Research On Technology And Mechanism Of Vanadium Separation And Purification From Stone Coal Acid Leach Solution With Variety Of Impurity Ions By A New Anion Exchange Membrane

The sulfuric acid leaching is broadly employed in vanadium extraction from stone coal, which is characterized by high vanadium recovery and wide adaptability for raw ore. However, as the vanadium recovery increases significantly with this strong acid leaching method, many impurities including Fe, Al, Mg, K, Na etc. are leached with vanadium at the same time. And also the residual H+concentration is too high in acid leaching solution. The above vanadium solution is characterized by variety of impurities and their high content, super low pH value and low vanadium concentration for precipitation recovery. So the key steps for vanadium recovery after this strong acid leaching process are separating impurities, recovering acid and concentrating vanadium.The methods for pre-treating acid leaching solution with variety of impurities are discussed. The extraction and ion exchange behaviors of vanadium and various impurities in acid system are investigated contrastively. The extraction and ion exchange of thermodynamics and kinetics are theoretically analyzed. The suitable separation and purification process for vanadium extraction from above acid leaching liquid is determined, which is vanadium acid solution-sulfuric acid separated by membrane-purified by solvent extraction-vanadium precipitation. And a new anion exchange membrane (AEM) was made for high acid recovery and vanadium rejection. The Fourier Transform Infrared Spectroscopy (FTIR) and Nuclear magnetic resonance (NMR) are employed for characterization of its function groups.The acid leaching solution with variety of impurities is obtained by roasting-sulfuric acid leaching process to the stone coal from Hubei area, of which the pH is-1.08. The commercial DF120AEM is used to recover sulfuric acid as a pre-treatment method from above acid solution. The results show that sulfuric acid recovery can reach to84%, and vanadium, iron and aluminum rejection can attain93%,92%and85%with the feed flow rate of0.21×10-3m3/(h·m2), flow rate ratio of water and feed of1.1-1.3. The AEM is proved to be characterized by high recovery of acid and well V rejection for pre-treating the strong acid solution. The rejection of V, Al and Fe ions are found to increase with the increase of feed flow rate and the decrease of the flow rate ratio of water to feed. Both the acid recovery and metal ions (V, Al and Fe) rejections are increased by raising the concentrations of these ions. The pH value of treated solution increases from-1.08to0.8, which meets the requirement of the next separation and concentration process. But the DF120AEM has a serious water osmosis problem after long term use.The comparison study of ion exchange and solvent extraction is conducted after the vanadium acid leaching solution is pre-treated by DF120AEM, where the pH increases to0.8. Ion exchange test results show that ZGA414resin has the optimal adsorption performance of V(V), and the resin has the lower adsorption capacity of V(IV). Fe(III) has the most serious negative influence on V(V) adsorption in the acid leaching solution, which leads to resin poisoning. Other impurity ions such as Al, Mg and K have no obvious effect on V(V) absorption. Thermodynamic research results show that the V(V) absorption on the ZGA414resin is endothermic process, which is in accordance with the Freundlich isothermal adsorption equation. The adsorption thermodynamics parameter ΔH=3.97kJ/mol, ΔS=47.83J/(mol/K), ΔG298.15=-10.29kJ/mol. Kinetics study of V(V) adsorption on ZGA414resin shows that the process is in line with the simulative secondary exchange kinetics of adsorption process. The theory maximum V(V) adsorption content is217.39mg/g at pH value of2.0, and the adsorption rate constant k298.15=0.0011g/(mg-h). At the same time, the adsorption process is mainly controlled by particle diffusion. Extraction test results show that the V(IV) extraction ratio is significantly higher than that of V(V) under the condition of the O/A1:1with15%D2EHPA as extraction agent and5%TBP as the phase modifier. The effect of Fe (II) on the V(IV) extraction is not obvious, but the V(IV) extraction is seriously affected while Fe(III) concentration is higher than5g/L. Al, Mg, Na and K have no obvious negative effect on vanadium extraction. V(IV) thermodynamics study in this system shows that the extraction reaction apparent equilibrium constant K=0.9152, ΔH=9.367kJ/mol, ΔS=0.031J/(mol/K), ΔG298.15=0.22kJ/mol. The extraction mechanism of V(IV) with D2EHPA studies have shown that VOR2(HR)2compound generated when pH value is low (<1.0), and VOR2compound generated under the condition of high pH value (>1.5). Separation factor of V(IV) to Fe(III) and Fe(II) in sulfuric acid medium is1.6and102respectively at pH value of1.5. Sequence of three kinds of ion extractions with D2EHPA is:V(IV)> Fe(III)> Fe(II). So solvent extraction is a more suitable separation and purification technology to separate impurities and concentrate vanadium from acid leaching solution with variety of impurities in this study. The vanadium recovery can reach to99%by a five-stage extraction and a eight-stage stripping process from the real acid leaching solution.The water-osmosis problem is easily found when the commercial DF120AEM is used. For overcoming this defect, the polyphenylene oxide (PPO) is used as a base membrane material. The bromination of PPO is operated with weight ratio of PPO:Br2<1.42first at25℃for3h and then at150℃for8h, and the total bromination degree of aryl and benzyl position of PPO is96%. The hydrophility of membrane can be controlled by changing the bromination degree in aryl and benzyl position of PPO. The homogeneous and nonporous brominated PPO (BPPO) is prepared by using casting film forming method. The base BPPO is cross-linked by ammonia solution and aminated with trimethylamine(TMA) and ethylenediamine(EDA) mixed solution (TMA:EDA=2:1, v/v) for16h at45℃. The novel AEM with well mechanical property is fabricated. Static diffusion dialysis experiment with this new membrane is carried out, the acid recovery and vanadium rejection is good and the water-osmosis problem is solved. FTIR, NMR, SEM and contact angle tests are used for this AEM characterization. It is certified that the film bromination reaction significantly is the key step for the followed amination reaction and the properties of the final film in the whole preparation process. The water-osmosis problem can be solved by properly increasing aryl bromination degree and amination cross-linking degree within a certain degree.