Selective anchoring of phosphate groups coupled with swift interlayer cation exchange for record-high capacity cobalt adsorption

Abstract

Against the backdrop of rapid development in new energy, cobalt recovery is becoming increasingly crucial. The recovery of cobalt is significantly restricted due to its always coexistence with nickel, making the exploration of high-capacity adsorbents for selectively separating cobalt both challenging and significant. Here, we designed and synthesized magnesium sodium hydrogen phosphate (MgNa₃H(PO₄)₂, MgNaP) to achieve the first-ever recovery of Co(II) from complex waters. The batch experiments demonstrated that MgNaP exhibited record-breaking selectivity performance, with a selective separation coefficient for cobalt over nickel reaching 18.49. Meanwhile, MgNaP showed a record-high adsorption capacity (511.32 mg⋅g^-1) through cation exchange with sodium and cobalt. The outstanding adsorption properties of MgNaP were confirmed through advanced characterization and calculation tools, with these attributes being attributed to the synergistic effect of ion exchange and the complexation of cobalt with phosphate groups. This work provides a novel technique for the deep separation of Ni-Co ion mixed systems.