Chapter 1
General Introduction
Chapter: 1 General Introduction
1.1 Preamble
Metals have been in service of mankind since the early days of
civilization. The history of metallurgy probably began with the
accidental discovery that certain stones could be melted by fire, thus
releasing those materials known as "metals". The history of mankind
from time immemorial shows intimate and inalieanable relationship
with minerals and metals. Mineral-metals play significant role for the
economy and industrial growth of any developing nation. The birth of
hydrometallurgy resulted from the discovery that the water dripping
from the roof of underground mine working or flowing out of ore
dumps often contain metallic compounds and that these compound
could be readily recovered by simply letting the liquor dry up in
suitable pond. The earliest records of the wide spread practice of
hydrometallurgy go back to ancient mining around 166 A.D., in the
island of Cyprus, famous for its copper mine (1).
Metals In the minerals are generally present as carbonates,
oxides and sulphides. The minerals in which the metals are
sufficiently concentrated and form commercial source of desired
metals are called ore (2). A process applied to obtain pure metals after
excavation of ore from the mine is referred to as mineral processing
(3). The con\entional mineral processing or metal recovery from the
high-grade ores and concentrates can be categorized as
pyrometallurgy and hydrometallurgy. Pyrohydrometallurgy includes
the combination of both the above processes (4-6).
Bioleaching refers to the conversion of insoluble solid metals
values into their water-soluble forms using microorganisms and/ or
their products (7). Biooxidation describe the microbiological oxidation
of host mineral, which contain metal compound of interest. As a result
metal values remain in the residues in a more concentrate form. In
1
Chapter: 1 General Introduction
gold mining, biooxidation operation is used as a pre-treatment process
to remove (partially) pyrite of arsenopyrite. This process is also called 11 biobeneficiationll where solid materials are refined and unwanted
impurities are removed (8). The term llbiomining11,
11 bioextractionll or 11 biorecoveryll are applied to describe the mobilization of elements from
solid materials mediated by bacteria and fungi. Biomining concerns
mostly applications of microbial metal mobilization process in large
scale operation of mining industry for an economical metal recovery
(9, 1 0). 11Biohydrometallurgyll covers biomining or bioleaching process.
Biohydrometallurgy represents an interdisciplinary field where
principles of microbiology, geochemistry, biotechnology,
hydrometallurgy, mineralogy, geology, chemical engineering and
mining engineering are combined (11). The term II biogeotechnology 11
is also used instead of 11 biohydrometallurgy11• Since the advent of
biohydrometallurgical processing many ma.Jor breakthroughs have
been achieved and this economically profitable and sustainable
technology that now finds wide applications in various field ranging
from metal extraction to environmental clean up. So, more attentions
are needed for rationalization and optimisation of
biohydrometallurgical processes (12). Three main areas of application
of biohydrometallurgy are identified;
fi] Metal extraction from minerals and rocks.
fii] Pre-treatment of minerals to make them amenable to further
processing.
(iii] Environmental protection.
Recent advancement in the use of biotechnological principles
for the successful extraction and recovery of metals from low and high
grade ore, selected concentrates and industrial waste are expected to
make a significant contribution to fulfil the future demand of many
precious metals.
2
Chapter: 1 General Introduction
Bioleaching is a simple effective, clean and economically viable
supplementary technology to the conventional process (13).
Biohydrometallurgical processes have been applied for the extraction
of copper, gold, uranium, cobalt, zinc, nickel, gallium, molybdenum,
cadmium, manganese, antimony, lead, and iridium from their metal
sulphide and oxides. Sulphide mineral occluding platinum grade
metals viz. platinum, rhenium, rubidium, palladium, osmium and
iridium can also microbiologically pretreated. Academic and
commercial applications of biohydrometallurgy are extensively
increasing in laboratory, pilot and commercial scale operations
(14,15).
1.1.1 The advantages of biomining processing
Microorganisms are the backbone for the biomining activity. A
variety of microorganisms are found in leaching environment and have
been isolated from leachate and acidic mine drainage. Very rich
microbial diversity is found in the bioleaching environment, which
include bacteria, fungi, algae and some of the yeast (16). The Rio Tinto
mines in south western Spain are usually considered the cradle of
biohydrometallurgy. The copper mine of Rio Tinto was probably the
first large-scale operation in which the major role is played by
microorganisms. The role that microorganisms plays in biomining
process was demonstrated in 194 7, when Colmer and Hinkel isolated
bacteria belonging to the Thiobacillus genus from acid mine water ( 1 7).
Later Thiobacillus ferrooxidans and Thiobacillus thiooxidans were
isolated and characterized. (18, 19) Thiobacillus ferrooxidans and
Thiobacillus thiooxidans have been recently renamed as
Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans
respectively (20). There are many advantages of biomining operation
as compared to the conventional mining processes (15), which are
listed here;
3
Chapter: 1 General Introduction
Use of naturally occurring key components: microorganisms, water
and air
Work at ambient pressure and temperature
Simple stepwise expandability by a single reactor or in modules of
reactors
Process is simple to operate and maintain
Low energy input and capital cost
Dust and S02 free process
Applicable for bulk complex concentrate
Low to moderate capital investment
Provide essential pre-treatment for refractory ores for selective
leaching
Economically viable for extraction of metal from low grade ores and
major mine waste
Flexible for the treatment for mineral resources with a variety of
metals and in variable concentrates
Environment friendly process.
Recent detail investigation, based on molecular methods such
as DNA-DNA hybridization, 16S rDNA sequencing, PCR based
methods with pnmers derived from rRNA sequencing and
immunological techniques revealed that microbial bioleaching
communities are composed of a vast variety of microorganisms
resulting in the complex microbial interaction (synergism, mutualism,
competition and predation) and nutrient flow (21). Selected
microorganisms of these communities are given in Table 1.1.1 (22).
4
Table 1.1.1. Microbial diversity of acidic bioleaching environments and acidic mine d tage (22).
Domain Organism Nutrition Type Main p tange pH Temperature Leaching Agent Opt. (oC)
chaea Acidianus ambivalens facult.heterotrophic sulfuric acid Acidianus brierleyi facult.heterotrophic sulfuric acid ac Jhilic 1.5-3.0 45-75 Ferroplasma acidiphilum chemolithoautotrophic ferric iron 1.: .2 1.7 15-45 Metallosphaera sedula chemolithoautotrophic ferric iron, ac Jhilic extr.
sulfuric acid thermophilic Sulfolobus acidocaldarius chemolithoautotrophic ferric iron, 0.~ .8 2.0-3.0 55-85
sulfuric acid Sulfolobus brierleyi chemolithoautotrophic ferric iron, extr.
sulfuric acid thermophilic Sulfolobus metallicus chemolithoautotrophic Sulfolobus yellowstonii chemolithoautotrophic ferric iron, extr.
sulfuric acid thermophilic Bacteria Acidiphilium cryptum heterotrophic organic acids 2.( 0 mesophilic
Acidobacterium capsulatum chemoorganotrophic 3.( 0 mesophilic Bacillus coagulans heterotrophic 5.£ 0 22 Bacillus megaterium heterotrophic citrate Gallionella sp. autotrophic ferric iron 6.£ 8 6-25 Leptospirillum ferrooxidans chemolithoautotrophic ferric iron 2.5-3.0 30 Q Leptospirillum chemolithoautotrophic ferric iron 1.7-1.9 45-50
$::) ""'::t
thermoferrooxidans !i .. Leptothrix discophora facult.autotrophic ferric iron, sulfuric 5.f 8 5-40 .....
acid C'l !!
Metallogenium sp. heterotrophic ferric iron 3.~ 8 4.1 ~ Pseudomonas putida heterotrophic citrate, gluconate -5<
"'to a ~ !"\ "'to ... c ::::
Table 1.1.1 Continue ...
Domain Organism Nutrition Type Main Leaching Agent
Thermothrix thiopara chemolithoautotrophic sulfuric acid Thiobacillus acidophilus mixotrophic sulfuric acid Thiobacillus albertis chemolithoautotrophic sulfuric acid
chemolithoautotrophic sulfuric acid Thiobacillus capsulatus chemolithoautotrophic sulfuric acid Thiobacillus concretivorus chemolithoautotrophic sulfuric acid
Thiobacillus delicatus mixotrophic sulfuric acid Thiobacillus ferrooxidans chemolithoautotrophic ferric iron, sulfuric
acid Thiobacillus intermedius facult.heterotrophic sulfuric acid Thiobacillus kabobis mixotrophic sulfuric acid Thiobacillus neapolitanus chemolithoautotrophic sulfuric acid Thiobacillus novellus chemolithoautotrophic sulfuric acid Thiobacillus rubellus chemolithoautotrophic sulfuric acid Thiobacillus thiooxidans chemolithoautotrophic sulfuric acid Thiobacillus thioparus chemolithoautotrophic sulfuric acid
Eukarya Actinomucor sp. heterotrophic succinate Fungi Alternaria sp. heterotrophic citrate, oxalate
Aspergillus niger heterotrophic oxalate, citrate, gluconate, malate, tartrate, succinate
Aspergillus ochraceus heterotrophic citrate Fusarium sp. heterotrophic oxalate, pyruvate
malate, oxalacetate Paecilomyces variotii heterotrophic citrate, oxalate Penicillium ch so enum heterotro hie
p ~ange pH Opt.
ne· u 1.~ 0 3.0 2.( 5 3.5-4.0
0.~ 0
5.0-7.0 1.-' 0 2.4
1.~ 0 6.8 l.f 0 3.0 3.( 5 6.2-7.0 5.( 0 7.8-9.0
5.0-7.0 0.~ 0 2.0-3.5 4.~ ).0 6.6-7.2
Temperature (oC)
60-75 25-30 28-30
45
25-30 28-35
30 28 28 30
25-30 10-37 11-25
27 32 30
28
28
(j
! &" ..
Table 1.1.1 Continue ...
easts
Organism
Rhizopus japonicus Trichoderma lignontm Trichoderma viride Candida lipolytica Rhodotontla sp. Saccharomyces cerevisiae Tontlopsis sp. Trichosporon
Nutrition Type
heterotrophic heterotrophic heterotrophic heterotrophic heterotrophic heterotrophic heterotrophic heterotrophic
Algae, Protozoa and Amoebae are not identified
Main Leachin ent
pH 1ge pH 0 t.
Temperature (oC)
24-26 32 30
28
Chapter: 1 General Introduction
The bioleaching microorganisms obtain a large portion of their energy
from the oxidation of inorganic substance includes oxidation of
sulphidic minerals to soluble sulphates and ferrous iron to ferric form.
The mesophilic chemolithotrophic iron and/ or sulphur oxidizing
bacteria notably Acidithiobacillus ferrooxidans, Acidithiobacillus
thiooxidans, and Leptospirillum ferrooxidans are the most extensively
used microorganism in the biomining and metallurgical industries for
the oxidation of sulphidic minerals (23).
The organism studied the most is Acidithiobacillus ferrooxidans.
Although this is the best-known organism from acidic habitats, one
may not conclude that this organism is dominant in this ecosystem.
Recently in 2002, it has been found that under specific environmental
condition Leptospirillum spp. 1s even more abundant than
Acidithiobacillus ferrooxidans suggesting an important ecological role
in the microbial community structure of bioleaching habitat (24,25).
Thermoacidophilic archaeobacteria have been known for bioleaching
process since many years. All thermophiles belong to the Sulfolobales
a group of extremely thermophilic sulphur and ferrous oxidizers
including genera such as Sulfolobus, Acidianus, Metallosphaera and
Sulphurisphaera (26).
1.1.2 Why extremophilic bioleaching consortium?
Microorganisms that are able to develop under extreme
conditions have recently attracted considerable attention because of
their peculiar physiology and ecology. These extremophiles also have
important biotechnological applications. Acidic environment 1s
especially interesting because, in general, the low pH of the habitat is
the consequence of microbial metabolism and not a condition imposed
by the system as is the case in many other extreme environment such
as, ionic strength, high ferrous and ferric as substrate and product
respectively, temperature, radiation, pressure, etc. (22).
8
Chapter: 1 Getteral Introduction
Ferrous oxidation ability of acidophilic bacteria is exploited for
bioextraction of metals from sulphidic minerals. In non-contact
bioleaching mechanism, acidophilic iron oxidizers play a key role in
production of ferric iron as a lixivient. The ferrous-ferric ratio has a
dominating effect on the solution redox potential in biooxidation
systems. The acidophilic iron oxidizing microorganisms mesophilic or
haemophilic that increase the redox potential resulting in metal
sulphide biooxidation. The iron biooxidation rate and extent of
regeneration of ferric iron by the microorganisms play an important
role in heap, percolation leach system and even in the agitation
leaching. In two stages of indirect bioleaching with effective
separation process, the first stage of ferrous biooxidation should be
improved with fast kinetics of ferric iron production, this can be
achieved by developing iron oxidizing consortium at extreme high
concentration of ferrous, ferric and H+ ion and ionic strength. During
bioleaching process, large amount of jarosite precipitation is
unwanted phenomenon, which can be minimized by lower pH value.
High ferric iron concentration and extreme acidic pH are the most
favourable conditions for high yielding metal extraction process. Many
researchers have proved that mixed cultures (consortium) of
bioleaching bacteria are more promising than pure cultures (22,25).
So, it is essential to develop bacterial consortium in extreme
conditions, such as high concentration of ferrous, ferric, H+ ion and
ionic strength for sulphidic mineral bioprocessing. The commercial
use of thermophilic bacteria with their ability to operate at
temperature exceeding 45 oc has great potentials for improving the
kinetics of metal extraction from sulphidic minerals. Several
commercial bioleaching plants are using thermophilic bacteria for
extraction of base metals (Cu, Zn and Ni) from metal sulphides and
their concentrates (26).
9
Chapter: 1 General bttroduction
1.1.3 Microbial metal leaching mechanism
There are three types of mechanism involved in the microbial
mobilization of metals. The bacterial cell can affect metal sulphide
dissolution by contact and non-contact mechanism, which are also
known as direct and indirect mechanism respectively, and third is
galvanic conversion. The non-contact mechanism assumes that the
bacteria oxidize only dissolved ferrous to ferric ions. The later can
attack metal sulphides and be reduced to ferrous, which in turns, can
be again microbially oxidised. The contact mechanism requires
attachment of bacteria to the sulphide surface. The pnmary
mechanism for attachment to pyrite is electrostatic in nature. In case
of Acidithiobacillus ferrooxidans, bacterial exopolymers contains ferric
iron each complex by two-uronic acid residue. The resulting positive
charge allows attachment to the negative charge pyrite. Thus, the first
function of complex ferric iron in the contact mechanism is mediation
of cell attachment while second function is oxidative dissolution of the
metal sulphide, similar to the. role of ferric ions in non-contact
mechanism. In both cases, the electrons extracted from the metal
sulphide reduce molecular oxygen via a complex redox chain located
below the outer membrane, the periplasmic space and the cytoplasmic
membrane of leaching bacteria. The dominance of either
Acidithiobacillus ferrooxidans or Leptospiri.llum ferrooxidans in
mesophilic leaching habitats is highly likely to result from differences
in their biochemical ferrous iron oxidation pathway, especially the
involvement of rusticyanin (27). Several biomolecules are involved in
the aerobic respiration on reduced sulphur and iron compounds. It
has been found that up to 5% of soluble protein of Acidithiobacillus
ferrooxidans is made of an acid stable blue copper protein called
rusticyanin. Additionally the ferrous iron respiratory system contains
(putatively) a green copper protein, two types of cytochrome c, one or
more type of cytochrome a, a porin and an ferrous sulphate chelate.
10
Chapter: 1 General Introduction
The acid stability of rusticyanin suggests that it is located in the
peri plasmic space (22).
The following equations describe the Contact and Non-contact
mechanism for the oxidation of pyrite (28,29).
Contact mechanism:
Iron and/or sulfur oxidizer
Non-contact mechanism:
Iron oxidizers
Chemical 3FeS04+ 2S
......... ( 1)
.......... (3)
The third mechanism of sulphidic mineral oxidation is known as
"Galvanic interaction". It is inherent phenomenon in mix sulphidic
minerals that operate automatically in a heterogeneous system or
wherever two or more different environments coexist (30).
The role of galvanic interaction in the bioleaching of mixed
sulphidic minerals has been reported extensively. Mineral with a
comparative lower rest potential value behave anodically and undergo
dissolution (oxidation) whereas the mineral with the higher rest
potential value acts as a cathode at which reduction of oxygen occurs
(31). The electro chemical reactions involved are as below (32),
Anodic reaction on active sulphide sites:
MS -----lllo•M+ + so +2e- (Where 'M' is bivalent metal ....... (4)
11
Chapter: 1 General Introduction
Cathode oxygen reduction on noble mineral:
02 + 4H+ +4e- ............. (5)
The mru.n two mechanisms are "Contact" and "Non-contact"
bioleaching. One step bioleaching process have slow kinetics resulting
in the residence time of several day to few weeks, which restricts its
commercial application for the metal recovery from the concentrate by
the stirred tank process. With respect to the bioleaching process with
indirect mechanism the possibilities for the faster kinetics are more
promising. It can be achieved by performing the bioleaching process
into two separate stages;
(i) The chemical oxidation of sulphide by ferric Iron (chemical
stage)
(ii) The biological oxidation of the ferrous iron produced (biological
stage)
By applying the Indirect Bioleaching with Effective Separation
(IBES) process each stage can be separately optimised. The biological
stage can be improved by performing the ferrous iron oxidation in
separate reactor and chemical stage can be improved by raising the
operation temperature, by the use of catalysts (for Cu extraction) and
control of the pH (33,34).
1.1.3.1 Integral model of indirect bioleaching of metal sulphide
Metal sulphides are degraded by mainly ferric irons and/ or
protons on the crystal lattice. The primary ferric irons are supplied by
bacterial extracellular polymeric substances (EPS), complex with
glucuronic acid. The mechanism and chemistry of attack is
predominantly determined by the mineral structure solubility product
12
Chapter: 1 General Introduction
of the metal sulphide and EPS glucuronic acid - ferric iron formation
around the minerals, an important prerequisite for bacterial leaching
to proceed. The role of bacteria is to regenerate the ferric iron and/ or
protons and concentrate them at the interface mineral/bacterial cell
wall, enhancing the metal dissolution. Extra cellular polymeric
substances (EPS) layer with a thickness of nanometer surrounding the
cell forms the site of chemical reaction.
Based on electronic configuration and solubility of metal
sulphide mechanism of indirect bioleaching of metal sulphide is
classified into two major pathways.
a) Thiosulphate pathway with ferric attack on the mineral
surface (FeS2, MoS2, WS2).
b) Polysulphide pathway with ferric and/ or proton attack on
the mineral surface (ZnS, CuFeS2, PbS, MnS2).
The term "Contact" is insignificant and that "Non contact"
mechanism is predominantly involved in leaching of metal sulphide.
The role of bacteria in metal sulphide leaching is to supply the
oxidizing agent namely ferric by oxidizing the ferrous iron formed
during chemical attack of the mineral. Hence, it has been also
concluded that predominantly most of the mineral leaching are
through chemical process and the role of bacteria is purely as
catalyst. Pathways of leaching of minerals based on their electronic
and molecular structure are shown in Table 1.1.2 (35).
13
Chapter: 1 General Introduction
Table 1.1.2 Pathways of leaching of minerals based on their
electronic and molecular structure (35).
Minerals Formula/ Nature Oxidizing Products Mechanism structure of the agents formed ofdegrada-
minerals due to tion the
attack Pyrite FeS2/ Acid Ferric Thio- TP
disulphide Insoluble iron Sulphate a
Molybdenite MoS2/ Acid Ferric Thio- TP layered Insoluble iron Sulphate a
Tungstenite WS2/ Acid Ferric Thio- TP disulphide Insoluble iron Sulphate a
Sphalerite ZnS/ Acid Ferric Poly- PM sphalerite Soluble and sulphides~
proton (H2Sn) Chalco- CuFeS2/ Acid Ferric Poly- PM pyrite sphalerite Soluble and sulphides~
proton (H2Sn) Galena PbS/halite Acid Ferric Poly- PM
Soluble and sulphidesf3 proton (H2Sn)
Hauerite MnS2/ Acid Ferric Poly- PM disulphide Soluble and sulphides~
proton (H2Sn) Orpiment As2S3/ Acid Ferric Poly- PM
layered Soluble and sulphidesf3 proton (H2Sn)
TP=Thiosulphate Pathway; PM=Polysulphide mechanism
Bacteria effective
in leaching
(I), (II)
(I), (II)
(I), (II)
(I),(II),(III)
(I), (II), (III)
(I), (II), (III)
(I), (II), (III)
(I), (II), (III)
a Thiosulphate 1s oxidized via tetrathionate, disulphane
monosulphonic acid and trithionate to sulphate in a cyclic manner.
~ : Polysulphides formed are primarily converted in to elemental
sulphur, which are further oxidized to sulphate by bacteria.
(I) At. ferrooxidans (II) L. ferrooxidans (III) At. thiooxidans
14
Clzapter: 1 Generallntroductiotz
(a) Thiosulphate pathway (FeS2, MoS2, W~)
Molecular orbital and valence bond theory proposes, that orbital of
single atom or molecule forms electron bond with highest energy
level is referred as valence bonds. In case of molybdenite (Mo82),
pyrite (Fe82), Tungstenite (W82), the valence bonds are derived from
orbital of metal atoms only, consequently the valence bonds do not
contribute to the metal-sulphide moiety (M-82-2) and hence these
minerals are acid insoluble. Hence M---82-2 bond is broken by
powerful oxidizing agent, ferric iron.
The ferric hexahydrate ions cleave the chemical bonding between
iron and disulphide (Fe---82-2) in pyrite lattice (Eq.6), after the
oxidation of disulphide group to thiosulphate and ferrous ion are
released in the medium. Then the ferrous iron is oxidized by the
bacteria to ferric iron, which in turn attack the mineral surface and
aiding in metal dissolution. The thiosulphate formed during the
attack, is converted to sulphate by chemical attack of ferric ion
(Eq. 7), via tetrathionate, disulphane-monosulphonic acid and
trithionate.
(b) Polysulphide pathway (ZnS; CuFeS2; PbS; MnS2)
In these groups of metal sulphides, the valence bonds of the
molecule are derived from both metal and sulphur orbital. Hence
the electrons can be removed easily either by ferric iron and/ or
protons from valence bonds and thereby breaking the bonding
between metal and the sulphur moiety of the disulfide group
(M---82-2). Hence, these metal sulphides are acid soluble.
15
Chapter: 1 General Introduction
__ __,..., .. M+2 + H ......... (8)
----+..., 0.125 Ss+ Fe+2 ......... (9)
........ (10)
Unlike pyrite or molybdenite in this group of minerals, metal
sulphide bond is cleaved first (M---82-2) by proton, before the
oxidation of disulfide to sulphate. The hydrogen sulphide released
(Eq. 8), is reduced chemically to neutral sulphur via tetrasulphide by
ferric ions (Eq. 9). The neutral sulphur is oxidized to sulphate by the
bacteria (Eq. 10).
This model of bioleaching indicates that predominantly metals
are leached by indirect mechanism and the degradation of minerals by
ferric irons operates through 'Thiosulphate' or 'Polysulphide' pathway
depending on the mineral lattice. It also shows that 'direct' leaching
as 'contact' leaching, where the extra polysaccharide substance (EPS)
forms contact with the mineral surface, forming junction where all the
above process of 'indirect' leaching proceeds (35). Schematic
mechanisms of thiosulphate and polysulphide pathway in bioleaching
of metal sulphide are depicted in Fig 1.1.1 (35) and the schematic
mechanistic bioleaching model is shown in Fig 1.1.2 (22).
16
Chapter: 1 General Introduction
Fig. 1.1.1 Scheme of thiosulphate (MoS2, FeS2) and polysulphide pathway (ZnS, CuFeS2) in bioleaching of metal sulphide
Thiosulphate
Mechanism
Fe +3
r Atf, Lf
' Fe +2
MS: Metal sulphide M +2: Metal ions S203-2: Thiosulphate
(Atf, Att)
Sn-2: Polysulphide with chain length (n) SsO: Elemental sulphur
Poly sulphide
Mechanism
Fe +3
T Atf , Lf
'\.
(Atf, Att)
Ss0
(Atf, Att)
MS- ZnS, CuFeS2, PbS
17
H+
Chapter: 1 Ge~teral Introduction
Fig. 1.1.2 Schematic mechanistic bioleaching model (22)
I
I
4··· -......... -.~ -... -~,
·-·"' -....... .
.. . . -~, .
, __ ~ ....... ~ ... i ·~.;:
:.!.::·.::--·.
·.~: ;__ ,'_: ...
. _,.._ -~- ~ . "':. . : -~ ......
, ...... ,.,_ __ ..... . .
.. ',- y >""' f'''"' ··-•• -
C: cytoplasm; CM: cellmembrane;
• PS
PS: periplasmaticspace; OM: outer membrane; EP: exopolymers; Cyt: cytochrome; RC: rusticyanin; MeS: metal sulphide
. .. ~ ... ' ..
18
Chapter: 1 General Introduction
1.1.4 Bioleaching techniques
Different laboratory, pilot and commercial scale bioleaching
techniques under practice are listed in Table 1.1.3
Table 1.1.3 Bioleaching techniques (1)
Laboratory Scale
Manometric techniques
-Constant volume manometry
- Constant pressure manometry
Stationary flask techniques
Shake flask technique
Percolator .
Air sparger
Bioreactors -Mechanically
agitated
-Air-lift
Pressure leaching
Pilot Scale
Columns
Agitated tanks and reactors
Commercial Scale
In situ leaching
Dump leaching
Heap leaching
Vat leaching
Agitation leaching
Reactor leaching
-Mechanically stirred reactors
- Air-lift reactors
19
Chapter: 1 General Introduction
The shake flask technique 1s suitable for assessment of the
amenability and also for the acquisition of some preliminary, basic
information on factors influencing process kinetics that is quite
inadequate as a faithful simulator of the pilot-scale or the commercial
operation. This inadequacy derives from the difficulty of adjusting and
controlling gas mass transfer effectiveness independently of agitation
speed and of carrying out a continuous operation. 'Scale-up' means
the study of the problems associated with transforming data obtained
in laboratory and pilot plant equipment to industrial production,
which requires a certain degree of physical similarity between the
laboratory or pilot scale and commercial equipment.
Bacterial leaching is usually performed by heap of ground ore
or by dumps of waste or spent material. Heaps and dumps are
irrigated in close circuit with an acidic liquor that contains a fraction
of the bacterial population, the rest of the population being attached
to mineral. When the desired metal concentrations attained the rich
liquor is pumped to the solvent extraction (SE) section and then sent
to the electrowinning (EW) where the fine material is recovered. The
SE section is recycled to the heap or dump and then spent liquor of
the EW section is recycled to theSE operation (36-38).
Heaps and dumps leaching presents a number of advantages
such as simple equipment and operation, low investment and
operation cost and acceptable yields. However, these operations suffer
some severe limitations viz, the piled material is very heterogeneous
and practically no process control can be exerted, except for
intermittent pH adjustment and the addition of some nutrients.
Moreover, the rates of oxygen and carbon dioxide transfer are low and
extended periods of operation are required in order to achieve
sufficient conversion (39). Some of these limitations can be solved by
the use of reactor in bioleaching. The use of reactor would allow good
controls of the pertinent variable resulting in a better performance.
20
Chapter: 1 General Introduction
Inspite of these, heap leaching will continue to be the choice to treat
low-grade ore and tailing, while tank-leaching technology will probably
increase its application for gold, copper and the other precious base
metal concentration (40). The future of bioreactors in mining appears
promising. Gold biooxidation operation tends to increase in number
and size in several countries of the world.
1.1.5 Factor influencing bioleaching
Metal bioleaching in acidic environment is influenced by a
series of factors, which are listed in Table 1.1.4. Physico-chemical as
well as microbiological factors are affecting rates and efficiencies of
metal extraction. In addition, properties of the solids to be leached are
of major importance (41). The effluence of different parameters such
as activities of the bacteria itself, source of energy, mineralogical
composition, pulp density, temperature and particle size was studied
for the oxidation of sphalerite by Acidithiobacillus ferrooxidans (42).
The best zinc dissolution was obtained at low pulp densities (50 g.l-1),
small particle SJ.Ze (+ 150 to -325 B.S.S#) and temperature
approximately 35 °C. The heavy metals such as copper, nickel, cobalt,
cadmium, uranium and thorium inhibit the iron oxidation rate by iron
oxidizer (43). Concentration of 3 to 7 mg.l-1 carbon dioxide showed
optimum growth rates of At. ferrooxidans (44), whereas more than 10
mgJ-1 was inhibiting the growth of At. ferrooxidans (45). Pulp density
more than 30 gJ-1 decreases the rate of iron oxidation. During
bioleaching processes co-precipitation of metals with minerals phases
such as jarosite can reduce leaching efficiencies (46). In Non-contact
bioleaching the first stage of ferrous biooxidation, the concentration of
ferrous and ferric act as a substrate and product concentration
respectively. This initial substrate and/ or product concentration
inhibits the growth of iron oxidizers that seriously ~feet the iron
oxidation rate. However, both ferrous and ferric concentration above
0.5 M proved to be toxic to Acidithiobacillus ferrooxidans (4 7).
21
Chapter: 1 General Introduction
Table 1.1.4 Factors and parameters influencing bacterial mineral
oxidation and metal mobilization (22).
Factors Parameters
Physicochemical temperature ~arameters of a bioleaching pH [environment redox potential
water potential oxygen content and availability carbon dioxide content mass transfer nutrient availability iron(III) concentration ionic strength light pressure surface tension .Qresence of inhibitors
Microbiological parameters microbial diversity jof a bioleaching population density !environment microbial activities
spatial distribution of microorganisms metal tolerance ad~tation abilities of microorganisms
!Properties of the minerals mineral type Ito be leached mineral composition
mineral dissemination grain size surface area porosity hydrophobicity galvanic interactions formation of second~ minerals
Processing leaching mode (in situ, heap, dump or tank leaching) pulp density stirring rate (in case of tank leaching operation) heap geometry ( in case of heap leachin_g_ o_Qeration)
22
Chapter: 1 General Introduction
Recently, Blight, K. R. et al. has proved that the ionic strength is
a significant variable in the growth of iron oxidation with batch
culture of chemolithotrophic bacteria (48).
Organic solvents such as floatation or solvent extraction agents,
which are added for the downstream processing of leachates from
bioleaching, are responsible for inhibition. It has been demonstrated
recently that the addition of small amounts of amino acids (e.g.
cysteine) resulted in increased pyrite corrosion by At ferrooxidans as
compare to control (49). It was reported that Tween 80 increases the
attachment of At ferrooxidans on molybdenite and the oxidation of
molybdenum in the absence of ferrous iron (50).
1.1.6 Why bioreactor in mineral processing?
The ore or mineral concentrates functions as a substrate for the
growth of the microbial population and the bioleaching process.
Contact bioleaching is enzymatic process, which transforms the
mineral and the solubilization rate of the mineral is directly related to
the growth rate of the microbial population.
Nowadays, bioleaching is being applied as the main process in
large-scale copper mining operation and as an important pre
treatment stage in the processing of refractory gold ores. From a
process-engineering standpoint, the complex network of biochemical
reaction encompassed in bioleaching would be well performed in
reactor. The use of reactor would allow a good control of the pertinent
variables, resulting in a better performance. Parameters such as
volumetric productivity and degree of extraction can be significantly
increased (51).
The selection of a suitable reactor for a bioleaching process and
its design should be based on the physical, chemical and biological
23
Chapter: 1 Getzeral ltztroductiou
The selection of a suitable reactor for a bioleaching process and
its design should be based on the physical, chemical and biological
characteristics of the system. Adequate attention should be paid to
the complex nature of the reaction sludge composed by an aqueous
liquid, suspended and attached cells, suspended solids and air
bubbles (52). Because of very large volume of material to be processed,
to obtain optimum bioleaching and biooxidation rate, the best
performed in a continuous mode of operation in which volumetric
productivity is high and reactor volumes can be kept low. Considering
the kinetic characteristics of microbial growth, continuous stirred
tank reactor (CSTR) appears as the first choice. An important
consideration in selecting suitable reactor refers to the autocatalytic
nature of microbial growth.
The bioreactor appears to offer the best potential for leaching
operation since pronouncedly higher reaction rates can be achieved as
compared to conventional processes. Various types of reactor that
have been studied for their application in biomining are the
percolation column, the air-lift column and some special design such
as fixed-film column and rotary disc reactor (53).
1.1.7 Global scenario of commercial scale bioleaching operations
Academics and commercial applications are extensively
increasing in laboratory, pilot and commercial-scale operations of
bioleaching. Several bacterial species are used in many commercial
applications of biohydrometallurgical process, which has gained
acceptance and gaining prominence in several parts of the world, such
as South America, Australia, South Africa, China, Canada, Spain and
even in India. The Rio Tinto mines, Huelva in south western Spain are
considered the cradle of biohydrometallurgy that has been exploited
since pre Roman times for their copper, gold and silver values. Today,
the contribution of bioleaching is estimated to be approximately for
24
Chapter: 1 Ge11eralltrtroductio1l
30, 25 and 13% of the total world production of copper, gold and
uranium respectively (40).
The current situation of commercial size bioleaching operations
and ongoing projects in developing countries are blossoming especially
for copper and gold bioextraction. Major large-scale bioleaching
operations are located in developing countries. This is not purely
accidental, but the necessary result of two important factors, like
many developing countries having significant mineral resources and
mining constitutes one of their main sources of income, the second,
bioleaching is a technique especially suitable for developing countries
because of its simplicity and low capital cost requirement (54, 55).
Literature data shows that biohydrometallurgical technology can
significantly contribute to the economic and social development of a
country. Developing countries like Chile, Indonesia, Mexico, Peru and
Zambia share over 50% of world copper production, which are shown
in Table 1.1.5, and world production of zinc is shown in Table 1.1. 7 .In
case of gold mining Brazil, Chile, Ghana, Indonesia, Papua, New
Gauine, Peru and Uzbekistan rank among 13 top producers countries
with 33% of the world production which are also shown in Table 1.1.8.
A breakthrough in bioleaching practice was the establishment of
the first copper mine exploited solely by bacterial technology, which
was achieved at Minera Pudahuel in Chile, when in the mid-eighties
they switch from a mixed acid and bacterial leaching to full bacterial
heap leaching of an ore containing 1 to 2% copper rendering 14,000
tons of fine copper per year (13,55). The process consisted of crushing,
agglomeration, heap leaching, solvent extraction and electrowinning.
Soon after the start up of the Pudahuel process several other copper
bioleaching operations were established for copper bioleaching in
Chile, which are shown in Table 1.1.6.
25
Chapter: 1 General Introduction
Table 1.1.5 World copper mine production (thousand of tons)
Country 2000 2001 2002 2003 2004
Australia 829 869 883 830 850 Canada 634 633 600 558 560 Chile 4600 4740 4580 4900 5380 China 590 590 585 610 620 Indonesia 1012 1050 1160 979 860 Kazakhstan 430 470 490 485 485 Mexico 365 367 330 361 400 Peru 554 722 843 831 1000 Poland 456 474 503 495 500 Russia 570 620 695 675 675 United State 1440 1340 1140 1120 1160 Zambia 240 300 330 330 400 Other country 1480 1510 1500 1400 1600 World Total 13200 13700 13600 13600 14500
Table 1.1.6 Copper bioleaching operations in Chile
Mine
Lo Aguirre Quebrada Blanca Cerro Colorado Zaldiwar Ivan-Zar Aldacollo-Cobre
Chunquicamata Los Bronces Zaldivar
Production, tons/Year Heap leaching
Dump leaching
14,000 75,000
1,00,000 1,50,000
12,000 21,000
Over 15,000 11,000 12,500
26
Chapter: 1 Geueral Introduction
Table 1.1.7 World zinc mine production (Metric tons)
Country 2000 2001 2002 2003 2004
Australia 1420000 1519000 1154000 1480000 1492500
Canada 1002242 1012048 894399 1000000 9525000
China 178000 1700000 1550000 1650000 1526000
India 144000 146000 129000 162000 165000
Ireland 262877 225135 252700 250000 255600
Mexico 392791 428828 446104 460000 456800
Peru 910303 1056629 1221830 1250000 1285000
Poland 156900 152700 152200 150000 146500
Russia 136000 124000 130000 125000 125300
Spain 201000 164900 69900 70000 76000
United 852000 842000 780000 738000 780000
States
27
Chapter: 1 General Introduction
Table 1.1.8 World gold mine production (Kilograms)
Country 2000 2001 2002 2003 2004
Australia 296410 286030 273010 282000 420000
Canada 156207 158875 151504 140559 171000
Chile 54142 42673 38688 40000 42000
India 6200 3700 3800 3100 3500
Indonesia 124596 166091 142238 140000 120000
Mexico 26375 26300 20617 20000 21000
Peru 132585 138022 157013 171551 160125
Poland 367 349 296 300 310
Russia 143000 152500 168411 170068 180400
United 353000 335000 298000 277000 247000
States
Zambia 600 630 635 640 620
Total 2590000 2600000 2580000 2590000 2470000
28
Chapter: 1 General l~ttroductiou
A number of copper bioleaching projects are at this time understudy
and development. Among them the most important one is being
carried out jointly by the Chunquicamata Division of CODELCO
(Chilean National Copper Corporation) and BHP Billiton. The project
aims the large-scale operation of a plant for the bioleaching of copper
concentrate in continuous stirred tank reactors using thermophilic
microorganism. The projects involve the construction of a US $ 60
million large pilot plant able to produce 20,000 tones of copper
cathode per year. Another exciting experience is being carried on in
Mexico; Panoles S.A. in association with Mintek has been able to
produce several tons of copper cathodes in their demonstration plant
in Monterry. The plant is an integrated tank bioleaching, solvent
extraction and electrowinning facility capable of producing 500 kg
copper per day (40).
Bioleaching is also successfully applied in gold m1n1ng, when
the metal is covered with a film of insoluble metal sulphide that
hurdle the extraction of gold with cyanide solutions. In this case, the
sulphide film must be removed in order to obtain satisfactory gold
recoveries and bioleaching is one of the alternative choice for such
pre-treatment step. In 1999, Newmont Mining Corporation
commissioned the first biooxidation heap facility for pre-treatment of
refractory gold ore (56).
The South African company, Gencor (now Billiton) pioneered
commercial tank bioleaching of refractory gold bearing sulphide
concentrates, implementing the world's first such plant at the Fairview
Gold Mine during 1986. The implementation of the other plant was
achieved after approximately ten years of in-house research including
a 75 kg per day pilot plant facility with superior recovery of gold.
Nearly 1000 tones concentrates are processed daily in reactors up to
900m3 in size (57).
29
Chapter: 1 Generallutroductiou
The BIOX® process for pre-treatment of refractory sulphide gold
ores such as pyrite, arsenopyrite and pyrrhotite was developed to
increase gold recovery rates during the metal extraction process. The
gold in these sulphide ores is encapsulated in sulphide minerals,
which prevent the gold from being leached by cyanide. The BIOX®
process solublizing the sulphide minerals and exposes the gold for
subsequent cyanidation and increase recovery rates. Gold recovery
was 30-39% before biooxidation, increasing to 49-60% after
biooxidation. The BIOX® process has many advantages over
conventional refractory process such as roasting, pressure oxidation
and nitric acid leaching. Ashanti, Ghana, is the largest plant in the
world for the treatment of refractory gold ores. Several recent and
ceased large-scale commercial bioleaching operations for gold, copper
and cobalt are shown in Table 1.1.9 (22). The BIOX® stirred tank
leaching also had application 1n base metal, although first
investigation were associated with biologically assisted heap leaching
of low-grade nickel ores termed BioNIC™. It was tested at a
demonstration facility at Billiton Process Research in South Africa in
1996-1997. The copper bioleaching process was termed BioCOP™
CODELCO as the world largest copper producers was approached
regarding the establishment of a pilot plant facility at its
Chunquicamata operation in Chile. BioNIC™, BioCOP™ and BioZINC™
have been successfully demonstrated on a pilot scale (13). The
GEOCOAT process, developed by Geobiotics, Lakewood, Colorado, is a
unique heap leach system for biooxidation pre-treatment of refractory
precious metal concentrates and bioleaching of copper, zinc and
nickel sulphide concentrates (58). The Rio Tinto Mine, Spain
commissioned the Indirect Bioleaching with Effects Separation (IBES)
process for copper-zinc sulphide concentrate, where the capacity of
plant is 105 tones per year and operating cost was about US $ 141
per ton of concentrate. It is a two-stage process and silver is used as
catalyst with 8 to 10 h of retention time. Copper and zinc recovery of
95 and 94% are reported by this process (59,60).
30
Table 1.1.9. Selection of recent and ceased industrial bioleaching operations for gold, nickel~ >per, and cobalt
Country Locality, Metal Mineral Source Technology :apacity Metal Designation [t d ·1) Yield[t y - 1 ]
Australia Harbour Au Flotation concentrate Tank leaching 40 Lights (160m3) Girilambone Cu Chalcocite Heap leaching 16,000 14,000 Gunpowder Cu Chalcocite, bornite in situ leaching 13,000 Maggie Hays Ni Concentrate Tank leaching 7
(pilot plant) Beaconsfield Au Tank leaching 70 Wiluna Au Flotation concentrate Tank leaching 115
(480m3) Youanmi Au Flotation concentrate Tank leaching 120
(6.480 m3) Brazil Sao Bento Au Flotation concentrate Tank leaching 150
(550m3) Canada Gold bridge Au Pyrite, markasite, Tank leaching 75
arsenopyrite (225m3) Chile Andacollo Cu Chalcocite Heap leaching 10,000
Cerro Cu Chalcocite Heap leaching 16,000 60,000 Colorado
Q Dos Amigos Cu Chalcocite Heap leaching 3,000 ~ Quebrada Cu Chalcocite Heap leaching 17,300 75,000 ~
Blanca "'t .. Zaldivar Cu Chalcocite Heap leaching 20,000 .....
G"}
Ghana Sansu Au Floatation concentrate Tank leaching 1000 ~ ~ -S' :t Q
§-(")
'"" .... w Q ..... ::
Table 1.1.9 Continue •••••
Country Locality, Metal Mineral Source Technology Desi nation
Ghana Ash anti Au Floatation concentrate Tank leaching (6.900 m3
) India Hutti Au Tank leaching (pilot
plant) India Malanjkhand Cu Malachite, chalcocite, Heap leaching 2.5
bornite, covellite Peru Tamborque Au,Ag Arsenopyrite from zinc Tank leaching
flotation (pilot plant 1 m3)
South Fairview Au Flotation concentrate Tank leaching 35 Africa (90m3
) Uganda Kasese Co Flotation concentrate Tank leaching 1,000
(4.1.350 m3)
USA Carlin Au Au - containing Heap leaching 10,000 sulphidic ore
Chino Cu Chalcocite, chrysokolla Heap leaching 55,000 San Manuel Cu Chalcocite in situ leachin 20 000
Q ~ !i .. t-1
C':l ~ !II
~ -S" a §-~ "'to w ...
N §
Chapter: 1 General Introduction
1.1.8 Indian scenario of metal bioleaching
The mineral wealth of India is a gift of nature and a part of great
inheritance. India is the biggest consumer of gold in the world. Next to
gold, copper, zinc and lead are very essential metals and their demand
is also increasing day by day. The domestic scenario shows the
significant demand supply gap, which is expected to widen in near
future. In other words, more attention has to be paid to the growth of
supplementary metal production and to reduce the import
dependence, which affects the economy of the country. The mineral
resources of India are summarized in Table 1.1.10. As can be seen
from the table, India ranks 2nd in the resources of manganese ore, 3rd
in pyrites and iron ore, 4th in chromites, bauxite and magnetite, 5th in
coal and lignite in the world. A Recent Price Water House report has
identified India as the most promising mining location worldwide
(62,63).
India produces 65 minerals including fuel, metallic, non
metallic and atomic minerals (64). Metals are strategic and the
important role they play in the national economy both during peace
and war can not be underestimated. The yardstick of the per capita of
metal consumption is the measure of the prosperity of the country
and the people. The usage of metal is expected to rise by 8-12 %
annually. Even at present, India is not self sufficient for its demand of
metals (Tablel.l.11). India has a variety of untapped mineral
resources, largely subsurface and hidden due to lack of modem
technology, adequate exploratory efforts and intensive mineral
investigation (Tablel.1.12) (65).
The Demonstration Biooxidation Tank leaching plant was
commissioned in 2002 at Hutti Gold Mines, Karnataka State, India.
The plant was designed for treating gold and silver bearing
arsenopyrite concentrate and can also be used for the bioleaching of
copper, zinc, nickel and other base metal concentrate (40).
33
Chapter: 1 General Introduction
Table 1.1.10 Mineral resources of India (65)
Metals Ore/Mineral Reserve Geographical distribution (Mt)
Iron Hematite 11950 Bihar, Orissa
Magnetite 4900 Karnataka, Goa, Madhya Pradesh
Manganese Pyrolusite 370 Orissa, Bihar, Madhya Pradesh
Psilomelane Maharashtra, Karnataka
Brunite Gujarat, Goa
Cobalt and Sulphide ores Uttar Pradesh, Rajasthan
Nickel in copper
mines
Copper Chalcopyrite 425 Bihar, Andhra Pradesh Rajasthan
Outer Himalaya
Gold Quartz reefs 30 Karnataka, Andhra Pradesh,
Arsenopyrite Madhya Pradesh, Ladakh
Aluminium Bauxite 279.9 Bihar, MadhyaPradesh,
Maharashtra, Gujarat, Kashmir
Uranium Pegmatitic Bihar, Andhra Pradesh. Rajasthan
Monazite Himalayas, East and West Coast of
India
Zinc Sphalerite 107.1 Rajasthan, Kashmir, Sikkim
Gujarat
Lead Galena -100 Rajasthan, Andhra Pradesh,
Gujarat, Tamilnadu
34
Chapter: 1 General Introduction
Table 1.1.11 Degree of metal self-sufficiency in India (1998-99) (65)
Thousand tons Order of self-Metals Domestic Domestic supply sufficiency(%)
demand Zinc 232 142 61.2
Copper 273 38 13.9
Lead 129 48 37.2
Aluminium 643 543 84.4
35
Chapter: 1 Getzeral Introduction
Table 1.1.12 Indian scenario of gold, copper, zinc and lead production (65)
Metals 1999 2000 2001 2002 2003
Gold 2468 6082 8356 4486 3176
(Kilogram)
Copper 3316056 3292709 4298892 3252839 2875307
ores
(tons)
Zinc 343328 365730 399804 462095 607677
concent.
(tons)
Lead 62094 57485 51733 57169 68877
concent.
(tons)
36
Chapter: 1 Gmeral Introduction
Thus, the metal sulphide biooxidation technology would be developed
that could significantly contribute to the economic and social
development of India.
1.1.9 Economy of metal bioleaching
Economical factors for commercial scale bioleaching applications
can be divided into capital costs associated with construction, operation
and maintenance cost (66). Operation costs include the running of the
process equipment, the supply of the reagents, services and labour (67).
However, capital costs are generally smaller. According to Barrett et. al
these costs depend on the method of application and it increase in the
order (68),
Dump < Vat ~ Heap < Agitated reactors
Major factors affecting costs of bioreactors are construction
material and equipment. Equipment required for agitated bacterial
oxidation processes includes conventional tanks with impellers to
suspend the solids and disperse the air, compressor for air supply,
thickeners for solid/liquid separation and conventional sluny pumps
for delivering and removing the slurry from the plant. Construction
material needs to be acid resistant, which further more, withstands
temperature of 30-50 °C. In general technical equipments for
bioleaching process is less expensive as compared to physico-:-chemical
processes (22).
Nowadays, between 25-30% of copper produced yearly is based
on microbiological treatment of mineral resources. Together with other
metals such as cobalt, gold, nickel, uranium, or zinc, biological metal
extraction processes result in a surplus value of over 10 billion US
dollars (22). Recovery of gold from ores could be increased by 2-13% if
biotechnological methods are applied. In comparison to ore roasting
37
Chapter: 1 Geueral Iutroductiou
capital cost for industrial scale treatment plants are reduced by
12-20%, operating cost by 10% (69). Cost of US $ 4.3 per ton ore have
been calculated for bacterial ore treatment compared to US $ 4.1 and
US$ 4.5 with pressure oxidation and roasting respectively (67).
The technical and economical benefits of thermophiles have also
been investigated for nickel, copper-nickel and zinc concentrates. The
increased rates of reactions as well as lower capital and operating cost
are significantly compelling to the conveyance Billiton that thermophiles
at least for stirred tank applications are the key to the future in base
metal bioleaching. The mining industries recognize that biotechnology
offers important tool for economic recovery of metals values (70).
1.1.10 Scope and objectives of the present work
1.1.10.1 The scope of complex sulphidic mineral bioprocessing
Metal recovery from such complex ore and bulk concentrate is
equally important for the economical growth of nation. Recent
advances in bioextractive metallurgy have also opened the door of
metal extraction from complex sulphidic minerals.
The depletion of high-grade mono-mineral ore deposits and
increasing demands for base metals have led mining companies to
consider exploiting multi-metallic and lean ores, which represents
important resources of nonferrous and precious metals. The complex
ore is generally composed of chalcopyrite, galena, sphalerite, pyrite
and/ or pyrrhotite (71). Metal extraction from complex ores and
concentrates can be achieved pyrometallurgically or
biohydrometallurgically. A pyrometallurgical process for complex ores
requires "selective floatation process". To obtain individual
concentrates from complex sulphide ores, a fine grinding step (or ultra
grinding) is required to liberate the mineral species to be separated,
38
Chapter: 1 General Introduction
which is an energy-consuming, expensive operation, necessitating
skilled labour. So, flotation separation of complex sulphide ores into
individual concentrates has been a difficult task, often due to the size
of liberation and possible interactions among sulphide minerals (32,
72). Moreover, this solution is not satisfactory and economical, in
practice, owing to the high costs of the differential flotation process,
low flotation recovery and to the poor quality of the resulting
concentration, which hinder their access to the market (1,32).
"Bulk flotation" shows significant advantages as compare to
differential flotation in terms of less water and reagents consumption,
higher metal efficiency and less grinding cost. Inspite of these
advantages, at present, the main difficulty lies in selecting an efficient,
inexpensive and flexible leaching process (1,73). This situation
prompted an examination of alternatives in arnving at an
economically sound process to extract metal from finely inter-grown
complex sulphide concentrates. In this respect, Biohydrometallurgical
process is considered as an interesting choice (73).
Biohydrometallurgical methods are currently used In
commercial leaching processes for the recovery of copper, uranium
and gold from sulphidic minerals (74,75). In the future, these
processes will become important for zinc, nickel, cobalt and
molybdenum from the complex ores (76, 77). 'Combination processes'
involving an initial bulk flotation followed by selective leaching of
certain sulphide minerals could prove attractive in the processing of
refractory complex ores (32). It is of tremendous interest to explore if
selectivity could be achieved in the leaching of multi-metal sulphides
(32).
Bacterial leaching, either of the run-of-mine ore or bulk metal
sulphides concentrate appears promising. Production of the later
39
Chapter: 1 General Introduction
usually involves a relatively coarse grind and is characterised by
satisfactorily high recoveries (78).
Bacterial leaching has been found to be effective in the
dissolution of several sulphide minerals. Possible selectivity for
sulphide mineral oxidation of complex sulphides by bacteria depends
on the following key factors (73),
• Bacterial ability to produce ferric iron for selected sulphide
mineral and indirect microbial attack.
• Chemical interaction between sulphide mineral and
ferric/proton ions.
• Increase the rate of metal extraction.
• Bioregeneration of ferric for the dissolution of metal sulphide.
Application of bioleaching to the processing of complex sulphide
such as the ores containing Pb-Zn-Cu-Fe, Cu-Ni-Mo-Fe and Cu-Ni-Fe
metals is of great importance since flotation-beneficiation of these·
multi-metal ores to yield individual clean concentrates (for
pyrometallurgical processes) is extremely difficult (79). A combination
process would prove to be very efficient in these cases (30). However,
information concerning the bioleaching of multi-metal (complex)
sulphides is limited. To date, experiments have been carried out only
on a laboratory scale on complex sulphide run-of-mine ores, on mixed
metal sulphide flotation concentrates and on synthetic mixtures of
chemical grade base-metal sulphides and sulphites (77).
Two-stage metal bioextraction process was used for copper and
zmc concentrates of Rio Tinto mine, Spain. The maximum
bioextraction of zinc and copper were 85 and 90% respectively (33).
In this context, it is necessary to investigate the amenability and
detailed behaviour of two-stage bioextraction profile for GMDC
40
Chapter: 1 General Introduction
(Gujarat Mineral Development Corporation) polymetallic concentrate.
This study will help to utilise the national reserves of the mineral
resources, which are not exploited due to the lack of technology. It
also provides some economical benefit by recovering metal value from
the polymetallic concentrates, which are not amenable to conventional
procedure due to obvious reasons.
1.1.10.2 Objectives
The research program was undertaken with the objectives in
mind to develop extremophilic iron oxidizing consortium with special
reference to two-stage bioextraction process to treat copper-lead-zinc
bulk concentrate. The development of extremophilic bioleaching
bacteria and two-stage process is not limited to polymetallic
concentrate but it can be also applied to various sulphidic minerals.
The research programme was designed with following objectives;
• Selection and development of iron oxidizing bacterial consortium
· to improve iron oxidation rate ..
• Development of iron oxidizing consortium in extreme conditions
such as;
-High ferrous sulphate concentration
- High ferric sulphate concentration
- Highly acidic pH
• Metal tolerance study of iron oxidizing bacteria in the presence of
heavy metals such as copper, zinc, cobalt and nickel.
+ Optimization of various physico-chemical parameters for 1ron
oxidation in shake flask study.
• Enhancement of iron oxidation rate by adaptation and selection.
+ Designing of fixed film column bioreactor with developed iron
oxidizing bacteria on different supporting materials such as glass
tubes, glass beads and acrylic pieces for two-stage metal
extraction bioprocess.
41
Chapter: 1 General Introduction
+ Enhancement of iron oxidation rate by developed fixed film PVC
column/ airlift percolating column bioreactor.
+ Isolation and identification of pure culture of 1ron oxidizing
bacteria from developed fixed film bioreactor.
- 16S rDNA sequencing
- Scanning Electron Microscopy
+ Optimization of chemical oxidation of GMDC polymetallic bulk
concentrate by microbially produced ferric iron.
+ Detail investigation of two-stage microbially produced ferric
mediated cyclic process for bioextraction of copper and zinc.
+ Recycling and bioregeneration of ferric lixivient for two-stage
metal extraction biotechnology.
42
Chapter: 1 General Introduction
1.2 References
1. Rossi, G. ( 1990). Biohydrometallurgy, Mc-Graw Hill, Hamburg.
2. Evans, A. M. (1993). Ore and ore deposits, ore-geology and
industrial minerals - An Introduction. Blackwell Scientific
Publication, Oxford.
3. Bull, R. (1993). Mineral processmg: In: McDivitt, J. F (Ed},
International mineral development source book, Forum for
international mineral development, USA, 131-133.
4. Mandre, N. R., Sharma, T. (1992). Direct leaching of Pb and
Zn from complex sulphide ore and concentrate, Extractive
metallurgy of gold and base metals, Kalgoorlie 259-264.
5. Mandre, N. R., Sharma, T. (1992). Recovery of zinc from
sphalerite concentrate by ferric chloride leaching. Trans. I.M.M.,
101, C118-Cl20.
6. Shukla, L. B., Panchanadikar, V. V. (1993). Bioleaching of
lateritic nickel ore using an indigenous microflora. In: Torma,
A., Wey, J. and Lakshmanan, V (Eds), Biohydrometallurgical
Technologies, TMS, 1: 373-380.
7. Brierley, C. L. (1997). Mining biotechnology, Research to
commercial development and beyond In: Rawling, D.E., (Ed),
Biomining: Theory, Microbes and Industrial Processes, Springer
Verlag, Berlin, 3-17.
8. Groudev, S. N. (1999). Biobeneficiation of mineral raw
material. Minera. Metall. process. 16: 19-28.
9. Rawlings, D. E. (1997). Biomining: Theory, Microbes and
Industrial Processes, Springer-Verlag, Berlin.
10. Woods, D., Rawlings, D. E. (1989). Bacterial leaching and
biomining, In: Marx J.L (Ed), A Revolution in Biotechnology.
University of Cambridge Press, Cambridge, 82-93.
11. Parker, S. P. (1992). Concise Encyclopedia of Science and
Technology. Mc-Graw Hill, New York.
43
Chapter: 1 General Introduction
12. Rossi, G. (2003). Biohydrometallurgy: a sustainable technology
in evolution. Abstract In: Proc. International Biohydrometallurgy
Symposium,IBS '03, Elsevier, Greece, 19.
13. Acevedo, F., Gentina, J. C., Bustos, S. (1993). Bioleaching of
minerals- a valid alternative for developing countries. J.
Biotechnol., 31: 115-123.
14. Brierley, J. A., Brierley, C. L. (2001). Present and future
commercial applications of biohydrometallurgy.
Hydrometallurgy, 59: 233-239.
15. http: //www.imm.org.uk/gilbertsonpaper.htm (2001).
Creating value through innovation biotechnology In mmmg,
Recent bioleaching development 1-9.
16. Lopez-Archilla, A. I., Marin I., Amlls, R. (1993). Bioleaching
and interrelated acidophilic microorganism from Rio Tinto,
Spain. J.Geomicrobiol., 11: 223-233.
17. Le Roux, N. W. (1970). Mineral attack by microbiological
processes In: Miller, J.A.D (Ed}, Microbial aspects of metallurgy,
American Elsevier Publishing Co, New York, 173-182.
18. Temple, K. L., Colmer, A. R. (1951). The autotrophic
oxidation of iron by a new bacterium: Thiobacillus ferrooxidans.
J. bacterial., 62: 605-611.
19. Temple, K. L., Delchamps, E. W. (1953). Autotrophic bacteria
and the formation of acid in bituminous coal mines. Appl.
Microbial., 1: 255-258.
20. Kelly, D. P., Wood, A. P. (2000). Reclassification of some
species of Thiobacillus to the newly designated genera
Acidithiobacillus gen. nov., Halothiobacillus gen. nov and
Thermithiobacillus gen. nov. Int. J. System. and Evolution .
. Microbial., 50: 511-516.
21. Johnson, D. B. (1998). Biodiversity and ecology of acidophilic
microorganisms. FEMS Microbial. Rev., 27: 307-317.
22. Brandl, H. (2001). Microbial leaching of Metals, In: Rehm, H. J.
and Reed, G, (Eds), 2nd edition Biotechnology, Vo1.10, 191-224.
44
Chapter : 1 General Introduction
23. Harrison, A. P. Jr. (1984). The acidophilic thiobacilli and other
acidophilic bacteria that share their habitat. Ann. Rev.
Microbial., 18: 265-292.
24. Sand, W. (1992). Evaluation of Leptospirillum ferrooxidans for
leaching. Appl. Environ. Microbial., 58: 85-92.
25. Rawlings, D. E. (1998). Industrial practice and the biology of
leaching of metals from ores: The 1997 Pan Labs Lecture. J.
Ind. Microbial. Biotechnol.J 20: 268-274.
26. Norris~ P. R., Burton,. N. P., Foulis, N. A. M. (2000).
Acidophiles in bioreactor mineral processing. Extremophiles. 4:
71-76.
27. Rohwerder. T., Gehrke, T., Kinzler K., Sand, W. (2003).
Bioleaching rev1ew part A: Progress 1n bioleaching:
fundamentals and mechanisms of bacterial metal sulphide
oxidation. Appl. Microbial. Biotechnol., 63: 239-248.
28. Murr_,. L. E. (1980). Theory and practice of copper sulphide
leaching in dumps and in situ. Min.Sci.Eng., 12: 121-189.
29. Sand, W., Gehrke, T., Jozsa, P. G., Schippers, A. (1999).
Direct versus indirect bioleaching In: Amils, R., Ballester, A
(Eds), Biohydrometallurgy and Environment Towards the Mining
ofthe 21st Century Vol. A., Elsevier, Amsterdam, 27-49.
30. Natarajan, K. A. (1998). Microbes, Minerals and environment,
Geological Survey of India.
31. Barr, D. W., Jordan, M. A., Norris, P. R., Phillips, C. V.
(1992). An investigation into bacterial cell ferrous iron, pH and
Eh interactions during thermophilic leaching of copper
concentrates. Mineral. Engg., 5 (3-5): 557-567
32. Natarajan, K. A., Iwasaki, I. (1985). Microbe-mineral
interactions in the leaching of complex sulphide In: Clum, J.A,
and Hass, L. A (Eds), Microbiological effects on metallurgical
processes TMS, Warrandale, PA, 1-13
45
Chapter: 1 General Introduction
33. Carranza, F., Palencia, I., Romero, R. (1997). Silver catalyzed
IBES process: application to a Spanish copper-zinc sulphide
concentrate. Hydrometallurgy, 44: 29-42.
34. Arm.entia, H., Webb, C. (1992). Ferrous sulphate oxidation
us1ng Thiobacillus ferrooxidans cells immo bilised 1n
polyurethane foam support particles. Appl. Microbial.
Biotechno~ 36: 697-700.
35. Sand, W., Gehrke, T., Josza, P., Schippers, A. (2001). (Bio)
chemistry of bacterial leaching - direct vs indirect bioleaching.
Hydrometallurgy, 59: 159-175.
36. Montealegre, R., Bustos, S., Rajas, J., Neuburg, H., Araya,
C., Yanez,H., Tapia, R., Rould, J. (1993). Application of the
bacterial thin layer process to Quebrada Blanca Ores, In:
Torma, A., Wey, J., and Laksman, V (Eds),
Biohydrometallurgical Technologies Vol.1., The Minerals Metals
and Materials Society, Warrendale, Pennsylvania, USA, 1-14.
37. Avendano, C., Domic, E. (1994). Engineering design of LX-SX
EW plants, In : Wilkomirsky, L .. Sanchez, N. and Hecker, C
(Eds) Chemical Metallargy, Vol. 2. Universidad de conception,
conception, Chile, 21-31.
38. Readett, D. J. (1999). Heap leaching In: Biomine '99'.
Conference proceedings, Perth, Australia, 23rd_ 24th August. 61-
80.
39. Acevedo, F., Gentina, J. C. (1989). Process engineering
aspects of the bioleaching of copper ores. Bioprocess. Engg., 4:
223-229.
40. Acevedo, F. (2002). Present and future of bioleaching 1n
developing countries. Elect. J. Biotechnol., 55-59.
41. Das, T., Ayyappan, S., Chaudkury, G. R. (1999). Factors
affecting bioleaching kinetics of sulphide ores using acidophilic
microorganisms. Biometals, 12: 1-10.
46
Chapter : 1 General Introduction
42. Ballester, A., Blazquez, M. L., Gonzalez, F., Munoz, J. A.
(1989). The influence of different variables on the bioleaching
of sphalerite. Biorecovery -1: 127-144.
43. Leduc, L. G., Ferroni, G. D., Trevors, J. T. (1997). Resistance
to heavy metals in different strains of Thiobacillus ferrooxidans.
World J. Microbiol. Biotechnol., 13: 453-455.
44. Acevedo, F., Gentina, J. C., Garcia, N. (1998). C02 supply in
the biooxidation of an enargite pyrite gold concentrate
Biotechnol. Lett, 20: 257-259.
45. Nagpal. S., Dahlstrom, D., Oolman, T. (1993). Effect of
carbon dioxide concentration on the bioleaching of a pyrite
arsenopyrite ore concentrate. Biotechnol. Bioengg., 41: 159-164.
46. Hiroyoshi, N., Hirota, M., Hirajima, T., Tsunekawa, M.
( 1999). Inhibitory effect of iron oxidizing bacteria on ferrous
promoted chalcopyrite leaching. Biotechnol. Bioengg., 64: 478-
483.
47. Jensen, A. B., Webb, C. (1995). Ferrous sulphate oxidation
using Thiobacillus ferrooxidans: a Review, Proc. Biochem., 30:
225-236.
48. Blight, K. R., Ralph, D. E. (2004). Effect of ionic strength on
iron oxidation with batch cultures of chemolithotrophic
bacteria. Hydrometallurgy, 73: 325-334.
49. Rojas-Chapana, J. A., Tributsch, H. (2000). Bioleaching of
pyrite accelerated by cysteine. Proc. Biochem., 35: 815-824.
50. Pistaccio, L., Curutchet, G., Donati, E., Tedesco, P. (1994).
Analysis of molybdenite bioleaching by Thiobacillus ferrooxidans
in the absence of Iron (II). Biotechnol. Lett., 16: 189-194.
51. Adamov, E. V., Po'lkin, S. I., Koreshkov, N. G., Karavaiko,
G. I. (1990). State of the art and prospects of bacterial tank
leaching in the production of non ferrous and rare metals. In:
Karavaiko, G. 1., Rossi, G. and Avakyan, I. A (Eds), International
Seminar on Dump and Underground Bacterial Leaching Metals
47
Chapter: 1 General Introduction
from Ores, Centre for International Projects- GKNT, Moscow,
and USSR. 15L6th June, 235-24.
52. Gormely, L. S., Brannion, R. M. R. (1989). Engineering
design of microbiological leaching reactors. In: Jackson Hole
(Eds), Biohydrometallurgy 1989: Proceeding of the International
Biohydrometallurgy Symposium, Wyoming. 13th - 18th August,
499-518.
53. Rossi, G. (1999). The design of bioreactors. In: Amils, R. and
Ballester, A (Eds), Biohydrometallurgy and the Environment
towards the Mining of the 21st century. Part A. Elsevier,
Amsterdam, Netherland, 61-80.
54. Acharya, R. (1900). Bacterial leaching: a potential for
developing countries. Gene. Engg. Biotechnol. Monitor., 27: 57-
59.
55. Gentina, J. C., Acevedo, F. (1985). Microbial ore leaching in
developing countries. Trends in Biotechnol., 3: 86-89
56. Tempel, K. (2003). Commercial biooxidation challenges at
Newmont's, Nevada operations In: 2003 SME annual Meeting,
Preprint 03-067. Soc. Mining, Metallurgy and Exploration
Littleton, Colo.
57. Brierley, C. L., Briggs, A. P. (2002). Selection and sizing of
biooxidation equipment and circuits. In: Mular. A. L. Halbe D.
N., Barret, D. J (Eds), Mineral processing plant designs. Practice
and control. Soc. Min. Engg., Letteleton Colo, 1540-1568.
58. Johansson, C., Shrader, V., Suissa, J., Adutwam, K., Kohr,
W. (1999). Use of the GEOCOAT'fM process for the recovery of
copper from chalcopyrite. In: Amils, R., Ballester, A (Eds),
Biohydrometallurgy and the Environment towards the mining of
the 21st century, IBS 99. Elsevier, Amsterdam, 569-576.
59. Palencia, I., Romero, R., Carranza, F. (1998). Silver catalyzed
IBES process: Application to a Spanish copper-zinc sulphide
concentrate. Part 2. Biooxidation of the ferrous iron and
catalyst recovery. Hydrometallurgy48: 101-112.
48
/2-lij Chapter: 1 Ge11eral l1ltroductio1l
60. Romero, R., Palencia, I., Carranza, F. (1998). Silver catalyzed
IBES process: Application to a Spanish copper-zinc sulphide
concentrate Part 3. Selection of the operational parameters for
a continuous pilot plant. Hydrometallurgy, 49: 75-86.
61. U. S. Geological Survey. (2005). Mineral Commodity
Summaries, USA, 55-95.
62. Rao, M. H. R. (1997). National mining policy of India- putting
India on the mineral map of world. Minera. met.. Rev., XXIII, 23-
27.
63. Tambawalla, A. H. G. (1998). Metals and national economy.
Minera. Meta., Rev., XXIII, 61-62.
64. Vidyanathan, K. R. (1997). Need for high-tech exploration in
mining. Minera. Meta. Rev., XXIII.,S.
65. Indian Minerals Yearbook. (2001). Indian Bureau Of Mines,
Nagpur, India, 5-125.
66. Brombacher, C., Bachofen, R., Brandl, H. (1997).
Biohydrometallurgical processing of solids: A patent review.
Appl. Microbial. BiotechnoL, 48: 577-587.
67. Bruynesteyn, A., Hackl, R. P., Wright, F. (1986). The
BIOTANKLEACH process, In: King R. P (Ed), Gold 100. Proc. Int.
Conf. Gold S.A.I.M.M. Johannesburg, 2: 353-365
68. Barrett, J., Hughes, M. N., Karavaiko, G. I., Spencer, P. A.
(1993). Metal Extraction by Bacterial Oxidation of Minerals.
New York, Ellis Horwood.
69. Brierley, C. L. (1995). Bacterial oxidation Engg. Min. J., 196:
42-44.
70. Olson, G. J., Brierley, J. A., Brierley, C. L. (2003).
Bioleaching review part B: Progress in bioleaching: applications
of microbial processes by the minerals industries. Appl.
Microbial. Biotechnol, 63: 249-257.
71. Barbery, G., Fletcher, A. W., Sirois, L. L. (1980). Exploitation
of complex sulphide deposits: a review of processing options
49
Chapter : 1 General Introduction
from ore to metal. In: Jones M.J (Ed), Complex sulphide ores.
The Institution of Mining and Metallurgy, London, 135-150.
72. Groudev, S. N., Groudeva, V. I. (1992). Complex utilization of
polymetallic sulphide ores by means of combined bacterial and
chemical leaching. Proc. gth Int. Biotechnol. Symp. and
Exposition, Virginia, USA, 1-9.
73. Carranza, F., Iglesias, N., Romero, R., Palencia, I. (1993).
Kinetics improvement of high-grade sulphides bioleaching by
effects separation. FEMS Microbial. Rev., 11: 129-138.
74. McCready, R. G. L., Gould, W. B. (1990). Bioleaching of
uranium. In: Ehrlich H. L. and Brierley C. L (Eds), Microbial
mineral recovery. McGraw Hill Book Co., New York, 107-125.
75. Lawrence, R. W. (1990). Biotreatment of gold ores. In: Ehrlich
H. L. and Brierley, C. L (Eds), Microbial mineral recovery,
McGraw Hill Book Co., New York, 127-148.
76. Bosecker, K. (1997). Bioleaching: metal solubilization by
microorganisms. FEMS Microbial. Rev., 20: 591-604.
77. Dave, S. R., Mathur, P. (1987). Factors affecting multi-metal
ore leaching by Thiobacillus ferrooxidans. Indian J. Microbial.,
27: 51-54.
78. Carta, M., Ghiani, M., Rossi, G. (1980). Beneficiation of a
complex sulphide ore by an integrated process of flotation and
bioleaching. In: Jones, M.J (Ed), Proc. Complex Sulphide Ore
Conf., Institute of Mining and Metallurgy, London, 178.
79. Natarajan, K. A. (1988). Electrochemical aspects of
bioleaching multisulphide minerals. Trans. I.M.M., 5: 61-65.
50