Co-Effects Of Chlorine And Heavy Metals On Minerals And Solidification Of Heavy Metals In Cement Clinker

In the process of collaborative disposal of solid waste using cement kiln,heavy metals,chlorine and other elements are often brought into it.These elements may impose impacts on the firing,mineral composition and pollutant emission of cement clinker.To provide a theoretical reference for the cement kiln collaborative disposal of solid waste with the goal of harmless disposal,quantitative reduction and resource utilization,investigation was conducted to explore the influence of the coexistence of chlorine and heavy metals on the volatilization and solidification of heavy metal elements and the quality of clinker.In this paper,Ca Cl₂ was used as chlorine source,and heavy metal elements（Cu,Zn,Pb）with different volatility characteristics were selected to mix into cement raw meal.In addition,focusing on the effects of different chlorine content on the volatilization and solidification of heavy metals in clinker,the effects of different chlorine content and different heavy metal elements on the firing,minerals and ultra-early hydration characteristics of the clinker were discussed.The main conclusions are as follows:（1）As the chlorine content increased in the clinker,the volatilization rate of Cu,Zn and Pb increased.Specifically,the content of doped chlorine possessed the greatest influence on the volatilization rate of Cu,followed by Zn and Pb.Moreover,heavy metal oxides in the clinker reacted with chlorine to form heavy metal chlorides,causing a decrease in the solidification rate of heavy metals and chlorine.Hence,the incorporation of chlorine is not conducive to the solidification of Cu,Zn,Pb.（2）Chlorine and Cu,Zn,and Pb elements are mainly distributed in the clinker mesophase.With the increase of chlorine content,there were no obvious changes in the distribution of Cu and Zn,except that Pb migrated from mesophase to silicate phase.In addition,the presence of chlorine will convert part of Cu²⁺to Cu⁺and replace Ca²⁺in the clinker,and weaken the substitution effect of Pb²⁺on（3）With the increase of chlorine content,the content of f-Ca O first increased and then decreased in the clinker containing Cu and Zn,and reached the maximum at 1.0 wt.%chlorine,while the content of f-Ca O continuously increased in the clinker containing Pb.Moreover,the content of silicate phase increased in the clinker containing Cu and Zn but did not significantly change in the clinker containing Pb.Furthermore,the content of mesophase in the three groups of clinker samples decreased to some extent,among which the content of C₃A decreased first and then increased,while the content of C₄AF decreased.（4）The presence of chlorine hinders the conversion of C₁₂A₇ to C₄AF and C₃A,resulting in the residual of C₁₂A₇ in the clinker prepared at 1450℃.The content of C₁₂A₇increases with increasing chlorine solidification content,but the appearance of C₁₂A₇ is not related to doped heavy metals.（5）The solidification content of chlorine and the type of incorporated heavy metals affect the content of aluminum phase salts C₃A and C₁₂A₇,causing the first hydration exotherm peak and ultra-early hydration activity of cement increased with increasing aluminate C₃A and C₁₂A₇ content.At the same time,the content of the hydration products AFt and AFm increases with increasing C₃A and C₁₂A₇content,respectively.