ETD Collection
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Item Mineral resource evaluation of a platinum tailings resource: a case study(2017) Muthavhine, Mashudu InnocentThe project investigated the application of geostatistical techniques in evaluating a mechanically deposited platinum tailings resource. The project was undertaken on one of the Anglo American Platinum tailings dams, the identity of which cannot be revealed, due to the agreement in place or permission given. Remnant unrecovered minerals of economic potential still exist in tailings dams. These unrecovered minerals have influenced several mining companies to turn their attention to the economic potential that still exists in tailings, making them a key strategic component of their resources and reserves. Geostatistics has been developed and thoroughly tested or improved to address challenges experienced in estimating in situ geological ore bodies. The main aim of this Research Project is to test whether these fundamental principles and theories of geostatistics are relevant and appropriate in evaluating man-made ore bodies, such as a Platinum tailings dam, without any significant changes needed on the underlying principles or estimation algorithms. The findings on the Case Study tailings resource can be applied in the evaluation of other tailings dams, as well as any other man-made structures such as low grade rock dumps, muck piles, with related characteristics. A standard approach (methodology) was followed to evaluate the Case Study tailings resource. Drilling and sampling was conducted through sonic drilling. It is a dry drilling technique that is suitable for sampling unconsolidated particles such as tailings. Thereafter, 2 samples were sent to the laboratory to establish grade (concentration) of Platinum Group Metals (Platinum, Palladium and Rhodium), Gold and Base Metals (Copper and Nickel). Density was also measured, and comprehensively analysed as part of variables of interest in this research. Statistical analyses were performed on all variables of interest contained in the dam: which are Platinum (Pt), Palladium (Pd), Gold (Au), 3E (two PGMs plus Gold), Copper (Cu), Nickel (Ni) and Density. The underlying statistical distributions of all metals and density were found to be non-symmetrical and slightly positive skewed. The skewness of the distributions was established to be marginal. Differences between raw data (untransformed) averages and the log-normal estimates were analysed and found to be insignificant. As such Ordinary Kriging of untransformed data was concluded to be the appropriate geostatistical technique for Case Study tailings resource. Analysis of mineralisation continuity (variography), a pre-requisite for geostatistical techniques such as Ordinary Kriging applied on the case study tailings resource, was also performed. Reasonable and sufficient mineralisation continuity was established to exist in the Case Study tailings resource. Although characterised by high nugget effect, these spatial correlations were established to be continuous with ranges of influence well beyond 450 m in all variables. Anisotropic variograms were modelled for all variables and are comprised of nested structures with two to three spherical models. Resource estimation was conducted through Ordinary Kriging in Datamine. All the seven variables were successfully interpolated into each cell of the 5m x 5m x 5m block model. Rigorous validation of the resource model was performed to establish the quality and reliability of the estimation carried out. Estimated resource model was analysed against the original borehole data, through comparison of grade profiles, statistical analysis, QQ Plots and histograms. The grade profile was recognised to be similar between boreholes (5 m composites) and the adjacent cells that have been estimated. Furthermore, statistical analyses revealed minimal differences between means of the estimated model and the original borehole data: the highest difference being 1.7% realised on 3E, followed by 1.1% on Density and Gold (Au). The rest of the variables (Pt, Pd, Cu, and Ni) have differences that are below 1%. 3 QQ plots and histogram were plotted from resource model with 5m x 5m x 5m cells and 5 m composited boreholes. Although these data sets are of different (slightly incompatible) supports, the intended purpose of comparing distributions was achieved. QQ plots and histograms revealed approximately identical shaped distributions of the two data sets, with some minor deviations noticeable in graphs of only two variables (Au and Density) that are underlain by two populations. The validation process carried out gave a compelling assurance on the quality and reliability of the resource model produced. The Case Study tailings resource therefore is successfully estimated by Ordinary Kriging. The results achieved on the Case Study tailings dam has successfully proved that geostatistical principles and theories can confidently be applied, in their current form or understanding, to any man-made tailings resourceItem Extraction of platinum, palladium and rhodium from tailings by a metal chloride based leach reagent(1993) Cocksedge, Mark BurdenHigh extractions of the platinum group metals' from a refractory tailings concentrate (PGM Concentration : Pt 81.5ppm, Pd 21.5ppm, Rh 17.5ppm) was achieved after short. low-temperature roasting and subsequent leaching with a zinc chloride based leach reagent containing nitric acid under atmospheric pressure at temperatures from 105-C to 120-C. [Abbreviated Abstract. Open document to view full version]Item Reducing the magnesium oxide content in Trojan's nickel final concentrates(2016) Pikinini, SebiaTrojan 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.