Study On The Application And Mechanism Of Polymer Inclusion Membrane With Green Solvent As Carriers In Separation And Recovery Of Gallium

Gallium is an important rare metal,which is the pillar of"electronic industry"and widely used in high-tech field because of its excellent physical and chemical properties.However,gallium is difficult to be mined alone in nature,so the development of new technologies and methods to recover gallium from fly ash and other secondary resources can not only reduce the shortage of supply,but also reduce the environmental pollution of gallium-containing waste.Polymer inclusion membrane（PIM）is a membrane separation technology developed on the basis of supported liquid membrane.The carriers are combined with other components inside the membrane material through intermolecular forces and polymer chain entanglement,and the whole membrane material is involved in the ion transport with good stability and economy.In this paper,we use polymer inclusion membrane with green solvent ionic liquid and deep eutectic solvent as carriers to separate and recover gallium from fly ash,and investigate the influence of different carrier components and transport conditions on gallium separation and recovery,analyze the transport mechanism of different carriers of PIM,and finally combine electrodialysis（ED）with PIM,aiming to improve the transport performance of gallium and the separation effect with other metals.The main contents and conclusions are as follows:（1）Two structurally similar quaternary phosphonium ionic liquids Cyphos 104 and Cyphos 101 were selected as carriers for the preparation of PIM,and suitable base polymer CTA were screened.The effects of carrier content,feed acidity,feed chloride ion concentration and strip solution concentration on the transport effect of Ga（Ⅲ）were investigated,and the similarities and differences of the transport behavior of the two PIMs were compared.The results showed that there is a threshold value of carrier content on Ga（Ⅲ）transport,indicating that the transport mechanism of gallium is a fixed-site jumping mechanism,and only when the carrier content is sufficient can the transport be promoted to the maximum extent.The transport rate of Ga（Ⅲ）is highest when the carrier content is 60%.The increase of acidity and chloride ion concentration of feed solution helps to produce Ga（Ⅲ）anion complex Ga Cl₄^-and increase the concentration difference between hydrogen ion and chloride ion on both sides of the membrane to increase the mass transfer driving force.The increase of HCl concentration in the strip solution favors the transport of Ga（Ⅲ）by PIM with Cyphos 104 as the carrier,which is determined by the difference of hydrogen ion concentration between PIM/stripping solution,independent of the difference of chloride ion concentration;the decrease of HCl concentration in the strip solution favors the transport of Ga（Ⅲ）by PIM with Cyphos 101 as the carrier,which depends on the difference of chloride ion concentration between PIM/stripping solution,independent of the difference of hydrogen ion concentration.Water becames a good strip solution.The extraction rate of Ga（Ⅲ）by both PIMs under optimal conditions reached about 90%,the stripping rate was higher than 80%,and the permeation coefficient was about 5μm/s.The transport of Ga（Ⅲ）in both PIMs was further determined by thermodynamic calculations to be in accordance with the fixed-site jumping mechanism,and the two PIMs maintained good stability in the cycling experiments,the transport efficiency of the PIM with Cyphos 101as the carrier was better than that of the PIM with Cyphos 104 as the carrier.The two PIMs showed good selectivity in the separation with other interfering metals such as Al（Ⅲ）,Cu（II）,Mg（II）,Zn（II）,and the separation with Fe（Ⅲ）and In（Ⅲ）could be achieved by reducing the acidity of the feed solution,and good separation could be achieved at 2 M acidity.（2）Two new deep eutectic solvents TOPO/Dec A and TOPO/HTTA were synthesized by combining tri-n-octylphosphine oxide（TOPO）with decanoic acid（Dec A）and 2-thiophenecarbonyl trifluoroacetone（HTTA）,and PIMs were prepared by using them as carriers.PIM with deep eutectic solvent to donor molar ratio of 1:1 were found to have the best transport performance and better membrane formation effect and transport rate compared with TOPO alone.The comparison of PIM with different base polymers showed that the highest transport rate was achieved when PVDF-HFP was used as the base polymers,and the permeation coefficients of both PIMs for Ga（Ⅲ）were up to 6.78μm/s and 7.90μm/s.The investigation of the carrier content also revealed the permeation threshold,which confirmed that the transport mechanism was still a fixed site hopping mechanism.The study on the concentration of the stripping solution found that the reduction of the concentration of HCl in the strip solution was beneficial to promote the dissociation rate of Ga（Ⅲ）in the PIM/strip solution side so as to promote the transmission.Water became the two kinds of excellent stripping solution of PIM.It has high selectivity for Ga（Ⅲ）and the associated metals Al（Ⅲ）,Cu（II）,Mg（II）,Zn（II）,and the extraction rate of Ga（Ⅲ）still exceeds 80%after five times of membrane reuse,which is a green and efficient technology for enrichment and recovery of Ga（Ⅲ）.（3）The transport and separation performance of Ga（Ⅲ）was enhanced by using a coupled PIM-ED system composed of electrodialysis technology and PIM.The PIM-ED system could not promote the transport of Ga（Ⅲ）at high HCl concentration but could accelerate the extraction rate of Fe（Ⅲ）and In（Ⅲ）.The extraction rate of Fe（Ⅲ）and In（Ⅲ）can be accelerated by the PIM-ED system.After probing the current density,it was found that the permeability coefficients of Fe（Ⅲ）and In（Ⅲ）could reach 9.62μm/s and 16.86μm/s at a current density of 15 m A/cm²,while Ga（Ⅲ）was almost not transported.The separation factors of Ga（Ⅲ）/Fe（Ⅲ）and Ga（Ⅲ）/In（Ⅲ）increased from52.21 and 11.57 without electric field to 103.57 and 15.43 which improves the separation performance of Ga（Ⅲ）and Fe（Ⅲ）/In（Ⅲ）,and the working voltage is less than 4V,the energy consumption is low with good economy,so it becomes a promising separation and recovery process.The PIM-ED system with TOPO/HTTA as the carrier at low HCl concentration（p H=2）can greatly enhance the transport rate of Ga（Ⅲ）,and its permeability coefficient is 6.73μm/s at a current density of only 5 m A/cm²,and the extraction rate can reach 100%,the extraction rate is much higher than that of the traditional solvent extraction method,which becomes a promising separation and recovery process.