Study On Sulfuric Acid Acidolysis-leaching Of Spent SCR Catalyst And Separation Of Ti,V,and W From Leaching Solution

China has implemented strict NO_xemission standards for coal-fired thermal power plants since 2014.V₂O₅-WO₃/Ti O₂SCR catalyst has been widely used in flue gas denitration of thermal power plants,Theoutput of spent SCR catalyst exceeds 40000 tons every year.The spent SCR denitration catalyst contains V₂O₅and a few As₂O₃,it is listed as hazardous waste.However,because it contains Ti O₂,V₂O₅,and WO₃with great economic value,the regeneration and recovery of spent SCR catalysts have important environmental and economic significance.In this paper,the"concentrated sulfuric acid acidolysis and water leaching"method is proposed to extract Ti,V,and W from spent SCR catalyst.The leaching solution is separated and extracted by crystallization method and extraction method.The main contents and results are as follows:（1）The spent SCR catalyst was acidolysis with sulfuric acid and leached with water.The factors affecting the leaching efficiency,the behavior and trend of each element in the acidolysis and leaching process were studied.It is found that WO₃and Ti in the spent catalyst form H₄Ti W₁₂O₄₀into the leaching solution,therefore,Ti,V,and W are leached;Further study found that the activity of WO₃played a crucial role in the formation of H₄Ti W₁₂O₄₀.The experimental results show that the spent SCR catalyst is acid acidolysis for 150 min under the conditions of200℃,acid ore ratio of 1.8:1,mineral particle size<150μm and sulfuric acid concentration of 80%.The acid acidolysis products are leached in water at a liquid-solid ratio of 6:1 and 75℃for 50 min.the leaching of Ti O₂,VO₂,and WO₃are 96.52%,97.5%,and 97.7%,respectively.（2）The method of recovering valuable elements from leaching solution containing Ti,V,and W by crystallization was studied.It is found that V and W co-crystallize with Ti when crystallizing Ti O₂·H₂O.It is also found that the crystallized V and W are difficult to be removed by alkali washing.When Ti OSO₄was crystallized from the leaching solution,W crystallizes with Ti,while V remained in the crystallization mother solution.The experimental results show that when the concentration of Ti in the leaching solution is 70 g/L,H₂SO₄is 7 mol/L and the temperature is 120℃for 100 min,the crystallization of Ti and W are91.52%,80.26%,and V are 7.53%,respectively,β_Ti/Vandβ_W/Vis 132.53and 49.93.Anatase Ti O₂composite powder containing W can be obtained by calcining Ti OSO₄at 700℃for 5h.The particle size of the powder is about 40nm,with uniform particle size and good dispersion.（3）When extracting and separating Ti,V,and W from the leaching solution,it is found that N1923 can extract Ti and W at the same time,V remains in the raffinate,and the loaded organic phase is step-by-step stripping to realize the separation of Ti and W.The experimental results show that under the conditions of H₂SO₄concentration of 0.91mol/L,O/A=3:1,and extraction time of 1 min,35%N1923+5%sec octanol+sulfonated kerosene system is used to extract the leaching solution,after three-stage countercurrent extraction,The extraction of Ti and W are 99.8%and 99.6%respectively,and the extraction of V is only2.5%.The loaded Ti and W organic phases were stripped with 6 mol/L H₂SO₄+10.6%H₂O₂at O/A=3:1 and 25℃for 3min,through seven-stage countercurrent stripping,the stripping of loaded Ti reaches 98.9%,and the stripping of W is only 1.3%.For the loaded W organic phase after stripping Ti,4.5 mol/L Na OH+1.5%H₂O₂is used to remove H₂SO₄and part of Ti.Then use 3 mol/L Na OH+1%H₂O₂to stripping for 2min under the condition of 30℃and O/A=6:1.After a three-stage countercurrent simulation stripping experiment,the stripping of W reaches 99.8%.V in the raffinate was extracted with P204 and recovered with H₂SO₄stripping.Based on research results,this paper proposes to recover the spent SCR catalyst by sulfuric acid acidolysis and water leaching method.The leaching solution is comprehensively recovered by crystallization method or separated and recovered by extraction method.The research provides a new method for the recovery of spent SCR catalyst,at the same time,it also provides a new idea and reference for the separation and recovery of Ti,V,and W from acidic solution.