Preparation Of Anti-hydration Environmentally Friendly Magnesia-calcium Refractory Material From Dolomite Phosphate Tailings

Phosphorus tailings is a large-scale mining solid waste produced after the extraction of phosphate concentrate from the phosphorus chemical industry.China's annual phosphate tailings discharge of about several hundred tons,but due to the low phosphorus comprehensive utilization of tailings,tailings long-term large amount of phosphorus in the tailings pile,which is not only a waste of resources,but also cause serious mine on the surrounding environment.According to the characteristics of high calcium,magnesium and low phosphorus in phosphorus tailings,the CaO content is about 30%,and the MgO content is about 18%.It can be regarded as a dolomite resource and used as a raw material for the production of magnesia-calcium refractories.CaO in magnesia-calcium refractory has good high temperature toughness,impact resistance,flaking resistance and corrosion resistance to high alkali slag,which has certain protection effect on high temperature steelmaking furnace and can also adsorb sulfur?S?,phosphorus?P?,oxygen?O?,and non-metallic inclusions such as silica?SiO₂?and alumina?Al₂O₃?to improve the purity of molten steel.In addition,magnesia-calcium refractories is an alkaline refractory material,which is consistently optimistic about the refractory industry and the steelmaking industry with low raw material prices,unique performance and environmental advantages.In this context,the paper proposes the use of dolomitic phosphate tailings to prepare magnesia-calcium refractories,which provides theoretical support for the comprehensive utilization of phosphorus tailings.The main findings are as follows:?1?Calculate the number of independent reactions occurring in the preparation of magnesia-calcium refractory system from phosphorus tailings by mathematical matrix theory.Independent reactions can be divided into two categories,the first type of main mineral dolomite decomposes into CaO and MgO,and the second type of CaO reacts with other impurities in the phosphorous tailings.Thermodynamic analysis of magnesia-calcium refractory system prepared from dolomite phosphorus tailings by HSC software,the results show that Dolomite phosphorus tailings decomposes MgO from 700K to 900K,and decomposes CaO at a temperature of 1100K.When the temperature is higher than 1213.15K,the dolomite phosphorus tailings basically decomposes completely as the temperature continues to rise,CaO easily reacts with impurities.Therefore,in the experiment of upgrading and reducing dolomite phosphorus tailings,the pre-calcination temperature should be controlled at70.1.23K¹213.15K,and the reaction of CaO and impurities can be reduced while ensuring more CaO and MgO content.?2?X-ray fluorescence spectroscopy?XRF?and X-ray diffraction?XRD?were used to determine the phase composition of dolomite phosphorous tailings,The results showed that the main chemical components of phosphorus tailings are CaO?32.04%?,MgO?18.68%?,a small amount of P₂O₅?4.34%?,Fe₂O₃?0.40%?,Al₂O₃?0.05%?,SiO₂?1.74%?and other impurities,the main phase is CaMg?CO₃?₂.The thermal decomposition process of dolomite phosphor tailings was detected by differential thermal analysis?TG-DSC?.The results show that the thermal decomposition of phosphorus tailings is divided into two stages,the first stage CaMg?CO₃?₂ decomposes CaCO₃,MgO and CO₂,the second stage is the decomposition of CaCO₃ into CaO and CO2.?3?The results of research on upgrading and doping of dolomite phosphor tailings indicate that The calcination temperature is 950?,the calcination time is 30min,the heating rate is 10?/min,and the raw material particle size is 200 mesh,The CaO content in the phosphorous tailings increased from 32.04%to 50.26%,increased by 18.22%,the MgO content increased from 18.68%to 28.53%,increased by 9.85%,the CaO activity used was 23.8ml,and the active MgO mass fraction was 59.04%.Both CaO and MgO activities are improved.?4?In order to avoid the existence of the mother salt illusion in the pre-calcined phosphor tailings,the pre-calcined phosphor tailings are treated by the digestion process to destroy the original lattice of the phase in the pre-calcined phosphor tailings,which contributes to the burning of the refractory material.The results showed that with the increase of digestion temperature,the prolongation of digestion time and the increase of water consumption,the lattice constants of MgO and CaCO₃ in pre-calcined phosphor tailings increased first and then decreased.When the digestion temperature is60°C,the digestion time is 10 min,and the water consumption for digestion is 15%,the lattice constant of MgO increases from 3.7429?to 4.0947?,and the lattice constant of CaCO₃ increases from 6.7186?to 7.4442?.?5?Investigate the effect of digestion process on the properties of magnesia-calcium refractories,the results showed that with the increase of digestion temperature,prolonged digestion time and increased water consumption,the performance indexes of refractory materials increased first and then decreased.When the digestion temperature is 60?,the digestion time is 10 min,and the water consumption for digestion is 15%,the bulk density of the refractory material increases from 2.84 g/cm³to 3.5 g/cm³,and the compressive strength at room temperature increases from 20.36MPa to 60.7 MPa,the residual pressure strength of thermal shock resistance increased from 10.09 MPa to 46.91 MPa,and the hydration weight gain rate decreased from 32.9%to 14.5%.?6?Study on the effect of preparation process on the properties of magnesia-calcium refractories,The results show that when the pre-calcined phosphorus tailings are digested,the raw material grade is 60%:20%:20%?crude:medium:fine?,and the calcination temperature is 1600?,the bulk density of refractory material increased from 2.63 g/cm³ to 3.58 g/cm³,the compressive strength at room temperature increased from 25.12 MPa to 56.93 MPa,and the residual pressure strength against thermal shock increased from 19.29 MPa to 41.76 MPa.The weight loss rate dropped from 27.9%to13.7%.?7?Study on the effect of nano-additives on the hydration resistance of magnesia-calcium refractories,The results show that the composite modification of nano-ZrO₂and nano-TiO₂ can improve the hydration resistance of refractories.When the mixing amount is 4%,TiO₂:ZrO₂=1:3,the hydration weight gain rate of refractories 6.6%,the hydration weight gain rate of the single additive is reduced by about 2%to 3%.