Mineral adsorbents for highly efficient Co(II) and Cu(II) remediation

Hydroxyapatite (HAP), magnetite, and layered double hydroxides (LDHs) are promising inorganic adsorbents for heavy-metal removal owing to their ion-exchange capacity, surface reactivity, and affinity for divalent metals. Here, lab-synthesized HAP, magnetite, and Mg-Al-Cl and Ca-Al-Cl LDHs, plus commercial HAP and magnetite, were evaluated for Co(II) and Cu(II) uptake in batch experiments, with XRD and XPS used to probe structure and adsorption mechanisms. Synthesized HAP removed 98.10 ± 0.27% Co(II) and 99.35 ± 0.20% Cu(II); commercial HAP performed comparably for Cu(II). Low-surface-area commercial magnetite was strongly dosage-dependent, reaching near-complete removal only at 1 g. In a second set, Ca-Al-Cl LDH gave the highest Co(II) removal (99.756 ± 0.076%) and synthesized HAP the highest Cu(II) removal (99.995 ± 0.004%). XRD confirmed apatite-type phosphate and iron oxide/oxyhydroxide phases. Uptake is attributed to multiple mechanisms, including diadochy. These materials show strong potential for remediating dilute Co(II)/Cu(II)-bearing waters.