| Abstract:The current processes for separating Mo and W from tungstate solution with high ratio of Mo/W (molybdenum/tugsten) have shortages such as high co-precipitation loss of W, incomplete removing of Mo, high cost and seriously environment pollution. Aiming at this situation, a novel cleaning efficient process for separating Mo and W from tungstate solution with high ratio of Mo/W, i.e. process of extraction separation of Mo and W by hydrogen peroxide (H2O2)-complexation with a mixture extractant tri-alkyl phosphine oxide (TRPO) and tributyl phosphate (TBP) was developed and the industrial test was carried out in this paper.Aiming at the difficulties presented in the acid regulation of the preparation of the H2O2-complexation solution from the ammonium tungstate solution, two methods, the evaporation deamination complex method and the dipolar membrane electrodialysis (BMED) complex method, on preparation of feed solution for extraction from the ammonium tungstate solution containing high Mo were proposed. The new methods were clean and environmental friendliness, and by which the consumption of mineral acid was largely decreased. The mixture extractant TRPO and TBP was used for separating Mo and W from the ammonium tungstate solution containing high Mo for first time. There was a synergistic extraction effect of Mo with TRPO/TBP and an antagonistic extraction effect of W with TRPO/TBP. Thus, the purpose of the increase of the removing of Mo and to decrease the extraction of W was carried out. In comparision to the traditional process for separating Mo and W, the new process provided obvious advantages including deep Mo removing, high recovery of W, high added value of Mo product, low cost, clean and environmental friendliness.The main research contents included the preparation of feed solution for solvent extraction separation of Mo and W by H2O2-complexation, single-stage extraction and stripping test, multi-stage extraction test, continuous running test, industrial test and fundamental theory research on extraction.The effects of H2O2dosage, pH value and temperature were investigated in the test of preparation of feed solution for extraction. The results indicated that the evaporation deamination complex method reduced the acid consumption by more than90%in comparison to the traditional directly acid regulation complex method. The H2O2-complex transformation rates of W and Mo were higher than95%and the decomposition rate of H2O2was less than15%at a H2O2dosage of k=1.9(k is the mole ratio of H2O2to W and Mo), temperature45?, initial pH1.90for60min in the H2O2-complexation transformation process. The results of BMED complex method indicated that the current efficiency was higher than72%and the direct current consumption (byNH4+) was less than0.088kW·h·mol-1at a pH of salt compartment solution of3.20-3.50and with running time210min in the electrodialysis process. There was no H2O2decomposed, and the transformation rates of W, Mo and utilization rate of H2O2were close to100%in the H2O2-complex transformation process. The qualified feed solution for extraction could be prepared by both the two methods.The single-stage extraction test of solvent extraction separation of Mo and W from feed solution was carried out using separating funnel with tri-alkyl phosphine oxide (TRPO)-tributyl phosphate (TBP)-kerosene system. The effects of concentra-tion of TRPO and TBP, contact time, temperature, H2O2dosage and pH value on the extraction were investigated. The results indicated that the addition of TBP in organic not only improved phase separation both in extraction and stripping, but also increased the extraction of Mo and decreased the extraction of tungsten (W), and hence improved the separation properties of Mo/W. The optimum extraction conditions were as followed:H2O2dosage k=1.2-1.5, storing time of feed solution24-48h, initial pH value of aqueous solution1.5-2.0, O/A phase ratio1:1, contact time5min, temperature15-25?. Under the optimum conditions, the extraction of Mo was higher than63%and the separation coefficient ?Mo/w was larger than80using aqueous solutions containing90-120g/L WO3and Mo/WO3mass ratio of10-15%with a mixture of2%(V/V) TRPO and80%(V/V) TBP in kerosene.The further separation of W and Mo was realized in stripping process. NH4HCO3was the optimum stripping agent since its good phase separation, effective stripping of Mo and high Mo/W selectivity. The optimum stripping conditions were as followed:NH4HCO310-1.2mol/L O/A ratio8:1-10:1, contact time10min and temperature15-25?. Under the optimum conditions, the stripping of Mo was higher than95%in comparison that of W less than15%after one contact with the organic loaded9.90g/L Mo and2.08g/L WO3, and the concentration of Mo in strip liquor was70-90g/LThe muti-stage cross-flow and countercurrent extraction were been simulated using separating funnel. The extraction isotherms for Mo were plotted under different conditions. The relationship between the stage of countercurrent extraction, concentrations of Mo and W in raffinate and the equilibrium pH value was calculated and analyzed by kremser equation. On this basis, the method of acid regulation in one of the middle stages was proposed and the distribution of equilibrium pH value in each stage of extraction was changed. The process of2-section countercurrent extraction was proposed and the positive effect of storing time on the deep removing of Mo was fully utilized. Thus, the purpose for the separation indexes optimization to increase the extraction of Mo and to decrease the extraction of W was carried out.The continuous running test of the BMED-solvent extraction separation of Mo and W by H202-complexation was carried out using mixer-settler. The conditions of the2-section12-stage countercurrent extraction and2-section stripping test were as followed:the organic phase was comprised of3%(V/V) TRPO and42%(V/V) TBP in55%(V/V) kerosene, the H2O2dosage and the storing time of the feed solution for extraction was k=1.5and48h respectively. In the first-section extraction there was8-stage countercurrent extraction and the1-3stage was the acid regulation stage, the initial pH of aqueous solution was2.00-2.05, the equilibrium pH of the1-3stage was0.96-1.20, the operation capacity of organic phase was7.57-8.97g/L Mo. In the second-section extraction there was4-stage countercurrent extraction, the feed solution of the second-section extraction was the raffinate of the first-section stage with storing time36h, and the initial pH value was1.00-1.05, the operation capacity of organic phase was0.12-0.26g/L Mo. In the first and the second section stripping, there were both4-stage cocurrent extraction, the stripping agent in the second-section stripping was0.05mol/L NH4HCO3, the stripping agent in the first-section stripping was the strip liquor of the second-section stripping with0.8mol/L NH4HCO3addition, both the O/A ratio in the two sections stripping were6:1. Under the conditions, the raffinate of the second-section extraction was containing102-123g/L WO3,0.0060-0.017g/L Mo, and in which the Mo/WO3mass ratio was less than1×10-4. The APT product was obtained by evaporation deamination from the raffinate of the second-section extraction with NH3·H2O addition. The product could meet the requirement of0grade of APT of the national standards GB/T10116-2007of China.The fundamental theory of extraction of Mo and W with the mixture extractant TRPO/TBP was researched. It was confirmed by a lot of experimental results and infrared (IR) analysis that there was a synergistic effect between TRPO/TBP and Mo, and a antagonistic effect between TRPO/TBP and W. Under the experimental condition, the synergistic coefficient of Mo and W was RMo,?=1.31-2.81and Rw,?=0.21-0.53respectively. The tungsten trioxide (WO3) hydrate without H2O2-complexation could be extracted by TRPO and formed a third phase. The extraction reaction was neutral complex mechanism. The coordination ability of the P=O bond in TRPO for W6+was weakened by the addition of TBP. Thus, the extraction of W was restrained, the third phase was eliminated and the separation properties of Mo/W were improved by the addition of TBP into TRPO.An industrial test production line for produce50tAPT per year was established in the factory. It had successfully and continuously running for about21month. The cost analysis indicated that, to the ammonium tungstate solution containing high Mo with Mo/WO3mass ratio of12.5%, the novel process for separating Mo and W by H2O2-complexation could save the cost of removing Mo of4472yuan per WO3in comparison to the selectively precipitation method. Compared with current process for separating Mo and W, the new process provided obvious advantages including deep Mo removing, high recovery of W, high added value of Mo product, low cost, clean and environmental friendliness, especially when the MO/WO3mass ration in the mixture solution was higher than5%. |
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