THE SOLUBILITY OF SELENATE-AFT AND SELENATE-AFM

In this study, bulk chemical analysis and X-ray diffraction were used to synthesize and characterize the Se(VI)-analogues of ettringite and monosulfate, selenate-AFt and selenate-AFm. Their solubility products were determined from a series of batch and resuspension experiments conducted at 25 deg C. For selenate-AFt suspensions, the pH varied between 11.37 and 11.61, and a solubility product was determined for a reaction. Selnate-AFm synthesis resulted in the uptake of sodium, which was leached during equilibration and resuspension. For the pH range of 11.75 to 11.90, a solubility product was determined for a reaction. Thermodynamic modeling suggested that both selenate-AFt and selenate-AFm are stable in the cementitious matrix; and that in a cement limited in sulfate, selenate concentration may be limited by selenate-AFm to below the millimolar range above pH 12. The solubilities of both selenate-Afm and selenate-Aft are relatively similar, suggesting that both solids may be stable in a cementitious system.