SORPTION PROPERTIES OF Zr-Ca-Mg AND Ti-Ca-Mg PHOSPHATES IN RELATION TO Sr(II) IONS

The synthesis of Zr-Ca-Mg and Ti-Ca-Mg phosphates of different composition was carried out and their sorption properties to Sr(II) ions were studied. The effect of pH of aqueous solutions, as well as of background electrolytes NaCl, CaCl2, the seawater solution on the sorption-selective properties of phosphate sorbents was studied. The sorption isotherms and kinetic regularities of the Sr(II) ion removal were studied, the mathematical modeling of the experimental data using various models was carried out. It was found that Ti-containing sorbents had the greatest selectivity to Sr(II) ions. The maximum sorption capacity for the Ti-2 sample reached 196.5 mg/g (2.2 mmol/g). Samples of Zr-Ca-Mg and Ti-Ca-Mg phosphates had a high sorption capacity in the 0.1 M NaCl solution and in seawater. The sorption kinetics for all sorbents with a high degree of confidence (R-2 >= 0.99) was described by a pseudo-second-order equation, due to the chemical interaction during the Sr(II) ions sorption. The study of the phase composition of sorption products indicated the ion exchange and chemisorption mechanism of the Sr(II) ions sorption.