Thesis (MScEng (Process Engineering))--University of Stellenbosch, 2011. / ENGLISH ABSTRACT: The extraction of mineral values from ore requires liberation of the minerals followed by
separation. Liberation is achieved by size reduction operations which are inefficient
processes typically accounting for up to 70% of the energy consumption in a mineral
concentrator (Tromans, 2008). As the grade of ores reserves declines, future viability of
mineral operations will be determined by the costs of comminution. Recent work has
shown that microwave treatment of secondary crusher product at specific microwave
energy consumption of the order of 1 kWh/t reduces the work index of the ore and
increases grade and recovery in batch flotation tests. Improved liberation at coarse sizes
was also demonstrated (Kingman, 2006). Based on these findings work is ongoing to
commercialise the technology.
The objective of this study is to develop a modelling framework to determine the value
proposition of microwave treatment of ore. It was noted that various models exist in
literature for modelling of mineral processing flotation flow sheets, but these models do
not incorporate the feed ore liberation property as an input variable in their calculations.
Thus, a fundamentally derived property based model was identified as appropriate for
flow sheet modelling of microwave treated ore, as it utilised liberation as an indirect
variable in calculating the flotation rate constant through the use of contact angle to
describe particle surface hydrophobicity.
The model was successfully incorporated into the flotation flow sheet units developed in
HSC Chemistry and used with Mineral Liberation Analyser (MLA) data to investigate the
effects of changes in feed ore liberation on rougher cell flotation recovery. Different
liberation scenarios based around modification of porphyry copper flotation feed were
created. A sensitivity analysis of the various feed stream liberation scenarios was carried
out to test the ability of the model to effectively model the differences in downstream
processing of microwave treated and untreated ores. For a single flotation cell of size 85
m3 with a solids feed flow rate of 890 tph, it was observed that below a certain size (120
μm in the case of the porphyry copper ore) changes in flotation feed liberation had no
significant effect on value mineral recovery. Significant differences in value mineral
recovery were observed only at coarser sizes above 120 μm. The results indicated that
improvement in recovery of value minerals due to improved liberation from applying
microwave technology has size limits and is significantly dependent on the feed grind
size.
Feed grind size sensitivity analysis was then carried on the same single cell flow sheet
utilising feeds with the same mineralogy but with different grind sizes. The results
indicated that maximum benefits from the application of microwave technology would be
best obtained by utilising coarse grinding at sizes between P70 = 200 μm and P70 = 300
μm for the porphyry copper ores considered in this study. Coarse grinding appears to be
the best way to exploit improved liberation in downstream processing of microwave
treated ores.
Investigations similar to those carried out on the single cell flotation flow sheet were then
carried out on a continuous plant rougher flotation flow sheet. The flow sheet consisted
of nine rougher cells in series each with a volume of 85 m3 with a solids feed flow rate of
890 tph into the bank of rougher cells. The results indicated that there was no significant
difference in final rougher bank overall cumulative recovery at fine grind sizes below a
P70 grind size of 120 μm with improvements in feed ore liberation. Feed grind size
sensitivity analysis showed a significant variation in cumulative recovery at coarse grind
sizes of above P70 = 129 μm .This variation was attributed to improvements in flotation
feed ore value mineral liberation from locked composite particles to the maximum
possible theoretical liberation scenario of fully liberated value mineral particles. A 7.2
percentage point improvement in cumulative value mineral overall recovery and a 2 to 3
percentage point improvement in enrichment ratio was also observed above the P70 = 250
μm grind sizes after improving the flotation feed ore value mineral particle liberation of a
typical flotation plant feed to a maximum. The increases in grade and cumulative
recovery at coarse sizes were attributed to improvements to the flotation plant feed ore
value mineral particle liberation. From the results, it was concluded that microwave
technology application will offer greater benefits in downstream processing of coarse
ground ores. / AFRIKAANSE OPSOMMING: Die ekstraksie van mineraalwaardes uit erts vereis bevryding van die minerale gevolg deur
skeiding. Bevryding word bereik deur verkleiningsprosedures wat ondoeltreffende prosesse is
en wat gewoonlik vir tot 70% van die energieverbruik in ʼn mineraalkonsentreerder
verantwoordelik is (Tromans, 2008). Algaande die graad van ertsreserwes afneem, sal
toekomstige lewensvatbaarheid van mineraalprosesse bepaal word deur die koste van
vergruising. Onlangse werk het getoon dat mikrogolfbehandeling van sekondêre
vergruiserproduk by spesifieke mikrogolf-energieverbruik van ongeveer 1 kWh/t die werkindeks
van die erts verminder en die graad en opbrengs in lotflottasietoetse verhoog.
Verbeterde bevryding by growwer groottes is ook aangetoon (Kingman, 2006). Werk gaan
voort op grond van hierdie bevindinge ten einde die tegnologie te kommersialiseer.
Die doel van hierdie navorsing is om ʼn modelleringsraamwerk te ontwikkel om die
waardeproposisie van mikrogolfbehandeling van erts te bepaal. Daar is in die literatuur
afgekom op verskeie modelle vir die modellering van vloeidiagramme vir flottasie van
mineraalverwerking, maar hierdie modelle inkorporeer nie die voerertsbevrydingseienskap as
ʼn insetveranderlike in hulle berekeninge nie. ʼn Fundamentele afgeleide eienskapgebaseerde
model is geïdentifiseer as geskik vir vloeidiagrammodellering van mikrogolfbehandelde erts,
aangesien dit bevryding as ʼn indirekte veranderlike by die berekening van die
flotteertempokonstante aangewend het deur die gebruik van kontakhoek om hidrofobisiteit
van die deeltjieoppervlak te beskryf.
Die model is suksesvol in eenhede van die flottasievloeidiagram wat in HSC Chemistry
ontwikkel is, geïnkorporeer en tesame met data van die mineraalbevrydingsontleder (MBO)
gebruik om die gevolge van veranderinge in voerertsbevryding op die opbrengs van
voorskeiselflottasie te ondersoek. Verskillende bevrydingscenario’s is geskep wat óm die
modifisering van porfierkoperflotteringstoevoer heen gebaseer is. ʼn Sensitiwiteitsontleding
van die verskillende voerstroombevrydingscenario’s is uitgevoer om die vermoë van die
model om die verskille in stroomaf-verwerking van mikrogolfbehandelde en onbehandelde
ertse te toets, doeltreffend te modelleer. In die geval van ʼn enkele flottasiesel van 85 m3 groot
met ʼn vastestof-toevoervloeitempo van 890 tph, is waargeneem dat veranderinge in
flottasietoevoer-bevryding benede ʼn sekere grootte (120 μm in die geval van die
porfierkopererts) geen beduidende uitwerking op die opbrengs van die waardemineraal gehad
het nie. Beduidende verskille in die opbrengs van die waardemineraal is slegs by growwer
groottes bo 120 μm waargeneem. Die resultate het daarop gedui dat verbetering in die
opbrengs van waardeminerale as gevolg van verbeterde bevryding ná die toepassing van
mikrogolftegnologie beperkinge ten opsigte van grootte het en opvallend afhanklik is van die
toevoermaalgrootte.
Sensitiwiteitstoetsing van toevoermaalgrootte is daarna op dieselfde enkele selvloeidiagram
wat voerders met dieselfde mineralogie gebruik uitgevoer, maar met verskillende
maalgroottes. Die resultate het daarop gedui dat maksimum voordele van die toepassing van
mikrogolftegnologie die beste verkry sou word deur gebruik van growwe maling by groottes
tussen P70 = 200 μm en P70 = 300 μm vir die porfierkoperertse wat in hierdie navorsing in
oorweging geneem is. Growwe maling skyn die beste manier te wees om verbeterde
bevryding in stroomaf-verwerking van mikrogolfbehandelde ertse te eksploiteer.
Ondersoeke soortgelyk aan dié wat op die vloeidiagram van die enkelselflottasie uitgevoer is,
is toe op ʼn deurlopende vloeidiagram van die aanlegvoorskeierflottasie uitgevoer. Die
vloeidiagram het bestaan uit nege voorskeiselle in serie elk met ʼn volume van 85 m3 met ʼn
vastestof-toevoervloeitempo van 890 tph in die ry voorskeiselle. Die resultate het daarop
gedui dat daar geen aanmerklike verskil in algemene kumulatiewe opbrengs van die finale
voorskeiry by fyn maalgroottes benede ʼn P70-maalgrootte van 120 μm met verbeteringe in
voerertsbevryding was nie. Sensitiwiteitsontleding van voermaalgrootte het ʼn beduidende
variasie in kumulatiewe opbrengs by growwe maalgroottes van bo P70 = 129 μm getoon.
Hierdie variasie is toegeskryf aan verbeteringe in waardemineraalbevryding van
flottasietoevoererts uit geslote saamgestelde deeltjies tot die maksimum moontlike teoretiese
bevrydingscenario van ten volle bevryde waardemineraaldeeltjies. ʼn Persentasiepuntverbetering
van 7.2 in die kumulatiewe algemene opbrengs van waardemineraal en ʼn
persentasiepuntverbetering van 2 tot 3 in die verrykingsratio is ook bo die P70 = 250 μmmaalgroottes
waargeneem ná verbetering van die bevryding van die waardemineraaldeeltjies
van die flottasietoevoererts van ʼn tipiese flottasieaanlegtoevoer tot die maksimum. Die
toenames in graad en kumulatiewe opbrengs by growwe groottes is toegeskryf aan
verbeteringe in die bevryding van die waardemineraaldeeltjies van die flottasietoevoererts.
Op grond van die resultate is daar tot die gevolgtrekking gekom dat toepassing van
mikrogolftegnologie groter voordele in stroomaf-verwerking van grofgemaalde ertse sal bied.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/6498 |
| Date | 03 1900 |
| Creators | Charikinya, Edson |
| Contributors | Bradshaw, S. M., University of Stellenbosch. Faculty of Engineering. Dept. of Process Engineering. |
| Source Sets | South African National ETD Portal |
| Language | Stellenbosch : University of Stellenbosch |
| Detected Language | English |
| Type | Thesis |
| Format | 183 p. : ill. |
| Rights | University of Stellenbosch |
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