Studies On Separation And Recovery Of The Valuable Metals From Spent Catalyst For Selective Catalytic Reduction Of NO_x

SCR denitration spent catalysts not only is the solid waste, but it also contains lots of precious metals such as Ti, W, Mo, V, Ni and Al. In order to separate and recover these valuable metals from deactivated catalyst, two treatment processes, sodiumzation roasting-water leaching and water leaching-NaOH sub molten salt were developed in this paper. In addition, ion exchange resins were used to recover Ni, Al and V in acidic fluid from water leaching process, and chemical precipitation technologies were adopted to separate W, Mo and V in alkaline solution from sub molten salt process.The results shows that the optimizing conditions for sodiumzation roasting-water leaching process are as following: the pretreatment temperature 700 ℃, pretreatment time 3 h, Na2CO3 is 1.5 g/g.cat. sodiumzation roasting temperature 700 ℃, roasting time 3 h. By this process, leaching rate of W, Mo, V, Si, Al is 91.4%, 91.9%, 92.6%, 91.9% and 92.6%, respectively can be obtained. The optimizing conditions of water leaching- NaOH sub-molten salt method are water-leaching temperature 95 ℃, solid/liquid ratio of 1:2, the leaching time of 5 h, stirring speed of 300 r/min; addition amount of NaOH the molten salt process 2.0 g/g.cat., the molten salt temperature 150 ℃, the time 3 h, stirring speed of 200 r/min, and the vanadium, molybdenum, tungsten metal oxide leaching rate can reach 96.5%, 96.5%, 98%,respectively. TiO2 content of filtration residue is up to 92 wt. %.The acidic solution is in turn dealed with strongly acidic cationic exchange resin, strongly basic anion exchange resin, weakly acid cation resin, respectively to adsorb vanadium, nickel and aluminium ions, and the effects of ion-exchanging temperature, time and the addtion amount of resins on the adsorption performance of exchange resin were investigated. The used resins were regenerated by HCl + NaCl mixed solution and recover the nickel, aluminum and vanadium compounds, respectively. The regenerated resin can be reused.The chemical precipitation process is used to separate and recover tungsten, molybdenum, vanadium, silicon and aluminum from the alkaline solution. First, by adding Al2(SO4)3 + MgSO4 composite precipitant to remove the silicon and aluminum ions of the alkaline solution. Results show that silicon and aluminum ions of 97.5% and 97.5% can be removed from the alkaline solution, respectively. The loss ratio of tungsten, molybdenum and vanadium is very low. Second, molybdenum was separated by adding Na2 S.Under the optimal conditions: S/Mo molar ratio 16, reaction equilibrium pH 7-7.4, water bath temperature 70 ℃ and reaction time 2 h, more than 98% of molybdenum can be recovered, and tungsten and vanadium loss rate were about 9.0% and 6.7%, respectively. After the filtration separation, excessive Ca(OH)2 was added to precipitate tungsten and vanadium. Vanadium was dissolved out from the precipitation by formic acid, and then adjusting the pH > 11 by ammonia solution to recover vanadium in the form of ammonium metavanadate. The remained CaWO4 precipitation was turned to H2WO4 crystals by hot HCl solution, then recovery WO3 by calcinating H2WO4.