Experimental Study On The Adsorption Of Heavy Metal From Fly Ash Calcined Gas

Fly ashes from MSW incinerator contain a great amount of heavy metals and their compounds. They are defined as hazardous waste because these fly ashes in having high leaching ratios of heavy metals,so it must be treated and disposed appropriately. The thermal treatment technology has gradually been one of the dominant for MSW thermal treatment in the world. Nevertheless the adsorption studies on gaseous of heavy metal from incineration fly ash volatilization gas are still rare. In this paper, the main study is the adsorption of the gaseous of heavy metals Cu, Cd, Zn and Pb from MSWI fly ash in high-temperature processes by mixed adsorption system made up liquid and solid, and to establish the kinetic model of the heavy metal in liquid and solid adsorbent.Firstly, this study uses the vertical high-temperature tubular furnace to calcined the MSWI fly ash, investigates the effect of different adsorbents and adsorption systems to the heavy metals Cu and Pb. The result shows that: in liquid adsorbents, the effect of (1mol/LHNO₃+10%H₂O₂) to the heavy metals Cu and Pb was the best, reach to 15 percent; in solid adsorbents, the effect of the activity carbon to the heavy metals Cu and Pb was the best, reach to 40 percent, the analysis showed that the heavy metals exsit mainly in chloride by XRD, the graphics of Scanning electron microscope showed that the activity carbon has small particles and complex structure, so the effect of adsorption is better. And in the adsorption systems, the mass balance effect of the (1mol/LHNO₃+10%H₂O₂+activity carbon) to the heavy metals Cu and Pb can reach to the 85 percent and 65 percent.Secondly, change the calcination temperature and calcination time and use the selected adsorption system to adsorb the tail gas, explore the impact of time to the adsorption of heavy metals. The result shows that: the adsorption rate of heavy metals was fall with the time increases, the analysis of 2h and 4h activated carbon by XRD was found that the heavy metals of adsorption mainly in chlorine and a part of PbO₂, while also found ZnO in 4h activated carbon. The heavy metals of volatile out was almost distributed in adsorption system and lotion from cleaning the reactor; The adsorption rate of heavy metals were all decrease with the the volatilization rate increase.Finally, according to the adsorption rate of the gaseous heavy metal(Cu, Cd, Zn and Pb) time-varying curve in high-temperature flue gas from MSWI fly ash, works out the kinetic of the adsorption of Cu,Cd,Zn and Pb in liquid and solid adsorbent. Kinetics study shows: in liquid adsorbent, heavy metal Cu, Cd and Zn'adsorption kinetics conform to the Lagergren first-order kinetic, the rate constants were 0.0114min^-1,0.0179min^-1 and 0.0169min^-1; but Pb conform to the second-order kinetic, the rate constant was 59.2278(g·min)^-1. In solid adsorbent, the four heavy metals all conform to the Elovich equation, the adsorption constants were 2.71×10^-4, 6.42×10-5, 7.42×10^-4 and 3.46×10^-4.