Selective recovery and separation of rare earth elements by organophosphorus modified MIL-101(Cr)

Development of state-of-the-art selective adsorbent materials for recovery of rare earth elements (REEs) is essential for their sustainable usage. In this study, a metal-organic framework (MOF), MIL-101(Cr), was synthesized and post-synthetically modified with optimised loading of the organophosphorus compounds tributyl phosphate (TBP), bis(2-ethylhexyl) hydrogen phosphate (D2EHPA, HDEHP) and bis(2,4,4-trimethylpentyl) phosphinic acid (Cyanex (R)-272). The materials were characterized and their adsorption efficiency towards Nd3+, Gd3+ and Er3+ from aqueous solutions was investigated. The MOF derivatives demonstrated an increase in adsorption capacity for Er3+ at optimal pH 5.5 in the order of MIL-101-T50 (37.2 mg g(-1)) < MIL-101-C50 (48.9 mg g(-1)) < MIL-101-H50 (57.5 mg g(-1)). The exceptional selectivity of the materials for Er3+ against transition metal ions was over 90%, and up to 95% in the mixtures with rare earth ions. MIL-101-C50 and MIL-101-H50 demonstrated better chemical stability than MIL-101-T50 over 3 adsorption-desorption cycles. The adsorption mechanism was described by the formation of coordinative complexes between the functional groups of modifiers and Er3+ ions.

Automated summary

The study synthesized a metal-organic framework derivative modified with organophosphorus compounds to enhance adsorption efficiency for rare earth elements in aqueous solutions. The derivatives showed improved adsorption capacity for Er3+ at optimal conditions, with exceptional selectivity and stability demonstrated throughout multiple cycles. The adsorption mechanism was attributed to the formation of coordinative complexes between the modifiers' functional groups and Er3+ ions.