Thesis (PhD) -- Stellenbosch University, 2014. / ENGLISH ABSTRACT: The process route for the production of base and platinum-group metals from
natural sulfide ores commonly requires the conversion of high-iron furnace matte
into an iron-lean converter matte. This is followed by pre-treatment through cooling
of the iron-lean molten matte, physical processing of the solidified matte and
hydrometallurgical metal extraction. Lonmin is the third largest producer of
platinum-group metals in the world and utilizes Peirce-Smith converters for blowing
high-iron furnace matte with air to a final iron concentration or endpoint. The
molten matte is water granulated and solidification occurs via fast-cooling. The
solidified matte is ground in a closed circuit ball mill with hydrocyclone classification
and subjected to first stage atmospheric leaching. The specification of an ideal or
desirable converter iron endpoint requires careful consideration. Most importantly,
it must ensure the crystallization of converter matte with mineralogical qualities that
are within the setpoints of the downstream unit processes and techniques. An
additional consideration is for the final blown converter matte to achieve an
optimum bulk concentration of the base metals Ni and Cu and platinum-group
metals Pt, Pd, Rh, Ru and Ir. Mattes characteristic of variable iron endpoints were regularly produced at the
Lonmin converter plant section. Uncertainty by plant metallurgists in knowing the
desirable iron endpoint, particularly within the context of the Lonmin base metal
refinery, and poor control has had detrimental effects on the mineralogical quality of
the final matte and hence on the processing characteristics of the solidified matte
particles downstream. A desirable iron endpoint required investigation, selection
and implementation at Lonmin. The primary focus of this study was therefore to
quantify the effect of a specific iron endpoint on the mineralogy and mineral
chemistry of solidified converter matte. A fundamental examination of the
solidification process upon cooling was regarded as critical to an in-depth
understanding of the attained mineralogy and mineral chemistry as a function of a
specific iron endpoint. It became equally important to quantify the effect of the resultant mineralogy, and hence iron endpoint, on the physical property of mineral
structures in relation to downstream grinding, liberation and leaching characteristics.
Despite considerable industry context, limited in-depth and coherent studies on the
effect of a specific iron endpoint on fast-cooled converter matte systems were found
in both industrial and scholarly literature. Previous findings in literature offered a
limited quantitative understanding of the effect on mineralogy and mineral
chemistry. Phase and cooling equilibria of multi-component, iron endpoint specific
Ni-Cu-S matte systems were also not fully available. These would have been
particularly useful in understanding the complexities of converter matte
solidification as a function of iron endpoint. Physical property knowledge of
converter matte mineral structures was hardly available and even less so in relation
to grinding, liberation and leaching processes. A comprehensive investigation was
therefore required to address these extensive knowledge gaps with respect to fastcooled
converter matte systems in an industrial framework.
Three Peirce-Smith converter production samples, representative of the extent in
variability of iron endpoints attained at the converter plant, were used in a
systematic investigation coupled to a novel combination of modern analytical
techniques, computational thermochemistry and metallurgical testwork. The
modern analytical techniques included the application of high resolution
transmission electron microscopy and focused ion beam scanning electron
microscopy tomography. Computational thermochemistry was applied through the
use of MTDATA phase diagram software. Metallurgical testwork involved laboratory
batch grinding at various specific energies. Closely associated leach experiments
were also considered relevant to this wide-ranging investigation. The Peirce-Smith converter samples investigated were indicative of mattes that
attained specific endpoints of 5.17%, 0.99% and 0.15 weight% Fe. The highest
combined bulk concentration of the important base and platinum-group metals was
achieved in the matte which attained a specific iron endpoint of 0.99%. The
mineralogy of all three converter mattes was dominated by nickel sulfide mineral
structures matched to the natural mineral of heazlewoodite. Mineral structures of copper sulfide, NiCu-alloy, spinel and OsRu-alloy were also constituents of the
different converter mattes. The attainment of a specific iron endpoint was found to
result in measurable mineralogical differences with respect to relative mineral
abundances, external morphological characteristics and mineral chemistry. The
mineralogical differences were particularly distinct between mineral structures of
the high (5.17%) and low (0.99% and 0.15%) iron mattes. Subtle mineralogical
differences were evident between mineral structures of the low iron mattes.
The 0.99% Fe matte was characteristic of a significantly higher NiCu-alloy relative
abundance, compared to the 5.17% Fe matte. The NiCu-alloy structures were found
to act as the primary collectors of the economically significant platinum-group
metals. Mineralogical observations were used to develop an understanding of the
underlying mineralization mechanism of NiCu-alloy structures. High-fidelity color and
grayscale 3D reconstructions were produced of the resultant mineralized structures.
It was shown theoretically that variations in iron endpoint specific starting
compositions of oxygen-free liquid matte systems alter the solidification pathway
towards the eutectic. Moreover, a quantitative understanding of liquid phase
solidification of the high and low iron matte systems, including oxygen, was
developed to within ±2.5 oC. Most of the specific energy available for grinding was
expended breaking the nickel sulfide matrix, particularly of the high iron matte. The
breakage rates of copper sulfide mineral structures in the 5.17% Fe matte were
calculated to be higher than in the 0.15% Fe matte at 25kWh/t specific energy. The degree of copper sulfide liberation was shown to be higher for the 5.17% Fe matte
than for the 0.15% Fe matte at the same specific energy of grinding. A higher degree
of Ni extraction and Cu cementation could be achieved when leaching low iron matte
particles. The production of converter matte attaining a specific iron endpoint of
0.99% was found to be the most suitable with respect to endpoint selection criteria.
A practical iron endpoint range of 1.6% to 1.0% was recommended for the
production of converter matte with a resultant mineralogical quality within the
constraints of the Lonmin base metal refinery. This study offers an integrated understanding of base and platinum-group metals
production as a function of a desirable iron endpoint at Lonmin. This was not
previously available in metal production literature. New technology for the
monitoring and consistent control of such a practical iron endpoint range can
subsequently be implemented. / AFRIKAANSE OPSOMMING: Die prosesroete vir die produksie van onedel en platinumgroepmetale uit natuurlike
swawelertse vereis gewoonlik die omsetting van ’n ysterryke hoogoondmat in ’n
ysterarm omsettermat. Hierna volg voorbehandeling deur die afkoeling van die
ysterarm gesmelte mat, fisiese verwerking van die soliede mat, en
hidrometallurgiese metaalekstraksie. Lonmin is die derde grootste produsent van
platinumgroepmetale ter wêreld en gebruik Peirce-Smith-omsetters om ysterryke
hoogoondmat met lug te blaas totdat dit ’n finale ysterkonsentrasie- of
ystereindpunt bereik. Die gesmelte mat word met water granuleer, en solidifikasie
vind deur middel van snelafkoeling plaas. Die soliede mat word in ’n geslotekringbalmeul
met hidrosikloonklassifikasie gemaal en aan eerstestadium- atmosferiese
loging onderwerp. Die spesifikasie van ’n ideale of gewenste ystereindpunt verg
deeglike oorweging. Bowenal moet dit verseker dat die omsettermat kristalliseer
met mineralogiese eienskappe wat binne die setpunte van die eenheidsprosesse en -
tegnieke verder af in die prosesstroom val. ’n Bykomende oorweging is dat die
uiteindelike geblaasde omsettermat ’n optimale massakonsentrasie van die onedel
metale Ni en Cu en die platinumgroepmetale Pt, Pd, Rh, Ru en Ir moet bevat.
Matte met die kenmerke van wisselende ystereindpunte is gereeld by die Lonminomsetteraanleg
geproduseer. Die onsekerheid van metallurge by die aanleg oor die
gewenste ystereindpunt – veral binne die konteks van die Lonmin-raffinadery vir
onedel metale – sowel as swak beheer het ’n nadelige uitwerking gehad op die
mineralogiese gehalte van die uiteindelike mat, en dus ook op die
verwerkingskenmerke van die soliede matdeeltjies verder af in die prosesstroom. Die
bepaling van die gewenste ystereindpunt het sorgvuldige ondersoek, seleksie en
toepassing deur Lonmin vereis. Hierdie studie is dus hoofsaaklik uitgevoer om die uitwerking van ’n spesifieke ystereindpunt op die mineralogie en minerale chemie
van soliede omsettermat te kwantifiseer. ’n Grondliggende ondersoek na die
solidifikasieproses by afkoeling is as noodsaaklik beskou vir ’n diepgaande begrip van
die verworwe mineralogie en minerale chemie as ’n funksie van ’n spesifieke ystereindpunt. Mettertyd het dit egter ewe belangrik geword om die uitwerking van
die gevolglike mineralogie, en dus die ystereindpunt, op die fisiese eienskappe van
minerale strukture met betrekking tot maling-, vrystellings- en loogprosesse verder
af in die prosesstroom te kwantifiseer.
Ondanks heelwat bedryfskonteks, het nóg bedryfs- nóg vakkundige literatuur veel
diepte- en samehangende studies oor die uitwerking van ’n spesifieke ystereindpunt
op snelafgekoelde omsettermatstelsels opgelewer. Vorige bevindinge in die
literatuur het boonop ’n beperkte kwantitatiewe begrip van die uitwerking op
mineralogie en minerale chemie getoon. Die fase- en afkoelingsekwilibriums van
ystereindpuntspesifieke Ni-Cu-S-matstelsels met veelvuldige komponente was ook
nie ten volle beskikbaar nie. Dít sou veral goed te pas gekom het om die
kompleksiteite van omsettermatsolidifikasie as ’n funksie van ystereindpunt te
verstaan. Kennis van die fisiese eienskappe van die minerale strukture van
omsettermat was kwalik beskikbaar, terwyl selfs minder inligting oor maling-,
vrystellings- en loogprosesse opgespoor kon word. Daarom was ’n omvattende
ondersoek nodig om hierdie beduidende kennisleemtes met betrekking tot
snelafgekoelde omsettermatstelsels in ’n nywerheidsraamwerk aan te vul.
Drie Peirce-Smith-omsetterproduksiemonsters wat die wisselende bestek van
ystereindpunte by die omsetteraanleg verteenwoordig, is in ’n stelselmatige ondersoek
gebruik, tesame met ’n vernuwende kombinasie van moderne ontledingstegnieke,
gerekenariseerde termochemiese bewerkings en metallurgiese toetswerk. Die moderne
ontledingstegnieke sluit onder andere in hoëresolusie-transmissie-elektronmikroskopie
(HRTEM) en gefokusdeioonstraalskandering-elektron-mikroskopie (FIB SEM) tomografie. Die gerekenariseerde termochemiese bewerkings is met behulp van MTDATAfasediagramsagteware
uitgevoer. Metallurgiese toetswerk het die maling van
laboratoriumlotte teen verskillende spesifieke energieë behels. Nou verwante
loogproefnemings is ook as relevant vir hierdie omvattende studie beskou.
Die bestudeerde Peirce-Smith-omsettermonsters het op matte met spesifieke
eindpunte van 5.17%, 0.99% en 0.15 gewig% Fe gedui. Die hoogste gekombineerde
massakonsentrasie van die belangrike onedel en platinumgroepmetale is in die mat met ’n spesifieke ystereindpunt van 0.99% gevind. Die mineralogie van ál drie
omsettermatte is oorheers deur die minerale strukture van nikkelsulfied, wat met
die natuurlike mineraal heazlewoodiet ooreenstem. Die verskillende omsettermatte
het ook die minerale strukture van kopersulfied, NiCu-allooi, spinel en OsRu-allooi
bevat. Daar is bevind dat die verkryging van ’n spesifieke ystereindpunt tot meetbare
mineralogiese verskille in die relatiewe volopheid van minerale, die eksterne
morfologiese kenmerke sowel as minerale chemie lei. Die mineralogiese verskille
was veral duidelik te sien tussen die minerale strukture van die ysterryke (5.17% Fe)
en ysterarm (0.99% en 0.15% Fe) matte. Fyn mineralogiese verskille is ook tussen die
minerale strukture van die ysterarm matte bespeur.
Die 0.99% Fe-mat het tipies beduidend meer NiCu-allooi as die 5.17% Fe-mat bevat.
Die NiCu-allooistrukture tree oënskynlik op as die hoofversamelaars van die
ekonomies belangrike platinumgroepmetale. Mineralogiese waarnemings is gebruik
om ’n begrip te ontwikkel van die onderliggende mineralisasiemeganisme van NiCuallooistrukture.
Die gevolglike gemineraliseerde strukture is met behulp van
driedimensionele rekonstruksies met hoë kleurgetrouheid sowel as in grysskaal
voorgestel. Daar is teoreties aangetoon dat variasies in ystereindpuntspesifieke
beginsamestellings van suurstofvrye vloeibare matstelsels die solidifikasieroete na
die eutetikum wysig. Daarbenewens is die vloeifasesolidifikasie van die ysterryke en
ysterarm matstelsels, wat suurstof insluit, op sowat ±2.5 oC gekwantifiseer. Die
meeste van die spesifieke energie wat vir maling beskikbaar was, is gebruik om die
nikkelsulfiedmatriks te breek, veral vir die ysterryke mat. Berekeninge toon dat die
breektempo’s van die minerale strukture van kopersulfied by die 5.17% Fe-mat hoër was
as by die 0.15% Fe-mat teen ’n spesifieke energie van 25 kWh/t. Die mate van kopersulfiedvrystelling was hoër by die 5.17% Fe-mat as by die 0.15% Fe-mat by
dieselfde spesifieke energie vir maling. ’n Hoër mate van Ni-ekstraksie en Cu-sementasie
is verkry toe ysterarm matdeeltjies geloog is. Wat eindpuntseleksiemaatstawwe betref,
is die produksie van ’n omsettermat met ’n spesifieke ystereindpunt van 0,99% as die
mees geskikte aangewys. ’n Praktiese ystereindpuntbestek van 1.6% tot 1.0% word
aanbeveel vir die produksie van ’n omsettermat met ’n gevolglike mineralogiese gehalte
wat binne die perke van die Lonmin-raffinadery vir onedel metale val. Hierdie studie bied ’n geïntegreerde begrip van die produksie van onedel en
platinumgroepmetale as ’n funksie van ’n gewenste ystereindpunt by Lonmin. Hierdie
inligting was nie voorheen in literatuur oor metaalproduksie beskikbaar nie. Nuwe
tegnologie vir die monitering en konsekwente beheer van so ’n praktiese
ystereindpuntbestek kan dus op grond hiervan in werking gestel word.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/95897 |
| Date | 12 1900 |
| Creators | Thyse, Elton Llyle |
| Contributors | Akdogan, Guven, Stellenbosch University. Faculty of Engineering. Dept. of Process Engineering. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
| Format | xxxvii, 212 p. : ill. |
| Rights | Stellenbosch University |
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