Removal of 85Sr, 134Cs, and 57Co Radionuclides from Acidic and Neutral Waste Solutions by Metal Doped Antimony Silicates

Abstract

Antimony silicates doped with a metal, (M)x,ySb2-xSi2-yO7 (M=W, Ti, Nb), were studied for the removal of the key radionuclides 85Sr, 134Cs, and 57Co from nuclear waste solutions. Emphasis was given to the removal of radionuclides from acidic effluents for which no efficient commercial exchangers are available. Initial screening tests showed that the undoped antimony silicates (Sb:Si molar ratio ∼1:1) are highly selective for 85Sr. Distribution coefficients (KD) of 35,500 mL g−1 were obtained in 0.1-M HNO3. The antimony silicates also have high or reasonable selectivity for 57Co, 59Fe, and 241Am; but the selectivity for 134Cs is low. An attempt to increase the selectivity for 134Cs was conducted by doping the antimony silicate with Ti4+, Nb5+, or W6+. Best results were obtained with a material doped with tungsten, which resulted in an almost ten-fold increase in cesium selectivity in acid. The pyrochlore structure of the materials was also expected to have an effect in creating cesium selectivity. The granular antimony silicate doped with tungsten performed very well in column tests, and high-breakthrough capacities were observed for 85Sr (>17,000 BV with 1% breakthrough) and 134Cs (5,000 BV) in 0.1-M HNO3, and for 57Co (5,200 BV) and 85Sr (11,000 BV) in neutral simulated pond water. In general, the performance of the metal doped antimony silicates was considerably better than that of commercial materials such as a zeolite, a sodium titanate, and a silicotitanate, which function effectively only in neutral or alkaline conditions and were tested in parallel for reference.