Study On Separation And Enrichment Of Vanadium With Synergistic Extraction-Ammonium Salt Precipitation System

In order to meet the growing demand for vanadium,a number of methods have been used to extract vanadium from vanadium-bearing shales.Sulfuric acid leaching is widely used in the vanadium extraction from vanadium-bearing shales because of its high vanadium recovery rate,short process and low energy consumption.However,many impurities such as iron,magnesium,aluminum are dissolved in the leaching solution together with vanadium,which makes the separation and enrichment of vanadium become a necessary step.Solvent extraction is the most commonly used separation and enrichment method for vanadium extraction from vanadium-bearing shale,but the traditional single extractant extraction system has disadvantages such as low extraction efficiency,long extraction series and poor separation efficiency.Therefore synergistic extraction system was adopted,and N235-P507 was selected as the best synergistic extraction system by studying the synergistic effect of different kinds of extractants with N235 on vanadium.According to the characteristics of vanadium acid leaching solution,the process parameters of vanadium extraction and precipitation were adjusted and the high-efficient and selective separation and enrichment of vanadium was achieved by the N235-P507 synergistic extraction system.Slope method and FT-IR analysis were used to study the structure of the extracted complex and elucidate the mechanism of the synergistic extraction.The main conclusions of the study are as follows:?1?P507 and N235 showed obvious synergistic effect,and the maximum synergistic effect coefficient of 1.42 was achieved with the extractant ratio of 8:12?N235:P507?.Under the optimal conditions of extraction:8%N235+12%P507 as extractant,sulfonated kerosene as diluent,the extraction solution pH of 1.70,the extraction time of 10 minutes,the temperature of 25°C and?O/A?=1:5,N235-P507synergistic extraction system had a good extraction rate of vanadium.After three stages countercurrent extraction,the total vanadium extraction rate was more than98%.And the vanadium-loaded organic phase was experienced two stages countercurrent stripping under the optimal conditions:NaOH concentration of 1mol/L,O/A=2:1 and stripping time of 6 min,the total stripping ratio of vanadium was over 99%and most of the impurities were effectively separated.?2?According to the slope analysis,the synergistic extraction reaction conforms to the cation exchange mechanism.In the extraction,1 mol H⁺was released when 1mol VO₂⁺was extracted.The molar ratio of vanadium:P507?H₂A₂?and N235?R₃NH⁺?was 1:2 and 1:1,respectively.Combined with FT-IR spectroscopy,hydrogen bond?NH···O=P?was formed between N235 and P507 molecules,resulting in the breakdown of P507 dimer and the increased activity of H⁺in P-OH.And?VO₂A·R₃NH⁺?₂SO₄^2-was formed by the cation exchange mechanism.?3?The stripping solution of vanadium was alkaline precipitated by ammonium salt under the conditions of pH=8.0,reaction temperature of 40°C,vanadium precipitation time of 40 min,n?NH₄Cl?=4 n?V?,and the vanadium precipitation rate was 99.52%.However,the vanadium product purity was not high,only 92.37%.Na will affect the purity of vanadium product in the alkaline ammonium salt precipitation process.2%NH₄Cl solution was used as a detergent to wash the product.After washing,the product was dried and calcined.The final product of V₂O₅ can reach the98 standard of vanadium pentoxide black metallurgical.The stripping solution of vanadium was acidic precipitated with ammonium salt under the conditions of pH=2.0,reaction temperature of 90°C,precipitation time of 60 min and n?NH₄Cl?=4 n?V?.The precipitation rate was only 65.38%.Further research shows the presence of Na had no significant effect on the vanadium precipitation rate and the purity of V₂O₅,while the presence of P had a great influence on the acid ammonium salt precipitation process which made the crystal of ammonium vanadate difficult to grow and led to the low vanadium precipitation rate.Meanwhile,the vanadium precipitated product had poor crystallinity,loose structure and large specific surface area,which made it easy to adsorb impurities in the vanadium precipitated product,leading to the decrease of the purity of the final V₂O₅ product.The P in the stripping solution was desalted by MgSO₄.Then the stripping solution of vanadium was acidic precipitated with ammonium salt.And the product was dried and calcined.The final product of V₂O₅ can reach the 99 standard of vanadium pentoxide black metallurgical.