Hydrometallurgical processing of a Nigerian sphalerite in hydrochloric acid: Characterization and dissolution kinetics

Abstract

This study is concerned with the physio-chemical characterization and investigation of the dissolution kinetics of a Nigerian sphalerite in hydrochloric acid (HCl). The effects of HCl concentration, temperature, particle diameter, stirring speed, solid/liquid ratio on the leaching of sphalerite were investigated. The XRF analysis showed that the sphalerite mineral consists of zinc and sulphur as major elements with Fe, Sn, Ag, K, Sb, Ca and Pb occurring as minor or trace elements. The XRD examination confirmed the originality of the sphalerite sample and it revealed the presence of associated minerals such as ilmenite (FeTiO 3), pyrite (FeS 2), siderite (FeCO 3), α-quartz and cassiterite (SnO 2). Optical microscopic examination also supported the above. The leaching experiments showed that sphalerite dissolution in HCl increases with acid concentration and temperature, but decreases with particle diameter and solid/liquid ratio. In HCl 4 M and at 80 °C, about 91.80% of sphalerite was dissolved within 120 min using − 112 + 63 μm particle diameter and solid/liquid ratio of 10 g/L. The activation energy calculated from the experimental data was 39.09 kJ/mol, while the reaction order, Arrhenius constant and reaction constant of 0.24, 13.46 s − 1 and 2.21 ± 0.4 × 10 3 were computed for the process respectively. Kinetic data analysis indicated that the rate determining step for the dissolution process followed a surface chemical reaction and the reaction data fitted shrinking core model for spherical particles. Finally, the XRD analysis of the post-leaching residue provided evidence for the presence of silica and traces of sulphur in the residual solid.