Microwave Heat Treatment For Slag Containing Rare Earth (La) Influence Of The Crystallization Behavior Of Glass-ceramics

The comprehensive utilization of tailings resources has always been a difficult problem restricting social development.Due to technical constraints,it is difficult to increase the secondary utilization rate of tailings.The tailings contain many precious elements and huge economic value.It occupies a lot of land resources and even pollute groundwater and human health.Therefore,the comprehensive utilization of tailings resources has become an urgent problem to be solved.As of early 2019,the cumulative total of mine tailings reached more than 17 billion tons,and metal tailings accounted for more than 90%.However,the utilization rate of tailings in China is far lower than that in developed countries.The oxides such as Ca,Mg,Al,and Si contained in the solid waste are the basic components for preparing glass-ceramics.Thus,the use of solid waste to prepare high-performance glass-ceramics has become a new way to solve accumulation of solid waste and improve the comprehensive utilization rate of tailings.The research on glass-ceramics has been relatively mature,and traditional processes consume a lot of energy and produce pollution.Finding a new green preparation method with low energy consumption has become an urgent problem to be solved.Hence,microwave sintering is characterized by its pollution-free,low energy consumption and sintering time.Microwave sintering has become one of the new ways to prepare glass-ceramics and has attracted widespread attention from the academic community.In this study,traditional and microwave methods were used to prepare slag glass-ceramics with Bayan Obo tailings as the main raw materials.The effect of rare earth La₂O₃ on the structure and properties of pyroxene phase slag glass-ceramics was studied by adding La₂O₃.The influence of microwave effect and La₂O₃ content changed on the microstructure and macroscopic properties of slag glass-ceramics.The high-speed iron tailings with similar composition and Bayan Obo tailings were used as raw materials.Moreover,the CMAS system slag glass-ceramics with the La₂O₃ content of 0%-4%were prepared by microwave heat treatment process for experimental research.In order to find the universal law of crystallization and heat treatment of slag glass-ceramics by microwave heating process,differential scanning calorimetry（DSC）,X-ray diffraction analysis（XRD）and Raman spectroscopy（Raman）were used to characterize the structure of slag glass-ceramics.Furthermore,field emission scanning electron microscopy（FEGSEM）and energy dispersive spectrometer（EDS）were used to analyze microstructure characteristics and main element distribution.The mechanical properties of slag glass-ceramics were analyzed through testing.By summarizing and analyzing the experimental results,they showed that::Microwave heating has successfully prepared slag glass-ceramics.Microwave heating and traditional heating have generated similar main crystal phases.The main crystal phases are pyroxene phases.The addition of rare earth oxides can inhibit the crystal tendency of the main crystal phases in the slag glass-ceramics.The microstructure of the slag glass-ceramic prepared by microwave sintering is similar to that of traditional sintering.But the crystal structure of the slag glass-ceramics prepared by the microwave sintering is denser and the crystal grains are more uniform.In addition,the rare earth ions are evenly distributed in the samples.Microwave heating has the characteristics of volume heating.The symmetric stretching vibration of non-bridging oxygen in the silicon-oxygen tetrahedron is larger and the peak intensity is stronger,which can further indicate that in microwave heating,the faster the grain growth rate is,the deeper the degree of crystallization is.As the content of rare earth oxides increases,the density of the slag glass-ceramics increases,but the acid resistance decreases.While the alkali resistance is the highest,reaching about 98%.