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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.

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.

Typescript. / Thesis (Ph. D.)--University of Hawaii, 1962. / Bibliography: leaves 392-406. / xxxiv, 406 leaves ill., diagrs

Masters Research - Master of Science / The jarosite group of compounds are yellow/brown clay like substances, both naturally occurring and synthetically produced in metallurgical processes. Jarosites have the structure MFe3(SO4)2(OH)6, where M can be numerous elements or compounds, most often potassium or sodium. The term jarosite refers specifically to the potassium form of the compound, but is synonymous with the whole group of compounds, often leading to confusion. In nature, jarosites can be associated with acid mine drainage and acid sulphate soils as an intermediate product of the oxidation of pyrite and other iron/sulphur bearing minerals. In industry, jarosites are used in metallurgical processes, synthetically produced to precipitate an easily filterable form of solid iron. Jarosites have properties that make them a chemically unstable solid. Upon decomposition the jarosite group of compounds will generate sulphuric acid. A literature review found many references to jarosites, their stability, methods of conversion to iron oxides, methods to extract reusable materials and environmental concerns. Most methods of recycling were unsuccessful. Accelerated conversion of jarosites to a form of iron oxide was a successful method of mitigating the risk of future acid generation. There were numerous specific ways of completing this task. The BHP Billiton patented nickel atmospheric leach process generates natrojarosite (sodium form of the compound) as a by-product, when extracting nickel from lateritic ores. The by-product of this process was tested for stability to understand the decomposition process. Accelerated decomposition of natrojarosite was attempted using limestone and hydrated lime at 90OC. Limestone did not react with the natrojarosite. Hydrated lime caused extensive dissolution of sodium and sulphur from the solid. However XRD analysis still reported natrojarosite as the solid material, suggesting incomplete decomposition and the formation an amorphous form of iron oxide not detected by XRD. Further decomposition tests were completed using elevated temperatures and pressures in an autoclave. Natrojarosite was not detectable in the solid phase after treatment at a temperature of 212OC, converting to haematite at temperature above 150OC. The stability of natrojarosite was measured using a number of methods on two natrojarosite samples sourced from the atmospheric leach process. The methods used were batch agitation, column testing and permeability testing. The aim was to provide a holistic result for the stability of natrojarosite if stored in a waste facility. Results obtained were compared against the standard TCLP test and found to be a more accurate method for measuring the stability of natrojarosite. The tests are more time consuming than TCLP testing but showed that natrojarosite was capable of decomposing to form sulphuric acid with time. This result was not obtained from TCLP tests, which suggested the solid material was stable. It was also found that salt water stabilised natrojarosite. Decomposition occurred in 40 and 80 days respectively, for two natrojarosite samples tested in deionised water. There was no evidence of decomposition after 150 and 280 days respectively for the same two samples. The common ion theory is thought to stabilise the natrojarosite which decomposes in an equilibrium reaction. Excess ions present in solution decrease the propensity for the solid to decompose. The two natrojarosite samples tested varied in calcium concentration. Limestone and hydrated lime were added to the natrojarosite during the nickel extraction process. Gypsum is theorised to form an impermeable layer around the natrojarosite, increasing the stability of the compound. Gypsum is sourced from the neutralisation reaction between limestone or hydrated lime and the acid generated from natrojarosite decomposition.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1938. / Typescript. Includes abstract and vita. eContent provider-neutral record in process. Description based on print version record. Bibliography: leaves 47-49.

The extraction of nickel and cobalt, from nickeliferous laterite, together with the hydrothermal precipitation of hematite has been investigated. In order to emphasize the relevance and significance of this process, an appraisal is made of the state of the nickel, cobalt and iron industries. A compilation of the annual production of the respective ores on the world market is included with an examination of the future uses and demand of nickel and cobalt. Solubility relationships for iron (III) compounds in aqueous solution are reviewed in terms of pH, solution composition and temperature. The thermodynamic data used at elevated temperatures between 60°C (333°K) and 200°C (473°K) have been estimated by using the "Entropy correspondence principle" method of Criss and Coble. A sample calculation is shown in Appendix A. The effects of (a) temperature; (b) ferric chloride concentration, (c) hydrochloric acid concentration and (d) pulp density were studied in order to evaluate extraction conditions. Generally, metal extraction increased with temperature and ferric chloride concentration. At 423°K, over 90 percent of the nickel was extracted with a ferric chloride concentration greater than 1M. Since appreciable amounts of gangue dissolved under most conditions, thereby consuming acid, a discussion on the recovery of hydrochloric acid is presented. Filtration of the precipitated hematite has proved difficult, because of the very fine nature of the particles. An overview of the nucleation and growth of particles in supersaturated solutions has therefore been included. This phenomenon is used to describe the phase changes which occurred during leaching experiments, and to propose an approach by which coarser particles might be achieved. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate

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With China’s continuing economic boom, the demand for nickel has seen unprecedented growth over the past 10 years. Most of the world’s nickel is present in nickel laterite deposits. These high volume, low grade deposits are now being exploited and processed. An understanding of nickel laterite rheology and the ability to obtain meaningful rheological data is essential to process intensification and stability. / The properties and physical characteristics of 8 industrial nickel laterite slurries as well as two alumina slurries were examined using various rheological techniques. The samples chosen covered a wide range of physical conditions such as differing pH, particle size distributions, solids densities and mineralogy as well as country and deposit of origin. The rheological parameters investigated were the yield stress and shear stress vs. shear rate of the particulate slurries. Considerable attention was focused on the techniques used in shear stress vs. shear rate characterisation, including capillary rheometry, smooth and roughened cup and bob rheometry and the vane in infinite medium technique. / This work confirmed the finding of previous works, showing nickel laterite slurry rheological behaviour ranging from time independent to thixotropic to rheopectic. It found the vane in infinite medium technique highly suitable for testing nickel laterites at process relevant yield stresses. This technique gave data that correlated well with vane yield stresses and capillary rheometry data. Cup and bob tests showed significant slip at lower shear rates. In a number of cases, the cup and bob techniques also showed erroneously high stresses at higher shear rates. / The vane yield stress was found to be a fast and accurate method for monitoring nickel laterite sample aging and the samples tested exhibited 100 Pa yield stresses at solids fractions ranging from 0.389 to 0.524. Blending of nickel laterites was found to be nonlinear, and confirmed that characterisation at various blend ratios is necessary if blending is to be utilised during production.