Enhanced adsorption capacity for phosphate in wastewater from thermally activated flue gas desulfurization gypsum

BACKGROUND: In this study, a flue gas desulfurization (FGD) gypsum was calcined as phosphate sorbent materials for the remediation of phosphate wastewater. RESULTS: In addition to the main crystalline phase of gypsum, FGD gypsum contains a small quantity of quartz, dolomite, calcite and magnesite. Moreover, FGD gypsum has a prismatic structure with a dense and smooth surface, whereas a pore structure and flaky structure appear with increasing calcination temperature. The kinetic adsorption process was well described by a pseudo-second-order model with a high correlation coefficient (R-2 > 0.99). The adsorption isotherms indicated that phosphate removal can be fitted by the Langmuir model. CONCLUSIONS: Calcination improved the performance of FGD gypsum towards phosphate sorption. The precipitation following chemical adsorption dominated the phosphate removal by the calcined FGD gypsum, and phosphate was ultimately immobilized by hydroxyapatite. Calcined FGD gypsum has excellent capacity for phosphate removal for three reasons: an enhanced content of active Ca by calcination, a novel nanoscale prismatic structure with a high specific surface area, and a favorable reactivity and alkaline environment produced by the decomposition of magnesite, dolomite and calcite. (C) 2017 Society of Chemical Industry