Applied Fundamental Study On Solvent Extraction Of V And Cr And Control Of Metal Ion Species By Primary Amines

Vanadium and chromium are not only strategic metals in China,but also heavy metal pollutants that should be controlled with priority.However,the elemental chemical properties of vanadium and chromium are similar,and the recovery and separation process have always been a big challenge in the hydrometallurgy and environment fields.In this thesis,a series of studies on the solvent extraction mechanism of vanadium and chromium have been carried out based on previous problems of the extraction,which has explained the behaviors of vanadium and chromium species in the molecular level,and then separated vanadium from solution with the control of metal ions.The extraction studies can not only guide the design of industrial route to meet the demand of high-purity vanadium products,but also reveal the universal mechanism of primary amine and amphoteric heavy metal ions.The main findings of this thesis were concluded as follows:(1)The structure-activity relationships of branched primary amine extractant(N1923 homologue)and amine-propionic acid complexes were studied.The optimal carbon chain number was between 17 and 25,which is consistent with that of actual extractant obtained by mass spectrometry.The stable structure of the complexes was optimized,and the RDG function was calculated to visualize the electrostatic interaction dominated by hydrogen bonds between the N and H regions in the complexes.(2)A controllable recovery strategy of polyoxovanadate acid compounds by solvent extraction from leaching/aqueous solution was proposed.The different states of the vanadium complexes(solid or liquid)were obtained.Subsequently,the compounds were comprehensively characterized and compared,then the hydrogen bonds in molecular structures were described.The solubility parameters were calculated,among which the solid complexes was the biggest,explaining the formation reason between different states.This approach is promising to recover high-value vanadium materials from waste water in one step,then the material application was discussed.(3)The thermodynamics of vanadium was studied and Pitzer-Pitzer and Pitzer-Margules models of vanadium extraction were developed.Then an efficient characterization method of tracking vanadium and chromium species in aqueous solution was developed by high-resolution electrospray ionization time-of-flight mass spectrometry(ESI-TOF-MS).Evolutions of four characteristic vanadium species,such as H₂VO₄^-(0-1%),V₂ species(0-1%),V₄ species(1-20%),and V₁₀species(60-95%),were studied from acidic to neutral conditions.Meanwhile,the typical polymerization state(Cr₂ species)of chromium species were significantly increased with increasing chromium concentration and acid addition in chromium-containing solution.This method can be widely used for the understanding of practical waste water,especially involving V(V),Cr(VI)ions or organic complexes.(4)The evolutions of vanadium and chromium species were semiquantitatively visualized in-situ by the system combined with annular centrifugal contactors(ACCs)and electrospray ionization time-of-flight mass spectrometry(ESI-TOF-MS).The active(V₄ and V₁₀ species)vanadium species in recovery process were discussed.Meanwhile,the vanadium species affected morphology and structure of recycled NH₄VO₃ products.Moreover,the transformation pathway of vanadium and chromium species in extraction was monitored.Consequently,the molecular simulation results of the characteristic vanadium and chromium species explained the differences between the two species on the extraction activity.A reasonable extraction path can be designed to achieve deep separation of vanadium and chromium based on the variation and dominant control of vanadium and chromium species.