Study On The Process And Mechanism Of Hydrothermal Impurity Removal And Selective Enrichment Vanadium By Chelate Resin From Black Shale Acid Leaching Solution

Vanadium is a rare metal with important application value.Black shale is an important vanadium ore resource.Sulfuric acid leaching process has been widely used for the vanadium extraction industry of black shale due to its high efficiency and low pollution.The acid leaching solution of black shale is often characterized by high impurity ions concentration and low vanadium concentration.The Fe and Al are easily co-extracted into the organic phase in the extraction process,resulting in the decrease of vanadium extraction efficiency and emulsification of the organic phase.In the ion-exchange resin process,Fe and Al will be absorbed into the resin and form flocculent sediment to block the ion-exchange column,causing resin poisoning.In addition,Fe and Al can attach or co-precipitate into vanadium products in the form of Fe VO₄,NH₄Al（SO₄）₂·12H₂O,NH₄Fe₃（SO₄）₂（OH）₆,etc.,reducing the purity of vanadium pentoxide.In this paper,the sulfuric acid leaching solution of black shale is taken as the research object to study the removal of impurities Fe and Al from the acid leaching solution of vanadium shale,as well as the process and related mechanism of purification and enrichment of vanadium by ion exchange process.Finally,99.5-P high-purity vanadium pentoxide meeting the industry standard is directly produced by precipitation of vanadium with ammonium salt.The main research contents are as follows:（1）Study on the process of removing iron by yavapaiite（KFe（SO₄）₂）formationBy adjusting the molar ratio of Fe³⁺and K⁺in the solution and controlling the reaction temperature,Fe³⁺can be effectively removed under the condition of high acidity.When the reaction temperature is 190℃,the reaction time is 5 h,the molar ratio of K⁺to Fe³⁺is 2.0,and the concentration of sulfuric acid is 10 vol.%（that is,the initial pH value of the solution is-0.15）,the precipitation efficiency of iron can reach 80.96%,and the loss rate of vanadium is 1.0%.Under hydrothermal environment,Fe³⁺,K⁺and SO₄^2-in the solution are associated with each other to form potassium ferric sulfate（K₃Fe（SO₄）₃）,and potassium ferric sulfate can be transformed into jarosite and yavapaiite.When the concentration of sulfuric acid is lower than 10 vol.%,jarosite and yavapaiite can be formed synchronously.With the extension of reaction time and the decrease of pH value,jarosite can be decomposed into yavapaiite.Finally,Fe³⁺can be precipitated in the form of yavapaiite.（2）Study on the process of removing aluminum by alunite（MAl₃（SO₄）₂·（OH）₆）formationUnder the same initial pH value of the solution,the precipitation efficiency of k-alunite（KAl₃（SO₄）₂·（OH）₆）is higher than that of natroalunite（Na Al₃（SO₄）₂·（OH）₆）.When the initial pH value of the solution is 0.4,the molar ratio of potassium（or sodium）to aluminum is 1:1,the reaction temperature is 220℃,and the reaction time is 5 h,the aluminum precipitation efficiency with potassium sulfate or sodium sulfate added is83.75%and 69.83%,respectively.To control the vanadium loss efficiency,the initial pH value of the solution should not exceed 0.4.During the hydrothermal precipitation reaction of alunite,water ionization generates a large amount of H⁺and OH^-,OH^-reacts with K⁺（Na⁺）,Al³⁺,SO₄^2-and then enters the alunite lattice,resulting in the increase of H⁺concentration in the solution and the decrease of pH value.As the reaction proceeds,the pH value of the solution decreases and the reaction is inhibited.Compared with the formation of natroalunite,alunite is more suitable for removal of impurity aluminum in acid leaching solution of black shale.（3）Ion exchange process by D418 aminophosphate chelating resinUnder the static adsorption conditions of pH 1.8,temperature 25℃and liquid-solid ratio 1:10 g/m L,the adsorption efficiency of V on the D418 chelate resin is 90.17%.When the concentration of Na OH is 3mol/L,the desorption efficiency of vanadium is99.7%.After V selective adsorption on-PO（OH）₂,Fe and Al adsorption on-NH,and selective desorption by Na OH,the concentration ratios of V:Fe and V:Al increased from 1.84 to 59.53,and 0.24 to 36.75 respectively,realizing the selective separation and enrichment of V.In the ion exchange adsorption process,-PO（OH）₂group reacts with H₂V₁₀O₂₈^4-by anion exchange,and H₂V₁₀O₂₈^4-coordinates with the P atom.Then,the exchange between the OH^-and H₂V₁₀O₂₈^4-is occurred during the desorption process by Na OH solution.However,Fe and Al ions can not be desorbed by OH^-because they coordinate with-NH mainly in the form of Fe SO₄⁺and Al SO₄⁺through the lone electron pair of nitrogen atom.After vanadium precipitation process,99.5-P V2O5 product meeting the industry standard can be obtained.（4）Exhausted resin regenetaedWhen the oxalic acid concentration is 0.8mol/L and the reaction time is 30min,the exhausted D418 resin can be effectively regenerated to obtain Ox@D418 Resin.Fe and Al eluted from the resin in the form of Fe（C₂O₄）₂^-,Fe（C₂O₄）₃^3-and Al（C₂O₄）₂^-,and the pore structure of the resin was restored.The-NH in the resin provides electrons to react with the-OH to form an amide group.The amide group in the Ox@D418 resin can react with vanadium ion,provding more reaction sites for vanadium ions.Compared with the original 418 chelate resin,the vanadium adsorption efficiency on Ox@D418 resin is increased by about 8%.In the static adsorption-desorption-regeneration adsorption recycling experiment,the vanadium adsorption or desorption efficiency on Ox@D418resin did not decrease,and remained at about 95%and 80%respectively.