Preparation of hydrous mixed metal oxides of Sb, Nb, Si, Ti and W with a pyrochlore structure and exchange of radioactive cesium and strontium ions into the materials

Twenty hydrous mixed metal oxides of Sb, Nb, Si, Ti and W have been prepared by both precipitation and hydrothermal reactions and characterized by powder XRD, TGA and elemental analysis. Antimony silicate, niobium silicate, antimony titanate and titanium tungstate based materials crystallized with a cubic pyrochlore structure being analogues of the hydrous antimony pentoxide. The materials were studied for the removal of radioactive cesium and strontium by determining the Cs-137 and Sr-89 distribution coefficients (K-D) in batch experiments in 0.1 M HNO3 and NaNO3. In an attempt to obtain materials with improved ion exchange properties a third element (W6+, Nb5+ or Sb5+) was substituted into the structures of the binary oxides. The capacity of SbSi for Cs+ increased with the addition of W6+, and the separation of Cs-137 from Na+ was improved in TiW compounds by doping with niobium. In general, the antimony silicate based exchangers have good Sr-89 uptake over a broad pH range, while the titanium tungstate compounds are effective in neutral and alkaline solutions. The affinity for Sr-89 at low pH of these materials could be increased by the addition of Sb5+. The antimony silicate pyrochlores have H+-exchange capacities of 2.2-2.9 mmol g(-1), while the titanium tungstates have capacities less than or equal to 0.5 mmol g(-1). (C) 2002 Elsevier Science Inc. All rights reserved.