Synthesis, Characterization, and Sorption Properties of Amorphous Titanium Phosphate and Silica-Modified Titanium Phosphates

Amorphous titanium hydroxyphosphate with formula Ti(OH)(1.36)(HPO4)(1.32).2.3H(2)O and a new silica-modified titanium hydroxyphosphate with a general formula Ti(OH)(2) HPO4)(2-x) - ySiO(2)center dot nH(2)O are synthesized and characterized using IR, TG, XRD, SEM, solid-state NMR, and BET techniques. It is concluded that SiO2 is evenly distributed within the titanium phosphate (TiP) agglomerates and that neither the separate silica phase nor the titanium silicates are formed during the synthesis of silica-modified titanium hydroxyphosphate. Correlations between the texture, ion-exchange properties of the amorphous titanium hydroxyphosphate, and the amount of SiO2 present within the TiP matrix are established. Sorption properties of silica-modified titanium hydroxyphosphate toward Cs+ and Sr2+ are studied in a series of samples with an increasing amount of silica, at different pH, and in NaCl solutions with a varying ionic strength. It is found that sorption of Cs+ does not depend practically on the amount of SiO2 present, whereas the Sr2+ uptake drastically decreases with an increase of silica amount. The effects of pH and of the electrolyte concentration on the sorption behavior of titanium phosphate are discussed in terms of ionic hydration shell and titanium phosphate structural specificity. The kinetics of sorption processes is also investigated, and the diffusion coefficients for cesium and strontium are obtained.