Regulating the interlayer spacing of Ca0.55ZrH0.9(PO4)2 for selective removal of Sr2+ from acidic wastewater

Abstract

Effective capture of the radionuclide strontium is essential for the sustainable development of nuclear energy. Zirconium phosphate, with its tunable interlayer spacing and excellent ion exchange properties, holds potential applications in this field. In this work, a calcium zirconium phosphate (Ca_0.55ZrH_0.9(PO₄)₂) with ultra-wide spacing was obtained by means of layer spacing modulation. The saturable adsorption capacity of this material for Sr²⁺ was close to twice that of commercial zirconium phosphate, reaching 226.9 mg g⁻¹. Particularly noteworthy is its saturation adsorption capacity at pH = 1, which is 6.7 times higher than that of commercial ZrP. Leveraging Ca²⁺ involvement in ion exchange reactions, calcium zirconium phosphate exhibits exceptional selectivity for Sr²⁺ capture in simulated acidic competitive ion solutions. Moreover, it demonstrates outstanding acid resistance and radiation tolerance. Through a comprehensive approach involving characterization techniques, experimental analyses, and density functional theory calculations, we elucidated its potential adsorption mechanisms at the molecular level. Crucially, the material synthesis and experimental processes are free from harmful ion byproducts, rendering it amenable to large-scale production. This advancement provides a promising avenue for the efficient capture of Sr²⁺ in practical wastewater treatment scenarios.