Study On Preparation Of Electrolyte For Vanadium Redox Flow Battery With Short Process From Sodium-polyvanadate Precipitated Wastewater By Solvent Extraction

A calcification roasting-sulfuric acid leaching-hydrolysis precipitation method,is adopted in vanadium extraction process by Xichang Vanadium Plant of Panzhihua Iron and Steel Group.Although the sodium polyvanadate precipitated wastewater produced was neutralized and filtered by lime,however,this resulted valuable metals loss for ages.Which have become the bottleneck restricting the sustainable development of enterprises.In this paper,the P204-sulfonated kerosene extraction system is used for the treatment and utilization of the sodium polyvanadate precipitated wastewater.According to the characteristics that the wastewater and the electrolyte for vanadium redox flow battery are both in sulfuric acid system and the main components are consistent,the electrolyte of vanadium redox flow battery was successfully prepared from the wastewater.After the manganese in the raffinate is extracted,the by-product,manganese sulfate is recovered.All the tail water is reused in the original vanadium extraction process.Which realizes the efficient and clean utilization of the sodium-polyvanadate precipitated wastewater.The following main conclusions are obtained:（1）After the sodium-polyvanadate precipitated wastewater is first reduced with CaSO₃,then extracted by first vanadium extraction process by using P204+sulfonated kerosene extraction system.In the extraction:initial pH 2.0,P204 concentration 15%（v/v）,phase ratio（O/A）1:3,extraction time 5 min,3 stage.Stripping:sulfuric acid concentration 0.5 mol/L,phase ratio（O/A）1:1,stripping time 5 min,3 stage.Under the optimal process conditions,1#vanadium stripping solution with vanadium concentration3.811 g/L,manganese concentration 0.42 g/L,and magnesium concentration 10.1 mg/L can be obtained.The recovery rates of vanadium,manganese and magnesium are 98.60%,0.92%and 0.05%,respectively.Which effectively separated the vanadium from other vanadium ions in the sodium-polyvanadate precipitated wastewater.（2）1#stripping solution is extracted by P204+sulfonated kerosene extraction system by second vanadium extraction for deep purification.In the extraction:initial pH 2.0,P204 concentration 15%（v/v）,phase ratio（O/A）1:2,3 stages,2#loaded organic phase was obtained.The organic phase was stripping by sulfuric acid concentration of 4.5 mol/L,phase ratio（O/A）10:1,extraction time of 10 minutes,3 stages.Degreasing:activated carbon as adsorption medium,carbon-liquid ratio 0.1 g/mL,magnetic stirring for 24 h under the best process conditions,electrolyte with vanadium concentration of 76.52 g/L can be prepared,and the recovery rate of vanadium is up to 98.60%.All ions complied with national standards（GB/T 37204-2018）.（3）Electrochemical test showed that E_p of SS（electrolyte for comparison）is 0.34 V,which is not much different from ES（electrolyte prepared by extraction method）.The anode peak current density(j_pa)of SS is 84.18 mA/cm²,and the anode peak current density(j_pa)of ES is 77.91 mA/cm²,and the j_pa/j_pc values are basically the same.There is no much difference between them.The energy efficiency（EE）,coulomb efficiency（CE）and voltage efficiency（VE）was 75.02%,81.46%and 93.27%,respectively.It shows that the electrolyte prepared from waste water has similar electrochemical performance to the comparison electrolyte.（4）Manganese in the 1#raffinate was separated and recovered with P204（saponification with Mg（OH）₂）+sulfonated kerosene extraction system.During extraction:initial pH 3.0,P204 concentration 30%（v/v）,phase ratio（O/A）1,extraction time is 4minutes,saponification rate is 50%,and the number of stages is 3.In the stripping:the sulfuric acid concentration is 1.5 mol/L,phase ratio（O/A）5:1,stripping time is 7 minutes,and the number of stages is 3.Under the optimal process conditions,the manganese content in the stripping solution obtained was 68.98 g/L,and the total recovery was 98.5%.The stripping solution is concentrated and crystallized to obtain industrial manganese sulfate,which complied with industry standards.（5）The electrolyte preparation process by solvent extraction can shorten the electrolyte preparation cycle time from 4.5 d to 2 d,which can effectively shorten cycle time.The project of preparing electrolyte for vanadium redox flow battery with the short process from sodium polyvanadate precipitated wastewater is feasible,which expected to invest 114 million yuan,the annual production cost is 117 million yuan,and the annual profit is 65 million yuan.It takes only 2.36 years to recover the investment cost after reaching production.