Synthesis and thermodynamic properties of arsenate and sulfate-arsenate ettringite structure phases

摘要

Arsenic is a toxic and carcinogenic contaminant of potential concern. Ettringite [Ca6Al2(SO4)3(OH)12·26H2O] has the ability to incorporate oxyanions as a solid solution with SO4²⁻, which could lower the soluble oxyanion concentrations. Therefore, ettringite containing SO4²⁻ and AsO4³⁻ has been synthesized. Results indicated that AsO4³⁻ could substitute for SO4²⁻ inside the channels of ettringite in the form of HAsO4²⁻, and a linear correlation existed between Xinitial solution and Xsolid. The thermodynamic characterization of the solid samples was investigated by means of Visual MINTEQ, a freeware chemical equilibrium model, and the solubility product logK of -48.4 ± 0.4 was calculated for HAsO4–ettringite at 25°C. The Lippmann phase diagram and XHAsO4–X_HAsO4,aq plot showed that the solid solution series containing arsenate has HAsO₄-poor aqueous solutions in equilibrium. These findings can be helpful to arsenate solidification and arsenate leaching modeling projects.