Alkaline leaching of nickel bearing ammonium jarosite precipitate using KOH, NaOH and NH₄OH in the presence of EDTA and Na₂S

Jarosite precipitates produced in base metal refineries contain substantial amounts of base metals. The dissolution of nickel from the jarosite precipitate was investigated in alkaline medium (KOH, NaOH and NH₄OH) at laboratory-scale in the presence of EDTA as a complexing agent and Na₂S as reducing agent. The leaching efficiency of nickel was 82.4%, 84.5% and 88.9% in NaOH, KOH and NH₄OH respectively in the presence of 0.1 M EDTA-Na₂S, pH 9-10, using - 75 μm of ammonium jarosite precipitate at 250 rpm, 45 °C, 5% solids and leaching time of 4 h. Thermodynamic feasibility was explored using Medusa software and the kinetics of the dissolution process was studied using the shrinking core model. The results show that the dissolution process is second order and diffusion controlled. The activation energy was found to be 32.34, 35.31 and 31.52 kJ/mol in KOH, NaOH and NH₄OH mediums respectively in the temperature ranges between 25 and 45°C. The effects of EDTA-Na₂S concentration, particle size, pH, solid-liquid ratio, stirring speed, temperature and contact time were explored.