Assessment of a sodium nonatitanate and pharmacosiderite-type ion exchangers for strontium and cesium removal from DOE waste simulants

Several inorganic ion exchangers were tested for Sr-89 and Cs-137 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) . 4-6H(2)O (M = H, K; A = Ti, Ge; B = Si, Ge)]; the layered sodium nonatitanate, Na4Ti9O20. XH2O; and two commercially available exchangers, AW-500 and clinoptilolite. Sr-89 and Cs-137 distribution coefficient (K-d) measurements showed that all of the synthetic exchangers removed at least 97% of the Sr-89 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 Cs-137 (>98%) from the same solution, except for sodium titanate, which exhibited the lowest K-d of 1210 mL/g for Cs+. These preliminary K-d 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 Cs-137 and Sr-89 in different nuclear waste simulants. While the materials showed little preference for Cs-137 in highly basic solutions containing large concentrations of NaMO3, a potassium titanosilicate and the sodium titanate yielded Sr-89 K-d values of 20 180 mL/g (DF = 91) and 235 120 mL/g (DF = 1177), respectively.