Study on efficient mercury recovery process from waste mercury catalysts
In order to further improve the mercury recovery rate of waste mercury catalysts,this paper studies the physical and chemical properties of waste mercury catalysts,the amount of lime added,the liquid-solid ratio,the temperature,the time and other process indexes that affect the mercury conversion rate and the mercury recovery rate in the pre-treatment process,and the mercury content of waste mercury catalysts averages about 2.5%through the testing of the composition and the surface properties of the waste mercury catalysts,which are formed mainly because of the accumulation of charcoal,sulphur-phosphorus poisoning and other factors.The mercury content of the spent mercury catalysts was about 2.5 per cent on average.Through theoretical calculations,the temperature point of maximum condensation intensity of mercury vapour is 196℃,and the condensation efficiency of mercury vapour in the interval of 20～200℃(where in the condensation efficiency of mercury in the temperature interval of 170～200℃is the maximum,which is up to 64.55%)is derived,and when the mercury vapour is condensed to less than 50℃,the mercury vapour can be obtained as 99.03%of mercury vapour condensation.After the test,the optimal process conditions for the pretreatment of waste mercury catalysts were found to be 20%lime addition,liquid-solid ratio of 0.4 L/kg,pretreatment reaction temperature of 95℃,and constant temperature for 4 hours.The best high-temperature pyrolysis roasting process conditions are as follows:roasting temperature 900℃,negative pressure in the furnace-50 Pa,roasting time 8 hours.Under the above optimal conditions of pretreatment and high-temperature pyrolysis,experiments on the recovery of gaseous mercury under different inlet temperatures of the three-stage condenser were explored,and when the inlet temperature of the first-stage condenser was controlled to be approximately 200℃,the recovery rate of mercury could reach more than 99%.
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