published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

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M. Tech. Chemical Engineering / The depreciation of high grade sulphide ores has resulted to the use of low grade laterites to meet the global nickel demand. Available low grade laterite ore reserves in South Africa are underutilised. Suitable metallurgical process for recovery of nickel from these reserves is not yet implemented because the mineralogy is not well understood. Hence, in this research the mineralogy and recovery of nickel from low grade laterites was studied through electrochemical process. The research shows that it is feasible to selectively recover nickel from the low grade laterite ore using electrochemical leaching method. It is recommended that optimization of the electrochemical cell design be looked into to evaluate the possibility of scaling up for industry application.

Abstract Air monitoring was conducted in a nickel base metal refinery to determine compliance with occupational exposure limits. The hypothesis stated that levels of airborne dust may pose a risk to worker health if compared to the relevant exposure limits. Exposure limits for nickel species are set for the inhalable nickel dust fraction. Personal air samples, representative of three selected areas were collected in the workers’ breathing zones, using the Institute of Occupational Medicine (IOM) samplers. Real-time personal samples were collected randomly over a two-month period in three nickel production areas. Filter papers were treated gravimetrically and were analysed for soluble and insoluble nickel through inductive coupled plasma-mass spectrometry (ICP-MS). Measured concentrations were expressed as time weighted average exposure concentrations. Results were compared to South African occupational exposure limits (OELs) and to the threshold limit values (TLVs) set by the American Conference of Governmental Industrial Hygienists (ACGIH) to determine compliance. Statistical compliance was also determined using the National Institute for Occupational Safety and Health procedure as prescribed by South Africa’s Hazardous Chemical Substances Regulations in 1995. In two of the areas it was found that exposure concentrations complied with the OELs. Some exposures exceeded the OEL values and most exposures exceeded the TLV values in the other area concerned. A comprehensive health risk assessment needs to be conducted to determine the cause of non-compliance.

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Falconbridge Dominicana C. Por A. operating in the Dominican Republic produces nickel as an iron-nickel alloy from laterite ore. Material that is rejected from their mining operations due to its incompatible chemistry is currently being stockpiled against mine depletion. Recent interest in recuperating nickel from this reject material led to the examination of the suitability of carbothermic reduction followed by magnetic separation for nickel recovery from this reject ore. Five parameters were considered in a Design of Experiment framework, namely: heating time; temperature; material type, coke addition and oxygen partial pressure. Magnetic separation was conducted with a Davis Tube and a low intensity hand magnet. / It was found that this reject material can successfully be treated using a carbothermic reduction process to produce 50 to 75 mum diameter metallic components within a gangue matrix. The recovery of nickel ranged from 61.7% to 21.9% to 16.4% in the high, low and non magnetic fractions, respectively, separated from the reduced material. The grade of nickel ranged from 1.97 wt% Ni to 1.58% to 0.75 wt% Ni in the high, low and non magnetic fractions, respectively. / Heating temperature had the greatest positive influence on the performance of the process followed by material type and heating time. Oxygen activity and coke addition were seen not to influence the performance. The Boudouard reaction was considered to be the rate controlling step and a maximum possible operating temperature was considered to depend on the physical properties of the material, specifically the softening temperature.

As part of a strategic research initiative at UBC to design and evaluate integrated underground mining and mineral processing systems, work has been done to determine how to utilize the coarse rejects of pre-concentration in the underground environment. An amenability study for nine orebodies from four of Xstrata Nickel’s Ontario operations evaluated both processing and waste disposal methods. Metallurgically the orebodies showed amenability to dense media separation and conductivity sorting. The dense media results showed high mass rejections and high metal recoveries for all nine orebodies. Conductivity sorter results were not as consistent, but still showed good results. Dense media rejects were examined to determine the applicability of their use in rockfills and composite minefills. The geotechnical properties indicated that the rejects would provide a competent material for minefills. The mix designs were examined for both strength and rheological properties and showed that fills utilizing rejects were comparable to fills currently used by industry. Composite fills containing rejects had significantly lower void ratios, decreasing cement requirements for a given strength requirement. Conceptual designs for pre-concentration systems based on the metallurgical, reject characterization, and mix design were developed for each of the four mines in the study. The designs took into consideration the current mining plans.

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