The sorption of selenite on various cement formulations

Twenty-seven cementitious formulations containing three levels of water/solids ratio (0.45, 0.50, and 0.55), three concentrations of silica fume (0, 10, and 20%), and three concentrations of clay (0, 3, and 5%) were evaluated for their ability to effectively sorb selenite (SeO32-) from an alkaline solution. A batch sorption procedure was utilized to determine distribution coefficients (Kd) for selenite between water and each cement formulation. Experimental Kd values obtained ranged from 250 to 930 l kg−1. The results indicated that varying the water and clay content of the mixes had little effect on selenite sorption, while adding increasing amounts of silica fume in a cement mix tended to decrease selenite sorption. A sorption/desorption study using several concentrations of selenium ranging from 6.5 to 1510 ppb was also conducted on cement formulations at one water/solids ratio (0.50), no silica fume, and three concentrations of clay (0, 3, and 5%). Freundlich isotherms were fitted to the sorption and desorption data. Results indicated that selenite sorption was irreversible under these conditions.