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UBC Theses and Dissertations

Selective leaching of molybdenum mixed copper-molybdenum sulfides Ismay, Arnaldo Andrés


A study has been made of the oxidation of molybdenite in solutions of hypochlorite. The reaction was found to be first order in reagent concentration with a reaction rate constant of 1.90 x 10⁻² min⁻¹ cm⁻² at pH 9 and 45°C. The oxidation rate increases with increasing pH and later decreases if the pH is raised above 9.5. An activation energy of 6.3 ± 0.8 kcal/mole was observed for this reaction which was controlled by either chemical or mixed diffusion and chemical reactions. Other factors studied were the agitation, surface area, surface characteristics and effect of sulfates, chlorides, chlorites and chlorates. It was observed that hypochlorite is capable of selectively leaching molybdenite from copper sulfides and positive results were obtained when applying this property to the extraction of molybdenite from copper rougher concentrates. The formation of oxides during drying and/or leaching of copper sulfides was found to be detrimental to the process because they act as catalysts in the decomposition reaction of hypochlorite. Rates of normal decomposition of the reagent were studied over the range 35 to 60°C and pH 7 to 10 and found to be negligible as compared to the rates of oxidation of molybdenite. The leaching of rougher concentrates with hypochlorite was found not to affect considerably the subsequent flotation operation. Data of on-site hypochlorite generator plants and factors that affect production and decomposition, have been presented with the purpose of proposing a process using the information obtained in this work for the extraction of molybdenite in the Copper Concentration Plants.

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