The Effect of Sorbent Composition on Sorption Properties of Materials Based on Ti-Ca-Mg Phosphates

Individual titanium and calcium-magnesium phosphates are widely known as effective sorbents. The sorption processes on these phosphates are based on different mechanisms. The sorption efficiency towards different cations depends on the phase composition of the sorbent. Composite materials with various ratio Ti:(Ca+Mg) have been synthesized. The sorption properties of samples obtained towards Cs⁺, Sr²⁺, Co²⁺, Cd²⁺, Zn²⁺, Cu²⁺, and Pb²⁺ have been studied to establish the effect of sorbent composition on metal removal. The adsorption isotherms have been analyzed using the Langmuir, Freundlich, and Redlich-Peterson models. The composition of sorbents has no effect on the level of removal of readily hydrolyzable Pb²⁺ and Cu²⁺ cations. Removal of lead occurs preferentially via the precipitation of metal phosphates and hydroxides. Copper precipitates as hydroxide in case of a high share of Ca-Mg phosphates in the composite sorbent. The removal of cesium proceeds according to the ion exchange mechanism only. For Cd²⁺, Co²⁺, Sr²⁺, and Zn²⁺ cations, the sorption efficiency on the composite materials synthesized is found to increase with the increase in titanium phosphate's share in the sample. All composite sorbents synthesized demonstrated a considerable increase in the level of purification of solutions studied compared with individual Ti and Ca-Mg phosphates due to the synergism of the components.