Fundamental Research On Physicochemical Properties Of Steel Slag Ultra-fine Powder And Its Applied In Desulfurization And Carbon Dioxide Sequestration

Steel slag is the solid waste produced during the steelmaking process,which is one of the lowest utilization of solid waste for iron and steel enterprises.Steel slag is the ideal secondary resource,and can be widely used in building materials,road asphalt and other fields.Making use of steel slag can provide strong support to the steel industry's green development,and bring huge economic and social benefits.China is the world's major energy consumer,which increase carbon emissions and cause global warming.Lots of toxic gases,SO₂,is produced during industrial production,seriously affecting the environment and human health.Ultra-fine powder?UFP?is an important way to efficient utilization of steel slag.For efficient utilization of steel slag,in this study,steel slag was crushed into UFP at first.Then,Physicochemical properties of steel slag UFP were systematically studied.Finally,using the steel slag UFP to mineralize CO₂ and desulfurization,providing basic dates for industrial application of desulfurization and carbon sequestration by using steel slag UFP.The main research contents and results are as follow:?1?Researching on testing conditions of particle size distribution for steel slag UFP.Particle size distribution?represented by D10,D50 and D90,which refer to the equivalent diameter size at which the cumulative number of particles is 10%,50%,90%,respectively?were measured by the laser particle size analyzer,and some influence factors of operating conditions were discussed,including dispersing mediums,the mass ratio of solid to liquid,ultrasonic dispersing time and rate of stirring.Next,the steel slag UFP particle size distribution was measured by SEM for comparing with the consequence tested by LSA.According to the research result,when using the LSA test steel slag UFP,anhydrous ethanol is the most suitable mediums ultrasonic dispersion.The mass ratio of solid to liquid range 0.10⁰.90mg/mL,the particle size decreased with the concentration increasing,and the figure of D10,D50 and D90 were almost constant when the ratio was 0.01⁰.10mg/mL.The ultrasonic dispersing time was longer than 30 min,the optimum dispersion effect of steel slag was better.The particle size distribution from the LSA testing is almost no difference with the change of the stirring rate.In addition,the results tested by LSA were coincident with the results tested by SEM.?2?The physicochemical properties of steel slag UFP were studied.The particle size distribution,chemical composition,phase composition and thermogravimetric characteristics were respectively analyzed by laser particle size analyzer,X-ray fluorescence spectrometer,X-ray diffraction and thermogravimetric analyzer.The results shown that the particle size?Represented by D50,which refer to the equivalent diameter size at which the cumulative number of particles is 50%.?of samples ranged from 3.15?m to15.78?m.With increasing the particle size,the mass fraction of Ca in the sample decrease,and the maximum reduction was 18.60%;the content of Fe,Mn,V and P increase with increasing the D50,and the maximum increment was up to 104.58%,154.90%,129.03% and 163.64%,respectively;The changes of D50 had less effect on the content of Si,Mg,Ti and Al.Apparent density of steel slag UFP increased with adding the content of Fe.With increasing of particle size,the diffraction intensity of Ca?OH?2 and CaCO3 by XRD plot weaken gradually and disappear finally.The diffraction intensity of RO phase minerals and Ca2Fe2O5 gradually enhanced,and the diffraction peak intensity of dicalcium silicate?C2S?and tricalcium silicate?C3S?changed not conspicuously.With decreasing the particle size,the lost weight of the decomposition of calcium and magnesium compounds?Mg CO3,Ca?OH?2 and CaCO3?increased.?3?The effects of different reaction conditions on the process of CO₂ mineralization in slag UFP were investigated.Using steel slag UFP mixed with water and then react with CO₂ in the mineralization reactor.The carbon content of the solid after the reaction was measured using an elemental analyzer,and the reaction end point and the reaction rate were judged fromthe curve of pH change.The results shown that the mineralization of CO₂ in slag UFP was mainly by the compounds of Ca and Mg reaction with CO₂.The efficiency of carbon sequestration significantly decreased with the the particle size increasing.With solid-liquid ratio of reactants increased,the reaction speed increased and the carbon sequestration rates remained constant.The reaction speed was slower at 25?,while the temperature was between35?to 65?,the speed significantly was accelerated.The total carbonation percentage increased slightly with increasing reaction temperature.The reaction speed was slower when the stirring rate was 140 r/min or 280 r/min.While the stirring rate was more than 560 r/min,the reaction speed was accelerated.In the above reaction,steel slag UFP's carbon sequestration rate was up to 28.33%.The reaction rate of calcium in the steel slag UFP was59.80%,and the reaction rate of magnesium in the steel slag UFP was20.86%.?4?The desulfurization with steel slag UFP were investigated.Steel slag UFP were mixed with water and then reacted with SO₂ in the mineralization reactor.The composition of the elements in the solid and the liquid phase after the reaction were measured by XRF.The results shown that the main products of this reaction were the solution of CaSO3 and the solid of CaSO3·0.5H2 O or CaSO4·0.5H2 O.The desulfurization rate of steel slag UFP was62.80%.After the reaction,24.12% of Ca were presented in the solid and75.88% of Ca existed in the liquid;For Mg,Fe and Al,respectively,the content of 20.59%?40.68% and 35.00% were presented in the solid,while79.41%?59.32% and 65.00% of content were existed in the liquid.For Si and Ti,the content in solid were 55.07% and 66.67%,while only 44.93% and33.33% of content were in the liquid products.