Assessment of a Sodium Nonatitanate and Pharmacosiderite-Type Ion Exchangers for Strontium and Cesium Removal from DOE Waste Simulants

Abstract

Several inorganic ion exchangers were tested for 89Sr and 137Cs removal from simulated DOE aqueous defense wastes (NCAW and 101SY-Cs5) and a Hanford groundwater solution (N-springs). The materials used in this scoping study consisted of the three-dimensional tunnel-structured pharmacosiderites [M3H(AO)4(BO4)3·4−6H2O (M = H, K; A = Ti, Ge; B = Si, Ge)]; the layered sodium nonatitanate, Na4Ti9O20·xH2O; and two commercially available exchangers, AW-500 and clinoptilolite. 89Sr and 137Cs distribution coef ficient (Kd) measurements showed that all of the synthetic exchangers removed at least 97% of the 89Sr from the N-springs groundwater simulant in a single static equilibration. This simulant also contained parts per million levels of Ca2+, Mg2+, K+, and Na+. Similarly, many of the same materials also efficiently removed 137Cs (>98%) from the same solution, except for sodium titanate, which exhibited the lowest Kd of 1210 mL/g for Cs+. These preliminary Kd values provide an indication that these exchangers may act as dual Cs+ and Sr2+ sorbers for groundwater remediation applications. The different phases were also tested as potential exchangers for 137Cs and 89Sr in different nuclear waste simulants. While the materials showed little preference for 137Cs in highly basic solutions containing large concentrations of NaNO3, a potassium titanosilicate and the sodium titanate yielded 89Sr Kd values of 20 180 mL/g (DF = 91) and 235 120 mL/g (DF = 1177), respectively.