Selective Co2+ recovery using MgNa3H(PO4)2 adsorbent from water

60Co recovered from radioactive wastewater can potentially be used in sterilization and medical therapy; however, a reliable Co2+ adsorbent with high selectivity and capacity has yet to be developed. Here, we designed a glaserite-type MgNa3H(PO4)2 (MSHP) where Mg2+ serves as a structural cation capable of replacing Co2+ alongside an interlayered Na+. The similarity in the ionic radii of Lewis softer Co2+ and Lewis hardest Mg2+ made the exchange of structural Mg2+ with Co2+ more favorable than that with Lewis harder Sr2+, which has a larger ionic radius. MSHP exhibited a remarkable Co2+ adsorption capacity of 443 mg/g. Notably, the separation factor of MSHP for Co2+ against Sr2+ was 480, which was 65-fold higher than that reported in a previous study. The findings indicate that introducing comparably sized ions, such as Mg2+, to selectively integrate Co2+ into the adsorbent backbone upon their release represents a novel approach for designing high-selectivity adsorbents.