Selective adsorption of rare earth ions from aqueous solution on metal-organic framework HKUST-1

Recovery of rare earth ions from wastewater holds an important strategy for the use of the precious resources. In this study, we found that a metal-organic framework (MOF), HKUST-1, exhibited a high affinity and selectivity towards adsorptive recovery of rare earth ions (Ce3 + and La3 +) in aqueous solutions. The adsorbent showed a remarkable adsorption capacity of 234 mg/g and 203 mg/g for Ce3 + and La3+ at pH = 6, respectively. More importantly, its adsorption selectivity of the rare earth ions was about 87% against other metal ions. The adsorption isotherm, kinetics, and mechanism in the process were also investigated. The adsorption process can be better fit by the Freundlich model in isotherm and the pseudo-second-order model in kinetics. A plausible mechanism for the adsorption of metal ions on the HKUST-1 was proposed by considering ion exchange and the covalent bonding between the adsorbent and metal ions. The selectivity can be attributed to the different bonding abilities to metal ions.