The Study On Rare Earth Elements Adsorption Properties By Metal-Organic Frameworks

In this paper,two kinds of metal-organic framework materials?MIL-101/UIO-66-NH₂?with good water stability were selected as matrix materials.More adsorption sites were introduced into the materials by modification of MOFs with acrylic acid or composited MOFs with graphene oxide.The adsorption behaviors of materials toward trace rare earth elements were explored.The experimental results were as follows:1.A series of metal-organic framework materials?named as y-AA-x@MIL-101s?were prepared by modification followed by graft polymerization with the MIL-101 as a matrix material and used for adsorption rare earth elements.Due to the polymerization of acrylic acid,more carboxylic acid groups were introduced on the surface of the material to improve the adsorption properties of the material.Through a series of spectrogram analysis such as XRD,HPLC,FT-IR and XPS,we found that the material had better stability within the range of acidity studied,and adsorption mechanism was chelation and ion exchange between carboxylic acid group of AA and rare earth elements.The adsorption curves of adsorbents on Sc?III?,Nd?III?,Gd?III?and Er?III?were accurately described by Langmuir model,and the maximum adsorption capacities was 90.21,104.59,58.29,and 74.94 mg·g^-1,respectively.The adsorption kinetics data was accurately described by pseudo-second-order models.Importantly,the adsorbent was better for selective recovery of Sc?III?not only from the16 REE mixed system but also the Cu?II?,Zn?II?,Mn?II?,Co?II?and Al?III?coexistence solution.Except for Sc?III?,the material displayed high affinity for Nd?III?in the light rare-earth mixture and for Gd?III?in the middle rare-earth mixture.After 5 cycles,the adsorption performance of material for Sc?III?can still reach more than 80%,which proved that the material had good practical application value.2.Graphene oxide has been used as a good adsorbent because of its large amount of oxygen-containing functional groups on its surface,chemical stability and easy to modify.In this work,a series of graphene oxide modified with carboxyl@metal-organic framework composites?named as GO-COOH-x@UIO-66-NH₂?were prepared by using UIO-66-NH₂ as matrix material and used for adsorption of rare earth elements.The GO material modified with chloroacetic acid was more easily complexed with UIO-66-NH₂ due to its more carboxylic acid groups on the surface.And duo to the modified with chloroacetic acid,more adsorption sites were introduced on the surface of GO to improve the adsorption properties for rare earth elements.From the adsorption experiments,we found that the composite material had a much higher adsorption capacity for rare earth elements than GO-COOH or UIO-66-NH₂.The adsorption curves of adsorbents on Sc?III?,Nd?III?,Eu?III?and Er?III?were accurately described by Langmuir model,and the maximum adsorption capacities was 181.32,146.24,130.96,135.15 mg·g^-1,respectively.The kinetics data was accurately described by pseudo-second-order.The adsorbent can selectively recover of Sc?III?from the 16 REE mixed system.Except for Sc?III?,the material displayed high affinity for Nd?III?in the light rare earth mixture,for Eu?III?in the middle rare earth mixture and for Er?III?in heavy rare earth mixture.The material can selectively recover Nd?III?in different concentrations of Cu?II?,Zn?II?,Mn?II?,Co?II?and Al?III?coexisting solutions.The FT-IR and XPS analysis showed that the adsorption mechanism was chelation and ion exchange between amino group and carboxylic acid group of the composite material and the rare earth element.After five cycles,the recovery rate of material for Nd?III?could still reach more than 80%,indicating materials had a good regeneration ability.In this paper,the new method for separation and recovery of rare earth elements was proposed and it was of great practical significance to realize the full utilization of rare earth resources.