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Aqueous oxidation of galena Andersen, John Enevold

Abstract

To complement the data, on the aqueous oxidation of sulphide minerals, that is, treatment of sulphides in aqueous solution at elevated temperatures under oxygen pressure, a study was undertaken of the aqueous oxidation of galena in sodium hydroxide solution. It was hoped by the study of the kinetics of the reaction to learn something of the mechanism involved. The reaction was followed by means of a cathoderay polarograph. A crystal of galena was mounted in a small autoclave equipped with suitable electrodes, and during the course of the reaction photographs were taken at intervals of the current-voltage curves. From the height of the lead wave relative concentrations could be recorded, and after a suitable time the run was stopped and the solution assayed to give absolute values to the wave heights. The variables of oxygen partial pressure agitation, sodium hydroxide concentration, temperature, silicate-ion, and electrical potential were investigated. It was found that the polarograph under these conditions gave reproducible results. On the basis of the experimental results three alternative mechanisms for the reaction were proposed. One of these was too indefinite to treat quantitatively, but the other two were examined by calculations using the theory of absolute reaction rates. One was found to give agreement in rate with experiment, a model in which desorption accompanied by hydration and ionization was the rate controlling step. The experimental results were reviewed in the light of this mechanism and appeared to show no serious contradictions, so this model is put forward as a postulate of the reaction of galena with oxygen in sodium hydroxide solution.

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