Sorption and desorption of selenium in cement formulations

Twenty-seven cementitious formulations containing three levels of water/solids (45%, 50%, 55%), three weight percentages of silica fume (0%, 10%, 20%), and three weight percentages of clay (0%, 3%, 5%) were evaluated for their ability to effectively sorb selenium at three pH levels (5.9, 8.7, 12.4). A Type V Portland cement was utilized. Distribution coefficients (K{dollar}\sb{\rm d}{dollar} values) determined for each cement formulation ranged from 250-1600 L kg{dollar}\sp{-1}{dollar}. Findings suggest that increased water/solids ratios tend to maximize selenium sorption while adding silica fume or 5% clay appears to decrease sorption. A sorption/desorption study was conducted on cementitious formulations containing three levels of w/s ratios (45%, 50%, 55%) and three weight percentages of clay (0%, 3%, 5%) at several concentrations of selenium (6.5 ppb, 26 ppb, 53 ppb, 126 ppb, 784 ppb, 1510 ppb) with sodium selenite added to vary the concentrations as needed. Freundlich isotherms fitted to the data indicate irreversible sorption by selenium