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
FULFILLMENT FOR THE MSc DEGREE IN ANALYTICAL CHEMISTRY
YEAR 2014
IN
PARTIAL
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.
Page 1 of 50
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
2.2
CO-COLLECTORS KNOWN FOR PGMS AND GOLD ANALYSIS .....................................................17
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
Page 2 of 50
CHAPTER SEVEN – RECOMMENDATIONS ............................................................................................................. 46
CHAPTER EIGHT - REFERENCES ............................................................................................................................. 47
APPENDIX ............................................................................................................................................................ 49
Page 3 of 50
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
Page 4 of 50
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.
Page 5 of 50
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
73
76
150
148
105
87
Tensile strength( kg mm-1)
14
17
71
112
165
-
Best solvent
Alkaline
Alkaline
Hot
Conc.
Conc.
Aqua
oxidizing
oxidizing
conc.H2S
HCl +
HNO3, HCl
regia
fusion
fusion
O4; conc.
NaClO3
+ Cl2
HCl +
at 125-
NaClO3 at
150oC
Thermal
conductivity(watts/metre/
o
C)
125150oC
(Rao and Reddi,2000)
Page 6 of 50
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)
Page 7 of 50
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. (MurraySmith,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.
Page 8 of 50
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. (MurraySmith,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
Page 9 of 50
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
Page 10 of 50
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. (MurraySmith,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)
Au3+ (aq) + 4 Cl- (aq)
Au3+ (aq) + 3NO2 (g) + 3 H2O (l) and
AuCl4- (aq)
Pt(s) + 4 NO3- (aq) + 8 H+ (aq)
Pt4+ (aq) + 6Cl- (aq)
Pt4+ (aq) + 4NO2 (g) + 4H2O (l)
PtCl62-(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
Page 11 of 50
correction of small fluctuations in flame temperature as well as correction for fluctuations in
sample aspiration rate. (Skoog,2007)
Closed fusion furnace until fusion is
complete
Fusion
cupel
Lead button
Remove slag
and cube
button
Cast button
prill
Dissolve the
prill in acid
AAS/ICP
instrument
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
Page 12 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 1050g 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)
Page 13 of 50
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-3000oC ) 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 14 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)
Page 15 of 50
1.2 AIM
The aim of the project is to determine whether iridium and ruthenium can be used as cocollectors 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.
Page 16 of 50
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 17 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 18 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 19 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 20 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 cocollectors. 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 21 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 22 of 50
3.3.2 Fusion
The fusion furnace was heated to between 1050oC and 1150oC 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 1000oC. 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 1530mins 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 23 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
1
Elements
Pt, Pd, Au, Rh
Aliquot from
Flask
1000ppm stock
Volume
200ml Pt, 200ml
500ml
Pd, 50ml Au and
Resultant Conc. In ppm
400ppm Pt; 400ppm Pd;
100ppm Au; 50ppm Rh
25ml 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 24 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
Table 4.2: Concentrate sample results using 100ppm Iridium co-collector
Concentrate sample
replicates
Pt (ppm)
Pd (ppm)
Au(ppm)
Rh(ppm)
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 25 of 50
Table 4.3: Concentrate sample results using 150ppm Iridium co-collector
Concentrate sample
replicates
Pt (ppm)
Pd (ppm)
Au(ppm)
Rh(ppm)
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
Table 4.4: Concentrate sample results using 1000ppm Iridium co-collector
Concentrate sample
Pt
replicates
(ppm)
Pd (ppm)
Au(ppm)
Rh(ppm)
Replicate 1
np
np
np
np
Replicate 2
np
np
np
np
Replicate 3
np
np
np
np
Replicate 4
np
np
np
np
Replicate 5
np
np
np
np
Replicate 6
np
np
np
np
Page 26 of 50
Table 4.5: Average concentrate sample results using 50,100,150 and 1000ppm Iridium cocollector
Collector concentration
Pt (ppm)
Pd (ppm)
Au(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
2.30
3.48
0.42
0.23
STDEV
Rh(ppm)
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)
Replicate 1
np
np
np
np
Replicate 2
np
np
np
np
Replicate 3
np
np
np
np
Replicate 4
np
np
np
np
Replicate 5
np
np
np
np
Replicate 6
np
np
np
np
Table 4.7: Ore sample results using 100ppm Iridium co-collector
Ore sample replicates
Pt (ppm)
Pd (ppm)
Au(ppm)
Rh(ppm)
Replicate 1
np
np
np
np
Replicate 2
np
np
np
np
Replicate 3
np
np
np
np
Replicate 4
np
np
np
np
Replicate 5
np
np
np
np
Replicate 6
np
np
np
np
Page 27 of 50
Table 4.8: Ore sample results using 150ppm Iridium co-collector
Pt
Ore sample replicates
(ppm)
Pd (ppm) Au(ppm) Rh(ppm)
Replicate 1
np
np
np
np
Replicate 2
np
np
np
np
Replicate 3
np
np
np
np
Replicate 4
np
np
np
np
Replicate 5
np
np
np
np
Replicate 6
np
np
np
np
Table 4.9: Ore sample results using 1000ppm Iridium co-collector
Pd
Ore sample replicates
Pt (ppm)
(ppm)
Au(ppm)
Rh(ppm)
Replicate 1
np
np
np
np
Replicate 2
np
np
np
np
Replicate 3
np
np
np
np
Replicate 4
np
np
np
np
Replicate 5
np
np
np
np
Replicate 6
np
np
np
np
4.1.3 Concentrate sample results using RUTHENIUM co-collector
Table 4.10: Concentrate sample results using 50ppm Ruthenium co-collector
Concentrate sample
replicates
Pt (ppm)
Pd (ppm)
Au(ppm)
Rh(ppm)
Replicate 1
np
np
np
np
Replicate 2
np
np
np
np
Replicate 3
np
np
np
np
Replicate 4
np
np
np
np
Replicate 5
np
np
np
np
Replicate 6
np
np
np
np
Page 28 of 50
Table 4.11: Concentrate sample results using 100ppm Ruthenium co-collector
Concentrate sample
replicates
Pt (ppm)
Pd (ppm)
Au(ppm) Rh(ppm)
Replicate 1
np
np
np
np
Replicate 2
np
np
np
np
Replicate 3
np
np
np
np
Replicate 4
np
np
np
np
Replicate 5
np
np
np
np
Replicate 6
np
np
np
np
Table 4.12: Concentrate sample results using 150ppm Ruthenium co-collector
Concentrate sample replicates
Pt (ppm)
Pd (ppm)
Au(ppm) Rh(ppm)
Replicate 1
np
np
np
np
Replicate 2
np
np
np
np
Replicate 3
np
np
np
np
Replicate 4
np
np
np
np
Replicate 5
np
np
np
np
Replicate 6
np
np
np
np
Table 4.13: Concentrate sample results using 1000ppm Ruthenium co-collector
Concentrate sample replicates
Pt (ppm)
Pd (ppm)
Au(ppm) Rh(ppm)
Replicate 1
np
np
np
np
Replicate 2
np
np
np
np
Replicate 3
np
np
np
np
Replicate 4
np
np
np
np
Replicate 5
np
np
np
np
Replicate 6
np
np
np
np
Page 29 of 50
4.1.4 Ore sample results using RUTHENIUM co-collector
Table 4.14: Ore sample results using 50ppm Ruthenium co-collector
Pd
Ore sample replicates
Pt (ppm)
(ppm)
Au(ppm)
Rh(ppm)
Replicate 1
np
np
np
np
Replicate 2
np
np
np
np
Replicate 3
np
np
np
np
Replicate 4
np
np
np
np
Replicate 5
np
np
np
np
Replicate 6
np
np
np
np
Table 4.15: Ore sample results using 100ppm Ruthenium co-collector
Ore sample replicates
Pt (ppm)
Pd (ppm)
Au(ppm) Rh(ppm)
Replicate 1
np
np
np
np
Replicate 2
np
np
np
np
Replicate 3
np
np
np
np
Replicate 4
np
np
np
np
Replicate 5
np
np
np
np
Replicate 6
np
np
np
np
Table 4.16: Ore sample results using 150ppm Ruthenium co-collector
Ore sample replicates
Pt (ppm)
Pd (ppm)
Au(ppm)
Rh(ppm)
Replicate 1
np
np
np
np
Replicate 2
np
np
np
np
Replicate 3
np
np
np
np
Replicate 4
np
np
np
np
Replicate 5
np
np
np
np
Replicate 6
np
np
np
np
Page 30 of 50
Table 4.17: Ore sample results using 1000ppm Ruthenium co-collector
Ore sample replicates
Pt (ppm)
Pd (ppm)
Au(ppm)
Rh(ppm)
Replicate 1
np
np
np
np
Replicate 2
np
np
np
np
Replicate 3
np
np
np
np
Replicate 4
np
np
np
np
Replicate 5
np
np
np
np
Replicate 6
np
np
np
np
4.1.5 Concentrate sample results using SILVER co-collector
Table 4.18: Concentrate sample results using 50ppm Silver co-collector
Concentrate sample
Pt
replicates
(ppm)
Pd (ppm)
Au(ppm)
Rh(ppm)
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
Table 4.19: Concentrate sample results using 100ppm Silver co-collector
Concentrate sample
replicates
Pt (ppm)
Pd (ppm)
Au(ppm)
Rh(ppm)
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 31 of 50
STDEV
6.93
6.90
1.12
0.48
Average
36.425
38.182
3.967
1.106
Table 4.20: Concentrate sample results using 150ppm Silver co-collector
Concentrate sample
replicates
Pt (ppm)
Pd (ppm)
Au(ppm)
Rh(ppm)
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
Table 4.21: Concentrate sample results using 1000ppm Silver co-collector
Concentrate sample
replicates
Pt (ppm)
Pd (ppm)
Au(ppm)
Rh(ppm)
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 32 of 50
Table 4.22e: Average concentrate sample results using 50,100,150 and 1000ppm silver cocollector
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
Ore sample replicates
Pt (ppm)
Pd (ppm)
Au(ppm)
Rh(ppm)
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
Table 4.24: Ore sample results using 100ppm Silver co-collector
Ore sample replicates
Pt (ppm)
Pd (ppm)
Au(ppm)
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
Rh(ppm)
Sample lost
STDEV
0.31
0.21
0.02
0.01
Average
1.103
1.063
0.137
0.019
Page 33 of 50
Table 4.25: Ore sample results using 150ppm Silver co-collector
Ore sample replicates
Pt (ppm)
Pd (ppm)
Au(ppm)
Rh(ppm)
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
Table 4.26: Ore sample results using 1000ppm Silver co-collector
Ore sample replicates
Pt (ppm)
Pd (ppm)
Au(ppm)
Rh(ppm)
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 34 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
Concentrate sample results using Ir co-collector
60.00
50.00
ppm
40.00
50ppm Ir Collector
30.00
100ppm Ir Collector
20.00
150ppm Ir Collector
10.00
1000ppm Ir Collector
0.00
Pt
Pd
Au
Rh
Metal
Fig 4.1: Comparison of average concentrate sample results using 50,100,150 and 1000ppm
Iridium co-collector.
Page 35 of 50
Concentrate sample results using Ag co-collector
60.00
50.00
ppm
40.00
50ppm Ag Collector
30.00
100ppm Ag Collector
150ppm Ag Collector
20.00
1000ppm Ag Collector
10.00
0.00
Pt
Pd
Au
Rh
Metal
Fig 4.2: Comparison of average concentrate sample results using 50,100,150 and 1000ppm silver
co-collector
Ore sample results using Ag co-collector
1.60
1.40
1.20
ppm
1.00
0.80
0.60
0.40
0.20
0.00
-0.20
Pt
Pd
Au
Rh
Metal
50ppm Ag Collector
100ppm Ag Collector
150ppm Ag Collector
1000ppm Ag Collector
Fig 4.3: Comparison of average ore sample results using 50,100,150 and 1000ppm silver cocollector
Page 36 of 50
Concentrate sample Pt results obtained using different cocollectors
60.00
50.00
ppm
40.00
Pt-Ir collector
30.00
Pt-Ag Collector
20.00
Pt-Ru collector
10.00
Certified value
0.00
50ppm
100ppm
150ppm
Collector concentration
1000ppm
Fig 4.4: Comparison of average Pt concentrate sample result with varying concentration of Ir,
Ru and Ag co-collectors
Concentrate sample Pd results obtained using different cocollectors
60.00
50.00
ppm
40.00
Pd-Ir collector
30.00
Pd-Ag Collector
20.00
Pd-Ru collector
10.00
Certified value
0.00
50ppm
100ppm
150ppm
Collector concentration
1000ppm
Fig 4.5: Comparison of average Pd concentrate sample result with varying concentration of Ir,
Ru and Ag co-collectors
Page 37 of 50
Concentrate sample Au results obtained using different cocollectors
7.00
6.00
ppm
5.00
4.00
Au-Ir collector
3.00
Au-Ag Collector
2.00
Au-Ru collector
1.00
Certified value
0.00
50ppm
100ppm
150ppm
Collector concentration
1000ppm
Fig 4.6: Comparison of average Au concentrate sample result with varying concentration of Ir,
Ru and Ag co-collectors
Concentrate sample Rh results obtained using different cocollectors
5.00
ppm
4.00
3.00
Rh-Ir collector
2.00
Rh-Ag Collector
Rh-Ru collector
1.00
Certified value
0.00
50ppm
100ppm
150ppm
1000ppm
Collector concentration
Fig 4.7: Comparison of average Rh concentrate sample result with varying concentration of Ir,
Ru and Ag co-collectors
Page 38 of 50
4.4
T-TEST
Certified results
Table 4.28: Certified reference values
Certified values
Pt (ppm)
Concentrate
Pd (ppm)
Au(ppm)
Rh(ppm)
50.782
42.839
5.311
3.935
1.571
1.312
0.230
0.126
Ores
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
| ̅ |=
tcal =
| ̅ |√
= 2.099
=
√
= 0.880
D.F = n-1 = 4-1 = 3
Page 39 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
Pt (ppm)
Pd (ppm)
Au(ppm)
Rh(ppm)
Ore-Certified values
1.571
1.312
0.230
0.126
Experimental value
0.000
0.000
0.000
0.000
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
Pt (ppm)
Pd (ppm)
Au(ppm)
Rh(ppm)
Concentrate -Certified values
50.782
42.839
5.311
3.935
Experimental value
0.000
0.000
0.000
0.000
Page 40 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
Pt (ppm)
Pd (ppm)
Au(ppm)
Rh(ppm)
Ore -Certified values
1.571
1.312
0.230
0.126
Experimental value
0.000
0.000
0.000
0.000
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 41 of 50
CHAPTER FIVE –DISCUSSION
Table 4.1 shows the results of PGMs and gold obtained when 50ppm of Ir was used as a cocollector. 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 cocollector 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 42 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 cocollector. 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 43 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 44 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 45 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 46 of 50
CHAPTER EIGHT - REFERENCES
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Page 47 of 50
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Page 48 of 50
APPENDIX
Page 49 of 50
Page 50 of 50