A novel method using CO2 to precipitate MnCO3 for a lithium-ion battery precursor

A novel method using carbon dioxide gas (CO 2 ) and ammonia (NH 3 ) to precipitate MnCO 3 for a lithium-ion battery precursor was investigated. This MnCO 3 was recovered from a high-tenor industrial MnSO 4 pregnant leach solution (PLS) containing Mg 2+ and Ca 2+ impurities. The leach solution consisted of at least 93.9 wt% Mn 2+ , 2.25 wt% Mg 2+ , and 0.14 wt% Ca 2+ . In this study, results from thermodynamic simulations were compared to experimental results. The effects of pH (5.0 to 6.6) and CO 2 bubbling time (1 to 12 h) were investigated in laboratory experiments where 0.4 L/min of CO 2 was sparged into a 1 L agitated reactor (500 rpm) containing the PLS. The thermodynamic simulation results showed that Mn 2+ recovery is optimal in the pH range of 5.9–11.7, with recovery increasing with pH. However, high Mn 2+ selectivity is favourable at pH < 6.6, while moderate selectivity is achieved at pH values from 6.3 to 7.2. The experimental results showed an optimal Mn recovery of 61.3 % at a pH of 6.6 and CO 2 bubbling time of 8 h. This was significantly lower than the values predicted from thermodynamic simulation (>94 % Mn recovery at pH above 5). This difference in recovery was attributed to the slow dissolution rate of CO 2 . The washed MnCO 3 precipitate contained 99.0 wt% Mn, 0.13 wt% Ca, and 0.05 wt% Mg. This was equivalent to rejections of 97 % Mg 2+ and 81 % Ca 2+ from the MnCO 3 precipitate, respectively. The product purity met the high-purity Mn specifications but was slightly lower than the battery-grade Mn specifications (ultra-purity Mn). This study showed that carbonate precipitation using CO 2 and NH 3 can selectively recover Mn 2+ from an industrial MnSO 4 leachate containing high Mg 2+ and Ca 2+ impurities, and this process has great potential for industrial application. • Optimal Mn 2+ recovery of 61.3 % achieved at a pH of 6.6 and 8 h CO 2 bubbling time. • More than 93.2 % and 67.1 % of Mg 2+ and Ca 2+ were rejected from the MnCO 3 , respectively. • Recovered MnCO 3 with 99.0 % Mn, 0.13 % Ca, and 0.05 % Mg, which meets high-purity manganese specifications.