A comparative analysis of the dissolution kinetics of lead from low grade oxide ores in HCl, H2SO4, HNO3 and citric acid solutions

In this study, the dissolution of lead from a low grade oxide ore in HCl, H2SO4, HNO3 and citric acid solutions was investigated in a batch reactor employing parameters expected to affect the dissolution rate such as stirring speed, liquid to solid (L/S) ratio, temperature and acid concentration. The maximum recovery of lead were obtained to be 85.52% after 90 min with inorganic acids at 20%, 80 degrees C, 500 rpm and L/S=20 ml/g, while the maximum dissolution was determined to be 73.81% with citric acid. Also, H2SO4 was not able to dissolve lead from low grade oxide ore. The dissolution kinetics of lead was examined according to heterogeneous models. It was found that the dissolution rate was controlled by the diffusion through the fluid film (1 - (1 - x)(2/3)) in HNO3 and citric acid solutions with the activation energies of 7.71 and 11.62 kJ/mol, respectively. Additionally, when the dissolution was performed in the presence of HCl, the surface chemical reaction in an initial stage (0-30min) and fluid film diffusion in a second stage (after 30min) were the rate controlling steps. The activation energies of these sequential steps were determined to be 60.94 and 28.24 kJ/mol, respectively.