Volatile Characteristics Of Heavy Metals During Co-processing Hazardous Waste In Industrial Furnace

With the rapid development of China’s industrial and economic, the number of hazardous wastes are increasing now. In this regard, over the past decade co-processing hazardous wastes in high temperature industrial furnaces, especially in cement kiln, are becoming one of recycle and reuse disposal ways for hazardous wastes. At the same time, sintering machine, as one of the high temperature industrial furnaces, which has the characteristics of high-temperature and stable working conditions can also provide the probability for co-processing hazardous wastes. However, when co-processing hazardous wastes, the environmental security problem, which is caused by the volatilization of heavy metals come from raw materials and hazardous wastes, is drawing the foucs of attention.This subject is come from the environmental public welfare projects: “Environmental risk control technology study on using high temperature industrial furnace to co-processing hazardous wastes”. In this study, these pure chemical reagents of PbCl2, ZnCl2, CdCl2, PbO, ZnO, CdO, PbS, ZnS, CdS and As2S3 were selected to substitute for heavy metals in hazardous waste. First thermal gravity analysis(TGA) experiments of these compounds were carried out, second is raw materials of sinter ore mixed with 1% proportion of chemical reagents were calcined in the sintering machine, and last is digestion experiments. The total contents of these heavy metals in the flue gas and sinter ores after calcining were analyzed, meanwhile studied the volatile characteristics of heavy metals during co-processing with sintering machine, and all volatilization laws of these heavy metals were modeled according to the chemical reaction kinetics, get the following results:(1)The results of TGA experiments show that there are large differences bewteen the three chemical forms compounds of Pb, Zn, Cd and As2S3, the temperature majority of chemical reagents begin evaporate rapidly is close to its melting point. However, the volatile temperature range is not the same as the extent from melting point to boiling point, moreover, the volatile temperature range of each chemical reagent is different from the others.(2)The results of calcining raw materials of sinter ore mixed with chemical reagents during co-processing with sintering machine show that the volatilization rate of As is decreasing with the temperature and time rising. When temperature is 1200℃, the volatilization rate of As is only 6.28% after calcining 30 min. Studies show the reason is that As reacts with Ca in raw materials of sinter ore to form Ca3(AsO4)2 which is a harder volatile substances, furthermore the higher the temperature, the more favorable the reaction. While the volatilizations of Pb, Zn, Cd are increasing with the temperature and time going up no matter the initial forms of heavy meatals are chlorides, oxides or sulfides.(3)The results of digestion experiments about sinter ore show that As in As2S3 gives priority to solidification reaction, and the higher the temperature, the bigger the curing rate, it is consistent with the volatilization law, when temperature is 1200℃, the curing rate of As is 93.72% after calcining 30 min, which results in that As can be solidified effectively in sinter ore. While as for Pb, Zn, Cd, their curing rates are decreasing with the temperature and time rising no matter what the initial chemical form is, which are also consistent with the volatilization laws.(4)The volatilization laws of Pb, Zn, Cd were modeled on the basis of chemical reaction kinetics, and results better. Only in view of chemical reaction activation energy, the volatility of the different chemical forms of lead is PbO> PbS> PbCl2, zinc is ZnCl2> ZnS > ZnO, and cadmium is CdS > CdCl2?2.5H2 O > CdO. Kinetics equations of the three elements with different chemical forms in the co-processing have been concluded. According to these equations, the volatilization rate of heavy metals in hazardous wastes can be calculated. Then it can be effectively controlled that how many hazardous wastes contained Pb, Zn, Cd should be added during co-processing with sintering machine, it will also minimize the damage which result from the volatilization of heavy metals to human health and environment.