Thiosulfate has been considered as one of the most promising of the non-toxic alternatives to cyanide for the leaching of gold and much work has been carried out with the aim of understanding and improving the ammoniacal thiosulfate leaching process. In particular the behaviour of gold in thiosulfate solutions containing copper in the absence of ammonia has received little attention. It has been shown in this study involving electrochemical and leaching tests that copper ions catalyze not only the oxidation of thiosulfate but also the dissolution of gold in alkaline thiosulfate solutions. Electrochemical studies have shown that copper has a positive effect on the anodic dissolution of gold with increasing concentrations of copper resulting in higher dissolution rates of gold at a potential of 0.3 V. Studies on the dissolution of gold powder in alkaline oxygenated thiosulfate solutions containing low concentrations of copper have shown that the role of copper in enhancing the dissolution rate of gold is possibly associated with the formation of a copper-thiosulfate-oxygen intermediate which is more reactive in terms of cathodic reduction than dissolved oxygen. The electrochemical experiments have been complemented by a leaching study which has shown that milling of gold powder in the presence of copper (added as ions, metal, or oxide) assists with the dissolution of gold in thiosulfate solutions.

Electrochemical techniques have been used to investigate the reduction and dissolution of two different ilmenite samples in 450 g L -1 sulfuric acid solutions at elevated temperatures. The results have shown that the dissolution rate of ilmenite (FeTiO 3 ) is low at potentials above about 0.3 V at which potentials the dissolution of ilmenite and the reduction of hematite (if present in the ilmenite sample) are the main reactions. At more negative potentials the dissolution of ilmenite increases simultaneously with reduction of ilmenite to trivalent titanium. These observations are consistent with those predicted from thermodynamic data. Hematite has a higher dissolution rate under reductive conditions than ilmenite. Studies of the effect of temperature on the dissolution of ilmenite at low potentials such as 0 V have shown that in the temperature range of 65-95 o C, the activation energy is about 50 kJ mol -1 and this together with the high ratio of the charge passed to metals dissolved suggests that the rate of the non-reductive dissolution reaction is not significant under these conditions.

Please cite this article as: Zhang, Suchun, Nicol, Michael J., Kinetics of the dissolution of ilmenite in sulfuric acid solutions under reducing conditions, Hydrometallurgy (2010), doi: 10.1016/j.hydromet.2010.03.019 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. A C C E P T E D M A N U S C R I P T ACCEPTED MANUSCRIPT ABSTRACTThe kinetics of the dissolution of titanium and iron from an ilmenite sample has been studied in moderately strong sulfuric acid solutions in the absence and presence of reducing agents such as titanium(III) ions and sulfur dioxide. The effects of particle size, temperature, solid/liquid ratio, sulfuric acid concentration and titanium(III) concentration on the kinetics of dissolution have been investigated. The results have shown that both particle size and acid concentration have relatively minor effects on the rate of dissolution of titanium while temperature has a significant effect under the studied conditions.The batch leach kinetics of ilmenite in acid solutions appears to fit a shrinking particle model, while in the presence of a decreasing titanium(III) concentration, the rate of dissolution of titanium can be fitted to a shrinking core model. Mathematical expressions for the batch leaching of the ilmenite have been established. The results suggest that the rate of dissolution of ilmenite in acid solutions is controlled by a slow chemical reaction on the surface of the mineral, while in the presence of a reducing agent such as titanous ions, the dissolution rate of ilmenite is significantly enhanced. The use of SO 2 as a reductant increases the dissolution of titanium only in the presence of ferrous ions. The role of Ti(III) ions and SO 2 during leaching is assumed to involve reduction of the iron(III) component in the mineral by a redox reaction on the surface.

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Cellular transplantation strategies have been explored for the treatment of spinal cord injury. In particular, olfactory nerve ensheathing cell (OEC) transplantation has been reported to improve functional outcome following injury. We investigated the effect of OEC transplantation using cells derived from adult animals on the restoration of function following a contusion injury to the spinal cord. The NYU impactor was used to create a moderate to severe spinal cord injury in 17 rats. Hoescht stained cultured OECs derived from adult rats (n = 7) or culture medium alone (n = 10) were injected into the injury site immediately following injury. Histological and functional outcomes were measured using immunohistochemistry and the Basso, Beattie, and Bresnahan (BBB) scale. All animals transplanted with OECs were found to have surviving Hoescht positive cells within the spinal cord when sacrificed 6 weeks following injury. Immunohistochemical staining of the explanted cords revealed that the surviving cells stained positively for nerve growth factor receptor. Functional outcomes were not different between the transplanted and control groups. OECs transplanted immediately following a contusion injury to the spinal cord survive during the first 6 weeks following injury. These cells do not appear to influence functional outcome during the first 6 weeks following injury. Additional studies are required in order to definitively determine the utility of this type of cellular transplantation for spinal cord injury.

Dorsal root avulsion results in permanent impairment of sensory functions due to disconnection between the peripheral and central nervous system. Improved strategies are therefore needed to reconnect injured sensory neurons with their spinal cord targets in order to achieve functional repair after brachial and lumbosacral plexus avulsion injuries. Here, we show that sensory functions can be restored in the adult mouse if avulsed sensory fibers are bridged with the spinal cord by human neural progenitor (hNP) transplants. Responses to peripheral mechanical sensory stimulation were significantly improved in transplanted animals. Transganglionic tracing showed host sensory axons only in the spinal cord dorsal horn of treated animals. Immunohistochemical analysis confirmed that sensory fibers had grown through the bridge and showed robust survival and differentiation of the transplants. Section of the repaired dorsal roots distal to the transplant completely abolished the behavioral improvement. This demonstrates that hNP transplants promote recovery of sensorimotor functions after dorsal root avulsion, and that these effects are mediated by spinal ingrowth of host sensory axons. These results provide a rationale for the development of novel stem cell-based strategies for functionally useful bridging of the peripheral and central nervous system.

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