Carbon dioxide mineralization with chromium mine tailings using wet and dry extraction methods

This paper presents process optimization, Mg salt carbonation and chemicals recovery using tailings from a chromium mine in Finland for industrial scale CO 2 mineralization. It was found that 26 % of Mg can be extracted using 1M sulfuric acid at 80°C and 2 h of reaction time and 39 % of Mg was extracted using ammonium sulfate in a solid/solid process at 440°C and 0.5 h of reaction time. Aqueous extraction experiments at 80°C are well reproducible with variability of less than 1 % while dry extraction experiments at 440°C are less reproducible with up to 10 % variability. Challenges with the tested tailings sample include presence of unreactive talc and carbonates. By increasing the solid/liquid ratio from 62.5 to 250 g/L, the Mg concentration increased from 0.1M to 0.21M and the use of ammonia for pH raise was reduced by 80 %, when using a 1M and 0.5M sulfuric acid concentration, respectively. Carbonation of magnesium sulfate reached 76 % at 35°C, 4 bar pressure, and 70 minutes reaction time. The recovery of sulfuric acid reached at least 31 % of the theoretical maximum in a two-compartment bipolar membrane electrodialysis setup.