LEACHING KINETICS OF LEAD FROM GALENA IN TRICHLOROACETIC ACID SOLUTIONS WITH HYDROGEN PEROXIDE

Abstract

The kinetics of leaching lead from galena in trichloroacetic acid (TCA) solutions with hydrogen peroxide (H2O2) were investigated with regard to particle size, temperature and concentrations of trichloroacetic acid and hydrogen peroxide. X-ray Diffraction (XRD) was carried out on raw and leached samples to establish the reaction mechanism. The XRD analysis of the raw sample indicated galena as the dominant mineral phase. The experimental parameters on leaching studies showed that the leaching process of galena in trichloroacetic acid solutions with hydrogen peroxide increases with increasing trichloroacetic acid and hydrogen peroxide concentrations and temperature, while it decreases with particle size. Oxidation of galena with hydrogen peroxide produced lead (II) salt which dissolves by complexing with trichloroacetate anion (CCl3CO2-) to form lead trichloroacetate (Pb(CCl3CO2)2). The mechanism of kinetics of leaching of lead from galena was established to follow the shrinking core model with diffusion as the rate controlling step with an activation energy of 39.89 kJ/mol in the temperature range of 303 -343 K. Both trichloroacetic acid and hydrogen peroxide affect the rate of extraction of lead as a trichloroacetate complex. The order of reaction was 0.55 and 0.44 with respect to hydrogen peroxide and trichloroacetic acid concentrations respectively, while the XRD analysis of the post leached residue showed the presence of elemental sulphur . The results of this research work will be useful in the selective extraction of lead from galena in hydrometallurgical industry.