DETERMINATION OF PLATINUM, PALLADIUM, RHODIUM AND …Iridium and Ruthenium are useful co-collectors for precious metals e.g Platinum, palladium, rhodium and gold in ores and concentrate

DETERMINATION OF PLATINUM, PALLADIUM, RHODIUM

AND GOLD IN ORES AND CONCENTRATES USING IRIDIUM

AND RUTHENIUM AS CO-COLLECTORS BY FIRE ASSAY.

BY

FUNGAI NDOVORWI (R062120P)

SUPERVISOR: Mr A WAKANDIGARA

THIS PROJECT WAS SUBMITTED TO THE DEPARTMENT OF CHEMISTRY UNDER

THE FACULTY OF SCIENCE, UNIVERSITY OF ZIMBABWE IN PARTIAL

FULFILLMENT FOR THE MSc DEGREE IN ANALYTICAL CHEMISTRY

YEAR 2014

Page 1 of 50

ACKNOWLEDGEMENT

The work presented in this thesis was carried out at the Zimplats Ngezi Laboratory. I wish to

thank the Zimplats Management for making this possible. I am also grateful for the support given

by the Zimplats Laboratory Management and laboratory personnel. The good working

environment and modern instrumentation of the Zimplats laboratory has been invaluable for

completion of the task. I wish to thank my colleagues Nokuzola Ndiweni, Donewell Tinonesana,

Robert Mahoso for their important contributions and co-operation in various phases of the work.

I am particularly indebted to my supervisor, Mr A Wakandigara for his valuable advice

throughout the project.

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CONTENTS

ACKNOWLEDGEMENT ............................................................................................................................................ 1

CONTENTS ............................................................................................................................................................. 2

ABREVIATIONS ....................................................................................................................................................... 4

ABSTRACT: ............................................................................................................................................................. 5

CHAPTER ONE - INTRODUCTION ............................................................................................................................ 6

1.1 BACKGROUND ......................................................................................................................................... 6

1.1.1 Platinum Group Metals (PGMs) ............................................................................................................... 6

1.1.2 Fire Assay ................................................................................................................................................. 7

1.1.3 Instrumentation ..................................................................................................................................... 14

1.2 AIM ............................................................................................................................................................ 16

1.3 OBJECTIVES ............................................................................................................................................ 16

1.4 PROBLEM STATEMENT ........................................................................................................................ 16

1.5 JUSTIFICATION ....................................................................................................................................... 16

CHAPTER TWO - LITERATURE REVIEW .................................................................................................................. 17

2.1 CO-COLLECTORS KNOWN FOR PGMS AND GOLD ANALYSIS ..................................................... 17

2.2 METHODS FOR PGMS AND GOLD ANALYSIS ................................................................................... 18

CHAPTER THREE - EXPERIMENTAL ....................................................................................................................... 21

3.1 METHODOLOGY ..................................................................................................................................... 21

3.2 APPARATUS AND REAGENTS ............................................................................................................. 21

3.3 PROCEDURE ............................................................................................................................................ 22

3.3.1 Weighing and fluxing ............................................................................................................................. 22

3.3.2 Fusion ..................................................................................................................................................... 23

3.3.3 Cupellation ............................................................................................................................................. 23

3.3.4 Dissolution and analysis ......................................................................................................................... 23

3.3.5 Preparation of working standards ......................................................................................................... 24

CHAPTER FOUR - RESULTS.................................................................................................................................... 25

4.1 RESULTS .................................................................................................................................................. 25

4.1.1 Concentrate sample results using IRIDIUM co-collector ........................................................................ 25

4.1.2 Ore sample results using IRIDIUM co-collector ...................................................................................... 27

4.1.3 Concentrate sample results using RUTHENIUM co-collector ................................................................ 28

4.1.4 Ore sample results using RUTHENIUM co-collector .............................................................................. 30

4.1.5 Concentrate sample results using SILVER co-collector ........................................................................... 31

4.1.6 Ore sample results using SILVER co-collector ......................................................................................... 33

4.2 STATISTICS ............................................................................................................................................. 35

4.3 RESULT COMPARISONS ....................................................................................................................... 35

4.4 T-TEST ...................................................................................................................................................... 39

CHAPTER FIVE –DISCUSSION ................................................................................................................................ 42

CHAPTER SIX - CONCLUSION ................................................................................................................................ 45

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CHAPTER SEVEN – RECOMMENDATIONS ............................................................................................................. 46

CHAPTER EIGHT - REFERENCES ............................................................................................................................. 47

APPENDIX ............................................................................................................................................................ 49

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ABREVIATIONS

PGMs Platinum Group Metals

Pt Platinum

Pd Palladium

Au Gold

Rh Rhodium

Ir Iridium

Ru Ruthenium

Pb Lead

NiS Nickel sulphide

ICP Inductively coupled plasma

AAS Atomic Absorption Spectrometry

HNO3 Nitric acid

HCl Hydrochloric acid

ppm parts per million

np No Prill formed

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ABSTRACT:

Determination of platinum group metals (PGMs) and gold also known as precious metals is

always a very difficult task, this is due to their availability in trace amounts in sample types of

complex composition. Little research has been done to improve the accurate analysis of PGMs

and gold in a cost effective manner. An area of research that has the potential of improving PGM

and gold analysis is the use of co-collectors. The aim of the project was to determine if both

Iridium and Ruthenium are useful co-collectors for precious metals e.g Platinum, palladium,

rhodium and gold in ores and concentrate material. Varying concentrations of Iridium and

Ruthenium collector solutions were each used in the analysis of PGMs and gold and the results

obtained indicated that Iridium is a useful co-collector for concentrate material only even at very

low concentrations, however iridium is not a useful collector for precious metal in ore material

even when high concentration are used. Ruthenium is not a useful collector for precious metals

in both concentrate and ore material even when high concentrations are used. Therefore Iridium

can be used as a co-collector in the analysis of PGMs and gold in concentrate material only and

Ruthenium cannot be used as a co-collector for PGMs and gold in both ore and concentrate

material.

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CHAPTER ONE - INTRODUCTION

1.1 BACKGROUND

1.1.1 Platinum Group Metals (PGMs)

Platinum metal exist in association with other metals namely palladium, rhodium, ruthenium,

iridium and osmium and they are termed platinum group elements. The platinum group metals

and gold are referred as precious metals because of their high economic value; these metals are

coloured and lustrous, malleable, electrically resistant. The platinum group metals are also

referred to as noble because of their relative lack of reactivity with mineral acids and oxygen.

(Rao and Reddi,2000;Lenahan and Murray-Smith,1986)

The nobility and catalytic activity are unique properties of precious metals that result in their

wide applications e.g as catalysts in various chemical processes, in electrical and electronic

industries as well as in jewelry.(Lenahan and Murray-Smith,1986;Balcerzak,2002)

Table 1: Physical properties of precious metals

Platinum Palladium Rhodium Iridium Ruthenium Osmium

Chemical symbol Pt Pd Rh Ir Ru Os

Density(g cm-3

) 21.45 12.02 12.41 22.65 12.45 22.61

Melting point(oC) 1769 1552 1960 2443 2310 3050

Thermal

conductivity(watts/metre/o

C)

73 76 150 148 105 87

Tensile strength( kg mm-1

) 14 17 71 112 165 -

Best solvent Alkaline

oxidizing

fusion

Alkaline

oxidizing

fusion

Hot

conc.H2S

O4; conc.

HCl +

NaClO3 at

125-

150oC

Conc.

HCl +

NaClO3

at 125-

150oC

Conc.

HNO3, HCl

+ Cl2

Aqua

regia

(Rao and Reddi,2000)

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The growing demand for rhodium, palladium and platinum has been due to the production of

autocatalysts. The determination of the precious metals is specialized and complex, because of

the close similarity of their chemistry, nobility and the typically low levels at which they occur.

The metals have to be separated from each completely and such procedures are generally time

consuming and intricate. Platinum group metal chemistry is an exceedingly active area of

research and this has led to many methods for the determination of PGMs. The absence of a

universally acceptable method is one of the drawbacks in the determination of PGMs.

(Balcerzak,2002)

1.1.2 Fire Assay

Determination of precious metals in geological and environmental samples may require

preconcentration prior to detection. An effective combination of the preconcentration, digestive

procedure and detection steps determines the reliability of results. Fire assay is one of the

methods used to preconcentrate precious metals.(Riita,1999)

Fire assaying is a section of quantitative chemical analysis, which is used for the determination

of precious metals in ore, scrap metal and metallurgical products, it is also a pyro-metallurgical

technique which separates the metal to be determined from the impurities and gangue present in

the sample. This is accomplished by employing dry reagents and heat in a selective fusion

process.

Fire assaying subject has generated an exceptional history since its inception. Literature shows

that the method has been used for many centuries. Fire assaying has always been considered

more of an art than a science this is due to the high degree of practical knowledge and

manipulative skills needed to complete a successful fire assay. The theoretical chemistry

pertaining to the fire assay has never been completely investigated. This has left us with a

process based upon some fundamental principles, which depends upon experience and

observation alone, without due regard for theory. The fire assay remain as an inexhaustible

subject for basic research.(Haffty et al,1977)

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The classical fire assay technique allows the use of large portions of up to 50 to 100g sample that

is representative which is a substantial benefit over other analytical methods. (Suominen et

al,2004) Fire assay is usually named after the collector used and the main types of collectors

used are lead oxide and nickel sulphide.( Murray-Smith,1986 ;Corby)

1.1.2.1 Lead oxide fire assay

The method consists of two consecutive pyrochemical separations. The finely ground sample is

fused with a suitable flux under reducing conditions which promotes the separation of the

precious metals from the gangues, with simultaneous collection as a lead alloy.

The basic principle of lead fire assay is the sample is mixed with suitable flux, transferred into a

fire clay crucible of suitable size and fused at elevated temperatures between 1100°C-1300°C.

Lead globules from the litharge in the flux form rain drops which collect the precious metals as

they sink downwards due to their heavier densities. The lead button is separated and cleaned of

the slag or gangue. The lead is removed by oxidizing fusion (cupellation) to concentrate the

precious metals into a prill. This is weighed to give total precious metal available or is dissolved

to determine the individual elements. For effective collection of the precious metals, the

composition of the flux, the temperature and its rate of increase must be optimized. (Murray-

Smith,1986 ;Corby;Riita,1999)

Flux composition and fusion

The determination of the optimum flux composition requires some knowledge of the ore type.

An ore with an acidic gangue will require a basic flux, whereas an ore with a basic gangue will

require an acidic flux. The slag should consist of borosilicates existing as a mixture of

metasilicates and metaborates. Lead oxide fire assay flux consist of sodium carbonate, litharge,

borax, silica, mealie meal/flour, paraffin and potassium nitrate

Reactions occurring in the fusion furnace

Sodium carbonate: Acts as an oxidizing and desulphurising reagent because of the formation of

sulphates and alkali silicates.

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FeS2 + 7PbO + 2Na2CO3 FeO + 7Pb + 2Na2SO4 + 2CO2

Na2CO3 + Na2SiO3 Na4SiO4 + CO2

Silica: Strongly acidic flux reagent which combines with metallic oxides to form silicates which

are fundamental to slag. The silicates are classified according to the ratio of oxygen in the base;

the metasilicate slag with the ratio of 1:2 is desirable because of its stability.

PbO+ SiO2 PbSiO3

Borax (anhydrous sodium tetraborate): Strongly acidic reagent which readily dissolves almost

all metallic oxides.

Na2B4O7 Na2B4O4 + B2O3

B2O3 (boric anhydride) reacts with metallic oxide e.g. zinc oxide, iron oxide, magnesium oxide

e.tc.

ZnO + B2O3 ZnB2O4

Litharge (lead oxide): Acts as an oxidizing and desulphurising agent and reacts with the required

reductant to produce the metallic lead that collects the noble metals.

FeS2 + 7PbO + 2Na2CO3 FeO + 7Pb + 2Na2SO4 + 2CO2

Maize meal/flour: acts as a reducing agent by providing carbon which removes oxygen from

substances, reduces lead oxide to lead metal.

PbO + C Pb + CO

Carbon monoxide or carbon dioxide can be evolved.

Potassium nitrate is commonly known as niter. It is a strong oxidizing agent and at higher

temperatures it decomposes giving off oxygen which oxidizes sulfur and other metals. (Murray-

Smith,1986 ;Corby)

A good flux will produce a slag with the following characteristics

a. It must have a formation temperature within the temperature range of the assay furnace

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b. It must remain sufficiently thick at or near its formation temperature to allow the

precious metals present to be released from their chemical or mechanical bonds with

the gangue before the flux allows the lead collector particles to drop down collecting

the precious metals.

c. It should become sufficiently thin when heated above its formation temperature to

allow the lead globules to settle through it easily.

d. It should completely decompose the gangue to fluid slag and should also have very low

affinity for gold and silver.

e. The chemical composition of the flux should not excessively attack or flux away the

crucible.

f. The specific gravity should be low enough to allow good separation between the lead

and the slag.

g. The slag formed should be homogeneous and easily removed from the button when

cold.

h. It should be free of sulfides.

There are certain precautions that also need to be taken during fusion and these include the size

of the crucible and the fluxed charge should not occupy more than half the total capacity of the

crucible to avoid loses due to splitting or boiling due to sudden generation of carbon dioxide.

The second precaution is that the temperature of the furnace should not fall below the critical

level during the pouring procedure. This might cause the last few crucibles remaining in the

furnace to freeze as the temperature of the furnace will have dropped below the melting point of

the slag. The ore sample to be analysed must be of an exceedingly fine state of division and

thoroughly mixed with the flux constituents. This ensures the intimate contact of each sample

particle with particles of the melting flux. Ideally this contact should be maintained during the

early stages of the fusion process. This is necessary to ensure a sufficiently complete reaction

between sample and flux and simultaneous production of the fine globules of lead by the

reduction of litharge . (Murray-Smith,1986 ;Corby;Haffty et al,1977)

Cupellation

The purpose of cupellation is to separate the precious metals from lead and cupellation is

basically an oxidizing fusion using cupels for the removal of lead and concentrating the precious

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metals. Cupels are moulds made up of bone ash or calcined magnesite and they are very porous.

As lead is heated in the cupellation furnace it is oxidized to litharge and begins to melt, the

porous cupels then absorbs the melting lead in its pores. Some of the lead is oxidized into

gaseous lead oxide in the presence of oxygen leaving spherically shaped prills of concentrated

precious metals. The precious metals do not melt due to their high surface tension because they

do not oxidize. (Murray-Smith,1986)

Reaction occurring in the cupellation furnace.

Pb(s) + O2(g) PbO(g) + PbO(l)

Prill dissolution

For determination of individual element concentration the prill require acid digestion and

subsequent instrument analysis e.g atomic absorption spectrometer or inductively coupled

plasma. Fire assay involving silver collector as a co-collector will require boiling the prill in

concentrated nitric acid first to dissolve the silver before adding other types of acids. (Murray-

Smith,1986) The solution is made up using HCl and the concentration of HCl is maintained high

so as to avoid the precipitation of silver chloride and possibly co-precipitation of analytes.

(Juvonen et al,2004)

Reactions occurring

Au(s) + 3 NO3-(aq) + 6 H

+ (aq) Au

3+ (aq) + 3NO2 (g) + 3 H2O (l) and

Au3+

(aq) + 4 Cl- (aq) AuCl4

- (aq)

Pt(s) + 4 NO3- (aq) + 8 H

+ (aq) Pt

4+ (aq) + 4NO2 (g) + 4H2O (l)

Pt4+

(aq) + 6Cl- (aq) PtCl6

2-(aq)

For Atomic absorption finish a releasing agent e.g Lanthanum maybe required. The releasing

agent for cations reacts preferentially with an anion to release the analyte. The releasing agent

should form a compound of higher stability than that formed by the analyte therefore preventing

ionization of the analyte. For ICP methods an internal standard may be necessary for the

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correction of small fluctuations in flame temperature as well as correction for fluctuations in

sample aspiration rate. (Skoog,2007)

Fig 1: Fire assay flow chart

1.1.2.2 Nickel Sulphide Fire Assay

The method of nickel sulphide fire assay is not very different from the lead oxide fire assay. The

NiS fire assay procedure involves fusion of the sample with nickel, sulfur, sodium carbonate,

Na2B4O7 and SiO2 in a clay crucible. The sample is then fused at a temperature between 1000⁰C

- 1300⁰C. A silicate phase and a sulfide phase are formed in the melt during the fusion process.

The sulfide phase is denser that the silicate phase hence settles at the bottom of the fusion

crucible, and while falling through the melt, the sulfide phase collects PGMs and gold. The NiS

bead formed is separated from slag, and the slag is crushed and mixed with a different flux and

AAS/ICP

instrument

Closed fusion furnace until fusion is

complete

Cast button

Remove slag

and cube

button

cupel

prill

Dissolve the

prill in acid

Lead button

Fusion

Page 13 of 50

fused again. The second NiS bead formed is separated from the slag. The two buttons are

combined and milled. Further concentration of precious metals in the nickel sulphide button is

done by treating the milled material with concentrated hydrochloric acid with ammonium

chloride to facilitate decomposition of copper sulphate. The insoluble residue is filtered and

dissolved in an acid and analysed using either AAS or ICP methods. (Hoffman et

al,1999;Balaram et al,2005;Juvonen et al,2002;Oguri,1998;Gros,2001)

The nickel sulphide flux contains Borax , sodium carbonate, sulphur, nickel carbonate, copper

sulphate, and silica. Borax, sodium carbonate and silica reactions are similar to those in lead

oxide fire assay and this has been explained earlier. Nickel carbonate reacts with sulphur to

generate nickel sulfide which then scavenges the precious metals. Nickel sulfide fire assays is

capable of collecting all of the PGMs, however the process is long and tedious.( Hoffman et

al,1999;Balaram et al,2005;Juvonen et al,2002)

NiCO3(s) + S(s) NiS(l) + CO2(g) + 1/2 O2(g)

Although fire assay has an advantage of collecting precious metals from large samples e,g 10-

50g of a complex matrix into relatively small bead of simple metal alloy success recovery of

precious metals requires an experienced and skilled assayer to optimize fusion conditions. High

amounts of salts introduced to the sample provide high procedural blanks and difficulties in the

direct analysis of the obtained solutions by instrumental analysis. Classical fire assay using lead

collector has a drawback of not being able to collect all the noble metals. This therefore requires

addition of co-collectors to optimize the collection of all noble metals. (Murray-Smith,1986)

1.1.2.3 Co-Collectors

Co-collectors are elements that are added to lead oxide flux. The purpose of co-collectors is to

facilitate concentration of precious metals into the lead button. Co-collectors normally used in

the collection of PGMs include silver, platinum, palladium and gold. This is because silver is a

better collector of gold than lead and platinum is a better collector for gold, silver, palladium and

rhodium while palladium is preferred for silver and gold. The co-collectors are normally used in

conjunction with lead due to economic reasons. (Murray-Smith,1986;Riita,1999)

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1.1.3 Instrumentation

Flame atomic absorption spectrometer (FAAS)

FAAS is a technique that is largely used in the determination of precious metals, this is due to

the fact that FAAS is element specific, therefore most elements can be determined with little

interference effects. (Murray-Smith,1986;Riita,1999). Atomic absorption spectrometry is based

on the principle that a ground state atom is capable of absorbing light of the same characteristic

wavelength as it would normally emit. When light of the characteristic wavelength is passed

through the flame containing atoms of the analyzed elements, part of the light is absorbed. The

degree of absorption will be proportional to the population of ground state atoms in the flame

and hence the concentration of the element being analysed. Because of the low temperatures

employed in FAAs (2000oC-3000

oC ) the technique is relatively simple and spectral

interferences are minimal however, chemical interferences must be recognized and overcome.

The common chemical interferences encountered are formation of stable refractory compounds

and ionization. (Murray-Smith,1986;Skoog,2007)

Other advantages of FAAS include speed and low-cost operation and disadvantages include poor

sensitivity for some PGM’s eg iridium and the sequential nature of operation. (Corby)

Inductively coupled plasma-atomic emission spectrometry (ICP-AES)/ Mass Spectrometry

(ICP-MS)

Inductively coupled plasmas as atomization and ionization sources for analytes have been

applied to the determinations of precious metals in a variety of matrices. Plasma can be

explained as `luminous volume of partially ionised gas'. The plasma is generated from

radiofrequency (RF) magnetic fields induced by a copper coil wound around the top of a glass

torch. Introduction of the sample is done through a nebuliser forming a fine aerosol. The aerosol

then goes to the center of the plasma where it undergoes dissolvation, vaporisation and

ionization. The atoms and ions generated are excited in the plasma and as they revert to their

ground state, they emit light. The characteristic emitted light is then measured using an optical

Page 15 of 50

spectrometer in ICP-AES. In ICP-MS, ions are extracted from the plasma into a mass

spectrometer for analysis. The advantage of plasma techniques over atomic absorption is

a. Simultaneous multi-element determination

b. Lower detection limits

c. Fewer chemical interferences

d. Less significant ionization interference and

e. Wider dynamic range (Skoog,2007)

The disadvantages of the plasma technique are that it is expensive and complicated to use. Most

laboratories are migrating from using atomic absorption methods to plasma methods.

X-ray fluorescence spectrometry-XRF

XRF is the emission of characteristic "secondary" (or fluorescent) X-rays from a material that

has been excited by bombarding with high-energy X-rays. X-rays are applied to a sample

material, dislodging electrons from the atoms. However, if the ejected electron comes from one

of the tightly-bound inner shells of electrons of an atom, a very unfavourable “hole” is left in the

electron shell. Another of the atom’s electrons then fills this hole, and the change in energy is

accompanied by emission of a new photon of radiation - this is known as fluorescence. XRF

spectroscopy involves measuring the energy of the outgoing radiation, and since the energy of

fluorescent radiation is element-specific, the amount of a certain element in the sample can be

determined. (Skoog,2007)

Very little work has been published on the determination of PGMs by XRF. The major

advantages of this technique are simultaneous determination of the entire PGM group and gold

without employing complex chemical separations and ability to analyse the samples in solid

form. The technique also has a greater precision than atomic absorption spectrometry. The

disadvantage of this technique is the occurrence of PGMs in many different metal matrices. The

varying mineralogy causes severe interference problems. (Skoog,2007)

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1.2 AIM

The aim of the project is to determine whether iridium and ruthenium can be used as co-

collectors in the determination of PGMs. The project will be about comparison of platinum

group metals (PGMs) and gold recoveries in ores and concentrate samples analysed using

different co-collectors namely iridium and ruthenium.

1.3 OBJECTIVES

a) To compare the effect of using iridium collector versus the use of silver collector in the

analysis of PGMs and gold in ores and concentrates by fire assay method.

b) To compare the effect of using ruthenium collector versus the use of silver collector in the

analysis of PGMs and gold in ores and concentrates by fire assay method.

c) To perform statistical analysis on the results obtained

1.4 PROBLEM STATEMENT

Determination of Pt, Pd, Rh and Au by fire assay is difficult because of the absence of a

universally acceptable method. The absence of a universally acceptable method is because the

available methods are either expensive, inefficient or difficult to use. Several co-collectors have

been used in the determination of PGMs however no research has been done to determine the

effect of Iridium and Ruthenium on collection of PGMs.

1.5 JUSTIFICATION

Ruthenium and Iridium co-collectors if found to be useful can be used as an alternative method

for PGMs analysis in a situation where palladium, platinum or gold collectors are unavailable.

Ruthenium and iridium are cheaper metals than gold, platinum and palladium metals that are

currently being used as co-collectors in PGMs determination. Therefore if found to be useful, the

use of Iridium and ruthenium will lower the cost associated with PGMs analysis.

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CHAPTER TWO - LITERATURE REVIEW

2.1 CO-COLLECTORS KNOWN FOR PGMS AND GOLD ANALYSIS

Different co-collectors have been used in the analyses of PGMs and gold and some of the work

published involving the use of co-collectors in PGMs and gold analysis is summarized below;

Suominen et al (2004) compared determination of palladium, platinum and rhodium using silver

and gold as co-collectors. They determined that fire assay is the most frequently used procedure

for the determination of PGMs. They also determined that when gold is used, Rh is recovered

quantitatively and it is essential that the amount of Au is optimised for Pd determination because

an excess of Au lowers Pd recovery however for Pt and Rh the amount of Au is not critical.

Suominen et al (2004) also highlighted other possible collectors that are used in the

determination of PGMs namely Pd used for Ag, Au and Pt, while Pt is used for Au, Pd, Rh and

Ir.

Haffty et al (1977) in A Manual on Fire Assaying and Determination of the Noble Metals in

Geological Materials outlined the use of gold and silver as co collectors in the determination of

PGMs and gold. They outline the important reasons of adding silver as a co-collector and these

are a) silver has a protective effect and thus reduces gold losses during cupellation stage, it

allows trace amount of gold to be easily transferred from the cupel to a suitable container of

analysis and also b) it provides a silver-gold bead that is easily dissolved.

Balcerzak (2002) also reviewed determination of PGMs by fire assay in the journal Sample

digestion methods for the determination of Traces of precious metals by spectrometric

techniques and indicated that lead collector does not provide an efficient recovery of all noble

metals. The journal also explains that modifications of lead fire assay have been made using

silver and gold as co collectors in the determination of PGMs.

Corby describes the use of silver as a co collector in the determination of platinum, palladium,

rhodium and gold in geological material.

Page 18 of 50

2.2 METHODS FOR PGMs AND GOLD ANALYSIS

Hoffman et al (1999) in Gold Analysis-Fire assaying outlines different methods for determining

gold and these include conventional lead oxide fire assay with atomic absorption finish and

Instrumental neutron activation analysis. The lead oxide fire assay method includes the use silver

and palladium as co collectors in the determination of gold and platinum group metals and he

concludes that this method remains the stalwart among analytical methods.

Barefoot and Van Loon (1998) reviewed advances in the determination of PGMs and gold and

indicated the presence of various methods used in the determination of PGMs in geological

material. These methods include fire assay, chlorination, acid dissolution, solvent extraction,

sorption and ion exchange. All these methods produce acceptable results, this shows that in the

determination of PGMs there is no single universally acceptable method. In the article about fire

assay by Everett et al (2005), they explain that lead, nickel sulphide, tin, copper and silver can be

used as collectors in the determination of PGMs, this indicates that there is no single universal

method used in the determination of PGMs by fire assay.

Riitta (1999) in the analysis of gold and the platinum group elements in geological samples

indicated that determination by lead fire assay reference sample results were in good agreement

with the declared values and gold is a better collector for rhodium and iridium compared to

silver. The comparison of NiS fire assay, lead fire assay and aqua regia leach found that both fire

assay methods gave equivalent values for gold, palladium and platinum for the reference

samples.

Balaram et al (2005) indicated that platinum group metals and gold can be determined using

nickel sulphide as a collector and showed that there is good agreement between the concentration

values obtained for PGE and Au in this study with those from the literature.

Corby in in Fundamentals for the analysis of gold, silver and platinum group metals explains that

other collectors other than lead such as copper or nickel sulfide can be used for PGM analysis.

Juvonen et al (2004) also used silver as a co-collector in the determination of gold, platinum,

palladium and rhenium lead oxide fire assay.

Page 19 of 50

The absence of one universally acceptable method in the analysis of PGMs and gold is one of the

major drawbacks in the determination of PGMs and gold in geological. This is due to the

disadvantages outlined below;

Advantages and disadvantages of the methods used in PGMs and gold analysis

Juvonen et al (2004) compared recoveries of gold, platinum, palladium and rhenium using lead

and nickel sulphide as collectors. The results indicate that for silicate rocks the recoveries for Au,

Pd and Pt by the two fire assaying procedures compare well, whereas high base metal content of

the sample can interfere in the NiS fire assay recovery especially Au and possibly also Pd. They

highlighted that high concentrations of sulfides would interfere in the fusion process therefore

there is need to roast the sample before fusion. If the sample contains large amounts of base

metals e.g nickel copper and cobalt they would be collected in the lead regules therefore to get

rid of these elements before cupellation, the lead regules should be purified by a process called

scorification. The process of scorification involves one or more fusion of lead regulus in a

scorification dish with added lead and borax.

Juvonen et al (2002) in Determination of gold and the platinum group elements in geological

samples by ICP-MS after nickel sulphide fire assay: difficulties encountered with different types

of geological samples indicates some of the difficulties encountered in using nickel sulfide as a

collector in determination of PGMs in some geological samples especially those containing

magnetite. This indicates that the NiS fire assay method cannot be universally used for the

determination of PGMs for all types of samples. Oguri et al (1998) in Quantitative determination

of gold and the platinum-group elements in geological samples using improved NiS fire-assay

and tellurium coprecipitation with inductively coupled plasma-mass spectrometry (ICP-MS)

indicate that for maximum recovery of PGMs using nickel sulphide as a collector there is need

for re fusing the slag after separation of the first NiS button. This increases the time taken for the

analysis of PGMs.

Gros et al (2001) in Analysis of platinum group elements and gold in geological materials using

NiS fire assay and Te coprecipitation; the NiS dissolution step revisited indicates that in the

dissolution of the nickel sulphide bead containing the collected PGMs in fire assay there are

volatile PGE losses. This makes the method of using NiS collector less efficient.

Page 20 of 50

Corby in Fundamentals for the analysis of gold, silver and platinum group metals compares the

advantages and disadvantages of both lead oxide and nickel sulfide fire assays. The advantages

of using nickel sulphide fire assay is that it involves a smaller flux to sample ratio and the

method is applicable to all platinum group metals and can also be applied to samples with high

nickel and sulfur content with no pretreatment required. The advantage of lead oxide fire assay

over nickel sulphide is that the procedure requires less time compared to NiS fire assay and also

it offers better recoveries for gold than NiS.

\

Page 21 of 50

CHAPTER THREE - EXPERIMENTAL

3.1 METHODOLOGY

Internally certified quality control samples QC C22 for concentrates and QC N249 for ores were

used as samples in the determination of PGMs and gold using Iridium and Ruthenium co-

collectors. These internally certified quality control samples were certified using African Mineral

Standards (AMIS) reference material (see appendix).

PGMs and gold analysis was carried out using fire assay lead collection techniques with silver

co-collector as a control. The analysis was repeated using various concentrations of Ir and Ru as

co-collectors.

Calibration standards were prepared using certified reference material from Industrial analytical

SpectraScan. The instrument used was an Atomic Absorption Spectrometer Agilent 240FS

model for the determination of the PGMs and gold concentration. The results obtained were then

be analysed using statistical methods e.g T-test

3.2 APPARATUS AND REAGENTS

Top Pan Balances

Spatula and brushes

Flux

Silver nitrate

Iridium 1000ppm reference solution

Ruthenium 1000ppm reference solution

Platinum 1000ppm reference solution

Palladium 1000ppm reference solution

Rhodium 1000ppm reference solution

Gold 1000ppm reference solution

Lanthanum oxide

Nitric acid

Page 22 of 50

Hydrochloric acid

50ml Measuring cylinder

Fireclay crucibles size No 3

Crucible trolley and racks

Flux measuring scoops for 200g

Crucible air loading forks for No 3 crucibles

Crucible and button tongs

Fusion and cupellation furnaces

Slag(cast iron) moulds on trolleys

Hammer

Cupels size 9

Tweezers

Volumetric Dispensers

Prill dissolution bottles

Hot plate

AAS 240FS Agilent instrument

3.3 PROCEDURE

3.3.1 Weighing and fluxing

Iridium and ruthenium working collector solutions of 50,100 and 150ppm were prepared from

1000ppm CRMs. A working solution of 1000ppm silver from silver nitrate was prepared.

Crucibles were prepared according to the number of samples and filled with 200 ± 20g flux.

25 ±2g of ore sample and 5 ± 1g of concentrate sample was weighed using a top pan balance.

The weight of sample was written against the sample ID on the sample weighing table sheet. The

weighed sample was then transferred into the flux filled crucible and mix thoroughly with the aid

of a spatula. 5 ± 1 mls of a working collector solution of silver nitrate, iridium or ruthenium

solutions was added to the crucibles with flux and sample. The collector name was recorded

against the sample ID on the sample weighing table sheet. The samples were then delivered to

the fusion stage.

Page 23 of 50

3.3.2 Fusion

The fusion furnace was heated to between 1050oC and 1150

oC and the crucibles were then

loaded into the fusion furnace. The samples were fused for 1 hour ± 5 minutes. Cast iron moulds

were arranged according to number of samples on the worksheet. After one hour, with the help

of crucible tongs, crucibles were withdrawn, one at a time and contents poured into the slag

mould and allowed the slag to cool for about 10 minutes. The lead buttons were detached from

the slag using a hammer and the buttons cleaned by hammering them into cubes. The lead

buttons were then taken to the next stage of cupellation.

3.3.3 Cupellation

The cupellation furnace was heated to a temperature between 900oC and 1000

oC. Size 3 cupels

were arranged according to the number of samples on the weighing table sheet and loaded into

the cupellation furnace. The cupels were preheated in the cupellation furnace for about 15-

30mins and using tongs, one button at a time was loaded into the preheated cupels. The samples

were cupelled for 40 ± 10 minutes, a mirror was used to check if cupellation was complete. The

cupels were unloaded and allowed to cool in the fume hood.

3.3.4 Dissolution and analysis

After cooling the prills in the cupels were picked and flattened using hammer and thrown one by

one into 10ml volumetric flasks. Approximately 1 ml nitric acid was added and boiled to

dissolve silver (Ag collector). Approximately 3ml hydrochloric acid was added boiled to

dissolve the precious metals and 3mls more of aqua regia were added and boiled further to

ensure all prills dissolve completely. The volumetric flasks were removed from the hot plate

when dissolution was complete. Lanthanum releasing agent was prepared by dissolving 23.46g

Lanthanum oxide (La2O3) in 100mls 1:1 HNO3 and making up to 1000mls with distilled water.

1ml of the prepared Lanthanum oxide solution was added to the volumetric flasks containing the

dissolved precious metals and topped upto the mark with 1:1 HCl. The solutions were presented

to the Atomic Absorption Spectrometer 240 FS Agilent instrument for analysis.

Page 24 of 50

3.3.5 Preparation of working standards

From the reference standards 1000ppm certified reference standard solution the stock reference

solution were prepared as per table below

Table 3.1: Reference standard solutions

Flask Elements Aliquot from

1000ppm stock

Flask

Volume

Resultant Conc. In ppm

1 Pt, Pd, Au, Rh 200ml Pt, 200ml

Pd, 50ml Au and

25ml Rh

500ml 400ppm Pt; 400ppm Pd;

100ppm Au; 50ppm Rh

2 Lanthanum Solution 23.46g 1000ml 2% La w/v

Working standards were prepared from the reference stock solution as per table below:

Table 3.2: Working standards

Resultant conc. ppm

Standard Flask 1 Flask 2 Volume Pt/Pd Au Rh

AA-PGM-Blank 0 20 200 0 0 0

AA-PGM-1 0.5 20 200 1.0 0.25 0.125

AA-PGM-2 2.5 20 200 5.0 1.25 0.625

AA-PGM-3 5.0 20 200 10.0 2.50 1.25

AA-PGM-4 10.0 20 200 20.0 5.00 2.50

AA-PGM-5 15.0 20 200 30.0 7.50 3.75

AA-PGM-6 30.0 20 200 60.0 15.00 7.50

Page 25 of 50

CHAPTER FOUR - RESULTS

4.1 RESULTS

4.1.1 Concentrate sample results using IRIDIUM co-collector

Table 4.1: Concentrate sample results using 50ppm Iridium co-collector

Concentrate sample

replicates Pt (ppm) Pd (ppm) Au(ppm) Rh(ppm)

Replicate 1 41.292 45.726 5.594 3.477

Replicate 2 44.7 47.974 5.951 3.773

Replicate 3 42.645 46.533 5.66 3.698

Replicate 4 44.503 50.155 6.099 3.759

Replicate 5 46.011 50.173 6.012 3.912

Replicate 6 43.309 47.227 5.491 3.635

STDEV 1.68 1.86 0.25 0.15

Average 43.743 47.965 5.801 3.709


Concentrate sample


Replicate 1 33.563 33.849 4.08 2.822

Replicate 2 28.118 26.619 3.394 2.376

Replicate 3 42.204 44.296 5.386 3.477

Replicate 4 45.947 51.121 6.033 3.898

Replicate 5 46.041 50.426 6.054 3.779

SAMPLE LOST

STDEV 8.00 10.72 1.20 0.65

Average 39.175 41.262 4.989 3.270

Page 26 of 50


Concentrate sample


Replicate 1 41.668 43.445 5.26 3.429

Replicate 2 42.662 43.372 5.507 3.657

Replicate 3 42.548 45.279 5.376 3.372

Replicate 4 41.147 43.111 5.314 3.311

Replicate 5 51.675 52.109 5.861 4.091

Replicate 6 31.838 30.714 3.837 2.427

STDEV 6.30 6.92 0.70 0.55

Average 41.923 43.005 5.193 3.381


Concentrate sample

replicates

Pt

(ppm) Pd (ppm) Au(ppm) Rh(ppm)

Replicate 1 np np np np






Page 27 of 50

Table 4.5: Average concentrate sample results using 50,100,150 and 1000ppm Iridium co-

collector

Collector concentration Pt (ppm) Pd (ppm) Au(ppm) Rh(ppm)

50ppm Ir Collector 43.743 47.965 5.801 3.709

100ppm Ir Collector 39.175 41.262 4.989 3.270

150ppm Ir Collector 41.923 43.005 5.193 3.381

1000ppm Ir Collector np np np np

STDEV 2.30 3.48 0.42 0.23

4.1.2 Ore sample results using IRIDIUM co-collector

Table 4.6: Ore sample results using 50ppm Iridium co-collector

Ore sample replicates Pt (ppm) Pd (ppm) Au(ppm) Rh(ppm)















Page 28 of 50


Ore sample replicates

Pt









Ore sample replicates Pt (ppm)

Pd

(ppm) Au(ppm) Rh(ppm)







4.1.3 Concentrate sample results using RUTHENIUM co-collector

Table 4.10: Concentrate sample results using 50ppm Ruthenium co-collector

Concentrate sample








Page 29 of 50


Concentrate sample









Concentrate sample replicates Pt (ppm) Pd (ppm) Au(ppm) Rh(ppm)








Concentrate sample replicates Pt (ppm) Pd (ppm) Au(ppm) Rh(ppm)







Page 30 of 50

4.1.4 Ore sample results using RUTHENIUM co-collector

Table 4.14: Ore sample results using 50ppm Ruthenium co-collector

Ore sample replicates Pt (ppm)

Pd

(ppm) Au(ppm) Rh(ppm)























Page 31 of 50









4.1.5 Concentrate sample results using SILVER co-collector

Table 4.18: Concentrate sample results using 50ppm Silver co-collector

Concentrate sample

replicates

Pt


Replicate 1 20.321 20.651 1.410 0.213

Replicate 2 25.129 26.291 2.771 0.570

Replicate 3 23.235 23.435 2.102 0.333

Replicate 4 21.579 20.11 1.541 0.360

Replicate 5 22.249 22.158 2.833 0.304

STDEV 1.81 2.47 0.67 0.13

Average 22.503 22.529 2.131 0.356


Concentrate sample


Replicate 1 32.47 34.914 3.124 0.941

Replicate 2 43.97 44.88 4.638 1.733

Replicate 3 43.951 46.387 5.631 1.477

Replicate 4 30.05 32.250 3.119 0.596

Replicate 5 31.684 32.480 3.324 0.785

Page 32 of 50

STDEV 6.93 6.90 1.12 0.48

Average 36.425 38.182 3.967 1.106


Concentrate sample


Replicate 1 33.737 31.78 3.277 0.515

Replicate 2 39.564 38.657 5.243 0.712

Replicate 3 26.209 24.26 2.098 0.295

Replicate 4 22.613 21.231 2.029 0.181

Replicate 5 40.417 35.685 4.122 0.673

STDEV 7.93 7.41 1.37 0.23

Average 32.508 30.323 3.354 0.475


Concentrate sample


Replicate 1 47.792 49.295 6.09 0.061

Replicate 2 48.377 48.752 6.04 0.024

Replicate 3 46.523 48.094 5.684 0.017

Replicate 4 44.691 43.290 5.479 0.005

Replicate 5 48.608 49.628 6.126 0.023

STDEV 1.62 2.59 0.29 0.02

Average 47.198 47.812 5.884 0.026

Page 33 of 50

Table 4.22e: Average concentrate sample results using 50,100,150 and 1000ppm silver co-

collector

Co-collector concentration Pt (ppm) Pd (ppm) Au(ppm) Rh(ppm)

50ppm Ag Collector 22.503 22.529 2.131 0.356

100ppm Ag Collector 36.425 38.182 3.967 1.106

150ppm Ag Collector 32.508 30.323 3.354 0.475

1000ppm Ag Collector 47.198 47.812 5.884 0.026

STDEV 10.21 10.82 1.57 0.45

4.1.6 Ore sample results using SILVER co-collector

Table 4.23: Ore sample results using 50ppm Silver co-collector


Replicate 1 1.191 1.214 0.200 0.013

Replicate 2 0.105 0.039 0.081 0.021

Replicate 3 0.055 0.001 0.026 0.042

Replicate 4 -0.126 -0.04 0.011 -0.009

Replicate 5 5.162 5.311 0.386 0.071

STDEV 2.23 2.30 0.16 0.03

Average 1.277 1.305 0.141 0.028



Replicate 1 0.648 0.783 0.116 0.005

Replicate 2 1.276 1.232 0.155 0.019

Replicate 3 1.311 1.213 0.144 0.024

Replicate 4 1.175 1.023 0.132 0.026

Replicate 5 Sample lost

STDEV 0.31 0.21 0.02 0.01

Average 1.103 1.063 0.137 0.019

Page 34 of 50



Replicate 1 1.128 0.828 0.131 0.015

Replicate 2 1.209 1.024 0.177 -0.02

Replicate 3 1.364 1.211 0.24 -0.012

Replicate 4 1.166 0.892 0.222 0.011

Replicate 5 1.649 1.153 0.212 0.033

STDEV 0.21 0.16 0.04 0.02

Average 1.303 1.022 0.196 0.005



Replicate 1 1.421 1.259 0.2 -0.005

Replicate 2 1.452 1.299 0.216 -0.006

Replicate 3 1.42 1.27 0.212 -0.005

Replicate 4 1.393 1.239 0.223 -0.006

Replicate 5 1.473 1.286 0.208 -0.002

STDEV 0.03 0.02 0.01 0.00

Average 1.432 1.271 0.212 -0.005

Table 4.27: Average ore sample results using 50,100,150 and 1000ppm silver co-collector

Co-collector concentration Pt (ppm) Pd (ppm) Au(ppm) Rh(ppm)

50ppm Ag Collector 1.277 1.305 0.141 0.028

100ppm Ag Collector 1.103 1.063 0.137 0.019

150ppm Ag Collector 1.303 1.022 0.196 0.005

1000ppm Ag Collector 1.432 1.271 0.212 -0.005

STDEV 0.14 0.14 0.04 0.01

Page 35 of 50

4.2 STATISTICS

4.2.1 Outlier test

Dixon Q test for outliers

Q =

There were no outliers in the set of results

4.3 RESULT COMPARISONS

Fig 4.1: Comparison of average concentrate sample results using 50,100,150 and 1000ppm

Iridium co-collector.

0.00

10.00

20.00

30.00

40.00

50.00

60.00

Pt Pd Au Rh

pp

m

Metal

Concentrate sample results using Ir co-collector

50ppm Ir Collector

100ppm Ir Collector

150ppm Ir Collector

1000ppm Ir Collector

Page 36 of 50

Fig 4.2: Comparison of average concentrate sample results using 50,100,150 and 1000ppm silver

co-collector

Fig 4.3: Comparison of average ore sample results using 50,100,150 and 1000ppm silver co-

collector

0.00

10.00

20.00

30.00

40.00

50.00

60.00

Pt Pd Au Rh

pp

m

Metal

Concentrate sample results using Ag co-collector

50ppm Ag Collector

100ppm Ag Collector

150ppm Ag Collector

1000ppm Ag Collector

-0.20

0.00

0.20

0.40

0.60

0.80

1.00

1.20

1.40

1.60

Pt Pd Au Rh

pp

m

Metal

Ore sample results using Ag co-collector

50ppm Ag Collector 100ppm Ag Collector

150ppm Ag Collector 1000ppm Ag Collector

Page 37 of 50

Fig 4.4: Comparison of average Pt concentrate sample result with varying concentration of Ir,

Ru and Ag co-collectors

Fig 4.5: Comparison of average Pd concentrate sample result with varying concentration of Ir,


0.00

10.00

20.00

30.00

40.00

50.00

60.00

50ppm 100ppm 150ppm 1000ppm

pp

m

Collector concentration

Concentrate sample Pt results obtained using different co-collectors

Pt-Ir collector

Pt-Ag Collector

Pt-Ru collector

Certified value

0.00

10.00

20.00

30.00

40.00

50.00

60.00


pp

m


Concentrate sample Pd results obtained using different co-collectors

Pd-Ir collector

Pd-Ag Collector

Pd-Ru collector

Certified value

Page 38 of 50

Fig 4.6: Comparison of average Au concentrate sample result with varying concentration of Ir,


Fig 4.7: Comparison of average Rh concentrate sample result with varying concentration of Ir,


0.00

1.00

2.00

3.00

4.00

5.00

6.00

7.00


pp

m


Concentrate sample Au results obtained using different co-collectors

Au-Ir collector

Au-Ag Collector

Au-Ru collector

Certified value

0.00

1.00

2.00

3.00

4.00

5.00


pp

m


Concentrate sample Rh results obtained using different co-collectors

Rh-Ir collector

Rh-Ag Collector

Rh-Ru collector

Certified value

Page 39 of 50

4.4 T-TEST

Certified results

Table 4.28: Certified reference values

Certified values Pt (ppm) Pd (ppm) Au(ppm) Rh(ppm)

Concentrate 50.782 42.839 5.311 3.935

Ores 1.571 1.312 0.230 0.126

Hypothesis

4.4.1 Iridium co-collector

a1) Ho : Iridium is a useful co-collector for PGMs and gold in concentrate sample

HI : Iridium is not a useful co-collector for PGMs and gold in concentrate sample

Table 4.29: Certified reference values and average concentrate sample results using Ir

collector

Pt (ppm) Pd (ppm) Au(ppm) Rh(ppm)

Concentrate -Certified values 50.782 42.839 5.311 3.935

Experimental value 41.614 44.077 5.328 3.454

Difference (d) 9.168 -1.238 -0.017 0.481

Ʃd=8.394

Difference standard deviation (Sd) = 4.77

| ̅ | =

= 2.099

tcal = | ̅ |√

=

√

= 0.880

D.F = n-1 = 4-1 = 3

Page 40 of 50

tcrit =t3;0.05 = 3.182

Since tcal < tcrit , Ho is cannot be rejected

Therefore Iridium is a useful co-collector for PGMs and gold in concentrate samples.

a2) Ho : Iridium is a useful co-collector for PGMs and gold in ore samples

HI : Iridium is not a useful co-collector for PGMs and gold in ore samples

Table 4.30: Certified reference values and average ore sample results using Ir collector


Ore-Certified values 1.571 1.312 0.230 0.126


No prills where produced when Ir was used as a co- collector in the analysis of ore samples.

Ho is rejected, therefore Ir it is not a useful co- collector for PGMs and gold in ore samples

4.4.2 Ruthenium co-collector

b1) Ho : Ruthenium is a useful co-collector for PGMs and gold in concentrate sample

HI : Ruthenium is not a useful co-collector for PGMs and gold in concentrate sample

Table 4.31: Certified reference values and average concentrate sample results using Ru

collector


Concentrate -Certified values 50.782 42.839 5.311 3.935


Page 41 of 50

No prills where produced when Ru was used as a co- collector in the analysis of ore samples.

Ho is rejected, therefore Ru it is not a useful co- collector for PGMs and gold in concentrate

samples

b2) Ho : Ruthenium is a useful co-collector for PGMs and gold in ore sample

HI : Ruthenium is not a useful co-collector for PGMs and gold in ore sample

Table 4.32: Certified reference values and average ore sample results using Ru collector


Ore -Certified values 1.571 1.312 0.230 0.126


No prills where produced when Ru was used as a co- collector in the analysis of ore samples.

Ho is rejected, therefore Ru it is not a useful co- collector for PGMs and gold in ore samples

Page 42 of 50

CHAPTER FIVE –DISCUSSION

Table 4.1 shows the results of PGMs and gold obtained when 50ppm of Ir was used as a co-

collector. The low standard deviation between the replicates indicates good repeatability. Table

4.2 shows the results of PGMs and gold using 100ppm Ir co-collector. The results had a high

standard deviation indicating poor repeatability. Table 4.3 also shows results of concentrates

obtained using 150ppm Ir co-collector. In this case also the standard deviation is higher than the

results obtained using 50ppm Ir co-collector. No prills were formed when 1000ppm Ir co-

collector was used (table 4.4). These results indicate that as Ir concentration increases

repeatability decreases in PGMs and gold analysis. However when average results are taken for

each set of different concentration co-collector used as per table 4.5, the results are comparable

to each other ranging from 41.923 to 43.743 Pt concentration, 41.262 to 47.965 Pd concentration,

4.989 to 5.801 Au concentration and 3.270 to 3.709 rhodium concentration, with the highest

results being obtained when 50ppm Ir co-collector concentration was used. The high melting

point of Ir may probably be the explanation of its lack of PGM and gold collection when

1000ppm Ir solution was used.

Fig 4.1 shows the comparison of average concentrate sample results obtained with varying Ir

concentration. The graph shows that the difference in results obtained when using 50,100 and

150 ppm Ir collector is small indicating that large increases in collector concentration is

independent on the collection of PGMs and gold especially for palladium, gold and rhodium

elements. However, the results obtained using 50ppm Ir co-collector were closer to the certified

reference values Table 4.28 than the results obtained using 100,150 and 1000ppm Ir co-collcetor.

This indicates that more accurate results are obtained at lower Ir concentrations.

Table 4.6 to table 4.9 shows that in the analysis of PGMs and gold in ores using Ir co collector

no prills were formed. This is probably due to the high melting point of iridium causing the metal

not to interact with the other alloyed PGMs in the lead button thereby failing collect the PGMs

during cupellation.

Table 4.10 to table 4.17 shows that in the analysis of PGMs and gold in both concentrate and ore

samples using Ru co collector no prills were formed. This is also probably due to the high

Page 43 of 50

melting point of ruthenium causing the metal not to interact with the other alloyed PGMs in the

lead button thereby failing collect the PGMs during cupellation.

Table 4.18 shows results obtained for concentrate sample when 50ppm silver co-collector was

used. The results show a very low standard deviation between replicate samples showing good

repeatability, however the results are half the expected concentration showing that when 50ppm

silver co-collector is used inaccurate results are obtained. Table 4.19 shows results obtained for

concentrate sample when 100ppm silver co-collector is used. The standard deviation between

replicate samples is high indicating poor repeatability. The average results obtained 36.425,

38.182, 3.967 and 1.106ppm for Pt, Pd, Au and Rh respectively also not comparing with the

certified results in table 4.28 proving that using 100ppm silver co-collector the results obtained

are inaccurate. Table 4.20 shows concentrate sample results obtained using 150ppm silver co-

collector. The results show a high standard deviation for replicates indicating poor repeatability.

The average results obtained 32.508, 30.323,3.354and 0.475 ppm for Pt, Pd, Au and Rh

respectively also not comparing with the certified results in table 4.28 proving that using 150ppm

silver co-collector the results obtained. This is probably due to less amount of silver interacting

with the PGMs therefore collecting less of the PGMs. Table 4.21 shows concentrate results

obtained using 1000ppm silver co-collector. The results show a very low standard deviation

between replicate samples showing good repeatability. The average results obtained also

compared well with the certified results in table 4.28

Table 4.22 shows the comparison of average concentrate sample results obtained with varying

silver concentration. This is also represented on fig 4.2 showing the difference in results obtained

when using 50,100,150 and 1000ppm Ag collector. The graph shows that Pt, Pd and Au

collected concentration increases with increase in silver collector added. This is probably due to

more silver concentration interacting with PGMs and gold during cupellation thereby increasing

the collecting of these precious metals.

Table 4.23 shows results obtained for ore sample when 50ppm silver co-collector was used. The

results show a high standard deviation between replicate samples indicating poor repeatability,

the average results 1.277, 1.305, 0.141 and 0.028ppm for Pt, Pd, Au and Rh respectively are also

not comparable to the certified values in table 4.28. Table 4.24 shows results obtained for ore

sample when 100ppm silver co-collector is used. The standard deviation between replicate

Page 44 of 50

samples is high indicating poor repeatability. The average results obtained 1.103,1.063,0.137 and

0.019ppm for Pt, Pd, Au and Rh respectively also not comparing with the certified results in

table 4.28 proving that using 100ppm silver co-collector the results obtained are inaccurate.

Table 4.25 shows ore sample results obtained using 150ppm silver co-collector. The results show

a high standard deviation for replicates indicating poor repeatability. The average results

obtained 1.303, 1.022, 0.196 and 0.005 ppm for Pt, Pd, Au and Rh respectively also not

comparing with the certified results in table 4.28 proving that using 150ppm silver co-collector

the results obtained. Table 4.26 shows ore results obtained using 1000ppm silver co-collector.

The results show a very low standard deviation between replicate samples showing good

repeatability. The average results obtained also compared well with the certified results in table

4.28.

Table 4.27 shows the comparison of average ore sample results obtained with varying silver

concentration. This is also represented on fig 4.3 showing the difference in results obtained when

using 50,100,150 and 1000ppm Ag collector. The graph shows that Pt, Pd and Au collected

concentration increases with increase in silver collector added. This is probably due to more

silver concentration interacting with PGMs and gold during cupellation thereby increasing the

collecting of these precious metals.

Fig 4.4 shows the comparison of average Pt concentrate results with varying concentration of Ir,

Ru and silver. The results show that the concentration of Pt remained lower than the certified

value even with increase in Ir concentration co-collector. Silver collector compared better at

1000ppm to the certified value than Ir and Ru.

Fig 4.5 shows the comparison of average Pd concentrate results with varying concentration of Ir,

Ru and silver. Ir co-collector compared better at 50,100 and 150ppm to the certified value than

Ru and Ag. The same trend is observed for gold and rhodium elements in fig 4.6 and 4.7

respectively. This indicates that Ir is a better co-collector for palladium, gold and rhodium

elements than silver.

Page 45 of 50

CHAPTER SIX - CONCLUSION

The conclusion based on the results obtained iridium is a useful co-collector for the

determination of precious metals in concentrate material only and not a useful co-collector for

precious metals in ore material. Iridium is also a better co-collector for palladium, gold and

rhodium in concentrates than silver.

Ruthenium is not a useful co-collector for precious metals in both concentrate and ore material,

even when high concentrations are used.

Page 46 of 50

CHAPTER SEVEN – RECOMMENDATIONS

Iridium can be used as a PGM and gold co-collector for concentrate material and ruthenium

cannot be used as co-collector in the analysis of PGMs and gold.

More research needs to be carried out in the determination of effects that make certain elements

to be better co-collector for PGMs and gold than others. Better results were obtained when lower

concentrations of Ir were used in the analysis of PGMs and gold. More work can be carried out

to determine the optimum concentration of Ir that can give useful results as the use of low

collector concentration is cost effective.

Page 47 of 50

CHAPTER EIGHT - REFERENCES

1. Balaram V., Mathur R., Banakar V.K., Hein J.R., Rao C.R.M., Rao T.G. and Dasaram

B.,(2005),Determination of the platinum-group elements (PGE) and gold (Au) in manganese

nodule reference samples by nickel sulphide fire assay and Te coprecipitatioon with ICP-

MS,Indian Journal of marine sciences,32(1),7-16

2. Balcerzak M.,(2002),Sample digestion methods for the determination of Traces of precious

metals by spectrometric techniques,Analytical Sciences,18,737-750

3. Barefoot R.R. and Van Loon J.V.,(1998),Recent advances in the determination of the

platinum group elements and gold,Talanta,49,1–14

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APPENDIX

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Documents

DETERMINATION OF PLATINUM, PALLADIUM, RHODIUM AND …Iridium and Ruthenium are useful co-collectors for precious metals e.g Platinum, palladium, rhodium and gold in ores and concentrate