Sr2+ Sorption and leach rate studies on synthetic calcium silicate hydroxy hydrate

Abstract

Abstract Synthetic calcium silicate hydroxy hydrate, which is identical to unsubstituted and substituted 1.1-nm tobermorite mineral, has the capacity to pickup selectivity Sr 2+ cation from mixed cationic solutions in the presence of 1,000 times concentrations of Na + , K + , Ca 2+ , Mg 2+ , and Ba 2+ . The selective uptake of Sr 2+ from mixed cationic solutions and simulated intermediate level waste (ILW) solutions has been quantified as distribution coefficient (K d ) and decontamination factors (Df). The sorption studies have been performed by analysis of Sr 2+ in solution both by atomic absorption spectrophotometry and radiometric measurements. The proportional depletion of β activity from strontium solutions labeled with isotope Sr 90 has been utilized to study the concentration and mass dependence of the Sr 2+ uptake by the exchanger. Kielland coefficient at 25°C have been determined from the isotherms plotted for the Sr 2+ ⇌ Ca 2+ system. Leach rate studies on the blocks made from ordinary portland cement (OPC) + tobermorite admixtures show that the release rate of Sr 2+ from cement matrix is drastically lowered when the additive is increased. By using 40 wt% Al-substituted tobermorite as an additive to OPC, we found that it was possible to fix about 77% of Sr in cement matrix against 17% fixation in the OPC.