chapter v pd ii selective liquid-liquid extraction...

Chapter 5 – Selective liquid‐liquid extraction of palladium(II) from salicylate media by n‐octylaniline in xylene

Analytical Chemistry Laboratory, Dept. of Chemistry, Shivaji University, Kolhapur 115

CHAPTER-5

SELECTIVE LIQUID-LIQUID EXTRACTION OF PALLADIUM(II) FROM SALICYLATE MEDIA BY n-OCTYLANILINE IN XYLENE

5.1 Introduction

Solvent extraction has attracted much attention as an effective and

energy saving type of separation technique for precious metals. This technique,

which has been extensively utilized in the mining industry, is one of the most

important process for the recovery of the precious metals from waste water or

scraps. At present there is a growing demand of precious metals for

technological application due to their outstanding physical and chemical

properties [1].

The abundance of palladium in the earth’s crust is 0.01-0.02 µg ml-1 and

it exists in various natural minerals, soils and rocks [2]. This element is of

immense importance to the electronic industries [3]. Palladium and its alloys

have a wide range of applications both in the chemical industry and in

instrument making. It also has widespread use in dental and medicinal devices

and jewellery manufacture [4]. The carcinogenicity of palladium(II)

compounds in rats and mice and their toxicity to mammals, fish and higher

plants are cause for environmental concern [5]. Therefore, these compounds are

usually considered as environmental pollutants [6].

Palladium(II) forms a number of complexes that are soluble in organic

solvents because of the labile character of its chloro complex, PdCl42- towards

several hydrophobic ligands [7]. This leads to the formation of several highly

extractable complexes at room temperature. Palladium prefers to coordinate

most strongly with polarizable atoms which has focused the development of an

extracting agents on those with donor atoms such as sulfur, phosphorus and

nitrogen. Nitrogen containing reagents, in particular, amines and their

derivatives are efficient extractants for some platinum group metals (PGMs)

and are widely used in technology and analysis. Modern techniques for the

extraction of PGMs provide rational approaches to choosing extractants from

the standpoint of their availability and selectivity and the development of


Analytical Chemistry Laboratory, Dept. of Chemistry, Shivaji University, Kolhapur

116

processes for one-step extraction of the target metal and its separation from the

associate metals.

5.2 Review of literature for liquid-liquid extractive separation of

palladium(II)

In recent years various reagents have been studied for liquid-liquid

extraction of palladium(II). These are hexadecylpyrimidinium bromide [8],

1-octyltheobromine [9], 1-[2-(2,4-dichlorophenyl)-4-propyl-1,3-dioxolan-2-

ylmethyl]-1H-1,2,4-triazole [10], N,N-dimethyl-N,N’-di-n-octyl-thiodigly-

colamide [11], LIX84I(2-hydroxy-5-nonylacetophenone oxime) [12], methyl-

alkylketones, such as 2-octanone, 2-nonanone, 2-undecanone, 2-tridecanone

and ketones containing symmetrical alkyl configuration, such as 5-nonanone,

5-decanone, 5-undecanone, and 6-undecanone exhibited significant extraction

of palladium(II) from nitric acid [13]. 1-Benzoyl-3-[6-(3-benzoyl-thioureido)-

hexyl]- thiourea [14] used for extraction of palladium(II). These methods were

applicable for extraction separation of either individual metal ion or group of

platinum metals and also suffers the incomplete recovery of the palladium [11,

12]. Sastre et.al. have reported selective liquid-liquid extraction of

palladium(II) from hydrochloric acid media by di-(2-ethylhexyl)thiophosphoric

acid (DEHTPA] [15] in kerosene. However, quantitative extraction requires

2 h shaking time. Solvent extraction behaviors of precious metal, palladium(II)

with 1-phenyl-3-methyl-4-benzoyl-5-pyrazolone (PMBP) [16] into molten

paraffin wax has been studied in the temperature range from 55 to 750C. The

extraction efficiency was up to 97 % at the experimental pH value. The

extraction properties of bis-acylated diethylenetriamine [17] are studied in the

extraction of palladium(II) from HCl solution. Method required higher reagent

concentration to ensure the complete extraction. Anyun Zhang et.al. have

investigated the extraction behavior of 4-aroyl derivative of 1-phenyl-3-

methyl-pyrazolone-5-one, a weakly acidic chelating extractant 1-phenyl-3-

methyl-4-(2-methoxybenzoyl)-pyrazolone-5-one and a trialkylamine [18] and

4-acylpyrazolone derivative of 1-phenyl-3-methyl-4-trifluoroacetylpyrazolone-

5-one and a tri-n-octylamine [19]. The methods are based on antagonistic



synergistic extraction of palladium(II) and were used for the separation of

palladium(II) from radioactive fission products. Tri-octylamine [20-23], was

reported for separation of palladium(II) from PGMs. The extraction of

palladium(II) from hydrochloric acid and hydrobromic acid, 5 % tri-iso-

octylamine [22] solution in carbon tetrachloride has been studied.

N-n-octylaniline [4, 24], alamine 336 [25-26], aliquat 336 [27], were reported

for the extraction of palladium. Schiff base extractant NN’-bis[1-phenyl-3-

methyl-5-hydroxypyrazole-4-benzylidenyl]-1,3-propylene diamine in

chloroform extract palladium(II) from nitric acid medium [28]. Extraction of

palladium(II) by bis-acylated diethylenetriamine [29] from hydrochloric acid

solution was studied. Palladium can be separated by this method from non-

noble metals. Extraction of palladium(II) from acidic solution at pH 1-4 by

using two hydrophobic analogs of N,N,N',N'-tetrakis[2-pyridyl-methyl]-1,2-

ethylenediamine (TPEN). N,N,N',N'-tetrakis[4-(2-butyloxy)-2-pyridyl-methyl]-

1,2-ethylenediamine (TBPEN) and N,N,N',N'-tetrakis(2-quinolinylmethyl)-1,2-

ethylenediamine (TQEN) [30] have shown enhanced solvent extraction

performance in more acidic media than TPEN. Liquid-liquid extraction of

palladium(II) and separation of it from other platinum group metals (PGM)

from Cl2/HCl leaching of the ores or concentrations converted into thiourea

eluate resin were studied, with high molecular weight tertiary amines [31] as

extractants. The extraction of palladium(II) from hydrochloric acid solution

with N-benzyl aniline in chloroform was investigated [32].

Extraction of palladium with triphenylphosphine (TPP) [33] in

1,2-dichloroethane from hydrochloric acid medium has been examined,

whereas at low acidity only palladium is quantitatively extracted. Addition of

stannous chloride as labilising agent makes possible a group separation of

platinum metals. Solvent extraction separation and recovery of palladium from

chloride leach liquors of spent automobile catalyst in tributylphosphate [34,

35] was studied. The extraction of palladium(II) by triphenylphosphine sulfide

[36] in benzene from nitric acid solutions has been investigated. The extraction

of palladium(II) was studied using a new series of bifunctional reagent alkane –



118

1, ω-diyl bis (0,0-diisobutyl phosphorodithioate) [37] in 1,2-dichloroethane

from chloride solution at pH 3.0. The method is useful for the selective

recovery of palladium from chloride leach sources. An aqueous solution of

palladium(II) in chloride medium at pH 2.4 was shaken with bis-(2,4,4-

trimethylpentyl)-phosphinodithioic acid [38] into chloroform to extract

palladium(II). Similarly, palladium(II) was extracted from same reagent but

from nitric acid medium [39]. p-( I ,1,3,3-tetramethylbutyl)phenyl hydrogen

[N,N-di(2- ethylhexyl)aminomethyl-phosphonate [40] was synthesized as a

novel type of extractant to investigate the extraction behavior of palladium(II)

from aqueous chloride media into toluene. Extraction of palladium(II) from

nitric acid solutions with NN-dialkylcarbamoylmethyl (diphenyl) phosphines

and its oxide was carried out [41]. Palladium(II) from nitric acid medium was

extracted with 1,5-bis-(diphenylphosphinoyl) pentane in toluene [42]. Liquid-

liquid extraction of palladium by a mixture of bis(2-ethyl-hexyl)

dithiophosphate and p-octylaniline [43] was studied. The extraction of

palladium(II) from chloride solutions by di(2-ethylhexyl)dithiophosphates of

tetraoctylammonium, tri-n-octylammonium and di-n-octyl-ammonium in

toluene has been investigated [44]. The extraction of chloropalladium

complexes by solutions of trioctylmethylammonium di(2,4,4-trimethylpentyl)

dithiophosphinate (Cyanex 301) [45] in toluene over a wide range of aqueous

acidities was examined. Liquid-liquid extraction of palladium(II) with Cyanex

921 [46] from aqueous hydrochloric acid media and Cyanex 923 [47] in

chloride media in toluene was studied. Extraction of palladium was carried out

from spent autocatalysts [46,47]. Phosphonium ionic liquid: trihexyl

(tetradecyl) phosphonium chloride (Cyphos®IL 101) [48] has been used as a

novel reagent in the presence of toluene to extract palladium(II) from

hydrochloric acid solutions of various concentrations. Cyphos®IL 101 can be

reused at least in 5 cycles of extraction-stripping process.

A number of extractants for platinum group metals have been

developed, however, the majority of them are those of sulphur atom donating

ligand type. The sulphide podand 1,12-di-2-thienyl-2,5,8,11-tetrathiadodecane



(TTD) [49] in chloroform or 1,2-dichloroethane has been used to extract

palladium(II) from hydrochloric acid medium but for phase separation 15 min

time was required. Di-octyl sulphoxide [50] in xylene was applied for

extraction of palladium(II) from nitric acid medium and spectrophotometric

determination using arsenazo III. The extraction of palladium(II) nitrate by

bis(2-ethylhexy1) sulphoxide (BBSO) [51] was evaluated over a wide range of

acidity. 1,2-Bis-(tert-hexylthio) ethane [52] has been used as an extractant in

toluene for palladium(II) from hydrochloric acid medium. A new extractant

bis-(2-butylthioethyl) sulfide in chloroform was used for palladium(II)

extraction [53]. Extraction of palladium(II) with dihexyl sulfide (DHS) [54-56]

from chloride solution, and the degradation of DHS to dihexyl sulfoxide

(DHSO) were investigated in this study. The solvent extraction of palladium(II)

from hydrochloric acid solution by some dialkyl sulfoxides were reported [57].

The solvent extraction and separation performances of Pd(II) and Pt(IV) from

hydrochloric acid solutions were investigated by using di-Bu sulfoxide [58]

diluted in kerosene. Separation was carried out from several common

impurities like Fe(II), Cu(II) and Ni(II). Extraction and separation of palladium

with normal Bu benzothiazole [59] sulfide ether was studied.

2-Mercaptobenzothiazole in chloroform [60] extracts palladium(II) from

acidified solutions of platiniferous samples. NN-dialkyl-N’-benzoylthiourea

extracts palladium(II) in Solvesso 150 [61]. Method is applicable for extraction

and separation of platinum group metals from solution containing base metals.

But the optimal pH range is narrow. N’N’-dihexyl and phenyl and N’-hexyl

and phenyl derivatives of N-benzoyl thiourea [62] extract palladium(II) from

chloride medium in toluene but the method demands large volume of the

extracting solvent to effect the quantitative recovery of metal. Extraction of

palladium(II) with NN-diethyl-N’benzoylthiourea (DEBT) [63] in toluene from

hydrochloric acid media has been also reported. Methyl isobutyl ketone

extracts palladium(II) from hydrochloric acid medium [64, 65] and also

β-diketone [66] have been reported for the extraction of palladium(II). The

chloroform extraction of palladium(II) from 0.1-8 M sulphuric acid in the



120

presence of potassium ethyl xanthate [67] has been studied. N-benzoyl-N’,N’-

diethylthiourea [68] was used for extraction of palladium(II). Theophylline

derivatives [69] was used in extraction of palladium(II). Extraction of

palladium(II) with thiocyanate [70] complexes by MIBK was reported.

N,N-Di(2-ethylhexyl) aminomethylquinonline [71] has been newly

synthesized to develop selective extractants for palladium(II). Mixture of protic

ionic liquids trioctylammoniumbis(trifluoromethanesulfonyl)amide ([TOAH]

[NTf2]) and trioctylammonium nitrate ([TOAH][NO3]) [72] were investigated

for palladium(II) extraction. The extractability of palladium(II) using

N,N,N’,N’- tetra-n-octyl-thiodiglycolamide (TOTDGA) [73] diluted with a

mixed solution of n-dodecane and 2-ethylhexanole were investigated by

solvent extraction and FT-IR measurements. Selective solid-phase extraction

and separation of trace palladium using activated carbon modified with ethyl-3-

(2-aminoethylamino)-2-chlorobut-2-enoate [74]. Liquid-liquid extraction of

palladium(II) was carried out with acylthioacetamides [75]. An aliquot

containing palladium(II) solution was extracted with 1,2,3-benzotriazole in

isobutyl methyl ketone from acetic acid-sodium acetate buffer at pH 4 [76].

The extraction behaviour of palladium(II) from the aqueous ammonium

chloride solution with the 7-tridecanone oxime in toluene was investigated in

terms of equilibrium and kinetics [77]. Dibenzylammonium dibenzyldithio-

carbamate (DBADBDC) was used as an extractant for palladium(II) into

chloroform at pH more than 4 [78]. N,N'-dimethyl-N,N'-diphenyl-

tetradecylmalonamide (DMDPHTDMA) [79] in 1,2-dichloroethane has been

investigated as a solvent extraction reagent to mainly perform the separation of

palladium from other PGMs and from some commonly associated elements

contained in concentrated hydrochloric acid media. The developed separation

scheme was applied to an automobile catalytic converter leaching solution.

Palladium contents in geochemical reference samples, rocks [80] were

determined by graphite furnace-atomic absorption spectrometry after digestion

of sample with aqua regia and HF and extraction of palladium as iodide by

methyl isobutyl ketone. Extraction of palladium(II) from hydrochloric acid



solutions with pyridinecarboxamides and ACORGA®CLX50 [81], was studied.

An extremely sensitive, reliable and simple procedure for extraction of

palladium(II) from human urine at pH 4 with pyrrolidinedithiocarbamate into

4-methyl-2-pentanone has been described [82]. Extraction mechanism of

complex in the presence of chloride ion was also discussed. Palladium(II) was

quantitatively and selectively extracted into a chloroform solution of

3-hydroxy-4 (1H-tetrazol-5-ylazo)- naphthalene –2,7-disulphonic acid [83] and

benzalkonium chloride and determined by atomic absorption spectrometry.

The extraction was investigated of halo complexes of palladium(II) by

dipyrazolonylmethanes [84] and method was developed for the chemical

atomic emission determination. Solvent extraction of the platinum and

palladium chloro complexes by tetraoctylhexylenediamine salts with di(2-

ethylhexyl)-phosphoric and dithiophosphoric acids [85] were studied.

Determination of palladium(II) from various geological samples by graphite

furnace-AAS [86, 87] was reported. The use of commercially available solid

phase extraction (SPE) [88] anion exchange cartridges for the separation and

preconcentration of palladium(II) was reported. A method for the separation of

bromide complex anions of palladium(II) with liquid solid extraction system of

polyvinylpyrrolidone-salt-water [89] was investigated. Cetylpyridinium

chloride (CPC) [90] used for separation of palladium(II). 1-[2-(2,4-

dichlorophenyl)-4-propyl-1,3-dioxolan-2-ylmethyl]-1H-1,2,4-triazole [91] was

studied for the extraction of palladium(II). N,N-di(2-ethylhexyl)

aminomethylquinoline (DEQ) [92] and separation and preconcentration of

palladium(II) by octadecyl- silica membrane disks [93] was reported. Di-(2-

ethylhexyl) thiophosphoric acid (DEHTPA) [94] in high sensitive sepration

method was reported. Separation of palladium(II) by bulk liquid membranes

during electrodialysis [95] was reported by Sadyrbaeva et. al.

Formazans-I in dichloromethane [96], Kelex 100 in toluene [97, 98],

Calix[4]arene in chloroform [99], 2,2 dithiodianiline [100], 18-crown-6,1,4,

7,10,13,16-hexa- azaoctadecane (hexacyclen) [101], Caffeine in chloroform



122

[102] were reported as extractants for palladium(II) mostly from hydrochloric

acid media.

In this work, n-octylaniline-salicylate system was studied to investigate

the extraction of aqueous palladium(II) solution as a function of concentration

of extractant, different weak organic acids, pH, various strippants etc. The

proposed method is used for rapid and selective separation of palladium(II)

from associated elements. It is also tested for the separation and determination

of palladium(II) from real samples such as alloy and catalysts. The review of

literature for comparison of liquid-liquid extractive separation of palladium(II)

is given in Table 5.1.



Table 5.1 Review of literature for comparison of liquid-liquid extractive

separation of palladium(II)

System Aqueous phase

Organic phase

Special features Ref.No.

Hexadecylpyrimidinium bromide (HDPB)

HCl Chloroform Shaking time only few min

% recovery of Pd(II) 99 %

8

1-Octyltheobromine HCl Toluene Study was carried out at 303 K

9

1-[2-(2,4-dichlorophenyl)-4-propyl-1,3-dioxolan-2-ylmethyl]-1H-1,2,4-triazole

HCl Toluene The extraction follows the

anion-exchange mechanism

10

N,N-dimethyl-N,N’-di-n-octyl-thiodiglycol-amide (MOTDA)

HCl - Extraction was nearly 100 % and very fast

11

LIX84I (2-hydroxy-5-nonylacetophenone oxime)

HCl - Pd(II) extraction was about 86 %

Thermodynamic values like ΔS, ΔH, G determined

Common impurities like Fe(III), Al(III), Zn(II), Cu(II), Ni(II) were separated

12

Methylalkylketones HNO3 - Pd(II) extraction behavior was fully investigated.

13

1-benzoyl-3-[6-(3-benzoyl-thioureido)-hexyl]- thiourea

HNO3 1,2-Dichloroethane

Stoichiometry of the extracted complexes has been determined

14

Di-(2-ethyl-hexyl)thiophosphoric acid (DEHTPA)

HCl Kerosene Selective extraction of palladium(II) over Pt(IV), Rh(III), Cu(II), Fe(III) and Zn(II)

15

1-phenyl-3-methyl-4-benzoyl-5-pyrazolone (PMBP)

- - Extraction has been studied in the temperature range 55 to 75oC.

Extraction efficiency was up to 97 %

16

Bis-acylated diethylenetriamine

HCl - Required higher reagent concentration to ensure the complete extraction

17

1-phenyl-3-methyl-pyrazolone-5-one

HNO3 Chloroform Synergistic extraction with trialkylamine (TiOA)

18



124

1-phenyl-3-methyl-4-trifluoroacetylpyrazolone-5-one

HNO3 - Antagonistic synergistic extraction (TOA)

19

Tri-octylamine HCl

Kerosene The extraction sequence of platinum metals was Au(III) > Pd(II), Pt(IV), Ir(IV) > Ir(III), Ru(III).

Separation of Pd(II) from PGMs.

20- 23

8.0 M HCl Thiourea

- Method was applicable for Pd(II) and Au(III)

Column packed with divinylbenzene

homopolymeric microcapsule

21

HCl< 4M CCl4 Rapid procedure 22

N-n-octylaniline HCl, Salicylate

Xylene Extraction of metal from synthetic mixture, alloys and catalyst.

4, 24

Alamine 336 (A336) pH, 2-3

- Pd(II) and Pt(IV) separated from each other by selective stripping with thoicyanate and thiourea.

25

HCl HClO4, Na2CO3 and thiourea used as stripping agents.

26

Aliquat 336 Salicylate Xylene Proposed method was described the scheme for the separation of Pt(IV), Ni(II), Cu(II), Co(II),Zn(II), Mn(II)

27

NN’-bis[1-phenyl -3-methyl-5- hydroxypyrazole -4-benzylidenyl] -1,3-propylene diamine

HNO3 or HClO4

Chloroform or toluene

The separation of palladium(II) from the mixed solution of Pd(II)-Pt(IV) was achieved.

28

Bis- acylated diethylenetriamine

HCl - In extraction process Pd(II) separated from non-noble metals

29

Nitrogen-donor ligand TPEN and TBPEN,TQEN

pH, 1-4 - More effective in more acidic media.

30

Tertiary amines Cl2/HCl - Palladium(II) separated from other PGMs from Cl2/HCl leaching of the ores or concentrations converted into thiourea eluate resin were studied

31



N-benzyl aniline HCl, < 1 M

Chloroform Thiourea excellent stripping agent.

32

Triphenylphosphine HCl 1,2-Dichlo- roethane

Stannous chloride used as labilizing agent. Useful for group concen-

tration before determination by AAS. Palladium was

quantitatively extracted at low acidity.

33

Tri-butyl phosphate HCl, 3.5-6 M

Toluene Monomeric anionic chloro complexes and polymeric aquachloro or aqua-oxo-complexes produced.

34

HCl Kerosene Palladium(II) recovery 99.9 %.

35

Triphenyl phosphine sulfide

HNO3, 2.5 M

Benzene No interference of the commonly associated radio -nuclides

36

Alkane-1, ω-diyl bis(o,o-diisobutyl phosphoro-dithioate)s (ADBDiBPDT)

Chloride solution 1.0 M pH, 3.0

1,2-Dichloro-ethane

Extractibility increases with the increase in the length of the alkane-1 ω chain-separating the two phosphorodithioate groups.

37

Bis-(2,4,4-trime -thylpentyl)pho-sphinodithioic acid (HBTMPDTP)

Chloride, 0.1 M pH, 2.4 HNO3

Chloroform Separation of palladium(II) from platinum(IV)

38, 39

P-(1,1,3,3-tetramethyl butyl)phenyl H N,N-di(2-ethylhexyl) amino-methyl phosphonate (HR)

HCl, 0.01-6 M

Toluene Extractant for precious metals. High lipophilicity leads to

higher extraction than that from N,N-di(2-ethyl/hexyl) amino methylphosphoric acid. Fe(III) interference.

40

NN-dialkylcarbamoylmethyl (diphenyl) phosphines, NN-dialkylcarbamoylmethyl(diph-enyl)phosphine oxide.

HNO3 - Extraction of Pd(II) 41

1,5-Bis(diphenyl phosphinoyl) pentane

HNO3 Toluene Pd(II) Successfully extracted

42

Mixture of bis(2-ethyl-hexyl) dithiophosphate and p-octylaniline.

- - Flameless atomic absorption determination

43



126

Di(2-ethylhexyl) dithiophosphates of tetraoctyl ammonium, tri-n –octylammonium and di-n-octylammonium

Chloride Toluene When binary extractants used in excess, palladium(II) complexed with reagent distributes into the organic phase.

44

Trioctylmethylammonium di(2,4,4-trimethylpentyl)dithiopho-sphinate (Cyanex 301)

HCl Toluene Increase in acidity and reagent concentration increase the percentage extraction.

45

Cyanex 921 HCl Toluene Recovery from spent autocatalysts

46, 47

Cyanex 923 HCl Toluene 1:1 HCl + HClO4 strippant. Method applicable for

recovery of metal ions from synthetic solution

47

Trihexyl(tetradecyl)phosphonium chloride (Cyphos®IL 101)

3 M HCl Toluene. 0.5 M ammonia solution used as strippant.

48

Sulphide podand 1,12-di-2-thienyl –2,5,8,11-tetra-thiadodecane

HCl Chloroform 15 min required for phase separation. Rate of extraction

considerably higher than dioctyl sulphoxide

49

Dioctyl sulphoxide HNO3, 0.5-1.5 M

Xylene Back extracted into a mixture of 2 M sodium carbonate and 0.05 M ammonia

50

Bis-(2-ethyl-hexyl)sulphoxide

HNO3, 8 M

Toluene Recovery of extractant by sodium thiosulfate.

51

1,2-bis(ter-hexyl thio)ethane

HCl Toluene Study was carried out at 303 K

52

Bis-(2-butylthio ethyl) sulfide

- Chloroform Decontamination factor 3x105.

53

Dihexyl sulphide (DHS) Chloride Insoluble substance was decreased by the addition of modifier like alcohol.

54-56

Extraction of platinum(IV) increased by increase of contact time and decrease of palladium(II) concentration.

Dialkyl sulphoxide HCl - Pd(II) extract at low acidity

57

Di-bu sulfoxide

HCl Kerosene Separation was carried out from several common impurities like Fe(II), Cu(II) and Ni(II).

58



Butyl benzothiazole - - Extraction 80 % of platinum(IV)

In two stage total extraction 98.7 %

59

2-mercaptobenzothiazole - Chloroform Method successfully applied for analysis of solid platiniferrous samples.

60

N-benzoyl-NN’-dihexylthiourea

pH, 3 Solvesso 150

Analysis of geological samples. Cu, Fe, Ni interfere in the extraction.

61

NN’-dihexyl and-phenyl and N’-hexyl and phenyl derivatives of N-benzoyl thiourea.

HCl, pH, 1-3

95oC temperature required. Separation from other platinum group metals and base metals.

62

NN’-diethyl-N’-benzoylthiourea (DEBT)

HCl, 1 M Toluene Extraction selectivity in order Pd(II)>Pt(IV)> Ru(III)>Rh(III) > Ir(III).

63

Methyl isobutyl ketone HCl Methyl isobutyl ketone

Palladium can be extracted quantitatively from small amounts of sample.

Analysis of converter matte. Useful for analysis of standard ore PTC-1.

64, 65

β-diketone (LIX 51) pH, 3.2 –6.0

- Palladium can be extracted quantitatively

66

Potassium alkyl xanthate H2SO4, 0.1-8 M

Chloroform Determination from organic phase by a a.s.

67

N-benzoyl-N’,N’-diethylthiourea

pH, 1-2

- Palladium can be extracted quantitatively

68

Theophylline derivatives

- - Selective extraction method for palladium(II)

69

Thiocyanate HCl MIBK At room temptature Pd(II) only form complex with thiocyanate. More than 95 %

extraction was observed. Extraction of secondary

PGMs

70

N,N-Di(2-ethylhexyl) aminomethylquinonline

HCl Toluene This method also applicable for Pt(IV)

71



128

Trioctylammoniumbis(trifluoromethanesulfonyl)amide ([TOAH][NTf2]) and Trioctylammonium nitrate ([TOAH][NO3])

HNO3 - Reagent was applicable for Pt(IV) Method was recyclable,

easy to handle, safe, and environmentally friendly. Slightly co-extracted

Na(I), Mg(II), K(I), Ca(II), Mn(II),Fe(III), Co(II), Ni(II), Cu(II), Zn(II), Ru(III), Rh(III)

72

N,N,N’,N’- tetra-n-octyl-thiodiglycolamide(TOTDGA)

HNO3- HCl

Mixture of n-dodecane and 2-ethyl hexanole

Extraction depends on the reagent concentration.

73

ethyl-3-(2-aminoethylamino)-2-chlorobut-2-enoate

- - Determination of Pd(II) by ICP-AES

74

Benzoylthioacetanilide (Acyl thioacetamides)

- Benzene Palladium extracted over wide pH range.

75

1,2,3-Benzotriazole Acetic acid Sodium acetate-acetic acid buffer pH, 4

MIBK Determination by γ-ray spectrometer

CN-, SCN-, S2O32-, Fe(III),

W(VI), Se(IV), Ag(I), Au(III), Co(II), Cu(II), Zn(II) interfered.

76

7-Tridecanone oxime (TDO)

HCl, 0.01M

Toluene Equilibrium and kinetics of extraction investigated

77

Dibenzylammonium dibenzyl- dithiocarbamate (DBADBDC)

pH =>4 Chloroform Extraction mechanism discussed

78

N,N'-dimethyl-N,N'-diphenyltetradecylmalona-mide (DMDPHTDMA)

HCl 1,2-Dichloroethane

Method was applicable for separation of palladium from other PGMs

79

MIBK - MIBK Platinum contents geochemical reference samples rocks were determined by graphite furnace atomic absorption spectrometry

80

Pyridinecarboxamides HCl - At low acidity Pd(II) separated from Pt(IV)

81

Pyrrolidinedithiocarbamate PH, 4 4-Methyl-2-pentenone

Extremely sensitive, reliable and simple procedure

82



3-Hydroxy-4-(1H-tetrazol-5-ylazo) naphthalene-2,7-disulphonic acid Benzalkonium chloride

- Chloroform Method applicable for determination of Pd(II) in sludges and pharmaceutical processes.

83

Dipyrazolonylheptane H2SO4, 0.25 M NH4Cl, 0.1 M

Chloroform Determination by emission spectroscopy Mercury interfered

84

Di(2-ethylhexyl)-phosphoric (II) and -Dithiophosphoric acids

- Toluene Decrease in acidity of aqueous phase diminution in phase contact in the organic phase.

85

Methyl isobutyl ketone - MIBK Palladium contents in geochemical reference samples rocks were determined by

graphite furnace atomic absorption spectrometry.

86, 87

Solid-phase extraction cartridges (SPE)

HCl - Method was used for group extraction

88

Polyvinylpyrrolidone-salt-water

HBr - Separation of Pd(II) from other PGMs

89

Cetylpyridinium chloride (CPC)

- - Process also studied for Rh(III), Pt(IV).

90

1-[2-(2,4-dichlorophenyl)-4-propyl-1,3-dioxolan-2-ylmethyl]-1H-1,2,4-triazole

HCl Toluene Method was used for group extraction

91

N,N-di(2-ethylhexyl) aminomethylquinoline(DEQ)

HCl Toluene Method was used for group extraction

92

Octadecyl- silica membrane disks

- - Separation of Pd(II)from other PGMs

93

Di-(2-ethylhexyl) thiophosphoric acid (DEHTPA)

HCl Kerosene Highly selective in separation of Pd(II) against Fe(III), Pt(IV), Rh(III) and Zn(II)

94

Bulk liquid membranes - 1,2-Dichloroet-hane

Separation of Pd(II) from Pt(IV)

95

Formazans-I - Dichloro-methane

Prolonged shaking (24 h) required.

96



130

Kelex 100 [7-(4-ethyl-1-methyloctyl) quinoline-8-ol]

Chloride, 1M Thio-cyanate

Toluene Equilibrium period 60 h. Presence of tin affects the extraction behaviour of noble metals. Stripping increases with increase in concentration of oxidizing agent

97, 98

Calix[4]arenes - Chloroform Introduction of amide functional group improved Pd(II) extraction.

Na interference.

99

2,2 dithiodianiline (DTDA)

pH, 1-6

MIBK Trace amount of Pd(II) was determined.

100

18-crown-6,1,4, 7,10,13,16-hexa- azaoctadecane (hexacyclen)

pH 3-11 Methyl isobutyl ketone

Separation of Pd(II) from iron, silver, mercury, copper and platinum.

101

Caffeine HCl Chloroform High selectivity over base metals and platinum(IV).

102



5.3 Experimental

5.3.1 Apparatus

Elico digital spectrophotometer model 12 Chemito 215D with 1 cm

quartz cells was used for absorbance measurements and pH measurements were

carried out using an Elico digital pH-meter model LI-127. All weighing

operations were done by using Tapson’s analytical single pan balance model

200 T having 0.001 gm accuracy.

5.3.2 Reagents

A stock solution of palladium(II) was prepared by dissolving 1 g of

palladium chloride hydrate (Johnson Matthey, UK) [103] in dilute analar HCl

(1 M) and diluting to 250 mL with water and standardized. A working solution

of 100 µg/mL was made by diluting the stock solution with water.

n-Octylaniline

The reagent n-octylaniline was prepared by the method of Pohlandt’s

[104] and its 0.07 M solution was prepared in xylene. All solutions were

prepared from A. R. grade reagents. Aqueous solutions were prepared with

water. Double distilled water was used throughout the experimental study.

Preparation of 4’-ChloroPTPT

1-(4’-Chlorophenyl)-4,4,6-trimethyl-(1H,4H)-pyrimidine-2-thiol (4’-

ChloroPTPT) were prepared by the method of Mathes [105-108]. A stock

solution (0.02 M) was prepared by dissolving 0.5329 g 4’-ChloroPTPT in

100 mL chloroform. Reagent solution was colorless and stable.

Standard solution of diverse ions were prepared by dissolving AR grade

reagents in water or dil HCl. All the organic solvents were used after double

distillation. All chemicals used were of AR grade.

5.3.3 General procedure for extraction and determination of palladium(II)

To an aliquot containing 200 µg palladium(II) in 25 mL volumetric flask,

0.034 gm of sodium salicylate was added to get the concentration of solution



132

0.085 M. The pH of the resulting solution was adjusted to 1.5 with dilute HCl

and NaOH solution. The aqueous solution was shaken with 10 mL 0.07 M

n-octylaniline in xylene for 5 min in separator funnel. After the phase

separation, the organic phase was stripped with three 10 mL portions of 5 M

ammonia. The back extracts were evaporated to moist dryness in order to

remove excess of ammonia. The residue was dissolved in minimum amount of

aqua regia, and evaporated with two 2 mL portions of concentrated HCl to

remove oxides of nitrogen. The residue was dissolved in 0.1 M HCl and

palladium(II) was determined spectrophotometrically by 4’-ChloroPTPT [109].

All the experiments were repeated on an average five times and the accuracy

determination of the metal concentration in the loaded organic phase was

realized by mass balance and checked by complete stripping of the loaded

organic phase followed by analysis of the stripped solution.

5.4 Results and Discussion

5.4.1 Extraction as a function of pH

The effect of pH on the percentage extraction of palladium(II) was studied

in the pH range of 0.3 to 10 with n-octylaniline in xylene in presence of

0.085 M sodium salicylate (Table 5.2). The extraction of palladium(II) was

found to be quantitative in pH range 1.0 to 2.0. Hence, all the extractions of

palladium(II) were carried out at pH 1.5 with 0.07 M n-octylaniline in xylene

(Fig 5.1).

5.4.2 Extraction as a function of n-octylaniline concentration

In the effect of reagent concentration, extractions were carried out with

various molar concentrations of n-octylaniline in xylene (Table 5.3). The

extraction of palladium(II) was quantitative with 10 mL of 0.060 - 0.080 M

n-octylaniline in xylene. However, 10 mL of 0.070 M n-octylaniline in xylene

was used for general extraction procedure (Fig 5.2).



5.4.3 Extraction as a function of weak organic acid concentration

The extraction of palladium(II) was carried out at pH 1.5 with 10 mL of

0.07 M n-octylaniline in xylene in presence of varying concentrations of

salicylate, succinate and malonate as weak carboxylic acid media (25 mL)

(Table 5.4). The extraction of palladium(II) was found to be quantitative in the

range of 0.080 to 0.095 M sodium salicylate. However, the extraction of

palladium(II) was incomplete in succinate (0.01 to 0.1 M) and malonate (0.01

to 0.1 M) media. Thus, 0.085 M concentration of salicylate (0.034 gm) was

used throughout the experimental work.

5.4.4 Effect of diluents

The studies were performed to find out the most suitable solvent for

n-octylaniline to ensure quantitative recovery for palladium(II) by the

extraction. The solution of n-octylaniline (0.07 M) in benzene, toluene, xylene,

n-butyl alcohol, amyl alcohol provides quantitative extraction of palladium(II).

The extraction of palladium(II) was incomplete if n-octylaniline is dissolved in

chloroform (% E = 25.1 %), carbon tetrachloride (% E = 61.0 %), methyl

isobutyl ketone (% E = 91.9 %), 1, 2-dichloroethane (% E = 51.9 %), kerosene

(% E = 46.4 %) and amyl acetate (% E = 28.3 %). Xylene showed minimum

toxicity and it provides better phase separation, as compared to other diluents

so it was recommended for general procedure (Table 5.5).

5.4.5 Effect of stripping agents

Stripping is the reverse of extraction, so it should be promoted by

those factors that affect extraction negatively, such as alkalies and salt media.

Acids were unsuccessful because the anion complex adhered in the organic

medium under these conditions. Ammonia solution (5 M) was preferred

because it was easier to remove from the aqueous phase by evaporation prior to

determining palladium(II) spectrophotometrically with 4’-ChloroPTPT as

compared to ammonia buffer solution. Hence, ammonia and ammonia buffer

are the most effective stripping agents for palladium(II) from organic layer.

The stripping percentage was calculated relative to the initial amount of



134

palladium(II) in organic layer. It was found that stripping was incomplete in

HCl, H2SO4, HNO3, NaOH, KOH, water and acetate buffer. In this work, three

10 mL portions of 5 M ammonia were used as a strippant (Table 5.6).

5.4.6 Effect of equilibration time

The period of equilibration was varied from 1 to 30 min (Table 5.7). The

extraction of palladium(II) was quantitative over a period of 3 min shaking of

the solution, but with prolonged shaking over 20 min (Fig. 5.3) there was

decrease in the percentage extraction of palladium(II) due to the dissociation of

ion-pair complex. Thus, equilibration time for 200 μg palladium(II) extraction

was kept about 5 min throughout the study.

5.4.7 Extraction behavior of palladium(II) as a function of metal loading

capacity

Varying concentrations of palladium(II) (100 to 5000 µg/mL) were

extracted with 10 mL portions of 0.07 M n-octylaniline in xylene from 0.085 M

sodium salicylate media. It was observed that extraction of palladium(II) was

quantitative up to 1500 µg/mL with 10 mL of 0.07 M n-octylaniline

(Table 5.8).

5.4.8 Extraction behavior of palladium(II) as a function of aqueous to

organic volume ratio

Palladium(II) was extracted from 10 mL to 50 mL aqueous solutions

containing 0.085 M sodium salicylate with 10 mL of 0.07 M n-octylaniline in

xylene. The extraction was quantitative when aqueous to organic volume ratio

was in the range 1:1 to 5:1 and above this ratio the extraction decreased

(Table 5.9)

5.4.9 Nature of extracted species

The probable composition of extracted species was ascertained by

plotting the graphs of log D[Pd(II)] against log C[n-octylaniline] at fixed sodium

salicylate concentration (0.085 M). The graphs were found to be linear and



having the slopes of 0.89 and 0.82, values at pH 4.0 and 7.0, respectively

(Fig. 5.4). Also, plots of log D[Pd(II)] against log C[Salicylate] at fixed n-octylaniline

concentration (0.07 M) were linear and the slope values were found to be 2.8

and 2.7 at pH 4.0 and 7.0, respectively (Fig. 5.5). The probable composition of

the extracted species was calculated as 1:3:1 (Metal: Acid: Extractant).The

possible mechanism of ion- pair complex is as follow:-

CH3(CH2)7C6H4 NH2(org) + H + (aq) [CH3(CH2)7C6H4NH3]+

(org) (5.1)

Pd2+(aq) + 3C7H5O3

-(aq) [Pd(C7H5O3)3]-

(aq) (5.2)

CH3(CH2)7C6H4NH3+

(org)+[Pd(C7H5O3)-3](aq) [CH3(CH2)7C6H4NH3

+Pd(C7H5O3)3-](org) (5.3)

The possible mechanism of the ion-pair complex extracted

appears to be protonated n-octylaniline which form cationic species as

CH3(CH2)7C6H4NH3+

,while salicylate combines with palladium(II) to form

anionic species as Pd (C7H5O3)-3 and both of them associate to form ion-pair of

the type [CH3(CH2)7C6H4NH+3Pd(C7H5O3)-

3](org), which being neutral

constituted extractable species.

5.4.10 Effect of temperature

The effect of temperature in the range 302-314 K on the extraction of

palladium(II) in a solution of ionic strength of 0.085 M sodium salicylate and

having pH 5.0, by 0.07 M n-octylaniline in xylene was studied. It was found

that in the extraction of palladium(II) by n-octylaniline in xylene, the

distribution coefficient increases with rise in temperature.

The change of the extraction equilibrium constant Kex with temperature

is expressed by van’t Hoff equation (5.4)

Δ log Kex /Δ (1/T)=Δ H/(-2.303 R) (5.4)

where T is absolute temperature and R is the gas constant.

The plot of Kex versus 1000/T is linear with a slope value of -3.407 and the

enthalpy change of the extraction carried out at constant pH 5.0 was evaluated

as Δ H = 65.23 KJ mol-1 which means it is an endothermic process. The free

energy ΔG and entropy ΔS were calculated form equation (5.5) and (5.6) and

are reported in Table 5.10.



136

ΔG= -2.303 RT log K (5.5)

ΔS = (ΔH – ΔG) / T (5.6)

The negative values of free energies imply that reaction is spontaneous.

The positive enthalpy value indicates that the extraction of palladium(II) with

n-octylaniline in xylene is favorable with rise in temperature (Fig. 5.6).

5.4.11 Effect of various diverse ions on percentage of extraction

The effect of a large number of foreign ions on the extraction of

200 µg/mL of palladium(II) with n-octylaniline was investigated following the

recommended procedure. The tolerance limit of individual foreign ions was

set so that error in percentage recovery was not more than ± 2 %. Thiourea,

tartarate, oxalate, EDTA, thiocyanate, thiosulphate, ascorbate interfere in the

extraction procedure of palladium(II) (Table 5.11).

5.5 APPLICATIONS

5.5.1 Separation of palladium(II) from associated metal ions

The method permits separation and determination of palladium(II) from

binary mixtures containing Pt(IV), Rh(III), Ir(III), Cu(II), Fe(III), Co(II),

Ni(II), Se(IV), Au(III) and Te(IV) (Table 5.12). Palladium(II) was separated

from these associated metal ions, under the optimum extraction conditions of

palladium(II) where, all the added metal ions were remained quantitatively in

aqueous phase from which they were determined spectrophotometrically by

standard methods [109-114]. Palladium(II) from organic phase was stripped

and estimated spectrophotometrically by 4’-ChloroPTPT method. Palladium(II)

was separated from Ru(III) by masking with 25 mg of citrate when

palladium(II) was extracted with 0.07 M n-octylaniline in xylene at pH 1.5.

While, Ru(III) remained in aqueous phase. Palladium from the organic phase

was stripped with ammonia and determined spectrophotometrically. The

masked Ru(III) was demasked with concentrated HClO4 and determined

spectrophotometrically by standard method.



5.5.2 Sequential separation of palladium(II), rhodium(III) and

ruthenium(III) form their mixture

Palladium(II) and rhodium(III) are used as auto exhaust catalyst as well

as palladium(II) and ruthenium(III) are used as hydrogenation catalyst in

organic chemistry. Hence, their separation and determination from mixture has

great importance (Table 5.13).

Palladium(II) was separated from ternary mixtures of rhodium(III) and

ruthenium(III) at pH 1.5, from 0.085 M sodium salicylate media by 0.07 M of

n-octylaniline in amyl alcohol. Rhodium(III) and ruthenium(III) remain

quantitative in aqueous phase while, palladium(II) was extracted into organic

phase. Separation is based on the use of amyl alcohol as a solvent for

palladium(II). Palladium(II) from organic phase was stripped with 5 M

ammonia (3 × 10 ml). The ammonia was evaporated and palladium(II) was

determined by 4’-ChloroPTPT [109].

The aqueous phase was evaporated to moist dryness and adjusted to

0.03 M sodium malonate, and then pH was adjusted to 9.0. Rhodium(III) was

extracted with 0.1 M of n-octylaniline in xylene . It is back stripped with 1 M

HCl (2 × 10 ml). It was determined spectrophotometrically by KI + SnCl2

method [110].

The aqueous phase containing ruthenium(III) was again evaporated to

moist dryness. It was adjusted to 0.05 M sodium malonate, the pH was

maintained 3.5 and extracted into 0.1 M of n-octylaniline in xylene. The

organic phase was stripped with 2 % NaCl + 1 M HCl (4:1) solution. Back

stripped ruthenium(III) in aqueous phase was estimated by 4’-ChloroPTPT

[109] (Flow sheet 5.1).

5.5.3 Determination of palladium(II) from synthetic mixture and

synthetic mixture corresponding to alloys

The proposed method was applied to the extraction and determination of

palladium(II) from salicylate media at pH 1.5 in various ternary mixtures.

Palladium(II) is extracted with 0.07 M n-octylaniline in xylene while Pt(IV),



138

Ir(III), Te(IV), Se(IV) remained unextracted in the aqueous phase. However,

Ru(III) masked by 25 mg citrate. The extracted palladium(II) was stripped with

5 M ammonia ( 3 × 10 mL portions) and determined by 4’-ChloroPTPT

method spectrophotometrically (Table 5.14).

Similarly, the proposed method was applied for analysis of synthetic

mixture corresponding to alloys such as oakay alloy, jewellery alloy, copper

alloy, antimony alloy. The real samples of these alloys were not available at

working place, which forced us to use synthetic mixture with corresponding

composition to alloys, the palladium(II) was extracted under its optimum

extraction conditions and determined spectrophotometrically, the result of

analysis are reported in Table 5.15.

5.5.4 Determination of palladium(II) in catalysts

A known weight of catalyst was dissolved in a mixture of concentrated

HCl and HNO3 (3:1). After the reaction was over, the solution was heated with

two 5 mL portions of concentrated HCl until complete removal of oxides of

nitrogen. The residue was dissolved in 10 mL of 1 M HCl and filtered to

remove carbon and barium sulphate. The residue was washed with diluted

hydrochloric acid. The filtrate and washings were collected and diluted with

water in standard volumetric flask. An aliquot of the sample solution was taken

and palladium(II) was extracted and determined by using the recommended

procedure (Table 5.16).

5.6 CONCLUSIONS

The developed method is reliable, as can be seen from the complete

agreement of the results observed for the analysis of various practical

samples with added palladium(II).

The satisfactory recovery of palladium(II) from these samples also indicated

that the developed method is suitable for the separation and concentration

of palladium(II) from solution of complex composition. It permits the

separation of palladium(II) from other platinum group metals, gold and base

metals.



The method is highly selective, rapid, and reproducible and permits the

rapid separation and determination of micro amount of palladium(II). The

extraction of palladium(II) with n-octylaniline in xylene is an endothermic

reaction.

n-Octylaniline synthesized by low cost with high yield in best purity and

recovered for reuse without loss of extraction efficiency. Low reagent

concentration (0.07 M) is required for quantitative recovery of

palladium(II). It is free from interference of large number of foreign ions

which are commonly associated with palladium(II) in its natural occurrence.



140

Table 5.2 Extraction of palladium(III) as a function of pH

Palladium(II) = 200 µg Sodium salicylate = 0.085 M

Aq:Org ratio = 2.5: 1 Extractant = 0.07 M n-Octylaniline in xylene

Strippant = 5 M ammonia (3×10 mL)

pH Percentage extraction, (% E) Distribution ratio, (D)

0.3 77.7

8.71

0.5 83.7

12.83

0.7 88.9

20.02

1.0 100 ∞

1.5* 100 ∞

1.7 100 ∞

2.0 100 ∞

3.0 77.4

8.56

4.0 72.8

6.69

5.0 66.7

5.00

6.0 61.7

4.02

7.0 52.6

2.77

8.0 19.3

0.59

9.0 18.7

0.57

10.0 17.5

0.53 * Recommended for general extraction procedure



Table 5.3 Extraction of palladium(III) as a function of reagent

concentration

Palladium(II) = 200 µg Sodium salicylate = 0.085 M

Aq:Org ratio = 2.5: 1 pH = 1.5


n-Octylaniline

concentration, M Percentage

extraction, % E Distribution

ratio, D 0.00 0.00 -

0.010 50.0 2.50

0.020 72.3 6.52

0.030 79.0 9.40

0.040 82.6 11.86

0.050 85.4 14.62

0.060 100 ∞ 0.065 100 ∞

0.070* 100 ∞

0.075 100 ∞

0.080 100 ∞ 0.090 95.5 53.0

0.10 92.0 28.75

0.11 79.0 9.40

0.12 61.3 3.95

0.13 54.6 3.00

0.14 46.9 2.20

0.15 36.0 1.40

0.16 26.5 0.90

0.20 21.9 0.70

0.25 20.8 0.65

* Recommended for general extraction procedure



142

Table 5.4 Extraction behavior of palladium(II) as a function of weak

organic acid concentration

Palladium(II) = 200 µg pH = 1.5

Aq:Org ratio = 2.5: 1 Extractant = 0.07 M n-octylaniline

Strippant = 5 M ammonia

(3×10 mL)

Acid concentration

(M)

Sodium salicylate Sodium malonate Sodium succinate

% Ea Db % E Db % E Db

0.010 70.3 5.91 14.9 0.43 18.9 0.58

0.020 73.3 6.86 20.9 0.66 22.0 0.70

0.030 75.8 7.83 47.9 2.29 25.8 0.86

0.040 84.5 13.62 58.9 3.58 30.3 1.08

0.050 87.5 17.50 61.8 4.04 37.0 1.46

0.060 88.2 18.68 48.8 2.38 46.9 2.20

0.070 93.7 37.18 35.2 1.35 55.3 3.09

0.080 100 ∞ 27.9 0.96 68.3 5.38

0.085* 100 ∞ 20.0 0.62 51.3 2.63

0.090 100 ∞ 11.0 0.30 50.0 2.5

0.095 100 ∞ 10.3 0.28 38.8 1.58

0.10 95.5 53.0 - - 19.8 0.61 * Recommended for general extraction procedure a = Percentage extraction b= Distribution ratio



Table 5.5 Extraction of palladium(II) with various diluents


Aq:Org ratio = 2.5: 1 Sodium salicylate = 0.085 M

Extractant = 0.07 M n-octylaniline Strippant = 5 M ammonia (3×10 mL)

Solvent Dielectric constant, ε

Amount of Pd(II) extracted, %

Distribution ratio, D

Xylene* 2.30

100

∞

Toluene

2.38

100

∞

Benzene

2.27

100 ∞

Chloroform

4.80

25.1 0.83

Amyl Acetate 4.80 28.3 0.98

Methyl iso butyl ketone (MIBK)

13.10

91.9

28.36

1,2-Dichloro ethane

10.50 51.9 2.69

Amyl alcohol 13.9 100 ∞

n-Butyl alcohol

17.80

100

∞

Kerosene - 46.4 2.16

Carbon tetrachloride

2.24 61.0 3.91

*Recommended for general extraction procedure



144

Table 5.6 Choice of electrolyte solution for the stripping of

palladium(II) from the organic extract


Sodium salicylate = 0.085 M Extractant = 0.07 M n-octylaniline in

Aq:Org ratio = 2.5: 1 xylene Strippant M / pH % E

Ammonia* 1-10 100.0

HCl 1-5 48.1

H2SO4 1-5 5.5

HNO3b 1-5 No stripping

Acetic acid 1-5 20.1

Water - 4.7

NaOH 0.1-0.2 13.7

KOH 0.1-0.2 18.7

Acetate buffer pH-4.7 39.3

Ammonia buffer pH-10 100.0

*Recommended for general extraction procedure, b organic extract decomposes in presence of HNO3.



Table 5.7 Extraction behavior of palladium(II) as a function of

equilibrium time


Aq:Org ratio = 2.5: 1 Sodium salicylate=0.085 M

Extractant = 0.07 M n-Octylaniline in xylene


Time in min

% E D

1 65.9

4.83

2 93.9

38.48

3 100

∞

4 100

∞

5*

100

∞

6 100

∞

7 100

∞

8 100

∞

9 100

∞

10 100

∞

15 100

∞

20 100

∞

25 63 4.25

30 34.3 1.30

* Recommended for general extraction procedure % E = Percentage extraction of Pd(II) D = Distribution Ratio.



146

Table 5.8 Loading capacity of n-octylaniline

pH = 1.5 Sodium salicylate = 0.085 M

Aq:Org ratio = 2.5: 1 Extractant = 0.07 M n-Octylaniline in xylene

Strippant = 5 M ammonia

(3×10 mL)

Metal concentration, μg

Percentage extraction, % E

Distribution ratio, D

100 100 ∞

200* 100 ∞

400 100 ∞

800 100 ∞

1000 100 ∞

1500 100 ∞

2000 93.3 34.81

2500 77 8.36

3000 63 4.25

4000 48 2.30

5000 32 1.17

*Recommended for general extraction procedure



Table 5.9 Extraction of palladium(II) as a function of aqueous to

organic volume ratio


Sodium salicylate = 0.085 M Strippant = 5 M ammonia (3×10 mL)

Extractant = 0.07 M n-octylaniline

* Recommended for general extraction procedure

Aqueous to organic volume ratio

Percentage extraction,

( % E )

Distribution ratio, ( D )

10:10 100 ∞

20:10 100 ∞

25:10* 100 ∞

30:10 100 ∞

35:10 100 ∞

40:10 100 ∞

50:10 100 ∞

70:10 94.7 44.66

100:10 50.4 2.46

150:10 45.8 2.11



148

Table 5.10 Effect of temperature and thermodynamic functions related

to palladium(II) extraction system

Palladium(II)= 200µg Sodium salicylate = 0.085 M

Aq:Org ratio = 2.5: 1 Extractant = 0.07 M n-Octylaniline in

Strippant = 5 M ammonia xylene

(3×10 mL) Temperature

(K)

Log Kex -∆ G

(KJ/mol)

∆ S

(J/ K/mol)

∆ H

(KJ/mol)

302

2.20

-12.75

275.58

305

2.22

-13.00

278.11

308

2.33

-13.74

291.2

65.23

311

2.43

-14.48

303.82

314

2.54

-15.31

318.33



Table 5.11 Effect of foreign ions on the extraction palladium(II)


Sodium salicylate = 0.085 M Aq:Org ratio = 2.5: 1

Extractant = 0.07 M n-octylaniline in xylene


Ratio of ions

Palladium: ion Mass tolerated /

mg Foreign ion

2:500 50 Iodide

2:250 25 Citrate, malonate, Zn(II)

2:150 15

Ni(II),Te(IV),Tl(III),Mo(VI), Se(IV), Ba (II), Ce (IV)

2:100 10 Mg(II), Cd(II), Sb(III),V(V), Pb(II), Sn(II), Bi(III), fluoride

2:50 5 Cu(II), Co(II), Fe(III)

2:20 2 Fe(II), Hg(II), Cr(VI)

2:6 0.6 Ag(I), Pt(IV), Rh(III)

2:5 0.5 Au(III)

2:4 0.4 Ru(III)a a Masked by 25mg citrate.



150

Table 5.12 Separation of palladium(II) from associated metal ions



Extractant = 0.07 M n-octylaniline in xylene


Metal ions Mass taken,µg

R* %

Chromogenic ligand

Ref. No.

Pd(II)

Ru(III)a

200

400

99.6

99.5

4’ChloroPTPT

[109]

Pd(II)

Ir(III)

200

100

99.7

99.6

SnCl2 - HBr

[110]

Pd(II)

Pt(IV)

200

300

99.7

99.6

SnCl2

[110]

Pd(II)

Rh(III)

200

200

99.8

99.5

KI + SnCl2

[110]

Pd(II)

Fe(III)

200

1000

99.7

99.6

Thiocynate

[110]

Pd(II)

Au(III)

200

150

99.8

99.6

SnCl2

[110]

Pd(II)

Cu(II)

200

2000

99.8

99.6

4’ChloroPTPT

[111]

Pd(II)

Co(II)

200

1000

99.7

99.6

Thiocynate

[112]

Pd(II)

Ni(II)

200

5000

99.8

99.6

DMG

[112]

Pd(II)

Se(IV)

200

300

99.8

99.7

4’-BromoPTPT

[113]

Pd(II)

Te(IV)

200

200

99.7

98.4

4’-BromoPTPT

[114]

a Masked by 25 mg citrate, * Average recovery Pd(II).



Table 5.13 Sequential separation of palladium(II), rhodium(III) and

ruthenium(III) form their mixture

Metal ion

Amou-nt

taken, µg

Aqueous phase (25 mL)

Stripping agent

Determination method

Recovery percentage*

Pd(II)a 200 pH =1.5, 0.085 M salicylate, 0.07 M n-octylaniline in amyl alcohol

5 M(3×10mL)

4’-ChloroPTPT [109]

99.7

Rh(III)a 200 pH =9.0, 0.03 M malonate, 0.1M n-octylaniline in xylene

1 M HCl (2×10 mL)

SnCl2 +KI [110]

99.6

Ru(III) 200 0.05 M malonate, pH =3.5, 0.1M n-octylaniline in xylene

2 % NaCl + 1 M (4:1)

4’-ChloroPTPT [109]

99.6

*= Average of Six determination



152

Table 5.14 Determination of palladium(II) in synthetic mixtures



Extractant = 0.07 M n-octylaniline Strippant = 5 M ammonia

in xylene (3×10 mL)

Synthetic mixture

Ions

Metal mass/µg

Palladium(II) found, (µg) R (%) R.S.D.

(%)

Pd(II)

Ru(III)a

Pt(IV)

200

100

100

199.2 99.6 0.4

Pd(II)

Ir(III)

Pt(IV)

200

100

100

199.4 99.7 0.3

Pd(II)

Ir(III)

Ru(III)a

200

100

100

199.2 99.6 0.4

Pd(II)

Pt(IV)

Te(IV)

200

200

200

199.4 99.6 0.4

Pd(II)

Pt(IV)

Se(IV)

200

200

200

199.5 99.8 0.2

aMasked by 25mg citrate, R (% ) = Extraction recovery of Pd(II).



Table 5.15 Determination of palladium(II) from synthetic mixture

corresponding to alloys



Extractant = 0.07 mol/L n-octylaniline in xylene


Alloys Metal mass, (µg)

Palladium(II) mass found,

(µg) R (%) R.S.D.

%

Oakay alloy Pd10.5,Pt20, Ni60,V9.5. Pd18.2,Pt18,Ni54,V9.1

105 104.5 99.5 0.5

Jewellery alloy Pd95.5,Rua 4.5

105 104.5 99.5 0.5

Pd-Cu alloy 190 189.6 99.7 0.3

Pd60,Cu40 120 119.6 99.6 0.4

Pd75,Sb25 150 149.7 99.8 0.3

a masked by 25mg citrate. R (%) extraction recovery of Pd(II).



154

Table 5.16 Determination of palladium(II) in catalysts

Catalyst Palladium(II)

mass found /µg

R (%)

R.S.D.

(%)

PdCl2 on Carbon 239.2 99.2 0.8

PdCl2 on Carbon (5%) 239.5 99.3 0.7

PdCl2 on Carbon (10%) 239.2 99.2 0.2

PdCl2 on CaCO3 239.5 99.3 0.7

PdCl2 on BaSO4 239.7 99.4 0.6



Flow Sheet 5.1

Sequential separation of palladium(II) , rhodium(III) and ruthenium(III) form their mixture.

Pd(II)+Rh(III)+Ru(III) (200 µg in each)

Adjust the acidity to 0.085 M sodium salicylate in total volume of 25 mL and pH 1.5, extract with 0.07 M n-octylaniline in amyl alcohol for 5min.

Aqueous phase Organic phase Pd(II) Rh(III)+Ru(III) backstripped with 5 M adjust the acidity 0.03 M ammonia (3 × 1 mL) sodium malonate in total volume of 25 mL and pH 9.0, extract with 0.1 M n-octylaniline in xylene for 3 min Aqueous phase estimated by

4’-ChloroPTPT [109] (R=99.7 %)

Aqueous phase Organic phase Ru(III) Rh(III) backstripped Adjust the acidity 0.05 M with 1M (2 × 10 mL) sodium malonate in total volume of 25 mL and pH 3.5, extract with 0.1M n-octylaniline Aqueous phase in xylene for 5 min. Rh(III) estimated by KI+SnCl2 [110] (R=99.6%) Aqueous phase Organic phase Rejected Ru(III) backstripped with 2% NaCl+1M HCl (4:1) Aqueous phase Ru(III) estimated by

4’-ChloroPTPT [109] (R = 99.6 %)



156

0

10

20

30

40

50

60

70

80

90

100

0 1 2 3 4 5 6 7 8 9 10

pH

Perc

enta

ge e

xrac

tion

(% E

)

Fig. 5.1 Plot of pH versus percentage extraction of palladium(II)

(200 μg/mL) from salicylate medium (0.085 M) by using

n-octylaniline (0.07 M) as an extractant in xylene with 5 min

shaking time.



0

10

20

30

40

50

60

70

80

90

100

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2 0.22 0.24 0.26

n-octylaniline (M)

Perc

enta

ge e

xtra

ctio

n (%

E)

Fig. 5.2 Extraction of palladium(II) (200 µg/mL) at pH 1.5 from

0.085 M sodium salicylate as a function of n-octylaniline

concentration.



158

0

10

20

30

40

50

60

70

80

90

100

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30

Time in min.

Perc

enta

ge e

xtra

ctio

n (%

E)

Fig. 5.3 Extraction of palladium(II) (200 µg/mL) at pH 1.5 from

0.085 M sodium salicylate as a function of equilibration

period.



▲Slope at pH 4 = 0.89■ Slope at pH 7= 0.82

-0.17

-0.07

0.03

0.13

0.23

0.33

0.43

0.53

0.63

0.73

-2.1 -1.9 -1.7 -1.5 -1.3 -1.1 -0.9

Log C [n-octyaniline]

Log

D[P

d(II

)]

Fig 5.4 log D[Pd(II)] against log C[n-octylaniline] at fixed sodium salicylate



160

▲ Slope at pH 4 = 2.8

■ Solpe at pH 7 = 2.7

-0.45

-0.25

-0.05

0.15

0.35

0.55

0.75

-1.8 -1.7 -1.6 -1.5 -1.4 -1.3

Log C [salicylate]

Log

D[P

d(II

)]

Fig 5.5 log D[Pd(II)] against log C[Salicylate] at fixed n-octylaniline

concentration



Slope = -3.407

2

2.1

2.2

2.3

2.4

2.5

2.6

3.17 3.19 3.21 3.23 3.25 3.27 3.29

1000/K

Log

Kex

Fig 5.6 Effect of temperature on palladium(II) extraction



162

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