The Study On Leaching,Solvent Extraction Separation And Recovery Of Tungsten And Vanadium From V₂O₅-WO₃/TiO₂ SCR Catalyst

The V₂O₅-WO₃/TiO₂ SCR catalyst is widely used in the SCR denitrification system.In the process of denitrification of coal-fired flue gas,the catalyst is easily inactivated by the dust clogging and the poisoning of K,Na,As.The tungsten（W）and vanadium（V）in deactivation catalyst are classfied as important industrial raw materials,which are less distributed in nature and have high recycling values.The recovery of W and V from waste SCR denitration catalyst can not only alleviate environmental pollution,but also reduce the cost of denitration and realize the recycling of resources,which has important research values.The article point out a new idea of recovering valuable metals of W and V from V₂O₅-WO₃/TiO₂ SCR catalyst,the leaching of catalyst and the extraction separation and recovery of W and V from the leaching solution were investigated in this paper.Firstly,the leaching behavior of W and V in solid SCR catalyst was investigated by Na₂CO₃ roasting pretreatment and dilute H₂SO₄ leaching.The effects of calcination temperature and time,H₂SO₄ concentration,liquid-solid ratio,leaching temperature and time,mass ratio of Na₂CO₃ to catalyst and m（Na₂CO₃）/m（catalyst）on the leaching rate of W and V were investigated.The results showed that while the mixture of catalyst and Na₂CO₃ was calcined for 3h at 800 C,of which m（Na₂CO₃）/m（catalyst）=1.2,Then the roasted mixture was leached for 4 h at 80 C with 2%H₂SO₄with the ratio of liquid to solid was 8:1.The leaching rate of W and V can be as high as 99.08%and 98.49%,respectively.Secondly,the extraction of W and V from the acidic leachate was investigated using TOA dissolved in aviation kerosene with iso-decanol,and the mechanism of extraction process is preliminarily speculated.The extraction efficiency of W and V were studied by varying organic to aqueous ratio,extraction time,initial pH and TOA concentration.The results show that maximum extraction efficiency of W and V were98.78%and 94.94%respectively with the O/A was 0.1,the pH of leachate was 2.50,the extraction time was 15min,and the TOA concentration was 12%.Then,the W and V in the loaded organic were stripped by NaOH as back-extractant,and the action mechanism of various factors on reverse extraction was analyzed.while the O/A was 1:3,the NaOH concentration was 2.5mol/L,the stripping time was15min,the stripping efficiency of W and V could reach 99.99%and 88.05%respectively,At last,the V in the stripping solution was precipitated as NH₄VO₃ by adding NH₄Cl after adjusting pH of the stripping solution to about 8.0 with H₂SO₄.After filtering,the pH of the filtrate was adjusted to 1.5,and CaCl₂ was added to precipitate W as calcium tungstate which was then washed with hydrochloric acid.Finally,the ammonium metavanadate and tungstate were calcined at 500℃for 1h to get the corresponding oxides and the purity of the oxides of W and V was above 99%.