Mineral carbonation of red gypsum via pH-swing process: Effect of CO2 pressure on the efficiency and products characteristics

Abstract The objective of this study was to investigate the feasibility of indirect carbonation of red gypsum through pH swing process. The effect of CO 2 pressure as one of the major controlling parameters in carbonation process was investigated in details. The dissolution of red gypsum was performed using 2 M H 2 SO 4 at 70 °C for 60 min reaction time. The pH was regulated using NH 4 OH, which also precipitated out the impurities from the solution. Finally, the calcium rich solution was poured in an autoclave reactor and CO 2 was injected into the reactor for carbonate precipitation. The experimental results showed that the Fe, the main impurity can be effectively separated prior to carbonation stage (92–95%). At low pH the Fe was separated while at high pH Ca was precipitated as carbonate. The carbonation efficiency was directly affected by the CO 2 pressure and the maximum efficiency (100%) was achieved when 8 bar CO 2 pressure was used. In addition, carbonation experiments resulted in CaCO 3 production in the form of calcite, aragonite, and vaterite with 98% purity.