SCR Catalyst Recycle

Tungsten vanadium titanium based SCR catalyst is widely used in China's thermal power plant pollution control catalyst. The effective time of the catalyst is 3 years. When the time comes, it needs to be replaced. Then, the hazardous waste catalyst which has been replaced by the professional department can be centralized and the valuable metals such as tungsten, vanadium and titanium can be recovered efficiently and safely without polluting the environment.

At present, there is no mature method to extract valuable metals such as tungsten and vanadium from SCR catalyst. Although the waste catalyst contains V₂O₅, it can not be classified as waste vanadium catalyst because of its low content (0.5% - 1%). Moreover, it is not practical under the existing technology specializing in waste vanadium catalyst recovery enterprises. Now, vanadium and tungsten are separated and purified, so the comprehensive recovery of valuable metals from spent catalysts is still a new field in China.

Recently, some domestic scholars have proposed a simple process, less waste by-discharge, effective harmless treatment of hazardous waste catalyst and comprehensive recovery of its valuable metals tungsten, vanadium and titanium. The operation steps are as follows:

Step (1) sodium roasting: the spent vanadium-tungsten-titanium denitrification catalyst was finely ground to - 300 mesh, then mixed with sodium carbonate and roasted in muffle furnace for 1-4 hours at 500-1000 ℃. The mass ratio of sodium carbonate to spent vanadium-tungsten-titanium denitrification catalyst was 10% - 200%.

Steps (2) water leaching reaction: the calcined material is added to water according to the liquid-solid ratio (2-5): 1, and the water leaching reaction is carried out at 50-100 ℃ for 0.5-3 hours; after the reaction, the liquid-solid separation is carried out, and the solid phase is washed to neutral by dilute acid, which is used as titanium-rich material; the dilute acid is dilute sulfuric acid, dilute hydrochloric acid or dilute nitric acid with the concentration of 0.5-3 hours.

Step (3) dehybridization: adding dehybridizer to the liquid phase obtained by step (2) and then reacting at 40-100 for 1-3 hours to obtain the dehybridization solution; the dehybridizer includes magnesium chloride and gelatin, the mass ratio of magnesium chloride to silicon in the liquid phase (4.8-5.2): 1, the mass ratio of gelatin to silicon in the liquid phase (2-5) : 1;

Calcium salt precipitation: According to the stoichiometric ratio of water-soluble calcium salt to tungsten (2.9-3.1): 1, water-soluble calcium salt is added to the dehybridization solution obtained in step (3) and the reaction is continued after boiling. The reaction time is at least 2 hours. After the reaction is finished, the solid phase is precipitated mixture.

Step (5), acid leaching reaction: The precipitation mixture obtained in step (4) was leached with hydrochloric acid of 40-80g/L at reaction temperature of 80-100 ℃ and reaction time of 1-4h. The liquid-solid ratio of the precipitation mixture to hydrochloric acid was (2-5): 1. After the acid leaching reaction, the precipitation mixture was naturally cooled to room temperature, and the liquid phase was vanadium-containing filtrate. The solid phase is tungstic acid.

After sodium roasting and water leaching, tungsten and vanadium in the spent catalyst enter the solution, and titanium enters the solid slag in the form of sodium titanate, thus realizing the separation of tungsten, vanadium and titanium. Among them, the content of titanium dioxide in the solid phase of sodium titanate after washing to neutral by dilute acid is more than 80%, which can be used as titanium-rich material for titanium industry companies.

The liquid phase is a solution containing tungsten and vanadium. After dedoping treatment and precipitation of calcium salt, the leaching rate of tungsten can reach more than 90% and then after acid leaching, the liquid-solid separation, the liquid phase is the filtrate with extremely low vanadium content. (Vanadium content less than 0.8mg / L), can be reused in the water immersion section, and the solid phase is tungstic acid, which can be used as a raw material for the vanadium tungsten titanium denitration catalyst preparation system.

• < Prev
• Next >