Martyn Pillinger

Sorption characteristics of radionuclides on synthetic birnessite-type layered manganese oxides

The removal of trace caesium (137Cs), trace strontium (89Sr, 90Sr/90Y) and trace cobalt (57Co) from aqueous solution by synthetic sodium and potassium birnessites has been studied by a batch technique. Distribution coefficients were determined as a function of pH in four solutions: water, 0.005xa0M sodium tetraborate, 0.005xa0M sodium citrate and 0.0001xa0M EDTA. Other effects studied were increasing sodium ion, potassium ion and complexing agent concentration. Key synthesis parameters (ageing time, MnO4−/Mn2+ ratio) were tuned in order to maximise trace cobalt sorption efficiencies. The optimised material was tested for the removal of caesium, strontium and cobalt from a nuclear power plant floor drain simulant. A sodium birnessite sample was also screened for the removal of 63Ni, 54Mn, 59Fe, 65Zn and 236Pu radionuclides.

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

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 (pHfinalxa0<xa01) and heating it at 60u2006°C overnight. An amorphous material (KSbSi) formed when KSb(OH)6 was mixed with tetraethylorthosilicate (TEOS) in acidic conditions and heated overnight at 77u2006°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 (KD) being 35u2006500xa0mLxa0g−1 for SbSi and 19u2006700xa0mLxa0g−1 for amorphous KSbSi in 0.1xa0M HNO3. They are very selective for 85Sr over a wide pH nrange, 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.