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The carbonation Mg-rich natural minerals or industrial wastes is an attractive route to store CO 2 . Recently, an approach involving the indirect mineral carbonation of serpentine with recyclable (NH 4 ) 2 SO 4 or NH 4 HSO 4 is receiving widespread attention. In this study, the solubilities associated with the mineral process (ternary system of (NH 4 ) 2 SO 4 −MgSO 4 − H 2 O) were measured and calculated using the isothermal method and Pitzer model, respectively. The effects of adding small amounts of H 2 SO 4 and iron sulfate on the solubilities were evaluated. The results showed that the crystalline region of MgSO 4 • (NH 4 ) 2 SO 4 •6H 2 O (boussingaultite) is larger than those of the other species, which indicates that boussingaultite is crystallized out easily. The presence of H 2 SO 4 at a concentration of up to 10 wt % and iron sulfate of 2.5 wt % almost had no effect of the solubilities. The minimal ratios of liquid to solid during the leaching unit were calculated as 3.45, 2.19, and 1.36 mL/g at 25, 55, and 80 °C, respectively. Compared with the case of 25 °C, the energy consumption for the evaporation could be reduced by 36.5% at 55 °C and 60.6% at 80 °C. During the crystallization of ammonium sulfate, high purity (NH 4 ) 2 SO 4 is hardly obtained due to the small crystalline field.

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