Phase Equilibrium of the MgSO₄–(NH₄)₂SO₄–H₂O Ternary System: Effects of Sulfuric Acid and Iron Sulfate and Its Application in Mineral Carbonation of Serpentine

Abstract

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.

Determination of Solid–Liquid Phase Equilibria of Na2SO4–(NH4)2SO4–MgSO4–H2O at T = 318.15 K

“…Comparison of solubility curves of the ternary system ((NH 4 ) 2 SO 4 –MgSO 4 –H 2 O) at 298.15, 303.15, 318.15, 328.15, and 353.15 K: (inverted triangle) solubility curve at 298.15 K, (diamond) solubility curve at 303.15 K, (triangle) solubility curve at 318.15 K (this work), (square) solubility curve at 328.15 K, and (circle) solubility curve at 353.15 K …”

Mechanisms of Mg carbonates precipitation and implications for CO2 capture and utilization/storage

“…16a shows a ternary phase diagram for the MgSO 4 -H 2 O-(NH 4 ) 2 SO 4 system, where the formation of mixed salts are noticed at 25 °C with MgSO 4 <50 wt% and -(NH 4 ) 2 SO 4 <40 wt%, showing that the double salt MgSO 4 •(NH 4 ) 2 SO 4 •6H 2 O had easy crystallization in the majority of the investigated SO 4 2− :CO 3 2− molar ratios. 139 The phase diagram of the MgCO 3 -MgSO 4 -H 2 O system at 25 °C is shown in Fig. 16b, where the solubility of magnesite is seen at point F (0.021%).…”

Phase Equilibria of the Ternary Systems ((NH4)2SO4–MNSO4–H2O) and ((NH4)2SO4–MGSO4–H2O) at 303.15 K

“…The solubility data of the supernatant and the wet slag content data in the experiment are connected with dotted lines. At the same time, the solubility data of the two systems ((NH 4 ) 2 SO 4 –MnSO 4 –H 2 O and (NH 4 ) 2 SO 4 –MgSO 4 –H 2 O) were compared with the literature values , as shown in Figure . In Figure a, the system of (NH 4 ) 2 SO 4 –MnSO 4 –H 2 O, we can find that the data of experimental temperature ( T = 303.15 K) and the data of different temperatures in literature have the same trend.…”