Study On Removal Of Heavy Metals In Municipal Solid Waste Incineration Fly Ash

The waste incineration technology has been widely used in the treatment of waste,but the heavy metal pollutants enriched in the fly ash produced by incineration are causing serious harm to the environment and people's health.The electrokinetic removal technology to deal with heavy metals in fly ash is a kind of effective processing method,and the three-dimensional electrode method is based on the traditional two-dimensional electrode method with dosed particle electrode,which has the better ability and effect of mass transfer.And the three-phase three-dimensional electrode method is the electrokinetic removal method based on the three-dimensional electrode method with the aeration device at the bottom to form the gas-liquid-solid three phase combination,which can effectively overcome the short circuit current in the three-dimensional electrode method,concentration polarization and hardening of fly ash phenomenon,and the processing effect of heavy metals in fly ash is significantly enhanced.This paper was mainly studied on the fly ash produced by a waste incineration plant in Chongqing,and the three-dimensional electrode method and three-phase three-dimensional electrode method were used to deal with heavy metals in fly ash,the removal mechanism was analyzed as well.The results of the research of physicochemical properties of fly ash showed that the particle size distribution of fly ash was large and distributed discontinuously,with a tendency to focus on small particle size;the concentration of Pb,Cd,Zn and Cu in fly ash were 1517 mg/kg,342mg/kg,1496 mg/kg and 722 mg/kg,respectively;the leaching toxicity was 1.8716?g/mL,1.3655?g/mL,7.2339?g/mL and 1.4449?g/mL,respectively.The experimental results of three-dimensional electrode showed that the removal rate of heavy metals increased first and then decreased with the increase of electrode ratio,when the ratio was 5%and the reaction time was 72 h,the removal efficiency of heavy metals was best,and the removal rates of Pb,Cd,Zn and Cu were 58.29%,83.57%,47.46%and 77.14%,respectively;the three-phase three-dimensional electrode experiment results showed that the the best experimental conditions of the treatment of heavy metals in fly ash were that the voltage gradient was 1.0 V/cm,remove time was 7 h,electrode dosing ratio was 5%and the aeration flow was 0.4 L/min,under that condition the removal rate of heavy metal Pb,Cd,Zn and Cu were 75.98%,88.64%,50.72%and 81.58%respectively.Compared with three-dimensional electrode method,the removal effect on heavy metal of three-phase three-dimensional electrode method is better,and the removal rate of heavy metal Pb,Cd,Zn and Cu were significantly improved.The removal rate of Cd was obviously increased from 29.43%to 88.64%;the removal rate of Zn was increased from 30.39%to50.72%;the removal rates of Cu and Pb were 81.58%and 75.98%,respectively.The mechanisms of the treatment of heavy metals in fly ash include electroosmotic percolation,electromigration,electrophoretic,electrolytic reaction,adsorption/desorption,convection and so on;the release processes of heavy metals include the external diffusion of H~+,the internal diffusion of H~+,the release of heavy metal ions from the reaction of H~+with active substances,the internal diffusion of heavy metal ions,and the external diffusion of heavy metal ions.The three dimensional electrode method increases the surface area of chemical reaction,improves the mass transfer effect of heavy metals,and improves the current utilization rate;the aeration agitation of three phase three-dimensional electrode method increases the oxygen capacity of the sample area,overcomes the current short circuit and concentration polarization in the three-dimensional electrode method,and restrains the hardening of fly ash,thus significantly strengthening the removal effect of heavy metals.