Study On The Mechanism Of Solidifying Heavy Metals In Cement Clinker Based On ²⁹Si Spectrum Of Solid NMR

With the sustainable development of our society,the harmless and resource-based utilization of industrial solid waste has gradually become a bottleneck restricting the development of solid waste discharge enterprises and local economy.The coordinated disposal of solid waste by cement kiln is a better way to solve this problem.In the process of collaborative disposal,heavy metals in solid waste will affect the sintering process of cement clinker,which is also the focus of scholars in this field.The purpose of this study is to explore the change of heavy metals in the formation process of cement clinker and clarify its curing mechanism by using solid-state NMR analysis technology.In this paper,the cement clinker containing Cr³⁺,Cd²⁺,Pb²⁺was fired with different heavy metal content;By using ²⁹Si NMR technology,the role of heavy metals in the formation of new mineral phase was analyzed,and the influence of three heavy metal ions on the mineral phase composition and structure of cement clinker was studied.Combined with X-ray diffraction technology,the compound types of three heavy metal ions in cement clinker were determined.The solidification of heavy metals in clinker was analyzed,The results show that:With the increase of Cr³⁺and Cd²⁺,the solidification rate of Cr and Cd in cement clinker increases;When the content of Cr³⁺is between 0.4%and 1.0%,the average curing rate of Cr is 12.64%,and when the content of Cr³⁺is not 5.0%,the curing rate reaches 32.90%;The average curing rate of Cd is 31.94%,and the average curing amount is 31.94 mg/g;The curing rate of Pb is 12.53%,which is independent of the amount of Pb²⁺.The results of chemical shift analysis of ²⁹Si NMR of cement clinker with Cr³⁺,Cd²⁺and Pb²⁺show that heavy metal ions partially replace Ca²⁺in calcium silicate minerals,and cause the phase structure of clinker to change;The insertion of heavy metal ions forms new substances:When the solidification amount of Cr³⁺increased to 25.22 mg/g,the new crystal form of Ca₃Cr₂?SiO₄?₃ was induced in the clinker;when the solidification amount of Cd²⁺exceeded 24.06mg/g,the material with of Ca₅₀Cd₅₀O was formed in the clinker;however,the new crystal form of Pb²⁺did not appear in the clinker.The cement clinker ²⁹Si NMR with Cr³⁺,Cd²⁺and Pb²⁺was analyzed by means of peak fitting technique,The results show that:Cr³⁺and Cd²⁺play a stabilizing role in the formation of cement clinker,which makes?-C₂S stable.With the increase of Cr³⁺and Cd²⁺curing amount,the relative content of C₃S gradually decreases,the relative content of C₂S gradually increases,and the particle size of C₂S becomes larger and denser;Cr³⁺is mainly soluble in C₂S,but not in C₃S and C₂S.When the amount of Pb²⁺is low?0.17mg/g?9.60 mg/g?,Pb²⁺can inhibit the formation of C₃S and promote the formation of C₂S;When the amount of Pb²⁺solidifying exceeds 17.81 mg/g,C₂S will be converted into C3S.The results of this study provide basic data for the comprehensive analysis of heavy metal migration in the process of cement kiln collaborative disposal of industrial solid waste,and lay a certain foundation for the expansion of solid NMR in the study of cement clinker microstructure.