Study On Extraction And Separation Technology And Mechanism Of Vanadium And Molybdenum From Fluoric Acid Leaching Solution Of Stone Coal

Stone coal contains vanadium,molybdenum and other valuable metal elements.At present,the fluorine-containing leaching solution produced by the total wet leaching technology contains a large amount of vanadium and a small amount of molybdenum,from which the comprehensive extraction and utilization of vanadium and molybdenum has high economic value.In the acid leaching solution of stone coal produced by traditional process,P204 is the most common extractant for vanadium extraction,but its selectivity is poor.A large number of iron,aluminum and other impurities in the solution enter the organic phase at the same time,which is not conducive to the purification of vanadium.In order to selectively separate and recover vanadium and molybdenum from fluoric acid leaching solution of stone coal,the technological route of N235 co-extraction and step-by-step stripping was put forward,and the solution chemistry,co-extraction-stripping process and co-extraction mechanism were studied in this paper.to provide theoretical basis and process for N235 to comprehensively extract vanadium and molybdenum from fluoric acid leaching solution of stone coal.The changes of the existing forms of vanadium and molybdenum in fluorine-containing solution were studied.After oxidation treatment,vanadium mainly contains VO2SO4-and VO2+,Vanadium coexists with VO2SO4-and VO2+in the solution with low pH value.With the increase of pH value,VO2SO4-increases and VO2+ decreases gradually.When the pH value is above 1.75,vanadium in the solution is mainly VO2SO4-,and the main molybdenum components in the solution are MoO3(H2O)3(aq)?H2MoO4(aq)and HMoO4-.The process parameters of N235 co-extraction were tested and optimized,the significant factors were selected from the influencing factors,and the equation model between the extraction rate of vanadium and molybdenum and the significant factors was established.After three-stage extraction,the extraction rates of vanadium and molybdenum are 99.32%and 99.33%,respectively,under the conditions of pH 1.80,20 vol%of N235,5 vol%of TBP,extraction ratio O/A=1:4,extraction temperature 25? and extraction time 3 min.The significant influencing factors were pH value,volume fraction of N235(vol%)and extraction ratio O/A.The equation models of vanadium extraction rate,molybdenum extraction rate and pH value,volume fraction of N235(vol%)and extraction ratio O/A were predicted by full factor test.Based on the difference of stripping effect of stripping agent on vanadium and molybdenum,acid stripping agent sulfuric acid stripping agent and alkaline stripping agent ammonia water stripping molybdenum were selected,and the step-by-step stripping process parameters were optimized.Under the conditions of H2SO4 concentration 2 mol·L-1,stripping ratio O/A=3:1,stripping temperature 25? and stripping time 3 min,the extraction rate of vanadium is 99.36%,while the stripping rate of molybdenum is only 2.84%.The effective separation of vanadium and molybdenum is realized.Under the condition of NH3·H2O concentration 2 mol·L-1,stripping ratio O/A=2:1,stripping temperature 25? and stripping time 3 min,the stripping rate of molybdenum is 99.28%,and the stripping effect is good.Through the verification test of the actual fluoric acid leaching solution of stone coal,it is verified that the N235 co-extraction-step-by-step reverse extraction process has strong applicability to the actual stone coal fluoric acid leaching solution,and the separation and enrichment of vanadium and molybdenum in the actual stone coal fluoric acid leaching solution is realized.Based on slope method,saturated volumetric method and thermodynamic calculation of extraction,the mechanism of co-extraction of vanadium and molybdenum with N235 was revealed.The structures of the extracted complexes of vanadium and molybdenum are[R3NH·VO2SO4]and[R3N·MoO3(H2O)3],respectively,and the extraction reaction formulas are[R3NH+]+VO2SO4-=[R3NH·VO2SO4]and[R3N]+MoO3(H2O)3=[R3N·MoO3(H2O)3],respectively.The reaction is exothermic,?G<0,and the reaction can be carried out spontaneously at room temperature.?S<0 is entropy reduction reaction,and the extraction ability of N235 is stronger than that of vanadium.