Leaching of Natural Stibnite Using Na2S and NaOH Solutions

First stage of the hydrometallurgical production of antimony is leaching of the raw material that contains antimonybearing mineral. The raw material can be ore or concentrate. Leaching can be carried out either in alkaline (Na2S+NaOH; NaOH) or acid (HCl; H2SO4; HF) solutions. In order to achieve good antimony recovery it is essential to leach the raw material under optimum conditions.Kinetics of the reaction between particulate stibnite and mixed Na2S + NaOH solutions were studied. The effects of concentrations of Na2S and NaOH, temperature, particle size and liquid-to-solid ratio were investigated. It was observed that the rate of leaching of stibnite: a) increased with an increase in both Na2S and NaOH concentration (from 0.5 wt. % to 2.0 wt. %), and temperature (from 292 K to 327 K); b) reached its maximum at Na2S: NaOH weight ratio equal to 1:1; c) decreased with an increase in particle size (from 40 μm to 500 μm) and L/S ratio (from 10 to 100). The results are presented in terms of the shrinking (nonreacted) core model and shrinking porous-particle model. Apparent activation energy is approximately 44 kJ mol and the apparent reaction order for Na2S varies from 1.4 to 1.7. Calculated values of the kinetic parameters indicate that the leaching process is controlled by both intrinsic chemical reaction between Sb2S3 and Na2S at the liquid/solid interface, and pore diffusion. Keywords-Stibnite, Kinetics, Alkaline leaching, Activation energy, Order of reaction