Leaching of selenium from cement-based matrices

Twenty-seven cementitious formulations containing three levels of water content (w/s ratios of 0.45, 0.50 and 0.55), three levels of silica fume content (0%, 10% and 20%), and three levels of clay content (0%, 3% and 5%) were evaluated for their ability to effectively immobilize selenium. Triplicate cement specimens from each formulation were spiked with a known amount of 75Se and subjected to the ANSI/ANS 16.1 leaching procedure for 90 days. Cumulative fractional release data suggest that reducing the w/s ratio of a cement formulation plays a somewhat limited role in its ability to immobilize selenium. However, there is a substantial decrease in 75Se leachability of a cement formulation concomitant with an increase in its silica fume and clay content. This effect is especially pronounced in mixes with low water content.