Beneficiation of Zimbabwean petalite : extraction, purification and compound synthesis

Lithium is one of the most strategically important minerals at the time of writing. The demand for lithium and lithium compounds to be used in lithium-ion batteries is increasing day by day. Zimbabwe possesses a considerable resource of lithium ore, estimated at 23 000 mt Li. Beneficiation of this lithium ore could indeed be a very promising business in the near future. This work focuses on processing of petalite concentrate from the Bikita deposit in Zimbabwe for production of Li2CO3, with subsequent preparation of LiF and LiCl. Analysis performed on the petalite showed that the average Li2O content is 4.10 %. The extraction method used involves roasting the pre-heated concentrate with concentrated H2SO4 followed by water leaching of the resulting Li2SO4, solution purification and precipitation of Li2CO3 with subsequent preparation of LiF and LiCl. Investigation of the roasting and leaching showed that the dissolution rates are significantly influenced by roasting temperature and stirring speed. 97.3 % optimum rate of extraction was attained at 320 rpm and roasting temperature of 300 C. Water-washed lithium carbonate with a purity of 99.21 %( metal basis) and an average particle size of 1.4 ìm was produced. Good quality LiF and LiCl can be produced with purity of 99.36 % and 99.02 % respectively. The pH, concentration and agitation have a great influence on the morphology of the precipitated LiF. Lower pH values and optimum concentration of the Li2CO3 solution results in smaller particle size. High recovery of 96.53 % LiF was realised. Anhydrous LiCl was found to absorb moisture when exposed to air at ambient temperature. The synthesised LiCl melts at 606.2 C with a corresponding enthalpy of fusion of 18.4 kJ mol-1, close to the values reported in the literature. CopyrightDissertation (MSc)--University of Pretoria, 2012.Chemical Engineeringunrestricte

Processing of a Zimbabwean petalite to obtain lithium carbonate

Processing of petalite concentrate from the Bikita deposits in Zimbabwe for production of high purity Li2CO3 has been studied. XRF and ICP‐OES analysis showed that the concentrate consists of oxides of Li, Si and Al as major components, with an average Li2O content of 4.10 %. XRD examination confirmed that the sample is a petalite. Processing of the petalite involves roasting the pre‐heated concentrate with concentrated H2SO4 followed by water leaching of the resulting Li2SO4, solution purification and precipitation of Li2CO3. The effects of roasting temperature, stirring speed, solid to liquid ratio, leaching temperature and time on the lithium dissolution are reported. The dissolution rates are significantly influenced by roasting temperature and stirring speed. Water‐washed lithium carbonate with a purity of 99.21 % (metal basis) was produced. Synthesised and commercial Li2CO3 samples were characterised and compared using X‐ray diffraction (XRD) and thermogravimetric analysis (TGA).University of Pretoria, the South African National Research Foundation (NRF) and the Fluorochemical Expansion Initiative (FEI)http://www.elsevier.com/locate/ijminpr

Gold Leaching in Thiosulfate-Oxygen Solutions

No abstract availabl

The adsorption of gold(I) on minerals and activated carbon (preg-robbing) in non-ammoniacal thiosulfate solutions - effect of calcium thiosulfate, silver(I), copper(I) and polythionate ions

The ability of some typical gangue minerals and activated carbon to adsorb gold(I) (preg-robbing) in non-ammoniacal thiosulfate solutions was examined at different calcium thiosulfate concentrations. In the absence of calcium thiosulfate, sulfide minerals such as pyrite and chalcopyrite, and carbon were highly preg-robbing with 100% gold being adsorbed within half an hour. The oxide minerals examined including kaolinite, goethite and hematite were significantly less preg-robbing under the same conditions. The presence of free thiosulfate can significantly reduce or eliminate the preg-robbing of gold on mineral surfaces. With an initial thiosulfate concentration of 0.1 M, gold adsorption by oxide minerals was completely eliminated, while that of sulfide minerals and carbon was insignificant at 0.2 M free thiosulfate. Copper(I) was found to enhance the preg-robbing of gold by oxide minerals but to reduce the preg-robbing of gold by sulfide minerals and by carbon. Similar effect of silver(I) was observed except for chalcopyrite. Trithionate, a by-product of thiosulfate degradation, has no significant effect on the preg-robbing of gold(I). Tetrathionate, another by-product of thiosulfate degradation, significantly increases the preg-robbing of gold(I) onto pyrite. Activated carbon enhances the degradation of tetrathionate to trithionate and thiosulfate, the latter helps stabilise the gold(I) in solution

A review of factors affecting gold leaching in non-ammoniacal thiosulfate solutions including degradation and in-situ generation of thiosulfate

Cyanide has been used for more than a century as a preferred lixiviant for extracting gold from ores and concentrates. While cyanide is very effective in treating certain ores and concentrates, it is not suitable for carbonaceous and high copper-bearing ores. Research activities over many decades have indicated that thiosulfate has potential as an alternative lixiviant for extracting gold from problematic ores/concentrates which are not amenable for cyanidation. A number of studies have shown faster gold leaching kinetics with thiosulfate in the presence of ammonia and copper(II) in the form of a cupric tetraamine complex that acts as an oxidant for gold. However, ammonia is toxic and the lixiviant system is highly complex due to the presence of several ligands, which particularly affects speciation of the copper ions and their reactions in the system. For this reason, recent studies have been focusing on alternative oxidants that do not use ammonia. In this article, a comprehensive review of fundamental studies of leaching of gold from different ores in ammonia-free thiosulfate solutions is presented with special emphasis on factors that affect gold leaching kinetics including mineralogical composition of ores and concentrates. Important aspects of thiosulfate gold leaching such as thiosulfate stability, in-situ generation and consumption of thiosulfate and passivation of gold are reviewed

A fundamental study of gold leaching in a thiosulfate‑oxygen‑copper system in the presence of activated carbon

Activated carbon has been found to significantly enhance the dissolution of gold in a thiosulfate‑oxygen‑copper system. Leaching tests using gold powder showed that the gold dissolution in a thiosulfate‑oxygen‑copper system in the absence of activated carbon was very slow, with only 2% gold dissolved over 24 h. In contrast, in the presence of activated carbon as an additive the gold leach recovery was dramatically improved to over 95% in the same period. Leaching and electrochemical studies using a gold rotating disc electrode have identified two impacts of activated carbon on the dissolution of gold: 1) enhancing the oxygen reduction half reaction via galvanic interaction and; 2) enhancing the gold oxidation half reaction via removal of the surface passivation. A combination of the two effects can potentially increase the gold leach rate to the same order of magnitude as a typical cyanidation rate (10−5 mol m−2 s−1). It has also been found that the presence of copper and the use of an elevated temperature are beneficial for the gold leaching; whilst the use of oxygen instead of air and change in pH between pH 7 and pH 10 have little impact

Gold dissolution in non-ammoniacal thiosulphate solutions: Comparison of fundamentals and leaching studies

Thiosulphate has received much attention as an alternative non-cyanide lixiviant for gold recovery over the last three decades. In particular, a number of studies have shown that an ammoniacal copper(II)/thiosulphate system offers fast leaching kinetics, but there are difficulties in controlling the complex solution chemistry and there are concerns over the use of ammonia. Recently, thiosulphate leaching of gold in the absence of ammonia has shown to be one of the most promising alternatives to cyanide, as evident from the thiosulphate gold processing plant recently commissioned at Barrick Goldstrike for treating pressure-oxidized double refractory ore. However, the published information on non-ammoniacal thiosulphate systems is limited. In this work, the dissolution of gold in non-ammoniacal thiosulphate solutions has been studied using a rotating electrochemical quartz crystal microbalance (REQCM), rotating gold disk, gold powder, and selected sulphidic gold ores. The electrochemical studies found that gold oxidation is enhanced by increases in temperature, thiosulphate concentration, and the addition of low levels of copper. Oxygen reduction was found to occur much more readily on sulphide mineral surfaces than on the gold surface, offering an opportunity for galvanic interaction. The subsequent leaching tests using REQCM showed that the gold leach rate in the oxygen-thiosulphate system without any additives is in the order of 10-7 mol m-2 s-1 , two orders of magnitude lower than a typical cyanidation rate. However, the use of elevated temperature, high oxygen concentration, and copper addition, in conjunction with the galvanic effect of sulphide minerals, dramatically improved the gold leach rate to the same order of magnitude as a typical cyanidation rate. This was supported by the results obtained from prolonged leaching tests using gold powder and sulphidic gold ores. This study hence shows that the oxygen-thiosulphate system could be a promising alternative to cyanidation for treating some sulphidic gold ores

Solution purification and valuable by-products formation during the production of battery-grade lithium from micas. MRIWA Project M479

The project, part of a major collaboration between the Minerals Research Institute of Western Australia (MRIWA), Murdoch University and sponsors Lithium Australia and Venus Metals Corp, sought to develop new technology for battery grade lithium production. The project also aimed to capture valuable byproducts from the extraction of high-grade lithium carbonate from certain groupings of minerals, known as micas