Abstract

Antimony silicate ion exchangers were prepared by precipitation using two different procedures. A crystalline product with a pyrochlore structure (SbSi) was obtained by mixing SbCl₅ in HCl with sodium silicate solution (pH_final < 1) and heating it at 60 °C overnight. An amorphous material (KSbSi) formed when KSb(OH)₆ was mixed with tetraethylorthosilicate (TEOS) in acidic conditions and heated overnight at 77 °C. In both cases the Sb∶Si molar ratio was 1∶1 in the starting mixture. The products showed high ⁸⁵Sr selectivity in acidic conditions, distribution coefficients (K_D) being 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 ⁸⁵Sr over a wide pH range, making them superior to other strontium selective ion exchangers such as zeolites, sodium titanates and silicotitanates, which function effectively only in neutral or alkaline conditions. The antimony silicate products had also a high or reasonable selectivity for ⁵⁷Co, ⁵⁹Fe and ⁶³Ni, but the selectivity for ¹³⁴Cs was low. An attempt was made to increase the selectivity for ¹³⁴Cs 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 increase in caesium selectivity. The original pyrochlore structure was retained in the W-doped SbSi.