Functionalized Mg/Fe layered double hydroxides with high adsorption capacity for rare earth elements from waste water

Abstract

With the surge in demand for rare earth elements in the modern high-tech industry and the emergence of water pollution during the mining and production of rare earth elements, the development of a green and efficient separation technology for rare earth elements is imperative. Layered double hydroxides can be used for the adsorption of rare earth elements, but the adsorption capacity is unsatisfactory. In this study, magnesium–iron layered double hydroxide (TC-MgFe LDH) modified with carboxyl and amino functional groups on its surface was prepared to enhance the adsorption of rare earth elements. TC-MgFe LDH had a very high adsorption capacity of 179.4 mg g⁻¹ for La³⁺. The adsorption process followed pseudo-second-order kinetics and the Freundlich isotherm model, confirming the multi-molecular layer chemical adsorption mechanism. XPS, FT-IR spectroscopy and zeta potential analyses revealed that the mechanism of the adsorption process involved coordination and electrostatic interaction. TC-MgFe LDH exhibited good regeneration performance and maintained more than 95% of the initial capacity after three adsorption–desorption cycles. In addition, TC-MgFe LDH maintained stable adsorption of La³⁺ over a wide pH range and in the coexistence of competitive ions such as Na⁺ and Ca²⁺. TC-MgFe LDH shows high potential for the adsorption and enrichment of rare earth elements, and this study can provide insights for the functionalization of LDHs.