Regeneration Of Spent Amidoxime Chelating Resin And Its Adsorption Properties For Lead,Copper,Zinc,Cadmium And Gallium

The Amidoxime chelating resin was widely used in the separation and recovery of radioactive metals,heavy metals,rare metals and precious metals.However,with the development of industry,the consumption of commercial amidoxime chelating resins rapidly increases,and then resulting in producing a large amount of waste resin.At present,waste resins are usually deposited,landfilled,and incinerated.But the stockpiling and landfilling occupy a vast land,and incineration would generate CO₂.It does not meet the advocacy of resource recycling and environmental friendliness.Many researches mainly focused on the regeneration and utilization of waste ion exchange resins by carbonization to preparing activated carbon.However,carbonization is carried out at high temperature,which consumes time and energy.Most importantly,the particle size of activated carbon is very small,which make it difficult to separate from liquids,and limit large-scale industrial applications.Moreover,most researchers focused on waste ion exchange resins;For waste amidoxime chelating resins（WAC-resins）,however,there was a lack of systematic research on the recycling.Therefore,this work conducted in-depth research on the regeneration and reutilization of the WAC-resin.Firstly,the basic structural characteristics and failure mechanism of functional group of amidoxime chelating resin were investigated,and then,the adsorption and desorption performance of the WAC-resin for lead（Pb）,copper（Cu）,cadmium（Cd）,zinc（Zn）was investigated.Secondly,pore of WAC-resin was improved by microwave and the adsorption performance of the WAC-resin after microwave treatment（MT-WAC-resin）for Pb（Ⅱ）were studied.Finally,waste resin-based solvent-impregnated resins（CA-12/SIRs）were prepared by using the MT-WAC-resin as a carrier to carry sec-octylphenoxyacetic acid（CA-12）extractant,and its adsorption property for gallium（Ga）were investigated.The main conclusions of the paper are as follows:（1）Although the physicochemical structure of the WAC-resin have been destroyed,the WAC-resin regenerated by hydrochloric acid and ethanol could still absorb Pb（Ⅱ）,Cu（II）,Cd（II）,and Zn（II）metal ions from acidic solution.The micropores and mesopores of the WAC-resin were almost completely blocked,showing a dense structure,and the amidoxime groups contained in the original amidoxime chelating resin had been destructed and oxidized to carboxyl functional groups.The maximum adsorption capacities of the WAC-resin for Pb（Ⅱ）,Cu（II）,Cd（II）,and Zn（II）metal ions reached 114.6 mg/g,93.4 mg/g,20.7mg/g and 24.4 mg/g,respectively.The adsorption mechanism is that the C=O and C-O groups of the residual carboxyl groups in the WAC-resin coordinated with metal ions.（2）Microwave treatment could make the pore structure of the WAC-resin more developed,and the MT-WAC-resin exhibited selectivity adsorption for Pb（II）.The maximum adsorption capacity of the MT-WAC-resin for Pb（II）was up to 80.0 mg/g and the partition coefficient（K_d）of lead（II）was 620 m L/g.The essence of adsorption was the ion exchange reaction between Pb（II）and H of the C-OH bond of the resin.（3）A solvent impregnated resin（CA-12/SIRs）was synthesized by loading CA-12 onto the MT-WAC-resin.CA-12/SIRs adsorbent exhibited excellent adsorption performance and high selectivity for Ga（Ⅲ）from hydrochloric acid simulated solution.The maximum adsorption capacity of CA-12/SIRs for Ga（Ⅲ）reached 28.49 mg/g and K_d exceeded 2500 m L/g.The adsorption mechanism was the cation exchange reaction between Ga（Ⅲ）and hydrogen ion released from the carboxyl group of CA-12.When CA-12/SIRs adsorbent was applied to purify and adsorb gallium（III）from actual hydrochloric acid and sulfuric acid solutions,recovery of gallium（III）could reach more than 99%.This work not only prolonged the service life of WAC-resin,but also provided scientific research basis for the recovery of metal resources by regenerated WAC-resin,and provided a new direction for the recycling of other types of waste resins.