Preparation of calcium carbonate by indirect carbonation desulfurization gypsum with renewable aspartic acid

Abstract

Abstract As an industrial by-product of flue gas desulfurization, flue gas desulfurization gypsum (FGD gypsum), whose main component is CaSO4 · 2H2O, is an ideal raw material for mineralization. The technical problem of indirect mineralization lies in the efficient recycling of leaching agents, while amino acids have the lowest solubility at their isoelectric point, and thus the mixture of amino acids can be separated by adjusting the isoelectric point. Therefore, this paper proposes the use of aspartic acid (ASP) as leaching agent to realize the recycling of leaching agent. The leaching efficiency of Ca2+ was regulated by changing the temperature, liquid-to-solid ratio, ammonia concentration, and the ratio of ASP to the amount of FGD gypsum substance. The results showed that ASP could sufficiently improve the leaching efficiency of Ca2+ from desulfurized gypsum under alkaline conditions provided by ammonia. The leaching concentration of Ca2+ was 7474.92 mg/L at 7% ammonia concentration, temperature of 30 °C, n(ASP): n(FGD gypsum) = 2.5:1, and liquid-solid ratio of 30:1 mL/g, which was 12 times higher compared with the leaching concentration of Ca2+ in pure water of 601.2 mg/L. While improving the leaching efficiency, ASP has lone electron pairs and can form soluble complexes with Ca2+ under alkaline environment, which can convert the crystalline form of the product CaCO3 to sphalerite during the mineralization process, and can regenerate ASP by adding acid to adjust the pH, and the recovery rate can reach 80.72%. This method effectively solves the problem of resource waste caused by the massive accumulation of desulfurization gypsum.