| Extraction of vanadium from vanadium-bearing shale has become one of the most important method to obtain vanadium-containing products.In order to improve the total recovery rate of vanadium,the sulfuric acid leaching process is commonly used in industry with high acid,high temperature and the addition of dipping agent,resulting in low selectivity of the leaching process.The dissolution of vanadium in mica is accompanied by the dissolution of other impurity elements in mica and gangue mineral elements,which brings great difficulty to the subsequent purification and enrichment process.In this study.a vanadium extraction process is proposed to improve the process flow and extraction efficiency.At the same time,the mass transfer mechanism of vanadium in the liquid film and the mechanism of synergistic extraction is analyzed in depth.The main research contents and conclusions are as follows:(1)Solution chemistry study of vanadium shale vanadate acid leaching solutionThe distribution of tetravalent vanadium ions,pentavalent vanadium ions,sulfates,fluoride ions,phosphorus oxyacid ions,aluminum ions,iron ions,potassium ions,sodium ions and magnesium ions in shale acid leaching solution was determined.Quantitative calculations were carried out for the different forms of specific ions at different pH values,and guidance was provided for the selection of subsequent purification and enrichment mechanisms based on the difference in the properties of impurity ions and vanadium ions.(2)D2EHPA emulsion liquid membrane extraction shale vanadium leaching process and mass transfer mechanismD2EHPA is superior to PC88A,Cyanex272 and N235 as the carrier of emulsion liquid membrane system.The effects of emulsification speed,emulsification time,D2EHPA concentration,span80 concentration,paraffin concentration,stripping agent sulfuric acid concentration,phase ratio(O/A),temperature,electric demulsification on liquid film stability and extraction efficiency were investigated.The migration of vanadium during the extraction of liquid membrane and the separation mechanism of vanadium and impurity ions were investigated.The separation process of the actual shale vanadium leaching solution was designed based on the influence of impurity ions on the D2EHPA carrier emulsion liquid membrane.The rate reached 97.2%.At this time,the extraction rates of impurity ions were Fe 8.5%,Al 11.1%,Mg 2.8%,K1.5%,and Na 1.9%.The kinetic model was established to describe the migration process of vanadium and related kinetics,and the parameters were calculated.(3)N235 supported liquid membrane extraction shale vanadium leaching process and mass transfer mechanismN235 is superior to D2EHPA,PC88A and Cyanex272 as a carrier in supporting liquid membrane.The optimal preparation and extraction conditions(N235concentration,solution pH value,stripping agent type and concentration,diluent type)of the supported liquid membrane were investigated.Under optimal conditions,the extraction rate of vanadium was 92.0%;The mechanism and separation process of the impurity ions of N235 supported liquid membrane system were studied,indicating that P,Fe and Al are mainly affecting impurity elements,because these three ions have an anion form which can be extracted by N235 The increase of concentration in a certain range has a competitive effect on the extraction of vanadium,which leads to the decrease of vanadium extraction rate,while the increase of Mg,K and Na concentration does not affect the extraction of vanadium;a first-order mass transfer kinetic model is established.The calculated results of the model are consistent with the experimental results,and the relevant mass transfer kinetic parameters are obtained.(4)Cyanex272-N235 mixed carrier supported liquid membrane extraction shale vanadium leaching process and the preparation of high purity of vanadium products.The Cyanex272-N235 mixed carrier is superior to the other single extractants used in this study as a supporting liquid membrane carrier.The optimum preparation and extraction conditions(extractant ratio,solution pH value,stripping agent type and concentration)of the supported liquid membrane were investigated.Under the optimal conditions,the extraction rate of vanadium reached 97.2%at 13h.;And the mechanism and separation process of the impurity ions of the mixed carrier supported liquid membrane are studied,P,Fe and Al mainly affect the impurity elements,and the concentration increase in a certain range has a competitive effect on the extraction of vanadium.The extraction rate of vanadium is reduced,and the increase of Mg,K and Na concentration does not affect the extraction of vanadium;the cycle performance of the extraction system is investigated,and the obtained vanadium-rich liquid is tested by weak alkaline ammonium salt.A V2O5 product with a purity of99.31%was obtained.(5)Mechanism of enhanced vanadium extraction by mixed carrier liquid membrane based on DFT theoryThe process of protonation of N235 is essentially the process of bonding the H protons with the N atoms HOMO lone pair electrons.Cyanex272 easily forms dimers and trimers spontaneously.During the hydrogen bond formation of dimers,the HOMO electrons of P=O bond O shift to the LUMO of OH bond H,which increases the electron energy around OH bond H.The formation of the polymer weakens the high-energy electron orbit near the P=O bond O atom,reducing the ability of the site to undergo electron transfer.The essence of vanadium extraction in the mixed system of N235 and Cyanex272 is that the OH of protonated N235 and the OH of Cyanex272monomer compete for the hydrogen bond formation of P=O bond.The energy analysis of this process shows that the complexation reaction can form spontaneously.The formation of the P=O···H-N bond is accompanied by the dissociation of the dimer and the release of free Cyanex272.At the same time,the polarity of the OH bond of Cyanex272 in the complex is enhanced,and H~+is more ionizable,which makes it easier to exchange reaction with VO2~+.The mixed extraction system has the ability to extract both anion and cationic vanadium ions,and also improves the extraction ability of vanadium ions in the acid leaching solution. |
PDF Full Text Request