Preparation Of Decorative Slag Glass-Ceramic And Study On The Solidification Mechanisms Of Heavy Metals Ion

With the rapid development of the national economy construction,the consumption of steel products has reached an extremely high level which result in large emission and accumulation of blast furnace slag in the process of blast furnace ironmaking.For example,it is reported that about 3.5 million tons of rare earth-containing blast furnace slag（REBFS）originated from Bayan Obo rare-earth iron ore deposit in Baotou of Inner Mongolia are generated each year.As a result,a large amount of land resources are occupied due to the the accumulation of REBFS,and the heavy metals in REBFS make much damage to the environment and seriously threatens the human health.Because the composition of REBFS are close to that of glass-ceramics,the preparation of high performance slag glass-ceramics not only consumes a large amount of REBFS,but also realizes the solidification of heavy metals.In addition,the decorative glass-ceramic for industry usage with different colors can be prepared by adding relevant heavy metals.At present,there are few researches on combined effect of the existing state and curing mechanism of multiple heavy metals in glass-ceramics,since REBFS usually contains many kinds of heavy metals.Moreover,there is still lack of in-depth research on the stability of the heavy metals used as coloring agent in glass-ceramics,which is not conducive to the long-term use of the decorative glass-ceramics in complex environments.In this study,glass-ceramics are prepared from BSBFS by melting method and Fe₂O₃and Cr₂O₃ are added as multiple nucleating agents due to the lack of effective nucleating agents in REBFS.The effects of Fe₂O₃ and Cr₂O₃ on the crystallization characteristics and properties are studied in depth.The purpose of this study is to investigate the combined effects of Fe₂O₃ and Cr₂O₃ on the structure and properties of glass-ceramics and to determine the optimum mixture ratio of Fe₂O₃/Cr₂O₃.On this basis,the preparation of architectural decorative glass-ceramics can be achieved by changing the addition amount of Mn O₂ and Cu O.Meanwhile,the existing state and coloration Mechanism of heavy metals Cr,Mn and Cu in glass-ceramics are studied deeply.The aim of this study is to examine the combined solidification effect of the multiple heavy metals in glass-ceramics by analyzing the curing effect and curing mechanism of heavy metals in glass-ceramics.The results show that Cr₂O₃ can be used as effective nucleating agents to promote precipitation of the crystalline phase of glass-ceramics than Fe₂O₃.Cr₂O₃ can strongly promote the crystallization of glass-ceramics by forming spinel nuclei,and the main crystalline phase of pyroxene grows preferentially along the normal direction of the spinel surface in the form of dendrites.With the decrease of Fe₂O₃/Cr₂O₃ ratios,the mode of crystallization of glass-ceramics changes from surface crystallization to bulk crystallization,and the main crystalline phase of glass-ceramics changes gradually from diopside to augite.Therefore,the appropriate proportion of Fe₂O₃/Cr₂O₃can effectively induce the formation of pyroxene with integrated interlocking crystal structure and the glass-ceramics show excellent physicochemical properties.Glass-ceramic with Fe₂O₃/Cr₂O₃ ratio of 1 possesses the most optimal combination of properties with bending strength of 138.93 MPa,Vickers hardness of 7.51 GPa and acid resistance of 97.75%.The REBFS glass-ceramics with different Mn O₂ additions are prepared,choosing optimal proportion of Fe₂O₃/Cr₂O₃ as nucleating agents.The existence state of Cr and Mn in glass-ceramics and the mechanisms of solidification and colourisation of heavy metals in glass-ceramics are studied.Manganese ions have two valence states in glass-ceramics,namely Mn²⁺and Mn⁴⁺,and the Mn ions are widely distributed in the spinel phase,the pyroxene phase and the glass phase.Where Cr and Mn can be collaborative solidified in spinel phases.With the increase of Mn O₂ additions,the manganese ion in glass phase can break the[Si-O]net structure and decrease the viscosity,and the crystal morphology of pyroxene changes from dendrite to spherulites like morphology.As a result,the density and Vickers hardness of glass-ceramics show an increasing trend,while the acid resistance and bending strength generally show a decreasing trend.The result of leaching characteristics of heavy metals in glass-ceramics suggested that the leaching concentration of heavy metals Cr and Mn were much lower than the standard value of leaching toxicity of hazardous waste（GB/T5085.3-2007）,which indicated that the glass-ceramics has a good stabilizing effect on heavy metals Cr and Mn.Meanwhile,the color of glass-ceramics changes from green to brown with the increase of Mn O₂ additions.The REBFS glass-ceramics with different Cu O additions are prepared,choosing optimal proportion of Fe₂O₃/Cr₂O₃ as nucleating agents.The existence state of Cu,Cr and Mn coexisted in REBFS and the mechanisms of solidification and colourisation of heavy metals in glass-ceramics are studied.The results show that the high electric field characteristics of Cr ions contribute to the generation of spinel phase,while Cu ions can enter the spinel crystal by replacement method and exist stably in spinel crystal.Where Cu,Cr and Mn can be collaborative solidified in spinel phases.The copper ions are widely distributed in the main crystalline phase,the spinel phase and the glass phase.The depolymerization effect of the copper ions in glass phase can improve the crystallization characteristics of the glass-ceramics,and promoted the transformation of the crystal morphology from dendrites to spherulites.Correspondingly,the hardness and density of the glass-ceramics are improved.At the same time,it is found that the increase in the Cu O contents contributed to the precipitation of cuprite in glass-ceramics,and the color of the glass-ceramics changed from green to copper red.The result of leaching concentration of heavy metals in glass-ceramics show that the leaching concentration of heavy metals Cu,Cr and Mn are much lower than the standard value of hazardous waste leaching toxicity,so that the copper red glass-ceramics can be safely used as a decorative building material.