Process And Mechanism Of Extraction And Separation Of Molybdenum And Vanadium From Acidic Media By Polymer Inclusion Membrane Electrodialysis

Molybdenum(Mo)and vanadium(V)have excellent physicochemical properties and play an important role in many high-end technologies.The contradiction between the growing demand for molybdenum and vanadium and their scarce resources is becoming increasingly acute at this stage.There is therefore an urgent need to recover valuable metals from waste materials.As a hazardous solid waste and a valuable secondary resource,spent catalysts contain high concentrations of Mo(VI)and V(V).However,the challenge of separating molybdenum(Mo)and vanadium(V),which have similar properties,poses great difficulties for the green recycling of spent hazardous catalysts and it is imperative to explore a sustainable and efficient technology for the recovery of Mo(VI)and V(V).This paper systematically investigates the performance and regulatory mechanism of polymer-coated membrane electrodialysis(PIMED)for the separation of molybdenum and vanadium from acidic solutions to meet the urgent need for efficient recovery of molybdenum and vanadium from secondary resources.The relationship between the membrane structure and the performance of the transported separated metals is clarified,and the influence of the process parameters on the transported separated metals and the transport mechanism in PIMED is discussed.Firstly,polymer inclusion membrane with methyltrioctylammonium chloride(Aliquat 336)as a carrier and PVDF-HFP,PVC and CTA as different substrates were prepared,and the structural variability between different PIMs was summarized by SEM,XRD,AFM,FTIR and other chemical characterization means.The results show that all PIMs have a dense,intact surface structure,while the infiltration of all PIMs exhibits hydrophilicity,both of which provide structural support for the use of PIMs in transport experiments.PVDF-HFP based PIMs exhibit a higher degree of crystallinity and surface roughness,which is more favourable for metal ion transport.The PIM was modified with PVDF-HFP as a base polymer and Aliquat 336 + tributyl phosphate(TBP),Aliquat336 + tri-n-octyl phosphine oxide(TOPO)and Aliquat 336 + di(ethylhexyl)phosphate(D2EHPA)as a synergistic carrier.The addition of the synergistic carriers significantly increased the hydrophilicity and the crystallinity of the PVDF-HFP based PIM.The three modified synergistic carrier PIMs were found to have a rougher surface structure than the single carrier PIMs by AFM,all of which provided advantages for the synergistic carrier PIMs during the metal separation process.Secondly,to address the challenge of separating molybdenum and vanadium,which have similar properties in acidic media,transport separation experiments were carried out using PIM prepared on Aliquat 336 as a carrier.The combination of selective extraction and stripping in the PIMED separation of Mo(VI)and V(V)overcame the complex combination of co-extraction and stepwise stripping in conventional solvent extraction.The influence of each parameter is systematically studied,as well as the selective transport mechanism and activation parameters.The results show that PIM has a stronger affinity for Mo(VI)than V(V)and that the strong interaction between Mo(VI)and the carrier results in low permeability intra-membrane migration.Transport was facilitated by disrupting interactions through a combination of regulated and controlled electrical density and stripping solution concentration.The optimised stripping efficiencies for Mo(VI)and V(V)were 93.1% and 1.8% respectively,with a separation coefficient of 333.4.This part of the work shows that the separation of similar metal ions can be improved through the modulation of affinity and interaction between metal ions and PIM and provides a new technological approach to the separation of similar recovered similar metal ions from secondary resources.Finally,to further enhance the affinity difference of PIM for Mo(VI)and V(V),a modified PIM with Aliquat 336 and D2 EHPA as synergistic carriers and PVDF-HFP as base polymer was prepared.The diffusion separation experiments proved that the synergistic carrier PIM showed a significant synergistic effect on the separation process of Mo(VI)and V(V)compared to the Aliquat 336 carrier PIM alone.The synergistic separation of Mo(VI)and V(V)by the synergistic carrier PIM in the ED system is further enhanced by the weakening of the interaction between molybdenum and the carrier in the membrane and the inhibition of vanadium extraction by the efficient transport of molybdenum.This affinity difference was also enhanced by fine-tuning the PIMED process parameters.Under optimal experimental conditions,the extraction of molybdenum by the synergistic carrier PIM reached 95.2%,while the extraction of vanadium was only 1.6%,with a separation factor of 630.2.After 100 hours of concentration of molybdenum to 3.6 times the initial concentration in a volumetric concentration experiment,the purity of Mo(VI)and V(V)reached 96.7% and 94.6%respectively.Further enhancing the difference in affinity for similar metal ions by altering the properties of the PIM,itself provides the basis for studying modified PIM in metal separation.