Teresia Möller

Ion exchange of 85Sr, 134Cs and 57Co in sodium titanosilicate and the effect of crystallinity on selectivity

The uptake of 85Sr, 134Cs and 57Co on a framework sodium titanosilicate of an ideal formula Na2Ti2O3(SiO4) · 2H2O was investigated. Samples of varying crystallinity were synthesized and this effect on cation affinity was studied. The material exhibited high affinity for cesium in slightly acidic to alkaline solutions, but potassium and the presence of sodium at high pH interfered significantly with selective 134Cs uptake. The weakly acidic exchanger took up 85Sr and 57Co efficiently above neutral pH in 0.1 M NaNO3. The crystallinity of the material proved to be an important factor in efficient removal of 85Sr from calcium bearing effluents. The semi-crystalline titanosilicates had a high affinity for 85Sr over Ca2+ at neutral pH. The affinity for cesium in the presence of potassium was improved as well in samples of lower crystallinity.

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

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 (kSr/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.

Separation of lanthanum, hafnium, barium and radiotracers yttrium-88 and barium-133 using crystalline zirconium phosphate and phosphonate compounds as prospective materials for a Ra-223 radioisotope generator.

Crystalline hybrid organic/inorganic ion exchangers based on zirconium phosphate and phosphonate compounds were evaluated for application in radium-223 generator for radiopharmaceutical applications. Various compositions were synthesized and the selectivity of these materials was determined for inactive lanthanum, hafnium and barium, and radiotracers yttrium-88 and barium-133. The hybrid materials show very efficient lanthanum/barium separation; the response for zirconium phosphate was even better. A small-scale column loaded with pelletized zirconium phosphate compound demonstrated excellent retention of (88)Y and release of (133)Ba.