Thesis (MScIng)--University of Stellenbosch, 2003. / ENGLISH ABSTRACT: This thesis investigates the control of calcium and magnesium in a base metal
sulphate leach solution containing nickel and cobalt. The presence of calcium and
magnesium in the hydrometallurgical processing of base metals, result in a number of
difficulties. These problems range from the contamination of the final product, to high
energy consumption and large bleed streams during electrowinning. Calcium poses a
greater problem in sulphate solutions due to the low solubility of its sulphate salts.
No conventional method exists for the control of calcium and magnesium. As part of
this study a review of possible control methods was conducted, which is listed within.
From this list the precipitation of fluorides was selected for further investigation. The
results showed that it is possible to control calcium and magnesium through the
precipitation of their respective fluorides, without the co-precipitation of nickel and
cobalt. For 10% stoichiometric excess of fluoride 96.5% calcium and 98.5%
magnesium were removed during batch experiments.
It is known that mixing and hydrodynamics plays an important role on the
characteristics of the formed precipitate, making these processes inherently difficult to
scale-up. To evaluate these effects on a continuous process, the three-zone model
proposed by Gösele and Kind (1991) was used. A precipitate with consistent
characteristics was produced while varying the mixing on the macro, meso and micro
scale.
Additionally, methods were investigated for the removal or possible recycling of the
unreacted fluoride, for which activated alumina was identified. It was observed that
activated alumina could adsorb fluoride to low levels in the presence of the base metal
solution, after which it could be regenerated again. The activated alumina (AA) had a
capacity of 8.65 gF/lAA at a 10 mg/l fluoride breakthrough level during column
tests. Based on the experimental results a conceptual process was devised whereby only a
portion of the leach stream is subjected to the fluoride precipitation process, after
which it is returned to lower the overall calcium and magnesium concentrations. This
method would reduce the effect of the observed dominance of magnesium
precipitation, in processes where the maximum removal of both elements is not
required. The fluoride precipitation process consisted of three steps being
precipitation, solid-liquid separation and adsorption of the unreacted fluoride.
Sufficient information is provided on the process for a cost estimation to be carried
out. Should this found to be feasible, a continuation of the project is recommended.
Different reactor configurations could be evaluated for precipitation. The scaling
observed during the continuous experiments should also be investigated to minimise
its effect. The investigation of activated alumina was only a secondary project and
more work is required on optimisation, particularly for the desorption cycle to enable
the recycling of the unreacted fluoride. / AFRIKAANSE OPSOMMING: Saamgestel in hierdie tesis is 'n studie van die beheer van kalsium en magnesium in 'n
basismetaal-sulfaatoplossing, bevattende nikkel en kobalt. Die teenwoordigheid van
kalsium en magnesium in dié oplossings veroorsaak 'n verskeidenheid van probleme,
wat wissel van produkkwaliteit verlaging tot hoë energieverbruik en groot bloei
strome tydens platering. 'n Groter probleem word ondervind met kalsium as gevolg
van die lae oplosbaarheid van sy sulfaatsoute.
Geen konvensionele metode kon gevind word vir die beheer van kalsium en
magnesium gedurende die oorsig van moontlike metodes nie. Hierdie moontlike
metodes is geïdentifiseer en kortliks bespreek in die tesis. Van die moontlike metodes
is die presipitasie van fluoried-soute gekies vir verdere eksperimentele ondersoek. Die
ondersoek het getoon dat dit moontlik is om kalsium en magnesium te beheer deur die
presipitasie van fluoriede sonder om die basismetale saam te presipiteer. Vir 'n 10%
oormaat fluoried toevoeging is 96.5% van die kalsium en 98.5% van die magnesium
gepresipiteer gedurende die enkelladingstoetse.
Dit is bekend dat vermenging en hidrodinamika 'n groot rol speel in die kwaliteit van
die presipitaat wat gevorm word. Dit bemoeilik die opskalering van presipitasie
prosesse. Vir die ondersoek oor die invloed van vermenging op 'n kontinu proses is
die drie-sel model van Gösele en Kind (1991) gebruik. Dit is gevind dat die karakter
van presipitaat relatief konstant gebly het vir variasies van vermenging op die makro,
meso en mikro skaal, wat opskaling behoort te vergemaklik.
Addisioneel is die verwydering of moontlike hersirkulasie van die ongereageerde
fluoried ondersoek, en geaktiveerde alumina is geïdentifiseer as 'n moontlike
adsorbeermiddel. 'n Eksperimentele ondersoek het getoon dat geaktiveerde alumina
fluoried tot lae vlakke kan adsorbeer in die teenwoordigheid van die basismetale,
waarna dit weer geregenereer kan word. Die kapasiteit van die geaktiveerde alumina
(GA) was bereken as 8.65 gF/lGA by 'n 10 mg/l fluoried vlak gedurende die kolom
toetse. 'n Konsep-proses is opgestel na aanleiding van die eksperimentele resultate,
waarvolgens slegs 'n gedeelte van die logingstroom na die fluoried presipitasie proses
gestuur word, waarna dit weer teruggevoeg word om die algehele kalsium en
magnesium konsentrasie te verlaag. Dié metode sal voorkom dat magnesium
presipitasie domineer vir 'n toepassing waar slegs 'n gedeelte van kalsium en
magnesium verwyder word. Die fluoried presipitasie proses behels drie stappe
waarvolgens die fluoriede eers gepresipiteer word, waarna dit geskei word, en dan die
ongereageerde fluoried geadsorbeer word.
Genoeg inligting is versamel sodat 'n kosteberaming van die proses gedoen kan word.
As die koste van die proses aanvaarbaar is, word dit voorgestel dat die ondersoek
voortgesit word. Verskillende reaktor konfigurasies kan vir die presipitasie stap
getoets word en daar moet ook ondersoek ingestel word hoe om die korslaag wat
gedurende die kontinu eksperimente geobserveer is, te verminder. Die ondersoek van
geaktiveerde alumina was ondergeskik in die projek en nog werk sal gedoen moet
word om dit te optimiseer, spesifiek gedurende die desorpsie siklus vir die
hersirkulasie van die ongereageerde fluoried.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/16409 |
| Date | 04 1900 |
| Creators | Pelser, Max |
| Contributors | Eksteen, J. J., Lorenzen, L., Aldrich, C., University of Stellenbosch. Faculty of Engineering. Dept. of Process Engineering. |
| Publisher | Stellenbosch : University of Stellenbosch |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
| Format | xvi, 233 leaves : ill. |
| Rights | University of Stellenbosch |
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