Thesis (MSc)--Stellenbosch University, 2003. / ENGLISH ABSTRACT: The determination of the platinum group metals (PGMs), platinum, palladium,
rhodium, iridium, ruthenium and osmium, remains a problem for the low-grade ore samples,
and the analysis of these samples in a routine laboratory relies entirely on the fire assay
technique. The use of large sample masses to overcome sub-sampling errors has been the
greatest advantage of this technique.
The increased economic value of PGMs and recent developments in instrumentation
such as inductively coupled plasma-mass spectrometry (ICP-MS) which is capable of trace
element detection as low as part per billion (Ppb) levels, have led to a search for
complementary methods to ensure the accuracy of fire assay results.
This work investigates the feasibility of direct dissolution of ore samples using
microwave-assisted dissolution followed by ICP-MS as the measurement technique. Due to
the limited sample mass that can be used, a thorough consideration had to be given to
sampling errors and analytical errors to assess the overall precision achievable.
Most PGM-bearing minerals occur as sulphides and these are highly resistant to acid
dissolution. It was found that roasting the Merensky type samples in air, prior to dissolution
gives quantitative recoveries for platinum. Recoveries up to 100% were obtained for
platinum, palladium, rhodium and gold for a Merensky flotation concentrate with excellent
precision (about 4%) except for gold which had poorer precision (16%). However, ore
samples presented a problem due to their lower PGM content and smaller sample masses
being used. Precision for all elements improved significantly (from about 20% to about 8%),
with the use of l g-sample aliquot compared to that ofO.25 g-sample.
Acid dissolution, even after roasting proved to be insufficient for the UG-2
chromitite samples. When roasting was followed with reduction under hydrogen flame the
solubility of the UG-2 flotation concentrate improved remarkably. The recoveries obtained
were approximately 95 ± 5% for platinum, 99 ± 5% palladium, 104 ± 12% gold and 102 ±
5% for rhodium with good precision (comparable to that of Merensky concentrate).
The accuracy and precision of the results depended very much on the sample mass
and air-flow in the furnace during the roasting procedure. For this method to be used
successfully, the air flow is very critical, and should lead to a better furnace design which
can rotate the crucibles to enable an even flow of air over all the samples during roasting. / AFRIKAANSE OPSOMMING: Die bepaling van platinumgroep metale (PGM'e), platinum, palladium, rhodium, iridium,
ruthenium en osmium is 'n voortdurende probleem vir die lae-graad erts monsters. Die analise
van hierdie monsters in 'n roetine laboratorium is geheel afhanklik van die klassieke "fire
assay"-tegnieke. Die groot voordeel van hierdie tegniek is die voorkoming van
monsternemingsfoute deur die gebruik van groter monster massas.
Die ekonomiese waarde van PGM'e saam met die onlangse ontwikkeling van instrumentasie
soos die induktief-gekoppelde plasma-massaspektrometrie (IGP-MS) wat in staat is om
spoorelemente in konsentrasies so laag soos dele per biljoen (ppb) te meet, het daartoe gelei na
soeke vir komplementêre metodes om die akkuraatheid van klassieke "fire assay" -tegnieke te
verseker.
Hierdie werk ondersoek die waarskynlikheid van direkte oplossing van ertsmonsters deur
gebruik te maak van mikrogolf-ondersteunde oplossing gevolg deur IGP-MS as
opmetingstegniek. As gevolg van die beperkte monster massa wat gebruik kan word, moes
deeglike oorweging gegee word aan monsternemingsfoute en analitiese foute, om die
oorkoepelende presiesheid te bepaal.
Meeste PGM-draende minerale bestaan in die vorm van sulfiede en bied groot weerstand teen
oplossing in 'n suur. Die gloei van Merensky-tipe monsters in lug voor oplossing gee
kwantitatiewe herwinning van platinum Herwinning tot 100% is behaal vir platinum,
palladium, rhodium en goud vir 'n Merensky-flotasie-konsentraat met uitstekende akkuraatheid
(4%) behalwe vir goud met 'n swak (16%) akkuraatheid. Die erts monsters was problematies as
gevolg van die laer PGM inhoud en kleiner monstermassas wat gebruik is. Presiesheid vir al
die elemente het beduidend verbeter (van 20% tot 8%) met die gebruik van 1 g- monster massas
vergelyk met 0.25 g-monsters. Ten spyte van die gloei van die monster is suur oplossing
onvoldoende vir die UG-2 chromatiet-houdende monsters. Wanneer die monster gegloei is
onder 'n waterstof vlam (reduksie) het die oplossbaarheid van UG-2 flotasie-konsentraat
aansienlik verbeter. Die herwinbaarheid wat behaal is, is 95 +/- 5% vir platinum, 99 +/- 5% vir
palladium, 104 +/- 12% vir goud en 102 +/- 5% rhodium met goeie relatiewe presiesheid
vergeleke met Merensky-konsentrate. Die akkuraatheid en presiesheid van resultate hang meerendeels af van monster massa en
lugvloei in die oond gedurende gloei. Die lugvloei is krities vir die sukses van hierdie metode en
sal moet lei tot beter oond ontwerp wat kroesies kan roteer en 'n gelyke vloei van lug oor die
monsters gedurende verbranding toelaat.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/53354 |
| Date | 04 1900 |
| Creators | Matsau, Eunice Nthabiseng |
| Contributors | Koch, K. R., Stellenbosch University. Faculty of Science. Dept. of Chemistry and Polymer Sciences |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
| Format | 123 p. : ill. (some col.) |
| Rights | Stellenbosch University |
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