Uptake of Sr-85, Cs-134 and Co-57 by antimony silicates doped with Ti4+, Nb5+, Mo6+ and W6+

Antimony silicate ion exchangers were prepared by precipitation using two d ifferent procedures. A crystalline product with a pyrochlore structure (SbS i) was obtained by mixing SbCl5 in HCl with sodium silicate solution (pH(fi nal) < 1) and heating it at 60 degreesC overnight. An amorphous material (K SbSi) formed when KSb(OH)(6) was mixed with tetraethylorthosilicate (TEOS) in acidic conditions and heated overnight at 77 degreesC. In both cases the Sb:Si molar ratio was 1:1 in the starting mixture. The products showed hig h Sr-85 selectivity in acidic conditions, distribution coefficients (K-D) b eing 35 500 mL g(-1) for SbSi and 19 700 mL g(-1) for amorphous KSbSi in 0. 1 M HNO3. They are very selective for Sr-85 over a wide pH range, making th em superior to other strontium selective ion exchangers such as zeolites, s odium titanates and silicotitanates, which function effectively only in neu tral or alkaline conditions. The antimony silicate products had also a high or reasonable selectivity for Co-57, Fe-59 and Ni-63, but the selectivity for Cs-134 was low. An attempt was made to increase the selectivity for Cs- 134 by doping the antimony silicates with Ti4+, Nb5+, Mo6+ or W6+. The best results were obtained by doping SbSi with W, which resulted in a 10-fold i ncrease in caesium selectivity. The original pyrochlore structure was retai ned in the W-doped SbSi.