School of Chemical and Metallurgical Engineering, Faculty of Engineering and Built in Environment, University of Witwatersrand, Johannesburg, South AfricaMay, 2016 / Trojan Nickel Mine in Bindura, Zimbabwe, produces nickel concentrates which, until 2008,
were then processed at their smelter operations (Bindura Smelter and Refinery) and the
subsequent product sent to the hydrometallurgical plant to produce nickel cathodes. However,
due to economic challenges the smelter and hydrometallurgical plant operations were closed
down in 2008. Currently, Trojan Mine produces nickel concentrates through flotation which
are then sold to Glencore International, in China, for further processing.
Since 2002, the MgO (also known as talc) content in the Trojan Nickel Mine final
concentrates has increased from around 12% to a peak of 22%. The average MgO content in
the concentrates for the year ending in March 2015 was 16.14%. An offtake agreement of sale
was made with Glencore International, in China, whereby a penalty is charged for all
concentrates with MgO levels greater than 5%. In the year 2015 alone, monthly revenue due to
smelter penalties amounted to an estimated total of US$141 000. Higher MgO levels in the
concentrates are prevalent when processing low grade ores, with nickel content ranging from
0.65-1.2%. This research focused on reducing the MgO content of the Trojan’s final
concentrate to 12%; which was the smelter’s set target while it was still operational.
In order to investigate the effect of pH and chemical depressants on the MgO levels in the
concentrate, batch flotation tests were carried out at pH 8.95 and 10.2, using several guargum
depressants namely: Betamin DZT 245 (standard), Cytec S9349, DLM PDE, DLM RS, and
CMC (carboxy methyl cellulose) depressants namely: Depramin 177, 267 and 347, and ND
521, 522 and 523. The concentrates were collected at 1, 5, 15 and 25 minute intervals in order
to understand the stage-wise recovery of nickel and MgO minerals. A flotation test, without a
depressant, was also carried out in order to understand the kinetics of the gangue minerals.
Stage addition of depressants was investigated, by adding another 50g/t dose of the DZT 245
depressant after 1 minute into the flotation test. Collector combination tests using SIPX,
SIPX:NC228, SIPX:NC236 and SIPX:PNBX, were also carried out to determine the best
reagent suite. To understand the recovery of nickel and MgO in the flotation circuit, a plant
survey was carried out, and the particle size distribution (PSD) and assays of collected
samples were determined.
Flotation tests results indicated that DLM RS and DLM PDE guargum depressants had better
selectivity towards MgO and higher nickel recoveries as compared to the Betamin DZT 245
depressant that is currently used in the plant. It is recommended that a plant trial be carried out
using the DLM RS depressant, which further reduced the MgO and mass of concentrate
recovered by 3.79% and 32% respectively. The stage recovery of MgO for a test carried out
without a depressant showed that 57.7% of the MgO was recovered during the first five
minutes of the test. Thus, there is need to effectively depress the fast floating MgO during the
early stages of the flotation process. Nickel recovery and grade were increased by 2.7% and
2.1% respectively, after adding the second dose of the depressant after 1 minute into the
flotation test. The results indicated that the fast floating MgO can depress the valuable mineral
if the depressing effect of the depressant is short-lived, which in turn leads to reduced nickel
recoveries. Hence, reducing the time between the two stage additions of the depressant in the
plant will help further supress the fast floating MgO silicates. It was also noted that at least
60% of the nickel was recovered during the first five minutes of the tests. Hence, reducing the
residence time of the rougher flotation bank would reduce MgO recovery into the concentrates
without adversely affecting the nickel recoveries.
Plant survey results showed that the scavenger bank feed that was deslimed, had less finer
MgO particles and MgO content as compared to the rougher bank feed. This indicates that
desliming before the coarse flotation process could reduce MgO slimes in the feed, reduce the
recovery of MgO due to slime coatings in the final concentrates and the reagent consumption
in the bank. Introducing the desliming unit could be beneficial since the desliming cyclones
have low installation and operational costs. / MT2016
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:wits/oai:wiredspace.wits.ac.za:10539/21143 |
| Date | January 2016 |
| Creators | Pikinini, Sebia |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | Online resource (91 leaves), application/pdf, application/pdf |
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