Volatilization of Heavy Metals (As, Pb, Cd) During Co-Processing in Cement Kilns

Abstract

Heavy metals emitted by flue gas during co-processing hazardous waste (HW) in cement kilns presents a serious threat to the environment. Volatilization characteristics of three semivolatile metals (As, Pb, and Cd) in different chemical forms (As 2 S 3 , NaAsO 2 , Na 2 HAsO 4 , PbS, PbO, PbCl 2 , CdO, CdS, CdCl 2 ) during co-processing with cement raw materials were studied. Thermogravimetric experiments were performed to tentatively predict the lower limits of volatilization temperatures. Experiments involving co-processing of these compounds with cement raw meals was carried out at different temperatures over different time periods in an electric heated tube furnace to gain more insight into the macroscopic kinetic characteristics of volatilization. Volatilization of As, Pb, and Cd during co-processing with cement raw materials increases with time initially, and after 25 min, they do not volatilize. Temperature and compound speciation significantly affect metal volatilization. For Pb and Cd, volatilization was higher at higher temperatures. Volatilization of As, however, decreased as temperature increased at temperatures above 1,000°C, which can be explained by three parallel reactions. Kinetic models on the volatilization of these compounds during co-processing with cement raw materials were obtained. These models can provide a preliminary theory basis for predicting the release of heavy metals (Pb, Cd, As) and be used to control the environmental risk posed by heavy metals through restricting their feeding rate during co-processing HW in cement kilns.

Adsorption of Dioxins on the Entering Raw Meal

“…The normalization is carried out by the weight of all the elements. CaO, CaCO 3 and SiO 2 are the main compositions of raw material in this study, which is consistent with the results of Cong et al (2015) reported.…”

“…The percentage of CaO in raw meal could even reach 42.5 wt.%, so alkaline environment will be easily built in raw material (Cong et al, 2015), which could be better for raw material to adsorb dioxins (Choy et al, 2004). Moreover, CaO addition was proven efficiently to inhibit the formation of PCDD/Fs during the thermal treatment at a low temperature .…”

Determination of the selected heavy metal and metalloid contents in various types of plastic bags

“…While the contaminant levels of other semivolatile and non-volatile HM such as As and Cr in PE, HDPE and LDPE bags; Cu in PE and HDPE bags; and Ba in all types of studied PB were similar. The combustion conditions include temperature, oxygen, partial pressure, and compound speciation significantly affects metal volatilization [15,48]. For Pb and Cd, volatilization was higher at higher temperatures while volatilization of As decreased as temperature increased at above 1000°C [15].…”

The partitioning behavior of trace element and its distribution in the surrounding soil of a cement plant integrated utilization of hazardous wastes

“…However, arsenic is also verified to be easily volatilized and can be released into flue gas in cement kiln (DaHai et al 2009). Cong et al found that the volatility of arsenic was affected by its chemical form and calcinations temperature (Cong et al 2015). Specifically, the volatilization proportion is large at low temperature zone but decreases with the increase of temperature.…”