Quantitative reductive leaching of a low-grade spessartine ore in acidic media

Abstract

The increasing demands for pure manganese and its compounds as a viable material in steel and chemical industries have prompted continuous efforts to develop a low-cost and eco-friendly technique for spessartine ore processing. Thus, this study focused on dissolution kinetics of a low-grade spessartine ore treated via reductive leaching in sulphuric leachant and oxalic acid reductant. During leaching, parameters such as leachant concentration, particle size and reaction temperature on the extent of ore dissolution were examined. At optimal leaching conditions (1.5 mol/L H2SO4 + 1.0 mol/L C2H2O4, 75 degrees C), 97.2% of the initial 10 g/L ore reacted within 120 min. The un-reacted product examined by X-ray diffraction (XRD) was found to contain silica (alpha-SiO2: 39-1425). The shrinking core dissolution model was adopted to evaluate the various dissolution parameters for better understanding of the rate determining step. Experimental results indicated that the reaction rate of the reductive leaching process was controlled by the diffusion model, with calculated activation energy (Ea) of 16.5 kJ/mol. The leached metal ion species at optimal conditions gave 2854.7 mg/L Mn2+, 1523.2 mg/L Fe3+, 205.3 mg/L Al3+, 43.1 mg/L Ca2+ and 28.1 mg/L Sn2+. Purification of the metal ions for industrial value additions will be reported in due course.