Dissolution And Release Kinetics And Mechanism Of Vanadium From Typical Vanadium Minerals

Vanadium(V)is a potentially toxic element,which is called metal vitamin.It is widely utilized for a variety of industries including mechanical,automobile,electronic,technology,railway,aviation and so on,vanadium redox battery(RVB),and as a catalyst for the manufacyure of suifuric acid and vulcanized rubber,ceramic colorants,developer.In the environment,the pollution of vanadium is more and more serious,In China,Comprehensive Prevention Planning of Heavy Metal Pollution has put it as 14(5+9)one of the key prevention and control of heavy metal.Vanadium is one of the advantages of resources in our country,and over half the world's vanadium is provided by China,which caused more and more the vanadium pollution in mining area.Environmental concerns have been aroused because of its serious pollution from anthropogenic emissions and dissolution release of ores,waste rock and backfililling.The existing research efforts regarding environmental chemistry,distribution,biological effectiveness and determination of V have increased recently.However,despite the growing economic importance of vanadium,kinetic and mechanistic aspects of the dissolution and weathering of vanadium minerals have not yet received much attention.Therefore,the paper is mainly aimed to study dissolution kinetics and mechanism of vanadium oxides(V2O5,VO2 and V2O3)and vanadium mineral(stone coal and vanadium titanium-magnetite),and the main influence factors in water.The results are helpful for deeper understanding of the geochemical cycle of V,and provide certain theoretical support for the vanadium pollution prevention and control.All results listed as follows: 1? Dissolution of the vanadium oxides under different condition showed that:Batch experiments were performed to derive the rate laws for the proton promoted dissolution of the main vanadium(III,IV and V)oxides at pH 3.1-10.0.The release rates of vanadium are closely related to the aqueous pH,and several obvious differences were observed in the release behavior of vanadium from the dissolution of V2O5 and vanadium(III,IV)oxides.In the first 2 h,the release rates of vanadium fromV2O3 are r = 1.14·([H+])0.269 at pH 3.0-6.0 and r = 0.016·([H+])-0.048 at pH 6.0-10.0;the release rates from VO2 are r = 0.362·([H+])0.129 at pH 3.0-6.0 and r = 0.017·([H+])-0.097 at pH 6.0-10.0;and the release rates from V2O5 is r = 0.131·([H+])-0.104 at pH 3.1-10.0.The zero points of charge(PZC)of vanadium(III,IV and V)oxides were estimatedas approximately 2 or less.The release rates of vanadium from three oxides increase with increasing temperature,and the effect of temperature is different at pH 3.8,pH 6.0 and pH 7.7.The activation energies of vanadium(III,IV and V)oxides(33.4-87.5 kJ·mol-1)were determined at pH 3.8,pH 6.0 and pH 7.7,illustrating the release of vanadium from dissolution of vanadium oxides have a surface-controlled reaction mechanism.The release rates of vanadium increase with increasing vanadium oxides dose,albeit not proportionally.This study,as part of a broader study of the release behavior of vanadium,can help to elucidate the pollution problem of vanadium and to clarify the fate of vanadium in the environment.2?Under the action of organic matter,dissolution of stone coal showed that:The effect of low-molecular-weight dissolved organic matters(LMWDOMs)on the release of vanadium under environmental conditions is part of a broader study on the release behavior of vanadium from major vanadium-bearing minerals.Eight typical naturally occurring LMWDOMs with carboxyl,hydroxyl,and amidogen groups were chosen: citric acid,oxalic acid,EDTA,salicylic acid,catechol,glycine,cysteine and glucose.Batch experiments for every LMWDOM were performed in inert buffers at pH values of 4.0,6.0and 8.0 in athermo statted vibrator(25°C).The results showed that the release of vanadium was largely promoted by LMWDOMs with carboxyl functional groups under acidic conditions and catechol under basic conditions.In the presence of citric acid,oxalic acid or EDTA at pH 4.0,the initial release rates of vanadium were approximately 25-39 times greater than the rates in the control experiments;the steady release rates were 164,95 and 49 times the rates in the control experiments,respectively.For catechol,the release rate at pH 8.0 was approximately 20 times the rate at pH 4.0.Amino acids and alcohols had a minimal effect on the release of vanadium.Furthermore,the organic ligand-promoted release mechanism of vanadium was proposed based on the characterization by attenuated total reflection infrared spectroscopy(ATR-FTIR)and electron paramagnetic resonance(EPR).This study helps understand the pollution risk of vanadium in some mine areas and the fate of vanadium in the environment.3?Release kinetics of vanadium from vanadium titano-magnetiteThe release behavior of V is largely affected by the studied conditions,pH,dissolved oxygen,temperature and ions.Release rate equations of V from the dissolution of vanadium titano-magnetite under acidic and basic conditions were established.The rate is proportional to the fractional powers of hydrogen ion and dissolved oxygen activities.The dependence on dissolved oxygen may also be described by the Langmuir adsorption of oxygen on the vanadium titano-magnetite surface,which has the advantage of explaining the observed saturation rate under acidic solutions.Similarly,saturation is predicted to occur in basic solutions at a much higher partial pressure of oxygen.The reaction temperature is another important factor that affects V release.The activation energy was found to be in the range for surface controlled dissolution mechanisms in acidic and basic solutions.The addition of ions was found to promote the release of V.In addition,the concentration of V in the solution was much less than the theoretical solubility of V2O5,which is ascribed to the adsorption and precipitation of coexisting components with dissolved V in the mineral sample.