Kinetic Study On Volatilization Of Heavy Metal Pb/Cd/Cu From Incineration Fly Ash

The thermal treatment technology has gradually been one of the dominant for MSW treatment in China even in the world. Fly ashes from MSW incinerator contain a great deal of toxic 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. Thermal treatment of municipal solid waste incinerator (MSWI) fly ash with the advantages of marked volume-reduction, high stability and resource-recycle is considered to be a prospective technology in MSWI fly ash management. Nevertheless the kinetic study of heavy metals'volatilization in fly ash is still difficult and rare. In this paper, the main study is to investigate the volatilization of three heavy metals Pb, Cd, Cu from MSWI fly ash in high-temperature processes, and to establish the kinetic model of the heavy metal used dynamic isothermal methods.Firstly, this paper explores the influence of calcination temperature, calcination time and atmosphere on the volatilization characteristics by using a high-temperature tubular furnace with a programmed temperature controller to investigate the volatilization of the heavy metals (Pb, Cd, Cu) in MSWI fly ash. The result shows that: temperature has an great impact on the behavior of heavy metals. There is a great difference for the behavior of volatilization of various heavy metals about time, all the three heavy metals vaporized with different degrees during the calcining process, the final volatilization rate of Cu is all less than 75 percent, while Pb, Cd's final volatilization rate is over 95 percent. The behavior volatilization of three kinds of heavy metals in the air and oxygen atmosphere is basically the same.Secondly, according to the heavy metal(Pb, Cd and Cu)volatilization rate of time-varying curve from the thermal analysis experiment, this chapter works out the kinetic models of the volatilization of Pb,Cd and Cu with different atmosphere, using the basic theories of constant temperature kinetic. Kinetics study shows: the reaction order of three heavy metals'kinetics model are different between air atmosphere and oxygen atmosphere, the reaction order in air atmosphere all is 1, and in oxygen is 1/2, 0, 1/2 respectively. The active energy of Pb, Cd, Cu are all between 70KJ/mol to 200KJ/mol, in air atmosphere the active energy of Pb, Cd and Cu is 79.38KJ/mol, 129.37KJ/mol, 192.45KJ/mol respectively, and in oxygen atmosphere is 77.70KJ/mol, 133.07KJ/mol, 198.06KJ/mol.Finally, this paper forecasted the volatilization of CdCl2 theoretically in slimulation fly ash system, under the air atmosphere, using Gibbs free energy criterion. This study finds out the main reaction in the volatilization course, and works out the thermodynamic equilibrium amount of Cd species at different temperatures, and study the influence of Ca/Si on volatilization of heavy metal Cd in slimulation fly ash system.