Kôichi Arai1 and Kiyoshi Terayama2
1Department of Metallurgy, Faculty of Engineering, Toyama University, Takaoka
The effect of chloride ion on the anodic dissolution of galena in dilute sulfuric acid solution was studied in order to obtain the foundamental data on acidic leaching. Electrolytes used are dilute sulfuric acid solutions containing sodium chloride with pH values of 2.5 and 6.2, and deaerated with nitrogen. The anodic dissolution behavior of galena electrode is measured by means of the galvanostatic and the potentiodynamic polarization methods.
The experimental results obtained are as follows:
(1) The anodic polarization behavior of galena in dilute sulfuric acid solution shows a typical activation-passivation curve and the anodic surface film is formed on the galena electrode. The limiting anodic current increases with lowering pH and elevating temperature, and the reaction of surface film dissolution is accelerated with lowering pH and elevating temperature.
(2) The surface film formed on the galena electrode in the solution is a lead sulfate and shows a characteristic behavior of ionic conductors. The thickness of the surface film is about 300 ∼ 2000 Å. The reaction of surface film formation is mass-transport control.
(3) The anodic dissolution of galena in dilute sulfuric acid solution containing chloride ion increases with lowering pH, elevating temperature and increasing concentration of chloride ion in the solution. The anodic polarization resistance decreases proportionally with increasing concentration of chloride ion in the electrolyte. The acceleration of the reaction in anodic dissolution of galena is caused by the effect of chloride anion, and the electrode interface is activated by chloride ion.
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