Effect of mixed cation acetate electrolyte on synthesis of α‐hemihydrate gypsum from phosphogypsum

Abstract The preparation of α‐hemihydrate gypsum (α‐HH) from phosphogypsum (PG) by atmospheric hydrothermal synthesis is a green and efficient method for the treatment of PG. The commonly used electrolyte solution today is mostly chlorine‐based. The prepared α‐HH based on chlorine salt solution is needlelike with a large aspect ratio, low strength, and high impurity. In this study, sodium‐ and calcium‐mixed cation acetate solution is designed and used as an organic multifunctional electrolyte to the synthesis of α‐HH for the first time. The effects of the mixed cation acetate electrolyte on crystal transformation, product morphology, and product purity of the prepared α‐HH were compared with those prepared with chloride solutions with the same mixed cations. Result showed that the morphology of α‐HH crystals prepared in acetate solutions is a stubby hexagonal prism. The aspect ratio of the prepared α‐HH crystals is close to 1, with 3‐day compressive strength four times higher than that of α‐HH prepared in chloride solutions. In addition, in comparison with chloride electrolyte, acetate electrolyte showed a complexation effect with impurity metal ions, which realized the efficient removal of impurities from PG and increased the purity of the synthesized α‐HH.