Migration Characteristics Of Heavy Metals Cd And Zn During The Incineration Of Chlorine-rich Waste

A tube furnace was used to simulate the incineration process of actual waste.The actual classified waste provided by the Shanghai Environmental Engineering Design and Research Institute was used as the experimental raw material.And 1%PVC or NaCl was added to the raw material as chlorine-rich waste,the effects of moisture,Na2SO4 and SiO2 on the migration characteristics of Cd and Zn at 600℃,700℃,800℃ and 900℃ were studied respectively.And HSC Chemistry 6.0 thermodynamics software was used to simulate the distribution of Cd and Zn,so as to further analyze their migration characteristics.When the waste contained 1%PVC or NaCl,moisture can inhibit the volatilization of Cd and Zn,and the lower the temperature,the higher the moisture content,and the higher the mass proportion of Cd and Zn in the bottom slag.The thermodynamic simulation results showed that with the increase of moisture,the content of CdCl2 and ZnCl2 decreased,while the content of CdO and ZnO increased.This showed that moisture can promote the conversion of heavy metal chlorides into metal oxides,thereby reducing their volatilization.When the waste contained PVC,the mass proportion of Cd and Zn in the bottom slag changed significantly from 600℃ to 700℃.When the waste contained NaCl,it changed significantly from 700℃ to 800℃.This is because PVC and NaCl releases Cl at different temperatures.The influence of Na2SO4 on the migration characteristics of Cd and Zn was as follows:For Cd,when the waste contained PVC,the mass proportion of Cd in the bottom slag increaseed with the addition of Na2SO4 at 600℃ and 700℃,its changing trend becomed flat at 800℃ and 900℃.When the waste contained NaCl,the mass proportion of Cd in the bottom slag increaseed with the addition of Na2SO4 at 600℃ to 800℃,and the change tended to be flat when it reached 900℃.For Zn,its mass proportion in the bottom slag increased with the addition of Na2SO4 at each temperature.The thermodynamic simulation results showed that Cd and Zn reacted with Na2SO4 to produce non-volatile CdSO4 and ZnSO4,while heavy metal sulfates were easy to decompose at high temperatures,and volatile heavy metal chlorides formed at the same time.In addition,the fluxing effect of Na2SO4 when containing PVC and the eutectic melting effect of Na2SO4 when containing NaCl will also affect the mass proportion of Cd and Zn in the bottom slag.The influence of SiO2 on the migration characteristics of Cd and Zn was as follows:For Cd,when the waste contained PVC,the mass proportion of Cd in the bottom slag increased with the addition of SiO2 at each temperature.When the waste contained NaCl,the mass proportion of Cd in the bottom slag increased with the addition of SiO2 at 600℃ and 700℃,and its changing trend becomed flat at 800℃ and 900℃.For Zn,its mass proportion in the bottom slag increased with the addition of SiO2 at each temperature.The thermodynamic simulation results showed that Cd and Zn reacted with SiO2 to produce CdSiO3 and Zn2SiO4,which were not easily volatile.However,the content of heavy metal silicate reduced due to the destruction of SiO2 at high temperature and the formation of heavy metal chloride.The fixation effect on Cd and Zn was weakened.