Hydrometallurgical treatment of an indigenous bismutite ore: process optimization and kinetics analysis

Abstract

Bismuth (Bi) has gained increasing attention as a potential substitute for lead (Pb) in consumer and industrial applica-tions owing to its comparatively benign environmental and health characteristics. In this study, the leaching behaviour of bismuth from bismutite ore was investigated using nitric acid, a commonly employed lixiviant in hydrometallurgical pro-cessing. The ore sample contained 78.56 wt% Bi, along with Si (11.51 wt%), Al (3.68 wt%), and Fe (1.20 wt%), and was primarily composed of bismutite, zinnwaldite, and quartz. Leaching experiments were conducted in a 1000 mL double-jacketed glass reactor equipped with a reflux condenser, mechanical stirrer, and temperature control system. The effects of nitric acid concentration, reaction temperature, and particle size on bismuth dissolution were systematically examined. Under optimized conditions (3.0 mol/L HNO3, 80 degrees C, particle size of 45 mu m, and 120 min), a maximum bismuth leaching efficiency of 91.60% was achieved. X-ray diffraction analysis of the leach residue identified quartz and sapphirine as the predominant undissolved phases. Kinetic evaluation indicated that the dissolution process followed the external liquid-film mass transfer control model, with a reaction order of 0.79 and an apparent activation energy of 15.77 kJ/mol. Thermo-dynamic and kinetic assessments were conducted to determine the feasibility of dissolution. The calculated changes in enthalpy (Delta H) and Gibbs free energy (Delta G) confirmed that Bi(III) recovery is endothermic and spontaneous within the temperature range of 301 to 353 K. The leach residue obtained under optimal conditions can be further processed as a potential SiO2 source for paint production.