Titanium antimonates in various Ti∶Sb ratios: ion exchange properties for radionuclide ions

Abstract

Ion exchange properties of titanium antimonates have been investigated with the main objective being selective removal of radionuclides from acidic nuclear waste solutions and in the presence of strongly interfering calcium. Five samples with Ti∶Sb ratios between 0.21–4.9 were synthesized by hydrolysis in distilled water under reflux. Products of either a mopungite, rutile or pyrochlore phase crystallized depending on the Ti∶Sb ratio, the order of metal prehydrolysis and the synthesis temperature (20 °C, reflux at ∼100 °C or hydrothermal treatment at 200 °C). The acidity of the exchanger and ⁸⁵Sr selectivity in acid increases with increasing antimony content, while Sr²⁺/Na⁺ exchange is favored as the acidity decreases. The tolerance for Ca²⁺ in strontium uptake has a reverse trend and the ⁸⁵Sr/Ca²⁺ selectivity coefficients (k_Sr/Ca) increase with the Ti∶Sb ratio from 1.2 to 130 in 0.01 M Ca(NO₃)₂. In addition to the Ti∶Sb ratio, the crystal phase directs the radionuclide affinity through the ion sieve effect. The pyrochlore structure favors strontium while the rutile phase seems to prefer caesium in acid.