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Microbiological leaching of a zinc sulfide concentrate Torma, Arpad Emil

Abstract

The applicability of microbiological oxidation for the recovery of zinc from a high-grade zinc sulfide concentrate has been investigated using a pure strain of Thiobacillus ferrooxidans. Factors affecting the bacterial activity and consequently the rate and extent of zinc extraction were studied. These factors were: temperature, pH, nutrient and substrate concentrations, solid particle size and surface area. The effect of carbon dioxide concentration in the air supplied to the oxidation was also studied. Larger scale experiments were carried out to simulate more closely possible industrial conditions. The optimum temperature was found to be 35°C, the optimum pH 2.3. Nutrient levels of 89 mg phosphate P/l and 636 mg ammonia N/1 were sufficient to avoid rate limitation and provide for maximum extraction, respectively. Increasing the particle surface area, the pulp density, or the total surface per unit volume of leach liquor increased the rate of zinc extraction up to a point beyond which further increases were not effective. Increasing the carbon dioxide content of the air had a similar effect. The larger scale experiments gave similar extraction rates to those observed in shake flasks but the extent of zinc extraction was significantly higher. The final concentration of zinc in leach solutions reached levels currently-employed in commercial electrowinning procedures. A form of the generalized logistic equation was shown to be capable of representing the complete extraction curve under a variety of experimental conditions.

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