Abstract:The separation of manganese from sulfate solutions containing 14.59 g/L Mn²⁺, 1.89 g/L Mg²⁺ and 1.54 g/L Ca²⁺ was preformed successfully by carbonate precipitation. The results of thermodynamic analysis and tests indicate that carbonate precipitation holds better selectivity for manganese over magnesium than hydroxide precipitation and the feeding method is the most critical factor for minimizing the co-precipitation of calcium and magnesium. Furthermore, with adding MnSO₄ solution to NH₄HCO₃ solution, the effects of the initial NH₄HCO₃ concentration, NH₄HCO₃ amount, solution pH value, reaction temperature and time on carbonate precipitation were evaluated and the optimum precipitation conditions were obtained. Under the optimum conditions, the precipitation rates of Mn²⁺, Ca²⁺ and Mg²⁺ are 99.75%, 5.62% and 1.43%, respectively. Moreover, the prepared manganese carbonate was characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) equipped with energy-dispersive X-ray spectroscopy (EDX). The results demonstrate that the product can be indexed to the rhombohedral structure of MnCO₃.

Key words: carbonate precipitation; separation; manganese; calcium; magnesium