Study On Leaching Behavior And Risk Assessment Of Heavy Metals In Baking-free Brick Prepared From Spent FCC Catalysts

The petroleum refining industry has developed rapidly,and the production of petroleum refining waste catalysts has also increased rapidly,making the treatment and disposal situation of urban industrial solid waste more severe.The Fluid Catalytic Cracking?FCC?spent catalyst is derived from the deactivated spent catalyst discharged from the FCC unit in the petroleum refining industry.In 2016,the newly revised“National Hazardous Waste List”of the Ministry of Ecology and Environment listed spent FCC catalysts as hazardous wastes,which made the enterprises in the city increase the pressure on the harmless treatment of spent FCC catalysts.The composition of spent FCC catalyst is similar to that of building materials,and the production of building materials is simple in operation and low in cost.The utilization of spent FCC catalyst production building materials is better than that of traditional hazardous waste landfills.Under the premise of safety,the utilization of spent FCC catalyst building materials has broader prospects.In this paper,spent FCC catalyst and its prepared burn-free bricks were studied.The basic physical and chemical characteristics,identification of metal contaminants and leaching characteristics of heavy metals in spent FCC catalysts are studied,and the leaching characteristics,release rules and mechanism of heavy metals in the simulated pavement scene of spent FCC catalyst prepared by spent FCC catalyst,and the use of burn-free bricks for environmental risk assessment of groundwater and human health under the exposure scene.the main conclusions are as follows:?1?Spent FCC catalyst is basically weakly acidic or neutral,and there is no strong corrosiveness;the color depth of spent FCC catalyst is not related to the size of burnout rate;the content of aromatic hydrocarbon organic pollutants in spent FCC catalyst is low.The main characteristic metal pollutants in spent FCC catalysts are Ni,V,Sb,Co and Zn;the main characteristic pollutants are in the order of Ni>V>Sb>Zn>Co;the leaching content of characteristic pollutants is in order.It is:V>Sb>Ni>Zn and Co,the concentration is lower than the limit of“Dangerous Waste Identification Standard Leaching Toxicity Standard”?GB 5085.3-2007?.?2?The main characteristic metal-contaminants in the burn-free bricks are V,Cr,Co,Ni,Sb and Ba.The toxic concentrations of heavy metals in the burn-free bricks prepared by different blending ratios of spent FCC catalysts meet the relevant national standards,while the leaching concentrations of heavy metals Sb exceed the three standard limits of the Groundwater Environmental Quality Standard GB/T 14848-2017.The release rate of Cr in the burn-free brick prepared by spent FCC catalyst is the smallest,less than 0.5%,and the release rate of Ba is the highest,which is 11%.?3?The experiments on the leaching of the burn-free bricks show that the release of Cr,Ni,Co and Ba in the 64-day burn-free bricks prepared with different spent FCC catalysts is smaller,and the cumulative release curve is gentle;The release of Sb and V is the largest,and the cumulative release curve is on the rise;and V,Cr,Co,Ni,Sb,and Ba are all released to the environment at a low rate.During the whole leaching process,the release mechanism of V,Cr and Sb in the burn-free brick prepared by different FCC waste catalysts is diffusion control,Co,Ni and Ba are surface scouring;The curve fitting shows that the Freundlich equation and the second-order kinetic equation can better describe the release law of six heavy metals in the burn-free brick.?4?An assessment of the environmental risks of human health and groundwater by metal contaminants in burn-free bricks show that the spent FCC catalyst is 10%,15%,and 20%of the six metal contaminants that have no carcinogenic effects in the burn-free bricks.The hazard quotients were 5.86×10^-6,1.07×10^-5 and 1.63×10^-5,which were much less than 1;the carcinogenic risk values of pollutants with carcinogenic effects were respectively 3.86×10^-11,8.63×10^-1111 and 2.70×10^-10,both less than 10^-6.The environmental risk of groundwater in the use of the spent FCC catalyst by different blending ratio is within an acceptable range of human health risks.From the perspective of disposal after the burn-free bricks are discarded,the burn-free bricks prepared by adding spent FCC catalyst with a ratio of 20%are harmful,and the risk of the groundwater environmental quality is greater.In summary,it is recommended to adjust the blending ratio of spent FCC catalyst in the burn-free bricks to a level of 10%,15%or less.