinning, electrorefining, hydrogen reduction, and crystallization. In both electrowinning and electrorefining, dissolved metal is precipitated out of solution by the direct application of electric current:
Cu2+ + 2e- = Cu (s) (1.14)
Au(CN)2- + e- = Au (s) + 2CN- (1.15)
In hydrogen reduction, the electron needed for the precipitation is generated from molecular hydrogen:
H2(g) = 2H+ + 2e- (1.16)
Table 1.8 Examples of surface functional groups on activated carbons
Name of Functional Group Structure
C
O
OH
OH
O
Carboxylic
Phenolic hydroxyl
Normal lactoneO
O
Quinone-type carbonyl
Table 1.9 Ion-exchange functional groups
Type of Ionic Group Structure
Strong acid
CO
O- H +P
S O-O
O
H +P
Weak acid
Strong base
P
H+N
Cl -
CH 3
CH 3
Cl -+P N
CH 3
CH 3 CH 3
Weak base
Chelating CH 2P N
COOH
COOH
P represents the resin matrix
Sulfonic acid
Carboxylic acid
Quaternary ammonium salt
Dimethyl amine
Iminodiacetic acid
Table 1.10 Selected solvent extraction reagents
Type of Extractant Name Structure
Anionic
Phosphoric acids OR O
R OP
OH CH CH 2 3
R = CH (CH ) CHCH 22 33
(Di (2-ethylhexyl) phosphoric acid)
Carboxylic acids CR1
R2 CH 3
COOH R1 = R2 = C6(Versatic 10)
Cationic Primary amines HNR
HR = (CH ) C(CH C(CH ) )422 333(Primine JMT)
HN
2R
R1 2R = C H CH CHCH 1 9 19
2 3223R = CH C(CH ) (CH C(CH ) ) 3 22
(Amberlite LA-1)
Secondary amines
Tertiary aminesN
2R
R1R3 R32RR1 == = 23CH (CH ) 7
(Alamine 300)
NCl -
R1
R2 (CH ) 3+
R3 = C - C 8 10R1 R2 R3==
(Aliquat 336)
Quaternary ammonium salts
RO
RO
RO
P OR = C H 4 9
Tributyl phosphate (TBP)
Neutral
Hydroxyoximes R = H, R = C H 1 9 192(Acorga P50)
R = H, R = C H 1 2 12 25(LIX 860)
9 1921R = CH , R = C H 3(LIX 84, SME 259)
C
OH
R2
1R
N OH
1.2.4 Ceramic Aqueous ProcessingAqueous processing is increasingly becoming an important technology in the manufacture of
ceramic materials. The main applications of aqueous processing are in materials synthesis and in suspension/colloidal processing. A related concern is the corrosion of ceramic materials. Traditionally, the manufacture of ceramic components relied primarily on dry powder-based techniques. For example, to prepare a complex oxide, such as barium titanate (BaTiO3), one would mix dry powders of barium
oxide and titanium oxide, hot press the mixture, and then sinter. In an alternative aqueous-based synthesis method, a complex barium titanyl oxalate salt is precipitated from solution, and this then serves as the precursor for BaTiO3 synthesis via thermal decomposition.
Aqueous synthesis offers a number of advantages over the conventional dry methods. In aqueous systems, mixing of the starting materials is typically achieved at the molecular level, and thus, chemical homogeneity is better achieved. Sintering is favored by small particle size and the necessary fine particles can be prepared by growth control during aqueous precipitation. The usual dry approach also requires grinding, which runs the risk of introducing impurities from the grinding media. The materials synthesized from solution include simple oxides and sulfides, such as ZnO and ZnS, as well as complex oxides, silicates, fluorides, and chalcogenides, as summarized in Table 1.11. The solid products may be in the form of gels, powders, and films.
Materials synthesis in aqueous systems typically involves three main steps: (a) solution preparation, (b) solvent removal, and (c) salt decomposition, as illustrated in Figure 1.7. On the basis of the method of water removal, materials synthesis techniques may be divided into three major categories: (a) precipitation-filtration (or-sedimentation), (b) solution volatilization, and (c) solvent-assisted dehydration. The most common technique is precipitation-filtration. Table 1.12 presents a summary of various synthesis techniques. Schematic illustrations of many of these processes, are provided in Figure 1.8.
Aqueous-based techniques are also exploited in ceramic forming processes. Forming converts a particulate feed material into a consolidated form characterized by a definite geometry and microstructure. Figure 1.9 presents flowsheets illustrating the three main powder-forming processes, i.e., pressing, casting, and injection. In pressing, a powder or granular feed material, contained in a die or a mold, is subjected to pressure. The casting technique is applied to slurries and among the main variations of this method are slip casting, where a porous mold is used, gel casting, which relies on a polymerizable binder, and tape casting, where a thin coating of the slurry is deposited on a carrier film.
As can be seen from Figure 1.9 all three forming processes first start by combining powders, water, and certain processing additives. The proportions of these components differ, however, for the various forming processes. Table 1.13 presents a collection of various types of processing additives.
Table 1.11. Materials synthesis in aqueous systems
Form of Material Metal and Metal Compound Method ________________
Metal Powder Au, Ag, Pt, Pd, Cu, Ni, Co Chemical PptnFe Electrolysis
Simple Oxide Powder MnO2 ElectrolysisFe2O3, Fe3O4, ZrO2, SiO2, Cr2O3, ZnO Chemical Pptn,Fe2O3 Spray Pyrolysis
Complex Oxide Powder BaTiO3, PbTiO3, LiTaO3, YBa2Cu3O7 Chemical Pptn.
Metal Films Au, Ag, Pt, Pd, Cu, Ni, Co, Cr Electroplating,Chemplating
Oxide Films Al2O3, TaO2 Anodizing, Pptn.
Chalcogenide Powders and CdS, ZnS, ZnSe, ZnTe, CdTe Pptn., Spray pyrol.Films
Salt Powders AgI, AgBr, AgI, etc. Chemical Precipitation
Metal Salts
Metallic Phases
Acids/Bases
Product
H O2
Salt Decompos'n
Solution Preparation
Solvent Removal
H O2
Figure 1.7 The main steps in materials synthesis
Ceramic and glass materials may be categorized in terms of the properties that are exploited in practical applications, i.e., electrical and electronic, magnetic, optical, chemical, thermal, mechanical, and biological. Tables 1.14 - 1.16 present a list of materials and corresponding applications, with emphasis on those which are or can be prepared by solution techniques.
Table 1.12 Types of materials synthesis techniques
Water Removal Method Precipitation Technique Process Description
Precipitation-Filtration Simple Precipitation Simultaneous addition of reactant solutions containing salts MA and KB, leading to reaction to form the single salt NB(s).
Coprecipitation Addition of cation-containing solutions (MA, NY) to an excess of precipitant solution (KB), leading to simultaneous precipitation of MB(s) and NB(s).
Homogeneous Precipitation In-situ generation of precipitant.
Alkoxide hydrolysis(sol-gel process)
Reaction of an alkoxide (ROM) with water to produce a hydrous metal oxide.
Hydrothermal Synthesis Use of hot solutions (frequently above the boiling point of the aqueous phase) to increase reaction rates and/or obtain solution conditions that favor precipitation.
Electrolytic Precipitation Electrolytically generated reactants (e.g., electrons, hydroxyl ions) are used as precipitants.
Solution - Volatilization
Direct (Simple) Evaporation Water is removed slowly be evaporation.
Spray Drying Salt solution is atomized and passed into a heated drying chamber.
Spray Roasting (EvaporativeDecomposition)
Similar to spray drying, except that higher temperatures are used in order to achieve drying (salt production) and salt decomposition in one step.
Fluid-bed Drying Feed salt solution is passed through a nozzle and is received as droplets by a fluidized bed of the solid particles contained in a furnace.
Emulsion Drying Small droplets of aqueous salt solutions are produced by using surfactants to stabilize water-in-oil (w/o) emulsions. Water volatilization is then accomplished via e.g., hot kerosene drying, freeze-drying.
Freeze Drying Liquid drops generated via spraying are rapidly frozen. Water is subsequently eliminated from the frozen drops by sublimation.
Hot Kerosene Process The aqueous salt solution is sprayed into a hot water-immiscible liquid (e.g., kerosene), resulting in the evaporative elimination of water.
Glassy Solid Process Salt solution containing an organic polyfunctional acid (e.g., citric acid) is subjected to rapid evaporative dehydration, followed by vacuum drying.
Solvent-assisted Dehydration
Liquid Drying An aqueous salt solution is sprayed into a polar organic solvent (e.g., acetone, ethanol). The lower solubility of the mixed organic-aqueous solvent leads to salt precipitation.
Gel-microsphere Process Preferential extraction of water by a polar organic liquid results in salt precipitation.
M + A + K + B = MB (s) + K + A
- -+ ++ -MIXING
FILTRAT'N
MA KBH O2
H O2MB(s)
(i) Simple Precipitation: Simultaneous addition of reactant solutions
(ii) Coprecipitation: Addition of cation solutions to an excess of precipitant solution
MB(s) + NB(s)
NY
MA + KB = MB(s) NY + KB = NB(s)
MIXING
FILTRAT'N
MA,KBH O2
H O2
(v) Hydrothermal Precipitation: Solubility product of MB (s) exceeded at high temperature
MIXING
FILTRAT'N
Heat
MA KBH O2
H O2MB(s)
(iii) Homogeneous Precipitation via in-situ generation of precipitant, NB
KX = NB MA + NB = MB(s) + KN
H O2
MIXING
FILTRAT'N
KXMAH O2
MB(s)
(iv) Alkoxide Hydrolysis
ROM + Alcohol
H O2 + Catalyst
ROM + H O = ROH + MOH MOH + MOH = M O + H O MOH + ROM = M O + ROH
22
22
M O2
H O2
MIXING
FILTRAT'NAlcohol
(vi) Electrolytic Precipitation
M + B = MB(s) + e
--
KB
MB (s)ELECTROLYSIS
Figure 1.8a. Precipitation-filtration processes.
Spraying Chamber
M + B -,
ooo
o
o
o
oo
oo
HeatMB(s)
(ii) Spray Drying(i) Direct (simple) Evaporation
MB(s)HeatM+
B-
H O2
(iii) Spray Roasting
MB(s)
ooo
o
o
o
oo
oo
Heat
M + X = MX(s) MX(s) = MB(s) (Decomposition)
+ -
M + X-,
(vi) Hot Kerosene Drying
H O2M+ B-, ,
ooo
oo
ooo
oo
MB(s)Heat Kerosene
(vii) Freeze Drying
H O2M+ B-, ,
Spraying/ Freezing
Frozen Drops
H O2 SUBLI- MATION
MB(s)
Cooling ooo
oo
ooo
oo
(viii) Glassy Solid Process
H O2M+ B-, ,
H O2 DEHY- DRATION Glassy Material
Organic Polyfunctional Acid
Gel
GELATION
(iv) Fluid-bed Drying
ooo
o
o
o
oo oo
oo
oo
o
oo
o
ooo
o
o
o
oo
oooo
ooo
oo
o
o
o
o
oo
ooo
o
o
oo
o
o oo o
o
o
oo
o
oo o
o
MB(s)(Deposited on fluidized particles)
M+ B-, , H O2
H O2
Heat
(v) Emulsion Drying
H O2M+ B-, ,
EMULSI- FICATION
Surfactant, Oil
MB(s)oo
oo
o
ooo
oo
KeroseneHeat
Emulsion
Figure 1.8b. Solution-volatilization processes.
MIXING/MILLING
GRANULATION
PRESSING
SINTERING
POWDERS, ADDITIVES, WATER
PRODUCT
MIXING/MILLING
CASTING
DRYING
SINTERING
POWDERS, ADDITIVES, WATER
PRODUCT
MIXING/MILLING
GRANULATION
INJECTION
DEBINDING/ SINTERING
POWDERS, ADDITIVES, LIQUID
PRODUCT
(a) Pressing (b) Casting (c) Injection
Figure 1.9 Powder-forming processes.
Table 1.13 Processing additives and their functions*
Additive Deflocculant
Functions Particle charging, aid and maintain dispersion
Coagulant Uniform agglomeration after dispersionBinder/Flocculant Modify rheology, retain liquid under pressure, yield strength,
green strength, adhesionPlasticizer Change viscoelastic properties of binder at forming temperature,
reduce Tg of binderLubricant Reduce die friction (external), reduce internal friction, mold releaseWetting agent Improve particle wetting by liquid, aid dispersionAntifoaming agent Eliminate foamFoam stabilizer Stabilize foamChelating agent/sequestering agent/precipitant
Inactive undesirable ions
Antioxidant Retard oxidative degradation of binder
*After J. S. Reed, Principles of Ceramics Processing, 2nd ed., 1995, p. 400)
Table 1.14 Industrial Applications of Single-Component Oxide Ceramics*
Functional Group Material Property Exploited Application
Electrical/Electronic Al2O3, Insulator IC SubstratesBeO Insulator IC SubstratesFe3O4 Magnetism Magnetic CoreSnO2 Semiconductivity Gas-sensorZnO-Bi2O3 Semiconductivity VaristorTaO2 Capacitorb-Al2O3 Ionic Conductivity NaS batteryStable ZrO2 Ionic Conductivity Oxide-Sensor
Mechanical Al2O3, ZrO2 Wear resistance Polishing materials Grindstones
Optical Y2O3 FluorescenceAl2O3 Transparency Sodium lamp
Mantle tubeSiO2 Light conductivity Optical Fibers
Thermal Al2O3 Heat resistance Structural refractoriesZrO2 Heat insulation Heat-insulating materialsBeO Heat conductivity Substrates
Nuclear UO2 Nuclear properties Nuclear fuelBeO Moderator
Chemical TiO2 Color, chemicalinertness, high refractiveindex
Paint Pigments
Fe2O3 Color Paint PigmentsAl2O3 Chemical inertness Catalyst Support
Biological Al2O3 Artificial teeth and bonesCa10(PO4)6(OH)2
*After N. Ichinose, ed., Introduction to Fine Ceramics, 1987, pp. 4-6.
Table 1.15 Industrial Applications of Complex Oxide Ceramics*
Functional Group Material . Property Exploited Application .Electrical BaTiO3 Dielectric Capacitor
BaTiO3 Semiconductivity Resistance junctionPb(Zr, Ti)O3(PZT) Piezoelectric Oscillators, ignition junctionLiNbO3 Piezoelectric Piezoelectric oscillatorsMgAl2O4 Insulator IC substratesMFe2O4 MagneticYBa2Cu3Ox Conductivity SuperconductorsLa2-xSrxCuO4 Conductivity Superconductors
*After N. Ichinose, ed., Introduction to Fine Ceramics, 1987, pp. 4-6.
Table 1.16 Industrial Applications of Chalcogenide and Related Ceramics*
Functional Group Material . Property Exploited Application .Optoelectronic ZnS, CdS, Optical/electronic Photodetectors
CdSe, GaAs,PbS, PbSeCdS, Cu2S Optical/electronic Phtovoltaic devicesCdTe, CuInSe2(Cd, Zn)SCuInS2
Chemical MoS2,MoS3 CatalystsCo9S8 Catalysts
*After N. Ichinose, ed., Introduction to Fine Ceramics, 1987, pp. 4-6.
1.2.5 Catalyst PreparationMany industrially important reactions occur at economically acceptable rates only in the presence
of catalysts. It is relatively easy to separate solid catalysts from soluble reaction products and therefore solid catalysts are the preferred choice in industrial practice. Table 1.17 presents a collection of some important commercial catalysts and their applications. For reactions occurring at surfaces, the key concern is to ensure that the surface has the desired activity, selectivity, and accessibility. This latter requirement means that the transport of reactants to the active surface should be as free as possible.
Table 1.17 Selected commercial catalysts and their applications (after Brunelle, 1978)
TYPE OF CATALYSTPROCESS DISPERSED METAL CARRIER
Auto-exhaust gases Post-combustion Alumina orOxidation catalysts Yes Pt+Pd Alumina coatedThree-way catalysts Yes Pt+Rh Cordierite
Selective hydrogenation of:Olefins streams in ethylene plants Yes Pd AluminaPyrolysis gasoline in ethylene plants Yes Pd Alumina
Catalytic Reforming Yes Pt (+Re,Ir,Au..) Alumina + Cl
Hydrocracking Yes Pd Y zeolite based
Isomerization of:Paraffins Yes Pt Alumina + Cl or
mordeniteXylenes Yes Pt Alumina + Cl or
Alumina-Silica
Dismutation of Toluene Yes Cu, Ni Zeolite
Fine organical chemistry Yes Pt, Rh, Pd, Ru, Ni Raney Charcoal
Off-gas Treatments Yes Pt, Pd Alumina
Fuel Cells Yes Pt, Pd Charcoal
Ammonia Oxidation No Pt + Rh -
Selective oxidation of ethylene in ethylene oxide
No Ag Alumina
Selective oxidation of methanol in formol No Ag Carborundum
Catalytic reactors may be fixed bed or fluid bed. In a fixed bed reactor, the pellet size is typically of the order of 1 mm, while it is much larger for fluid bed reactors, of the order of 30 mm. Particles in the size range of 1-30 mm do not provide enough surface area per volume of reactor for reaction to proceed
satisfactorily. Thus there is a need for the catalysts to have considerable porosity. In general, it is impractical to prepare the catalytically active materials in the form of pellets or particles, while at the same time securing the desired porosity. Hence there is a need for catalyst supports.
Two main types of catalytic materials are used commercially. These are noble metals, and less expensive metals, oxides, and sulfides. Since the noble metals are relatively expensive, they must be used sparingly (typically loadings of ~ 1 wt%). This means that they must be practically atomically dispersed at the support surface. In the case of the less expensive catalytic materials, it is possible to use higher loadings (e.g., up to 40 % and above). In the production of supported catalysts, two main methods are used: (a) Deposition of the active precursor onto a previously prepared support. (b) Preferential separation of a component or more from previously prepared fine particles.
1.2.6 Emulsion-based Photographic TechnologyThe silver-halide-based photographic process involves a number of steps: (a) exposure of the
photo-sensitive material to light, thereby forming the latent image, (b) treatment of the exposed film, resulting in the negative, a process termed development, (c) stopping of the development process, (d) fixing.
The active material in a photographic film is the silver halide, which is typically silver bromide (AgBr). Silver bromide is prepared by combining two water-soluble reactants, e.g., silver nitrate (AgNO3) and potassium bromide (KBr):
AgNO3 + KBr AgBr(s) + KNO3 (1.17)
Silver bromide particles are deposited as a thin layer on a transparent plastic substrate. Adhesion of the particle layer to the substrate is achieved by embedding the particles in gelatin, which is a protein-based material with the following general structure:
NHH
CH
R
C
O
N
H
CHR
C
N
CH
R
OH
C
OH
On
where the repeat unit is identified by the parenthesis and n ≈ 100-300. Photographic gelatin is transparent to light (thus, it does not interfere with the reception of light by the halide particles), it immobilizes the silver halide particles (particle movement would cause the image to become blurred); it has sufficient porosity to permit processing chemicals access to the halide particles. Table 1.18 presents a list of selected photographic processing chemicals and their applications.
In the exposure step, a photochemical reaction occurs:
AgX + Light ---> Ag + X (1.18)
Table 1.18 Photographic chemicals and their applications
Bath Type of Reagent Example Function
Developer Reducing Agent Hydroquinone Reduce silver ions to metallic stateActivator Hydroxide Ion Facilitates deprotonation of hydroquinoneRestrainer Potassium Bromide Minimize reduction of unexposed silver halide (fogging)Preservative Sodium Sulfite Inhibit decomposition of hydroquinone
Stop Bath Weak Acid Acetic Acid, Terminate the reduction reactionBoric Acid
Fixing Sol'n Sodium Thiosulfate Dissolve residual silver halide__________________________________________________________________________________________
This reaction results in the formation of small silver particles -so small that they are invisible to the naked eye, hence the designation as latent. The development step serves to enhance this latent image. This is accomplished via an aqueous-based chemical reaction which causes additional silver to be deposited around the initial ultrafine silver particles.
The silver deposition is made possible by the presence of a reducing agent (i.e., a reagent that can release electrons) in the developer. A common reducing agent in photographic developers is hydroquinone:
OH
OH= + 2H + 2e+ -
(Hydroquinone) (Benzoquinone)O
O(1.19)
Ag+ + e- = Ag (1.20a)AgBr + e- = Ag + Br- (1.20b)
The developer contains additional reagents, as listed in Table 1.18. The activator, the hydroxide ion (OH-), participates in the reduction process by facilitating the removal of the hydrogens from hydroquinone:
OH
OH=
O
O-
-
+ 2OH - + 2H O2
O
O
O
O-
-+ 2Ag+ 2Ag =+
(2AgBr) (+ 2Br )-
(1.21)
(1.22)
This silver reduction is a selective process. The silver ions nearest to the light-generated silver atoms respond more rapidly to the attack by the reducing agent. It is this selectivity that underlies the very possibility of latent image enhancement.
Following film development, it is typically observed that the entire film surface acquires a slightly dark coloration, termed a fog. This fogging reflects the fact that there is a general silver reduction over the entire film surface. The role of the restrainer is to minimize fogging by preventing the underexposed silver halide from undergoing the reduction reaction. Potassium bromide (KBr) serves as a common restrainer. This reagent functions by slowly dissolving AgBr via complex formation:
AgBr(s) + Br- AgBr2- (1.23)
Thus, now, the AgBr is subject to two competing reactions in the developer, i.e., the reduction reaction (Equation 1.20) and complex formation leading to dissolution (Equation 1.23). In the neighborhood of the exposed AgBr sites, the reduction reaction proceeds more rapidly than the complexation reaction and therefore darkening occurs readily. In contrast, for the unexposed AgBr, the dissolution proceeds me rapidly and therefore darkening is minimized.
Activated hydroquinone is unstable in the presence of air. This is because the molecular oxygen in air reacts with it:
= (1.24)+ 2H O2+ O 2 + 4OH -
O
O
O
O-
-
It can be seen that, as in the reaction with silver, benzoquinone is formed here too. It turns out that benzoquinone can accelerate the oxygen-hydroquinone reaction. In order to minimize the deleterious effects of this reaction, sodium sulfite (Na2SO3) is introduced into photographic developers as a
preservative. This reagent acts by sulfonating benzoquinone, thereby eliminating it from the reaction solution:
(1.25)OH
OHSO 3
-+ SO2-
3 + H O =2O
O+ OH -
It is considered that the film has been sufficiently developed when the reduction of silver is high enough to yield an acceptable image density. At this point, the film is immersed in a stop bath, whose function is to terminate the reduction reaction. The active ingredient in a stop bath is a weak acid, e.g., acetic acid (CH3COOH) or boric acid (B(OH)3). The stopping process is based on the destruction of the
activator (hydroxide ion) via a neutralization reaction:
H+ + OH- H2O (1.26)
The hydrogen ion (H+) shown in Equation 1.26 is generated through the ionization of the weak acid (HA):
HA H+ + A- (1.27)
Following development and stopping, the photographic film acquires two kinds of silver, i.e., reduced silver (Ag) responsible for the enhanced image, and the residual silver bromide (AgBr) residing in the unexposed regions of the film. In the fixing process, the remaining silver halide is eliminated from the film. The fixing solution typically contains sodium thiosulfate (Na2S2O3). The thiosulfate ion (S2O) can form water-soluble complexes with silver ions:
AgBr(s) + 2S2 Ag(S2O3)+ Br- (1.28)
1.2.7 Surface FinishingThe term surface finishing is the general name given to a variety of surface treatment processes
which serve to impart certain desired properties to the surface of a basis material. The process is termed metal finishing when the basis material is a metal. The term metal finishing is also applied to surface treatments in which metallic films are deposited on plastic basis materials. Examples of desired surface properties include enhanced corrosion resistance, improved electrical conductivity, and a heightened aesthetic appeal. The surface treatment induces physical and/or chemical changes which result in cleaning, hardening/softening, smoothing/roughening, and coating of the basis material. Table 1.1 lists a number of surface finishing processes. Before coatings are applied, the surface of the workpiece must be cleaned appropriately. Table 1.19 lists the kinds of soils that are frequently encountered and Table 1.20 provides a summary of the typical cleaning methods.
Table 1.19. Types of soil
Soil Type Common Constituents Pigmented drawing lubricants Bentonite, flour, graphite, lithopone, metallic soaps,
mica, molybdenum disulfide, white lead, whiting, zinc oxide
Unpigmented oil and grease Drawing lubricants, rust-preventive oils, quenching oils
Chips and cutting fluids Plain or sulfurized mineral and fatty oils, chlorinated mineral oils, soaps, amines, sodium salts of sulfonated fatty alcohols, alkyl aromatic sodium salts of sulfonates, metal chips generated by machining.
Polishing and buffing compounds Admixtures of burned-on grease, metallic soaps, waxes, metal and abrasive particles.
Rust and scale Metal oxides
Electroplating. In this technique, a metallic coating is deposited on the surface of a workpiece by using electrons generated with the aid of an externally applied voltage:
M2+ + 2e- = M (1.29)
Table 1.21 presents examples of metallic coatings and their applications. Different kinds of electroplating baths are used, as summarized in Table 1.22.
Figure 1.10 presents a simplified diagram showing the sequence of steps involved in an electroplating operation. The surface of the basis metal can have a significant influence on the physical and chemical characteristics of the electrodeposits. Therefore, prior to electroplating proper, it is necessary to subject the basis metal to various surface preparation processes. The surface of the basis metal is given a preliminary pretreatment which serves to remove oily materials
(e.g., grease, buffing compounds, drawing lubricants), scale, and heavy rust. Table 1.23 gives examples of such preliminary pretreatments.
Table 1.20 Cleaning methods
Method_______________________ Constituents of Cleaning Medium Cleaning Principles______________
Solvent cleaning Hydrocarbon and chlorinated hydrocarbon solvents, e.g., benzene, toluene, methylene chloride, trichloroethylene
Dissolution of contaminants
Emulsion cleaning Hydrocarbon solvents, e.g., kerosene, water, emulsifiable surfactants
Wetting of particulate contaminants, flotation of particulates by emulsion drops, solubilization by organic solvents
Alkaline cleaning Alkali metal hydroxides, surfactants (wetting agents, emulsifiers), sequestering agents, saponifiers
Hydroxide ions impart negative charge to surfaces, leading to particle detachment via electrostatic repulsion; oily soils removed via emulsification.
Acid cleaning Most common mineral acids (e.g., HCl, H2SO4, HNO3), phosphoric acid, organic acids (e.g., citric, acetic, oxalic, gluconic, tartaric acids), surfactants
Dissolution, especially, of oxides; organic acids function as complexants.
Electrolytic cleaning Gas (O2 or H2) generated by electrolysis of alkaline cleaning solutions
Tiny bubbles produced by application of electric current contribute scrubbing action and promote flotation of soil particles.
Abrasive cleaning Small abrasive particles, water jets, air streams
Under the influence of impact force provided by water jets and air streams, abrasive particles dislodge contaminant particles.
Ultrasonic cleaning Liquid cleaners plus high frequency sound waves
Tiny gas bubbles generated by ultrasonic waves provide scrubbing action.
Table 1.21 Types of metallic coatings and their functions(after J. Hyner, in Electroplating Engineering Handbook, 4th ed., p. 50)
Surface Coating____________ Basis Material___________ Desired Property____________________
Cu, Ni, Cr Steel, zinc die castings Corrosion resistance
Zn, Cd Steel Corrosion resistance
Cu, Ni, Cr Steel Decorative appeal
Ni, Ag ,Au Brass Decorative appeal
Cr, Ni Steel Superior hardness and better wear resistance
Au Brass, Cu Lower contact resistance and increased reliability for electrical contacts
Sn Brass Improved solderability and/or weldability
Ni (Under Au or Cr) Better base for other finishes
Ag Bronze Improved lubricity under pressure
Cu, Ni, Cr Plastics To strengthen the basis material and render it more temperature resistant
Cu Steel (for carburizing) To act as a stop-off in heat-treating
Bronze Steel (for nitriding) To act as a stop-off in heat-treating
Table 1.22 Electroplating baths
Bath Type Dissolved Metals
Sulfuric Acid Rh, Cu
Phosphoric Acid Rh
Sulfate In, Fe, Ni
Chloride Fe,Ni
Cyanide Cd, Cu, Zn, Au, Ag
Fluoborate Cu, Cd ,In, Fe, Pb, Sn, Ni
Pyrophosphate Cu
Chromic acid-sulfuric acid CrSulfamate (SO3NH2) Ni
PRELIM. TREATMENT
RINSE
ELECTROCLEAN
RINSE
ACTIVATE
PLATE
WORKPIECE
PLATED PART
Figure 1.10. Electroplating processing sequence
Table 1.23 Types of pretreatments for electroplating
Type of _ Pretreatment ____________
Reagents_______________________ Basis Material _________________
Removal of Oily Materials Alkali or emulsion-type cleanersSolvent degreasers (e.g., trichloro-ethylene or perchloroethylene)
For all basis metals
Scale Removal Alkaline bath (e.g., NaOH (180 g/L),NaCN (120 g/L), chelating agents (80 g/L) T = 40˚C)
Ferrous metal parts
Hydrochloric acid Low carbon steel; stainless steels
Sulfuric acid Low carbon steel; stainless steels; copper and copper-base alloys
Hydrochloric acid-nitric acid High-carbon, case-hardened steels, stainless steels
Sulfuric acid-hydrofluoric acid Cast irons
Nitric acid-hydrofluoric acid Stainless steels
Pickling. Scale and rust are oxidic materials (e.g., Fe2O3, FeO) and their removal generally involves reaction with acidic solutions, a process termed pickling. In the case of steel, one can write:
Fe2O3 + 6H+ = 2Fe3+ + 3H2O (1.29)
An important contribution to scale removal is the hydrogen gas released when the acid travels through
cracks in the scale and attacks the underlying metal:
Fe + H2SO4 = H2(g) + FeSO4 (1.30)
Fe + 2HCl = H2(g) + FeCl2 (1.31)
The subsequent pressure buildup dislodges the scale from the metal surface. Aside from its use as a
pretreatment step in electroplating, pickling is used extensively for scale-removal in metal-production
operations (e.g., steel making). Due to its low cost, sulfuric acid is the reagent of choice. However, a
number of other acids are also used, e.g., nitric acid-hydrofluoric acid (for stainless steels), hydrochloric
acid, and phosphoric acid.
Electropolishing. Where there is a need to produce a smooth and polished basis metal surface, this can frequently be accomplished by means of electropolishing. This is an electrochemical process in which metal is removed from the surface of the basis metal:
M = Mz+ + ze- (1.32)
The workpiece serves as the anode of an electrochemical cell. Upon the application of voltage, the projections on the rough surface dissolve faster than the depressions and this results in a smoothing of the surface. Table 1.24 presents a list of commercial electropolish baths. Typically acidic baths are used, with phosphoric acid combined with one more other acids.
Table 1.24 Types of commercial electropolishing baths and their applications
Bath Types Basis Metals
Fluoboric acid Al
Sodium phosphate-carbonate Al
Phosphoric acid Cu, Stainless Steels
Phosphoric-chromic acid Brass, Cu, Nickel-Silver, Steels, Stainless Steels
Phosphoric-sulfuric chromic acid Al, Ni, Stainless Steels, Steels
Phosphoric-sulfuric acid Ni, Stainless Steels, Steels
Phosphoric-sulfuric-hydrochloric Ni, Monel
Sulfuric acid Ni
Sulfuric-citric acid Stainless Steels
Potassium cyanide Ag
Caustic soda Zn
Phosphate Coating. When certain metals are subjected to controlled corrosion in a phosphate bath, a metal phosphate coating may develop on the metal surface. The physical and chemical characteristics of phosphate coatings are exploited in a number of ways, e.g., to facilitate the adhesion of organic coatings to metal substrates, to serve as corrosion barriers, and (upon lubrication) to aid cold deformation processing (wire drawing, etc).
Surfaces typically phosphate-coated are: iron, steel, galvanized steel, aluminum, electrodeposited zinc, and electrodeposited cadmium. The types of coating include manganese phosphate, zinc phosphate, iron phosphate, and aluminum-chromium phosphate.
Chromate Coating. Metallic chromate coatings are produced by subjecting the substrate metal to controlled corrosion in an aqueous chromate solution. Chromate coatings are given to electropolated metals (e.g., Zn, Cd, Cu, Sn, Cr, brass, Ag), zinc base die castings, copper and copper alloys, Al, Mg, 316 stainless steel, and galvanized zinc coatings. Applications include decoration, corrosion protection, and paint base.
Anodizing. When an aluminum workpiece is made the anode of an electrolytic cell filled with an acidic aqueous electrolyte, an adherent film of aluminum oxide is produced on the aluminum surface. In this process, the electric current drives oxide and hydroxide ions generated by the water molecules to the aluminum surface where reaction occurs to form the oxide coating:
2Al + 3H2O = Al2O3(s) + 6H+ + 6e- (1.33)
Electroless plating refers to the deposition of a metal coating on a substrate through the action of a chemical reductant. Metals such as Ni, Co, Pd, Pt, Cu, Au, Ag are plated commercially by electroless processes. A catalytic surface is required to initiate the deposition process and subsequent deposition depends on the catalytic ability of the deposited metal. Among the advantages of electroless plating that may lead to the preference of this deposition technique over electroplating are the following:
1. The ability to deposit uniform coatings on complex substrates2. The formation of relatively less porous coatings3. The elimination of the need for electrical energy and related equipment4. The ability to deposit coatings onto nonconductors5. The ability to produce deposits with special physical-chemical (e.g., magnetic) properties.
A plating bath is a complex aqueous solution. Table 1.25 provides a summary of the various reagent types and their functions. Typical reductants are hypophosphite (H2PO), formaldehyde (HCHO), hydrazine (H2NNH2), borohydride (BH) and amine borane (R2NHBH3).
Table 1.25. Types of Plating Bath Reagents
Types of Reagents Function Examples
1. Metal salts Provide the metal ions which are Metal chlorides and deposited sulfates
2. Reducing agents Provide the electrons needed for the Sodium,reaction Mz+ + ze- = M hypophosphite,
formaldehyde, hydrazine,sodium borohydride,dimethylamine borane
3. Complexing agents Maintain the metal ions as Hydroxyacetate, lactate,soluble complexes thereby counter- EDTA, ammonia,acting the tendency to citrateprecipitate insoluble compounds
4. Acids and bases Provide the appropriate pH regime NaOH, KOH, NH3 needed by the reduction reaction Na2CO3and the stability of the bath reagents.
5. Buffering agents Counteract drastic decreases in Lactate, bath pH and the resulting decrease hydrocyacetate,in deposition rate citrate
6. Deposition catalysts Enhance deposition rates bycatalyzing the reaction of thereducing agent.
7. Stabilizers Counteract spontaneous bathdecomposition. By adsorbingpreferentially on catalyticnuclei in the plating bath, stabilizers inhibit metaldeposition within the bath.
8. Brighteners Enhance the brightness of the deposit. Sodium benzene disulfonate______________________________________________________________________________________________
1.2.8 Semiconductor Device Microfabrication
Integrated circuits are based primarily on silicon technology; however, compound semiconductors, e.g., GaAs, are exploited for specialized applications. Wet chemical processing is used in three main areas of solid state device manufacture: (a) Wafer cleaning, (b) thin film etching for pattern definition, and (c) planarization of metallization structures. Another area of aqueous processing application is in electronic packaging, where the manufacture of printed circuit boards (PCBs) (also termed printed wiring boards (PWBs)) relies extensively on etching and plating techniques.
The production of an integrated electronic component involves several steps, as illustrated in Figure 1.11. In the first step, wafer preparation, a number of operations are performed, including, sawing of the single crystal Si boules into wafers, followed by mechanical polishing, chemical polishing, and chemical-mechanical polishing of the wafers. The wafer processing operation consists of the following: Thin film deposition, oxidation, diffusion, and implantation. The manner in which wafer processing is combined with the masking, and etch/clean circuits is illustrated in Figure 1.12 (Moreau, p. 4). In the wafer masking operation, a radiation-sensitive coating, called a resist, is applied to the wafer surface. The photolithographic technique for pattern definition is illustrated in Figure 1.13 (Speight, Fig. 1.3b). Tables 1.26 and 1.27 provide a listing of typical etchants used in pattern definition.
WAFER PREPARATION
WAFER PROCESSING
MASK GENERATION
WAFER MASKING
ETCH AND CLEAN
PASSIVATION
ASSEMBLY AND TEST
INTEGRATED CIRCUITS
SINGLE CRYSTAL SILICON BOULES
CHEMICALS/MATERIALS
Figure 1.11 Processing steps in semiconductor device fabrication
(after Moreau, p.3).
Table 1.26 Etchants for silicon and GaAs (Kern and Schnable, p.256).
Semi-Etchant conductor Composition Comments
CP-4A Si 3:5:3 Polishing,HF-HNO3-CH3COOH 80 µm min-1
Planar Si 2:15:5 Polishing, etch HF-HNO3-CH3COOH 5 µm min-1
White Si 1:3 Polishing etch HF-HNO3Polysilicon Poly-Si 3:50:20 0.8 µm min-1 etch HF-HNO3-H2OAlcohol-KOH Si 50g KOH, 200g Anisotropic
n-propanol,800g H2O
Br2-methanol GaAs 1:9 PolishingBr-CH3OH
Peroxide- GaAs 5:1:1 Polishing sulphuric H2SO4-H2O2-H2O
Table 1.27 Etchants for dielectrics and insulators used in silicon microelectronic devices(Kern and Schnable, p. 245)
NaOHHF- H3PO4 H2SO4 (30%
Material Form H2O BHF (hot) (hot) hot)
SiO2 Amorphous or H H L 0 Lcrystalline
SiO Amorphous 0 0 0 0Al2O3 Amorphous H H M 0 0
Crystalline 0 0 M 0 0Sapphire 0 0 0 0 0
Ta2O3 Amorphous M LTiO2 Amorphous H M L L
Crystalline L 0 L LAsSG Amorphous H MBSG Amorphous H L L 0 LBPSG Amorphous H H L 0 LPSG Amorphous H H L 0 LSi3N4 Amorphous L L M 0 0SiNxHy Amorphous H M H 0 0SiOxNyHx Amorphous H M L 0 0
Etch rates: H, high; M, medium; L, low; 0, nil.
Figure 1.12 Fabrication of metal-on-silicon (MOS) devices (Moreau, p.4).
Figure 1.13 The photolithographic technique for pattern definition(Speight, Fig. 1.3b).
Table 1.27 Etchants for dielectrics and insulators used in silicon microelectronic devices(Kern and Schnable, p. 245)
NaOHHF- H3PO4 H2SO4 (30%
Material Form H2O BHF (hot) (hot) hot)
SiO2 Amorphous or H H L 0 Lcrystalline
SiO Amorphous 0 0 0 0Al2O3 Amorphous H H M 0 0
Crystalline 0 0 M 0 0Sapphire 0 0 0 0 0
Ta2O3 Amorphous M LTiO2 Amorphous H M L L
Crystalline L 0 L LAsSG Amorphous H MBSG Amorphous H L L 0 LBPSG Amorphous H H L 0 LPSG Amorphous H H L 0 LSi3N4 Amorphous L L M 0 0SiNxHy Amorphous H M H 0 0SiOxNyHx Amorphous H M L 0 0Etch rates: H, high; M, medium; L, low; 0, nil.
Solid-state device processing is a thin-film-based technology. In this kind of technology surface contamination constitutes a major problem. The presence of contaminants (ions, molecules, particles) on the surface of the substrate can have adverse effects on the physical, chemical and electronic characteristics of the deposited films. The most widely accepted wafer cleaning technique is the RCA
method. This is a two-step operation: Standard Clean 1 (SC-1) NH4OH/H2O2/H2O solution (typical
volumetric ratio: 1/1/5); also referred to as ammonia peroxide mixture (APM). T = 70-90 C, t = 10-15 min. Standard Clean 2 (SC-2) HCl/H2O2/H2O (1/1/5).
An integrated circuit consists of several millions of devices (transistors, capacitors, resistors) on
a given chip. These devices are linked together electrically by metal wires called interconnects. In
order to minimize the length of the wiring (and therefore minimize signal delays) interconnect systems
consist of multiple layers of metals. Figure 1.14 presents a schematic illustration of the cross-section of
a four-layer multilevel metallization (MLM) interconnect system. The main structural components are
described in Table 1.28.
MLM interconnect systems are built up layer by layer by using a combination of processing
techniques, such as etching, deposition, and planarization. The surface of each layer must exhibit a high
degree of global planarity before the next layer is added. An increasingly important planarization
technique is chemical-mechanical polishing (CMP). In the CMP process an aqueous slurry containing
an abrasive (e.g., alumina, silica) and chemicals which can attack the dielectric material (e.g., NH4OH
for SiO2) or the metal (e.g., an oxidant plus a base, acid or a complexant) is used with a polishing tool as
illustrated in Figure 1.15. The slurry is formulated with a dispersant; particle aggregation has an adverse
effect on the surface roughness of the polished films.
Figure 1.14 Schematic illustration of a four-layer multilevel metallization (MLM) interconnect
system (After Wilson, Tracy, and Freeman, p. 2).
Figure 1.15 Chemical-mechanical polishing (Olsen and Moghadam, in Handbook of Multilevel Metallization)
Table 1.28 Principal structural components of multilevel metallization systems*
Structural Component Function_________________________ Material_______________________
ILD0 Provide dielectric insulation between silicon device components and the metal interconnect layers
Boron-doped and phosphorus-doped silicon glass (BPSG)
Contact Provides electrical connection from the interconnect to silicon components through ILD0
Ti + TiN/W
Metal 1 (M1) First layer of metal interconnect W or Al (Cu
Metal 2 (M2) Second layer of metal interconnect Al(Cu)
Metal 3 (M3) Third layer of metal interconnect Al(Cu)
Metal 4 (M4) Fourth layer of metal interconnect Al(Cu)
ILD1 Dielectric layer between M1 and M2 PETEOS
ILD2 Dielectric layer between M2 and M3 PETEOS
ILD3 Dielectric layer between M3 and M4 PETEOS
Via 1 Provides electrical connection between M1 and M2 through ILD1
W
Via 2 Provides electrical connection between M2 and M3 through ILD2
W
Via 3 Provides electrical connection between M3 and M4 through ILD3
W
Passivation Final dielectric layer, provides protective physical, chemical barrier to the circuit
PSG + Si3N4
*Modified from S. R. Wilson, C. J. Tracy, and J. L. Freeman, Jr., eds., Handbook of Multilevel Metallization for Integrated Circuits, 1993, p. 4.
Once the silicon-based devices have been fabricated, they are organized into various functional
and operating systems. This process is termed electronic packaging. In printed circuit boards (PCBs)
metallic films (primarily copper) provide the electrical conductor paths needed to link the various
mounted electronic components. Figure 1.16 illustrates the basic manufacturing steps used to lay down
the metallic materials (Figure 3.6, p. 3.12, Coombs). Table 1.29 lists various etching solutions used in
PCB manufacturing.
Figure 1:16 Basic steps in the manufacture of printed circuit boards (after H. Nakahara, in C. F. Coombs, Jr., ed., Printed Circuits Handbook, 4th ed., 1996, p. 3.12).
Table 1.29 Printed circuit board copper etchantsEtching Solution___________________ Chemical Reactions______________________
Alkaline Ammonia Cu + Cu(NH3)42+ = 2Cu(NH)2
+
4Cu(NH3)2+ + 8NH3 + O2 + 2H2O
= 4Cu(NH3)42+ + 4OH-
2Cu + 8NH3 + ClO2- + 2H2O
= 2Cu(NH3)42+ + Cl- + 4OH-
Sulfuric Acid - Hydrogen Peroxide Cu + H2O2 + H2SO4 = CuSO4 + 2H2O
Cupric Chloride Cu + CuCl2 = Cu2Cl2
Cu2Cl2 + 4Cl- = 2CuCl32-
Persulfate Cu + (NH4)2S2O8 = CuSO4 + (NH4)2SO4
Ferric Chloride Cu + FeCl3 + 2HCl = CuCl32- + FeCl2 + 2H+
Chromic-Sulfuric Acid 3Cu + 2HCrO4- + 14H+ = 3Cu2+ + 2Cr3+ + 8H2O
Nitric Acid 3Cu + 2NO3- + 4H+ = 3Cu2+ + 2NO2 + 2H2O
1.2.9 Cement TechnologyThe main use of cement is in the construction industry, where it is used in buildings and in civil
structures such as motorways, bridges, garages, and dams. Other fields of application include the petroleum industry, where it is used as a liner for oil wells. Cement powder is a mixture of pulverized gypsum (CaSO4.2H2O) and clinker particles. Clinker, in turn, is obtained by subjecting a mixture of
limestone (source of calcium), and clay or shale (source of silicon, aluminum, and iron) to a high temperature treatment. Typically, the particles in cement range in size from under 1mm to 100mm.
The practical utility of cement in construction stems from its ability, in the presence of water,
to transform into a porous solid. The stage at which this transformation is observed is termed the set
point. In order for setting to occur, the cement-water slurry must undergo a complex suite of chemical
reactions, which together, are described as cement hydration. Figure 1.17 presents an illustration of the complexity of the hydration process, using the language of cement chemistry. The following notations are used: A = Al2O3, C = CaO, S = SiO2; thus C3S = Ca3SiO5 (tricalcium silicate), CH = calcium
hydroxide (CaOH), CSH = amorphous or poorly crystalline calcium silicate hydrate. Typically, tricalcium silicate constitutes 50-70% of the cement particles and it is believed that the main reaction responsible for the setting of cement is the following:
C3S + nH2O = CSH + CH (1.34)
The reaction product CSH is a hydrated gel, and the setting of cement is associated with the progressive dehydration of this material. Another cement component which can undergo hydration is calcium aluminate (C3A). In fact, this material reacts much more rapidly than C3S and this can lead to
undesirable premature flash set of cement. An important role of gypsum in cement is to inhibit this reaction; The dissolution of gypsum releases sulfate ions which react with calcium aluminate to give the mineral ettringite:
C3A + Gypsum --> Ettringite (1.35)
Figure 1.17 The main chemical reactions associated with cement hydration(After Billingham and Coveney, 1993)
1.2.10 Battery TechnologyBatteries are devices that exploit electrochemical reactions to generate electricity. The active
unit of a battery system is the electrochemical cell. A cell has three key components: a positive electrode (cathode), a negative electrode (anode) and an electrolyte. When the anode is immersed in the electrolyte, it undergoes an electron-producing (oxidation) reaction with one or more of the aqueous phase constituents. On the other hand, the cathode undergoes an electron-consuming (reduction) reaction. When an external electrical connection is made between the two electrodes, electrons flow through this connection from the anode to the cathode. This electron flow constitutes an electrical current. Within the electrolyte, the current is carried by the transport of ions.
The electrochemical reactions consume the anode and cathode materials, and the cell becomes completely discharged when one of the electrodes is used up. In some cases, it is possible to regenerate the active materials by applying an external source of current but in the opposite direction. This process is termed recharging. We can, therefore, distinguish between primary cells, which are not rechargeable, and secondary cells, which are rechargeable. Tables 1.30 and 1.31 respectively present lists of typical primary and secondary cells. It can be seen that aside from oxygen, the cathodes are all metal oxides, while all the anodes are metals. The preferred electrolytes are those based on strong mineral acids (e.g., sulfuric acid, H2SO4), caustic alkalis (e.g., KOH), and salts of strong acids (e.g., ZnCl2).
Table 1.30 Primary cells (after M. Barak, ed., Electrochemical Power Sources, pp. 3, 99)
Electrodes Electrolyte Open-circuitCell Cathode Anode Aqueous Solution EMF(V) Overall Cell Reactions
Leclanché drycell
MnO2(C) Zn NH4Cl/ZnCl2 1.60 2MnO2(s) + 2NH4Cl + Zn 2MnOOH(s) + Zn(NH3)2Cl2(s)8MnO2(s) + 8H2O + ZnCl2 +
4Zn 8MnOOH + ZnCl2 .
4Zn(OH)2(s)
Alkaline Manganese cell
MnO2(C) Zn KOH 1.55 2MnO2(s) + H2O + Zn 2MnOOH(s) + ZnO(s)
Mercury cell HgO Zn KOH 1.35 HgO(s) + Zn Hg + ZnO(s)
Lalande cell CuO Zn KOH 1.10 CuO(s) + Zn Cu + ZnO(s)
Air-depolarised cell
O2(C) Zn KOH or NaOHor NH4Cl
1.45 O2 + 4NH4Cl + 2Zn 2H2O + 2Zn(NH3)2Cl2(s)
Table 1.31 Secondary cells (after M. Barak, ed., Electrochemical Power Sources, pp. 4, 328)
Electrodes Electrolyte Open-circuitCell Cathode Anode Aqueous
SolutionEMF(V) Overall Cell Reactions
Lead/acid PbO2 Pb H2SO4 2.10 PbO2(s) + H2SO4 + Pb PbSO4(s) + 2H2O
Nickel/cadmium NiOOH Cd KOH 1.29 2 NiOOH(s) + Cd + 2H2O 2 Ni(OH)2(s) + Cd(OH)2(s)
Nickel/iron NiOOH Fe KOH 1.37 2 NiOOH(s) + Fe + 2H2O 2 Ni(OH)2(s) + Fe(OH)2(s)
Silver/zinc AgO Zn KOH 1.85 AgO(s) + Zn + H2O Ag + Zn(OH)2(s)
Ag2O Zn KOH 1.60 Ag2O(s) + Zn + H2O 2 Ag + Zn(OH)2(s)
Silver/cadmium AgO Cd KOH 1.38 AgO(s) + Cd + H2O Ag + Cd(OH)2(s)
Ag2O Cd KOH 1.15 Ag2O(s) + Cd + H2O 2 Ag + Cd(OH)2(s)
Nickel/zinc NiOOH Zn KOH 1.74 2 NiOOH(s) + Zn + 2H2O 2 Ni(OH)2(s) + Zn(OH)2(s)
1.2.11 Solar Energy Conversion and Photoelectrochemical ProcessingThe amount of solar energy received on the earth's surface in two weeks is comparable with the
total (past and present) fossil fuel resources in the world. With the continuing depletion of these fossil fuel resources, there is some interest in developing ways to tap into the sun's energy for the generation of electricity as well as the production of chemicals. An aspect of solar energy conversion of direct relevance here concerns the use of photosensitive electrodes in aqueous systems. An especially attractive system is the conversion of water to hydrogen and oxygen:
H2O + Sunlight H2 + 1/2O2 (1.36)
Large amounts of water are readily available and as a fuel, hydrogen has the advantage that it is light and easy to transport, and its combustion produces no troublesome chemicals.
The operation of a photoelectrochemical (PEC) cell is illustrated schematically in Figure 1.16. When subjected to illumination of the proper energy, electron-hole pairs are created in the semiconductor (MA) (a hole, h+, is simply the absence of an electron):
MA + Light MA + h+ + e- (1.37)
In the case of the photochemical conversion of water, the electron travels through the external circuit to the counter electrode where it reacts with protons to give molecular hydrogen:
2H+ + 2e- + = H2 (1.38)
At the semiconductor/electrolyte surface, the hole reacts with hydroxyl ions to give molecular oxygen:
2OH- + = H2O + 1/2O2 (1.39)
Examples of the relevant photosensitive materials are semiconductors such as cadmium sulfide (CdS), titania (TiO2), and gallium arsenide (GaAs). The nature of the material determines which region
of the solar spectrum is accessible for the PEC process. A major issue in the operation of photoelectrochemical systems concerns the chemical stability of the electrode material. In the absence of light, the solid may dissolve in the aqueous solution. Also, a hole is capable of decomposing a solid unless there is an aqueous phase species which can react sufficiently rapidly with it:
MA + 2h+ = M2+ + A (1.40)
h+
e-
Light
Semicon- ductor Electrode
Counter Electrode
Figure 1.18 Schematic illustration of a photoelectrochemical (PEC) cell.
1.2.12 Waste Treatment and ControlIt can no longer be said that the work of the metallurgical or materials processing engineering is
over, once the refined metal has been produced, the workpiece has been plated, or the appropriate powder has been synthesized. We now live in an era where the job of the metallurgical/materials processing engineer extends to the treatment of the effluents generated while preparing the saleable product. In the U.S., for example, there are federal regulations on pollution control and hazardous waste treatment which have a direct bearing on the plant-level activities of industries engaged in metal extraction and materials synthesis and processing. These federal laws include: the Federal Water Pollution Control Act, the Toxic Substance Control Act (TSCA), the Resource Conservation and Recovery Act of 1976 (RCRA), and the Comprehensive Environmental, Compensation and Liability Act of 1980 (CERCLA). There are strict EPA definitions of hazardous materials based, on certain ignitability, corrosivity, reactivity, and toxicity criteria.
According to one report, the total volume of hazardous waste produced in the U.S. in 1986 amounted to 747 million tons, 58.8% of which was generated by the chemical and petroleum industries, 32.7% by the metal-related industries, and 8.5% by other industries (Brooks, p. 3). The metal-related industries include the primary metals industries, the fabricated metals industries, the electrical and electronic machinery industries, and the transportation equipment industries. Metallic wastes that have been classified as hazardous include those listed in Table 1.32.
Various waste treatment and control options are available and these can be categorized as: (a) waste volume minimization, (b) conventional technologies, (c) alternative technologies, (d) materials recovery, and (e) reagent substitution. Brief characteristics of these options are presented in Table 1.33. Figure 1.17 illustrates the manner in which waste treatment and materials recovery can be combined with conventional mineral processing, hydrometallurgical extraction, ceramic processing, and surface finishing.
Table 1.32 Selected hazardous metallic wastes (from Brooks, Metal Recovery from Industrial Waste, pp. 14-16).
Industry and EPAHazardous Waste No. Hazardous Waste
F006 Wastewater treatment sludges from electroplating operations.
F019 Wastewater treatment sludges from the chemical conversion coating of aluminum
F007 Spent cyanide plating bath solutions from electroplating operations.
K002 Wastewater treatment sludge from the production of chrome yellow and orange pigments.
K003 Wastewater treatment sludge from the production of molybdate orange pigments
K004 Wastewater treatment sludge from the production of zinc yellow pigments.
K007 Wastewater treatment sludge from the production of iron blue pigments.
K061 Emission control dust/sludge from the primary production of steel in electric furnaces
K062 Spent pickle liquor generated by steel-finishing operations of plants that produce iron or steel.
K069 Emission control dust/sludge from secondary lead smelting.
K100 Waste leaching solution from acid leaching of emission control dust/sludge from secondary lead smelting.
_____________________________________________________________________________
Table 1.33 Processing options for waste and control
Waste Treatment/Control Option Remarks
Waste Volume Reduction In-plant changes, e.g., modifications in the mode and amount of water and chemical additions, manipulation of equipment configuration, improved instrumentation.
Conventional Treatment Technologies Pollution control technologies currently well established in specific metals/materials processing industries, e.g., sulfur dioxide (SO2) for conversion of hexavalent to trivalent chromium, alkaline chlorination for cyanide destruction, hydroxide precipitation for heavy metal removal, coagulation/flocculation to enhance solids settling rates, filtration/gravity settling (thickening) for solid/water separation.
Alternative Technologies Necessitated by limitations in conventional technologies, e.g., in ability to meet effluent standards with hydroxide precipitation (replace with sulfide precipitation), generation of prohibitively high sludge volumes by conventional hydroxide precipitation, inefficient removal of finely divided solids, adverse environmental effects of waste treatment reagents (e.g., chlorine).
Materials Recovery Reclamation of process water and reagents for recycle; motivated by increasing costs of raw materials and waste disposal.
Reagent Substitution Use new formulations of process solutions with less toxic chemicals, e.g., replace cyanide solutions with non-cyanide solutions.
_______________________________________________________________________________
1.3 Common Denominators in Aqueous Processing1.3.1 Integrated Processing
In practice, there is a certain amount of linkage between the various aqueous processing application fields. In Section 1.2.12, we noted the respective links between waste treatment and hydrometallurgical extraction, and minerals/materials processing. Also, traditionally, mineral processing operations and hydrometallurgical plants are frequently located adjacent to each other and are linked by materials flow. Integration of mineral processing, hydrometallurgical extraction, ceramic processing and waste treatment is also possible, as illustrated in Figure 1.20.
WASTES RECYCLE
WASTE TREATMENTCHEMICALS ENVIRONMENTAL
DISPOSAL
MINERAL PROCESSING
ORE CONCENTRATE
(a)
REFINED METALS & METAL COMPOUNDS
WASTES RECYCLE
WASTE TREATMENTCHEMICALS ENVIRONMENTAL
DISPOSAL
ORE &
CONCENTRATE
HYDROMET EXTRACT'N
(b)
ENVIRONMENTAL DISPOSAL
WASTES RECYCLE
WASTE TREATMENTCHEMICALS ENVIRONMENTAL
DISPOSAL
CERAMIC PROCESSING
PRECURSORS POWDERS &FILMS
(c)
WASTES RECYCLE
WASTE TREATMENTCHEMICALS
PART &CHEMICALS
PLATED PART SURFACE FINISHING
(d)
Figure 1.19 (a) Combined mineral processing-waste treatment; (b) combined hydrometallurgical extraction-waste treatment; (c) Combined ceramic processing-waste treatment, (d) combined surface finishing-waste treatment.
1.3.2 Reagents, Solutions, and MaterialsIt can be seen from the above discussion that the applications of aqueous processing are many and
diverse. However, these different aqueous processing systems have many things in common. First, we recognize that water is the common solvent. Secondly, as illustrated in Table 1.34, a given reagent may have several different applications. Thus, for example, cyanide solutions are encountered in the hydrometallurgical extraction of gold and silver; cyanide baths are also exploited in the electroplating of these same metals.
From a chemical standpoint, similar solids are encountered in the various aqueous systems as illustrated in Table 1.35. Thus the silica/water interface is important in mineral flotation,
hydrometallurgical extraction, catalyst preparation, semiconductor device microfabrication, micromachining of micromechanical devices, and waste treatment. Manganese oxides are leached in hydrometallurgy, electrolytic manganese dioxide is prepared for the battery industry, and reactions at the MnO2/aqueous interface are exploited in batteries.
1.3.3 Unit ProcessesIn a given aqueous processing operation, the feed (raw) materials and the products are typically
linked by a series of processing steps. These steps, termed unit operations or unit processes, include grinding, dissolution, flocculation, coagulation, dispersion, filtration, gravity settling, evaporation, distillation, absorption, adsorption, ion-exchange, solvent extraction, chemical precipitation, and electrodeposition, as summarized in Table 1.36. A given unit process may find application in several different aqueous processing systems, as illustrated by the examples presented in Table 1.37.
1.3.4 Physicochemical ProcessesUnderlying each unit process is a mechanism of action. For example, both leaching and
precipitation rely on solubility phenomena. These mechanisms of action, in turn, are made possible by a variety of physicochemical processes, which are molecular-level events (such as collision of molecules, bond-formation, bond-breakage, electron transfer, molecular diffusion, ion migration) and colloidal and interfacial interactions such as aggregation, dispersion, and particle-fluid dynamics. Figure 1.19 presents a schematic illustration of selected interfacial and colloidal physicochemical processes. A major focus of the material in the following chapters is on the roles of these physicochemical processes in various aqueous processing systems.
Figure 1.20 Integrated processing: Combined mineral processing-hydrometallurgical extraction-ceramic processing-waste treatment.
Table 1.34 Reagents in aqueous processing
Reagents_______ Industries______ Applications_______ _
Sulfuric Acid Hydrometallurgy LeachingSolutionMetal production
Metal Finishing Pickling (steels)
Batteries Pb-acid cell
Hydrochloric Acid Hydrometallurgy LeachingSolution purificationMetal production
Metal Finishing PicklingElectroplating
Cyanide Hydrometallurgy Leaching(Au, Ag)Solution purificationMetal production
Metal Finishing Electroplating, Pickling
Phosphoric Acid Metal Finishing Electroplating (Rh), Electropolishing
Semicond. Microfab. Etching
Caustic Soda (NaOH) Hydrometallurgy Leaching (e.g. Al from bauxite ores)Precipitation
KOH Semiconductor Etching (SiO2, Si)Microfabrication
Micromachining Etching (SiO2, Si)
Batteries Electrolyte (alkaline storage batteries)
NH4OH Hydrometallurgy Leaching (Cu, Ni, Co)Solution purificationMetal production
Metal Finishing Electroplating
Semiconductor Etching (SiO2, Si)Microfabrication
Micromachining Etching (SiO2, Si)
Oxalate Hydrometallurgy Precipitation (e.g., rare earths)
Ceramic Processing Powder synthesis
Table 1.35 Materials in aqueous processing
Materials Industries Applications
Silicon dioxide Mineral Processing Flotation, Coagulation, Flocculation
Hydrometallurgy Leaching, Precipitation
Ceramic Processing Powder/Film synthesis, suspensionprocessing
Catalyst Preparation Synthesis of substrates
Cement Technology Cement hydration
Semiconductor Device Etching for cleaning and patternMicrofabrication definition
Micromachining Etching for microstructure development
Waste Treatment Silica precipitation, coagulation,flocculation
Alumina Mineral Processing Flotation, Coagulation, Flocculation
Hydrometallurgy Leaching, Precipitation
Ceramic Processing Powder/Film synthesis, suspensionprocessing
Cement Technology Cement hydration
Surface Finishing Anodic oxide coating on aluminum
Waste Treatment Adsorbent
Metal Sulfides Mineral Processing Flotation
Hydrometallurgy Leaching, precipitation
Ceramic Processing Powder Synthesis (e.g., ZnS)
Catalyst Preparation Synthesis of metal sulfides
Waste Treatment Metal removal as sulfide precipitate
Table 1.36. Types of Unit Processes and Unit Operations (1).
Name Feed Change Agent Products Principle of Action Practical ExampleEvaporation Liquid Heat Liquid + Vapor Difference in
volatilitiesConcentration of metal salt solutions
Drying Moist solid Heat Dry solid + humid vapor
Evaporation of water Drying of precipitates
Crystallization Liquid Cooling or heat + evaporation
Liquid + solids Temperature dependence of solubilities
Preparation of metal salts
Freeze drying Frozen water-containing solid
Heat Dry solid + water vapor
Sublimation of water Preparation of unagglomerated powders
Absorption Gas Nonvolatile liquid Liquid + vapor Preferential solubilitySolvent extraction Liquid Extractant in
Immiscible LiquidTwo liquids Referential organic
phase solubility of metal-extractant complex
Solution purification
Ion exchange Liquid Solid resin Liquid + solid resin Complex or ion-pair formation
Solution purification
Adsorption Liquid Solid adsorbent Liquid + solid Surface complexation Solution purificationDissolution or Leaching
Solids Aqueous-soluble chemical reactant
Liquid + solid Preferential solubility Gold extraction from ones; removal f coatings from substrates.
Washing Solids with sol'n entrainment
Aqueous sol'n Liquid + solid Dilution Recover entrained valuables; purify precipitates
Precipitation Liquid Chemical reactant Liquid + solid Conc'n. dependence of solubility
Solution purification; metal recovery; powder synthesis
(Table 1.36 contd.)
Name Feed Change Agent Products Principle of Action Practical ExampleElectrodeposition Liquid Electricity Liquid + solid Electrochemical
reactionElectrowinning of metals; electrorefining; electroplating
Dialysis Liquid Selective Membrane; solvent
Liquids Different rates of diffusional transport through membrane (no bulk flow)
Recovery of NaOH in rayon manufacture
Electrodialysis Liquid Anionic and cationic membranes; electric field
Liquids Tendency of anion-exchange membranes to pass only anion, etc.
Desalination of brackish waters
Liquid membrane Liquid Solvent liquid layer Liquids Different rates of permeation through liquid layer
Waste-water processing; metal separations.
Reverse osmosis Liquid sol'n. Pressure gradient (pumping power) + membrane
Two liquid sol'ns. Different combined solubilities and diffusivities of species in membrane
Seawater desalination
Ultrafiltration Liquid sol'n. Pressure gradient (pumping power) + membrane
Two liquids Differential permeabilities through membrane (molecular size)
Waste-water treatment
Froth flotation Mixed powdered solids
Added surfactants; rising air bubbles
Two solids Selective adsorption leading to hydrophobic solids
Ore flotation
Ion flotation Liquid sol'n. Added surfactants; rising air bubbles
Solid + liquid Selective electrostatic and/or complexation interactions leading to hydrophobic species
Ion separations
Coagulation Colloidal dispersion Electrolyte Solid aggregates + liquid
Modification of surface charge through adsorption
Solid/liquid sep'n.
Flocculation Colloidal dispersion Polymer Solid aggregates + liquid
Particle bridging through adsorption
Solid/liquid sep'n.
(Table 1.36 contd.)
Name Feed Change Agent Products Principle of Action Practical ExampleDispersion Colloidal aggregates
in liquidElectrolyte; polymer Colloidal dispersion Modification of
surface charge and surface layers through adsorption leading to destabilization to aggregates
Stabilization of suspensions
Calcination Solids Heat Solid (+ vapor) Temperature dependence of chemical stability
Production of oxides from metal hydroxides
Roasting Solids Heat + chemical reactant
Solid (+ gas) High temp. chemical reaction
Production of metal oxides from sulfides.
Sintering Porous Solid Heat Densified solid Interparticle diffusion Preparation of ceramics
Comminution Solid particles Mechanical energy + grinding media (e.g. balls)
Ground particles Particle breakage due to collision of solids with grinding media
Grinding of ores and ceramic powders
Size classification Solid particles Screen Two or more solids Size-selective passage through screen openings
Feed preparation for leaching; sorting of ceramic powder products into size fractions.
Settling Liquid + solid or another immiscible liquid
Gravity Liquid + solid or another immiscible liquid
Density difference Solid/liquid separation
Centrifugation Liquid + solid or another immiscible liquid
Centrifugal force Liquid + solid or another immiscible liquid
Density difference Solid/liquid separation
Filtration Liquid + solid Pressure reduction (energy); filter medium
Liquid + solid Size-selective passage through pores of filter medium
Solid/liquid separation
Mixing Solid + liquid Mechanical energy Solid-liquid suspension
_____________________________________________________________________________________(1) Based in part on Table 1-1, C. J. King, Separation Processes, 2nd ed., McGraw-Hill, New York, 1980.
Table 1.37 Unit Processes in Aqueous Processing
Unit Processes Industries Applications/Roles Dissolution Mineral Processing Surface modification in
mineral flotationHydrometallurgy Metal extractionCeramic Processing Fabrication of specialty glasses
Glass corrosion
Cement Technology Cement hydration
Surface Finishing Stripping of defective deposits
Batteries Discharging of cells
Semiconductor Device Etching for cleaning and patternMicrofabrication definition
Micromachining Etching for microstructuredevelopment
Waste Treatment Leaching (instability) of solidwastes
Precipitation Mineral Processing Surface modification in mineralflotation
Hydrometallurgy Solution purification, metal/metalcompound production
Ceramic Processing Powder/Film/Fiber synthesis
Cement Technology Cement hydration
Semiconductor Device Surface contaminationMicrofabrication
Surface Finishing Chemical plating
Batteries Electrode/electrolyte reactions
Waste Treatment Metal/anion removal as precipitates
Ion Exchange Hydrometallurgy Ion separations
Surface Finishing Process water purification
Waste Treatment Ion removal
Electrodeposition Hydrometallurgy Electrowinning, electrorefining
Ceramic Processing Electrosynthesis
Surface Finishing Electrodeposition, anodization
Batteries Recharging reactions
Waste Treatment Metal recovery
Figure 1.21 Interfacial and colloidal physicochemical processes.
FURTHER READING
1. P. A. Cox, The Electronic Structure and Chemistry of Solids, Oxford, New York, 1987.
2. J. Billingham and P. V. Coveney, "Simple Chemical Clock Reactions: Applications to Cement Hydration", J. Chem. Soc., Farad. Trans., 89, 3021-3028 (1993).
3. F. N. Kemmer, ed., The Nalco Water Handbook, McGraw-Hill, New York, NY 1979.
4. D. M. Considine, Ed., Chemical and Process Technology Encyclopedia, McGraw-Hill, New York, NY, 1974, pp. 926-929.
4a. Kirk-Othmer, Encyclopedia of Chemical Technology, Wiley-Interscience, New York, 1983.
5. Minerals Yearbook 1993, Volume 1, Metals and Minerals, U. S. Bureau of Mines, Washington, D.C. 1989.
6a. J. Leja, Surface Chemistry of Froth Flotation, Plenum, New York, 1982.
6b. F. Halverson and H. P. Panzer, "Flocculating Agents", in Kirk-Othmer Encyclopedia of Chemical Technology, Vol. 10, 3rd. ed., 1980, pp. 489-523.
7. C. K. Gupta and T. K. Mukherjee, Hydrometallurgy in Extraction Processes, Vols. I & II, CRC Press, Boca Raton, FL, 1990.
8. A. R. Burkin, The Chemistry of Hydrometallurgical Processes, Spon, Lond, 1966.
9. F. Habashi, Extractive Metallurgy. Vol. 2 Hydrometallurgy, Gordon and Breach, New York, NY, 1970.
9a F. Habashi, A Textbook of Hydrometallurgy, Métallurgie Extractive Québec, Enr., Sainte Foy, Quebec, 1993.
10. E. D. Jackson, Hydrometallurgical Extraction and Reclamation, Ellis Horwood, Chickester, U. K., 1987.
11. M. Streat and D. Naden, eds., Ion Exchange and Sorption Processes in Hydrometallurgy, W
12. J. Rydberg, C. Musikas, and G. R. Choppin, eds., Principles and Practices of Solvent Extraction, Marcel Dekker, New York, 1992.
12a. T. C. Lo, M. H. I. Baird, and C. Hanson, eds., Handbook of Solvent Extraction, Wiley, New York, 1983.
12b. G. M. Ritcey and A. W. Ashbrook, Solvent Extraction. Principles and Applications to Process Metallurgy. Elsevier, New York, 1979.
13. D. W. Johnston, Jr., "Nonconventional Powder Preparation Techniques", Ceram. Bull., 60(2), 221-224, 243 (1981).
14. L. S. Millberg, "The Synthesis of Ceramic Powders", J. Metals, August 1987, pp. 9-13.
15. D. W. Johnson, Jr., and P. K. Gallacher, "Reactive Powders from Solution", in Ceramic Processing Before Firing, G. W. Onoda, Jr., and L. L. Hench, eds., Wiley, New York, NY, 1978, pp. 125-139.
16. L. H. Yaverbaum, ed., Technology of Metal Powders. Recent Developments, Noyes Data Corp, Park Ridge, NJ, 1980.
16c. M. C. Fuerstenau, ed., Flotation, A. M. Gaudin Memorial Volume, AIME, New York, 1976.
16d. K. J. Ives, ed., The Scientific Basis of Flocculation, Sijthoff & Noordhoff, Alphen aan den Rijn, The Netherlands, 1978.
17. N. Ichinose, ed., Introduction to Fine Ceramics, Wiley, New York, 1987.
17a. J. S. Reed, Principles of Ceramics Processing, 2nd ed., Wiley, New York, 1995.
17b. M. N. Rahaman, Ceramic Processing and Sintering, M. Dekker, New York, 1995.
18. D. E. Clark and B. K. Zoitos, eds., Corrosion of Glass, Ceramics and Ceramic Superconductors, Noyes, Park Ridge, NJ, 1992.
19. H. H. Kung, Transition Metal Oxides: Surface Chemistry and Catalysis, Elsevier, New York, 1989.
20. O. Weisser and S. Landa, Sulfide Catalysts, Their Properties and Applications, Pergamon, New York, 1973.
21. J. P. Brunelle, "Preparation of Catalysts by Metallic Complex Adsorption on Mineral Oxides", Pure Appl. Chem., 50, 1211-1229 (1978).
22. J. W. Geus, "Production and Thermal Pretreatment of Supported Catalysts", in Preparation of Catalysts III, G. Poncelet, P. Grange, and P. A. Jacobs, eds., Elsevierr, New York, 1983, pp. 1-33.
23. B. H. Carroll, G. C. Higgins, and T. H. James, Introduction to Photographic Theory. The Silver Halide Process, Wiley-Intersciece, New York, 1980.
24. T. H. James, ed., The Theory of the Photographic Process, 4th ed., Macmillan, New York, 1977.
25. R. K. Bunting, The Chemistry of Photography, Photoglass Press, Normal, IL, 1987.
26. A. T. Kuhn, ed., Industrial Electrochemical Processes, Elsevier, New York, 1971.
27. D. Pletcher, Industrial Electrochemistry, Chapman and Hall, New York, NY, 1982.
28. F. A. Lowenheim, ed., Modern Electroplating, 3rd. Ed., Wiley, New York, 1974.
29. L. T. Durney, ed., Electroplating Engineering Handbook, 4th Ed., Van Nostrand, Reinhold, New York, 1984.
29a. Metals Handbook, 9th ed., Vol. 5. Surface Cleaning, Finishing and Coating, American Society for Metals, Metals Park, OH, 1982.
29a. G. Mallory and J. B. Hajdu, eds., Electroless Plating: Fundamentals and Applications, American Electroplaters and Surface Finishers Society, Florida, 1990.
30. J. Skalny and S. Mindess, Materials Science of Concrete II, The American Ceramic Society, Westerville, OH, 1991.
31. H. F. W. Taylor, Cement Chemistry, Academic, New York, 1990.
32. W. Kern, "The Evolution of Silicon Wafer Cleaning Technology", J. Electrochem. Soc., 137, 1887-1892 (1994).
33. J. Speight, "Overview", in The Chemistry of the Semiconductor Industry, S. J. Moss and A. Ledwith, eds., Chapman and Hall, New York, 1987, pp.1-16.
34. W. Kern and G. L. Schnable, "Wet Etching", in The Chemistry of the Semiconductor Industry, S. J. Moss and A. Ledwith, eds., Chapman and Hall, New York, 1987, pp.225-281.
35. W. Kern and C. A. Deckert, "Chemical Etching", in Thin Film Processes, J. L. Vossen and W. Kern, eds., Academic, New York, 1978, pp.401-496.
36. W. M. Moreau, Semiconductor Lithography. Principles, Practices, and Materials, Plenum, New York, 1988, pp.1-27.
36a. J. M. Steigerwald, S. M. Murarka, and R. J. Gutmann, Chemical Mechanical Planarization of Microelectronic Materials. Wiley, New York, 1997.
36b. S. R. Wilson, C. J. Tracy, and J. L. Freeman, Jr., Handbook of Multilevel Metallization for Integrated Circuits. Materials, Technology, and Applications, Noyes Publications, Park Ridge, NJ, 1993.
36c. W. Kern, ed., Handbook of Semiconductor Wafer Cleaning Technology, Noyes Publications, Park Ridge, NJ, 1993.
36d. C. F. Coombs, Jr., ed., Printed Circuits Handbook, 4th ed., McGraw-Hill, New York, 1996.
37. J. W. Patterson, Industrial Wasterwater Treatment Technology, 2nd Ed., Butterworth, Stoneham, MA, 1985.
38. J. W. Patterson and R. Passino, eds., Metals Speciation, Separation, and Recovery, Lewis Publishers, Chelsea, MI, 1987.
39. J. W. Patterson and R. Passino, eds., Metals Speciation, Separation, and Recovery, Vol. II, Lewis Publishers, Chelsea, MI, 1990.
40. A. J. Rubin, ed., Aqueous-Environmental Chemistry of Metals, Ann Arbor Science Publishers, Ann Arbor, MI, 1974.
41. L. D. Benefield, J. F. Judkins, and B. L. Weand, Process Chemistry for Water and Wasterwater Treatment, Prentice-Hall, Englewood Cliffs, NJ, 1982.
42. J. N. Lester, ed., Heavy Metals in Wastewater and Sludge Treatment Processes, Vol. I Sources, Analysis, and Legislation; Vol. II. Treatment and Disposal, CRC Press, Boca Raton, FL, 1987.
43. B. A. Bolto and L. Pawlowski, Wastewater Treatment by Ion Exchange, Spon, New York, 1987.
44. W. J. Eilbeck and G. Mattock, Chemical Processes in Waste Water Treatment, Wiley, New York, 1987.
45. S. D. Faust and O. M. Aly, Chemistry of Water Treatment, Butterworths, Boston, 1983.
46. S. D. Faust and O. M. Aly, Adsorption Processes for Water Treatment, Butterworths, Boston, 1987.
47. W. W. Eckenfelder, Jr., Industrial Water Pollution Control, 2nd ed., McGraw-Hill, New York, 1989.
48. P. Côté and M. Gilliam, eds., Environmental Aspects of Stabilization and Solidification of Hazardous and Radioactive Wastes, ASTM, Philadelphia, PA, 1989.
49. C. Calmon and H. Gold, eds., Ion Exchange for Pollution Control, Vols I and II, CRC Press, Boca Raton, FL, 1979.
50. G. C. Cushnie, Jr., Electroplating Wasterwater Pollution Control Technology, Noyes., Park Ridge, NJ, 1985.
51. C. S. Brooks, Metal Recovery from Industrial Waste, Lewis Publishers, Chelsea, MI, 1991.
52. M. R. Watson, Pollution Control in Metal Finishing, Noyes., Park Ridge, NJ, 1973.
53. J. H. L. van Linden, D. L. Stewart, Jr., and Y. Sahai, Recycling of Metals and Engineered Materials, Proceedings of Second International Symposium, TMS, Warrendale, PA, 1990.
54. D.J. Hurd, D.M. Muchnick, M.F. Schedler, and T. Mele, Recycling of Consumer Dry Cell Batteries, Noyes, Park Ridge, NJ, 1993.
55. M. Barak, ed., Electrochemical Power Sources, Peter Peregrines, New York, NY, 1980.
56. K.V. Kordesch, ed., Batteries, Vol. 1, Manganese Dioxide, Marcel Dekker, New York, NY 1974.
57. K.V. Kordesch, ed., Batteries, Vol. 2, Lead-Acid Batteries and Electric Vehicles, Marcel Dekker, New York, NY, 1974.
58. D. Segal, Chemical Synthesis of Advanced Ceramic Materials, Cambridge, New York, 1989.
59. W. Kern, ed., Handbook of Semicondutor Wafer Cleaning Technology, Noyes, Park Ridge, NJ, 1993.
60. Y. V. Pleskov, Solar Energy Conversion. A Photoelectrochemical Approach, Springer-Verlag, New York, 1990.
61. M. D. Archer, "Electrochemical Aspects of Solar Energy Conversion", J. Appl. Electrochem., 5, 17-38 (1975).
62. K. Rajeshwar, P. Singh, and J. DuBow, "Energy Conversion in Photoelectrochemical Systems - A Review", Electrochim. Acta, 23, 1117-1144 (1978).
63. A. J. Novak, "Photoelectrochemistry: Applications to Solar Energy Conversion", Ann. Rev. Phys. Chem., 29, 189-222 (1978).
64. M. A. Butler and D. S. Ginley, "Principles of Photochemical Solar Energy Conversion", J. Mater. Sci., 15, 1-19 (1980).
65. A. K. Kuczkowski, "Photoelectrochemical Processes at Semiconductors", in Photochemistry and Photophysics, Vol. III, pp. 103-136 (1990?).
66. H. Kisch and R. Kunneth, "Photocatalysis by Semiconductor Powders - Preparative and Mechanistiv Aspects", in Photochemistry and Photophysics, Vol. IV, pp. 103-136 (1990?).
______________________________________________________________________________________