Fundamental Research On The Preparation Of Glass Ceramics/Cast Stone From Cr-containing Solid Waste

Cr2O3 is commonly used as raw material for the preparation of silicate materials.As a nucleating agent,it can effectively promote the nucleation and crystallization of the main crystalline phase.In recent years,a large amount of solid waste containing chromium has been produced in China,so this part of resources can be utilized.Some relevant studies have been done,but the leaching mechanism of chromium and the function of chromium in silicate materials need to be further researched.The toxicity of Cr6+ is also the main reason that the solid waste containing chromium can not be fully used.In this research,based on the transformation of Cr-containing mineral phase,solid solution and leaching of chromium in different mineral phases and crystallization of main crystalline phases,the proper mineral phase structure of the material was obtained,and the silicate materials with excellent physical and chemical properties were prepared.At the same time,its environmental safety was also evaluated.The main contents and results of the research are as follows:(1)Through equilibrium experiments,the results show that Cr2O3 has a certain solubility in mineral phase,the maximum solubility in pyroxene phase is between 1wt%-3wt%,and excess Cr2O3 will form magnesia-chrome spinel.The soluble chromium has the ability of leaching,in contrast,the chromium in spinel is more stable.(2)The effect of Cr2O3 on the nucleation and crystallization of material was studied.It is found that Cr2O3 can simplify the network structure,refine the crystal grain and shorten the crystallization time of diopside.The crystallization activation energy of diopside-based glass ceramics is 274 KJ/mol and the Avrami parameter is 3.23,which indicates that the thermodynamic and kinetic conditions of crystallization are proper.Meanwhile,the material has a significant effect on chromium solidification.(3)Based on the above research,the microstructure of the material was also investigated.It is found that the combination of Cr2O3 and CaF2 results in a snowflake-like microstructure with spinel as the core and pyroxene crystals growing around it.The sample(1.5Cr2O3-3.5CaF2)has the highest flexural strength(149.85 MPa)and good chemical stability.The chromium leaching amount of 0.206mg/L is much lower than the national standard of 1.5 mg/L.The flexural strength(170.31 MPa)of the sample added with 2wt%ZnO is further improved,and the leaching amount of chromium is 0.349mg/L,which shows that the environmental safety of the material.(4)Based on two technical routes,glass ceramics and cast stone were prepared by using Cr2O3.It is found that the MgO-Al2O3-SiO2 glass-ceramics with 0.5wt%Cr2O3 added has the best flexural strength(71.62 MPa)and good linear thermal expansion(6.76×10-6/℃),which could be used as medium thermal expansion material.In the study of production of one-step pyroxene-based cast stone,the maximum flexural strength of the material reaches 98.52 MPa,but the chromium dissolved in it is easy to leach out.In combination with the previous studies,the stability order of chromium elements is:Chromium in Spinel,chromium in glass matrix,chromium in pyroxene of glass ceramics and chromium in pyroxene of cast stone.(5)In order to evaluate the industrial application value of the research,glass ceramics were prepared by using AOD slag as raw material.It is found that the samples with 50AOD slag had the highest flexural strength of 137.83 MPa.The results of long-term leaching experiments show that the leaching of chromium from AOD slag is persistent,and the structure of glass ceramics can effectively inhibit the leaching of chromium.The above research shows that it is completely feasible to prepare glass-ceramics and cast stone from chromium-containing solid waste.Based on the mineral phase structure proposed in this study,the leaching of chromium can be inhibited and the properties of materials can also be greatly improved.This study provides necessary theoretical guidance and basic data support for comprehensive treatment technology of chromium-containing solid waste in Chinese steel industry.