Separation Of Tungsten And Molybdenum Oxides From Spent Catalysts By Ion Exchange

Nowadays，a large number of cellular catalysts are consumed duringthe Selective Catalytic Reduction（SCR） system in the coal-fired powerplants, which would be stacked up into the “urban mines” afterdeactivation. Domestic treatment on cellular spent catalyst is usuallylandfill after crushed. But SCR spent catalyst due to toxic metals such ascontaining V₂O₅and WO₃, MoO₃, belong to the dangerous solid wasteand landfill processing should not be arbitrarily, otherwise it is easy toproduce serious pollution of environment and water. And cellular spentcatalyst contains high additional value metal oxide of tungsten trioxideand molybdenum trioxide, which is about5%. This content is higher thanthe ordinary molybdenum ore and tungsten ore, which should be recycledbecause of the high reusable value. Extraction and purificationtechnology can realize the separation of MoO₃and WO₃from spent SCRcatalyst, and the recovery of MoO₃. As an important strategic reserveresource, the price of molybdenum trioxide is￥160,000/t currently.Separation of tungsten and molybdenum from the spent catalyst ofthe flue gas denitrification in the power plants is concerned in this paper,the background and significance of the subject are introduced as well.Several current methods about separation of tungsten and molybdenumare introduced in the following parts. This paper details the principle andtest method. Then the extracted molybdenum trioxide had beencharacterized by element analysis, characterization of X ray diffractionand scanning electron microscope. In the research, the main componentsof the waste catalyst of the SCR system are Mo、W、O、Ti、Si、Al, anda bit of V、Ni、Ca as impurities. The results show that: Macroporous weakbasic anion exchange resin D301’s adsorption ability is strong onW10-12O41, while molybdate ion is hardly adsorbed. The adsorption effectis better after transformation type of Cl-. The adsorptivity of ion exchangeresin for W10-12O41could reach102.5mg/mL when the preset pH of tungsten and molybdenum mixture is7.3, the flow rate of ahead fluid isbetween0.8mL/min¹mL/min and the mesh of resin is between40and60, respectively. The resin has desorbed completely with1mol/L sodiumhydroxide solution as desorption agent. After extraction and separation,the purity of molybdenum trioxide could reach more than97%，theparticle presents layered orthorhombic crystals, the crystal length isbetween5μm and10μm while the thickness is below1μm. Crystal’s layerstructure is very obvious. This particular structure is very suitable for theembedment of other small molecules or ions and makes MoO₃could havegood electro-chromic，photochromic and catalytic.