Study On The Structure And Properties Of Glass-Ceramics Prepared From Chromium-Containing Steel Slag And The Solidification Of Heavy Metals

It is important to protect natural resources for human in life.The shortage of resources and energy is a serious challenge to global economic development,international peace and stability.However,the generation of solid waste occupies a large amount of land resources,which causes serious waste of mineral resources.Furthermore,it threatens to human health.In order to solve the waste of minerals,metallurgy and energy caused by solid waste,it has become a valid way to use the slag and coal fly ash produced by them to prepare glass-ceramics.In the work,CaO-Mg O-Al₂O₃-SiO₂（CMAS）slag glass-ceramics were prepared by using stainless steel slag,coal fly ash and quartz sand as the main raw materials and adding chemical reagents as fluxes.The crystallization kinetics and phase composition of slag glass-ceramics were studied by differential scanning calorimetry（DSC）,X-ray diffraction（XRD）and Raman spectroscopy（Raman）.Scanning electron microscope（SEM）and energy dispersive X-ray spectrometer（EDS）were used to study the micromorphology and grain size comparison,which further explained the role of heavy metal Cr in the glass-ceramics.The mechanical properties were analyzed by bending strength,hardness,thermal expansion and other test methods.Chromium valence were analyzed by X-ray photoelectron spectroscopy（XPS）.Finally,the content of unstable Cr in stainless steel slag,glass and glass-ceramics was explained by toxic characteristic leaching procedure（TCLP）,which further explained the solidified effect of chromium in it.The results show that:（1）Cr₂O₃ can be used as a nucleating agent for CMAS slag glass-ceramics to promote the formation of diopside phase.When the content of stainless steel slag was small,heavy metal Cr destroyed the structure of the silicon-oxygen network and led to polymerization.The degree of dendrite decreased,resulting in more phase separation points,which promoted the precipitation of diopside phase,and can refine the grains.The crystals transformed from large dendrites to small dendrites,and finally reached 0.7μm spherical crystals.（2）When the addition amount of stainless steel slag was 7%,the crystallization temperature decreased.But,when 20%stainless steel slag was added,the crystallization temperature started to rise again.And the calculated crystallization activation energy also decreased from 332.7 to 222.8 and increased to 362.8.The crystallization index changed from 1.31 to 2.67,the crystallization mechanism changed from 2 to 3,and the crystallization rates at different temperatures were seen to be continuous nucleation processing.（3）The main crystal phase of the CMAS system slag glass-ceramics was diopside,and the spinel phase was precipitated as the second crystal phase.With the increase of stainless steel slag,the spinel phase also increased.The increase of spinel phase made the mechanical properties of the samples from increase to decrease.When the content of stainless steel slag reached 16%,the maximum bending strength was 223.58MPa.When the content reached 14%,hardness was the excellent（878.3N/cm²）.（4）The valence state of chromium in it changed as Cr³⁺→Cr⁶⁺→Cr³⁺,and the relative content of the toxic characteristic leaching procedure proved that the heavy metal Cr in the stainless steel slag is effectively solidified in the glass-ceramics.