Si And Al-based Adsorbents Are Used To Simulate The Immobilization Of Heavy Metals In The Process Of Solid Waste Incineration

The intensification of human activities has accelerated the production of waste and caused serious environmental pollution.Because incineration can reduce effectively the volume of waste and be used for power generation,it is widely used to treat the waste.However,the volatile heavy metals produced by incineration are likely to cause secondary pollution,so it is necessary to use a sorbent to treat the heavy metals in the incineration tail gas.Si-Al sorbents are the most widely used sorbents.Aluminosilicates are usually formed with Si and Al elements during the adsorption of heavy metals.The sorbent has high surface area,high temperature resistance and porous characteristics.Therefore,two kinds of porous sorbents are prepared in this paper,and the adsorption behavior of PbCl₂ was evaluated in a self-made simulated incinerator and the characterizations are carried out.The two sorbents mentioned in this paper are NaA zeolite and Si-Al aerogel.The main research contents are as follows:（1）NaA zeolite was synthesized by hydrothermal method,and XRD,BET,FTIR and other tests were carried out to study its structural characteristics and active groups.The saturated adsorption capacity and unsaturated adsorption capacity of PbCl₂ were also carried out,the Kinetic parameters of PbCl₂ adsorbed in NaA zeolite were analyzed via the mathematical model of intra-particle diffusion and the method of adsorbing PbCl₂ is explored via XPS.SEM,TEM and EDS were used to observe the surface structure changes of NaA zeolite before and after adsorption,and the distribution of Pb in NaA zeolite was characterized.At 800℃,the saturated adsorption capacity of PbCl₂ is 353.8 mg/g,and the unsaturated adsorption capacity at low PbCl₂ concentration is 7.47 mg/g.And from 400 to800℃,temperature and adsorption capacity have a positive correlation.XPS result shows that the main adsorption mode is chemical adsorption,and the intra-particle diffusion model shows that internal diffusion is the rate-controlling step,and chemical adsorption occurs during the adsorption process.Combining the two results,it shows that the main adsorption mode of NaA zeolite is chemical adsorption.The various electron microscopys show that the morphology of the sorbent has no obvious change before and after adsorption,and it has high temperature resistance characteristics.The above results show that NaA zeolite has a good ability to adsorb PbCl₂ in the tail gas of simulated incineration of solid waste.（2）Si-Al aerogel was synthesized by sol-gel method and organic solvent evaporation method.The XRD result shows that its main component is Si O₂-Al OOH,the BET shows its high surface area and mesoporous characteristics,and the FTIR shows that the surface has adsorption sites-OH.The saturated and unsaturated adsorption capacities of PbCl₂ were measured by ICP-MS,the saturated adsorption process was fitted by the mathematical model of intra-particle diffusion,and the adsorption kinetic parameters were explored.XPS was used to analyze the way that Si-Al aerogel adsorbed PbCl₂.TEM and EDS were used to test the surface structure changes before and after the adsorption in Si-Al aerogel and the distribution of Pb in Si-Al aerogel.At 800℃,the saturated adsorption capacity of PbCl₂ is510.4 mg/g,and the unsaturated adsorption capacity at low PbCl₂ concentration is 8.82mg/g.And as the temperature increases from 400 to 800℃,the adsorption capacity increases.XPS result shows that Pb mainly exists in the form of Pb Si O₃ and PbCl₂,so chemical adsorption and physical adsorption occur at the same time.This result matches the fitting result of the intra-particle diffusion model.Electron microscopy shows that the morphology of the sorbent does not change significantly before and after adsorption,and it has high temperature resistance characteristics.What’s more,the addition of H₂O and CO₂and the slower gas speed are helpful to increase the adsorption capacity.The above results indicate that Si-Al aerogel has the potential to adsorb PbCl₂ in the tail gas of incineration of solid waste.Comparing the two sorbents,the Si-Al aerogel with higher surface area and larger pore size has higher saturated adsorption capacity and unsaturated adsorption capacity than NaA zeolite.The mathematical model of intra-particle diffusion shows that the internal diffusion in the adsorption PbCl₂process of NaA zeolite is the rate-controlling step,while the internal diffusion process has little effect in the adsorption process of Si-Al aerogel.This may be because PbCl₂ has less mass-transfer limitation to diffuse in larger pores.And at the same time,larger pores can also store more Pb,so Si-Al aerogel has a higher adsorption capacity.The paper guides of design of noval heavy metals sorbents and setting of engineering operating parameters.