Optimization Of Carbonation Condition Of Slurry Contained Steel Slag And Its Effect On Cement Hydration And Performances

Steel slag is an industrial byproduct obtained from steel industry.It is produced as a residue by melting iron ore in an electric arc furnaces or basic oxygen furnace.Because of a low pozzolanic reactivity,landfilling is still the most common way to manage steel making slag in China.In recent years,mineral carbonation of alkali solid wastes is envisaged to be an effective method to sequester carbon dioxide(CO2)and turn the alkaline solid wastes into more valuable products.Basic oxygen furnace slag(BOFS)contains a high content of calcium oxide,which is a potential medium to sequestrate CO2 via the carbonation process.Hence,these were studied in this project.Research contents:The aqueous carbonation(slurry carbonation)of BOFS were studied by considering five reaction parameters including solid to liquid ratio(S/L),CO2 flow rate,temperature,volume of water and carbonation time,to maximize CO2 sequestration.The carbonation degree and reaction products of aqueous carbonated BOFS were evaluated and compared with those produced by dry carbonation(solid carbonation)method.In addition,the potential of using carbonated BOFS and carbonated slurry contained BOFS as a cement replacement(10%,20%and 30%by mass)was also investigated.Research methods:The physico-chemical properties of the carbonated BOFS were also characterized by thermogravimetric analysis(TGA),X-ray diffraction(XRD)and scanning electron microscopy technique(SEM).And the mechanical,hydration heat and microstrucutre properties were systematically studied through a series test of tests to investigate the impact of carbonated BOFS powder and its slurry on cement hydration.Research results showed that:1.The optimum reaction conditions of aqueous carbonation of aqueous carbonation BOFS particles were S/L of 0.30 g/ml,CO2 flow rate of 2 L/min,600 ml of water,temperature of 40℃ and carbonation time of 2 hours.Under optimum condition,the maximum amount of CO2 sequestration at 16.35%(or carbonation degree of 50%)can be achieved and the carbonation product was calcite.Also,among them,temperature had the greatest influence on aqueous carbonation of BOFS.2.In comparison with aqueous carbonation,only a small of calcium hydroxide in BOFS(water content of 0)reacted with CO2 under dry route(an ambient temperature)for 28 days.As for dry carbonation of BOFS,the carbonation product found was mainly aragonite,and the CO2 sequestration was about 4.91%.Moreover,the specific surface area of aqueous carbonated BOFS particles(37.34 m2/g)was 10 times higher than that for dry carbonated BOFS particles(3.67 m2/g).3.Besides,the results demonstrated that aqueous carbonation preforms slightly better than dry carbonated BOFS for an equal replacement ratio of cement in the blended cement paste.As a small ratio of aqueous carbonated BOFS(10%～20%)blended in the cement paste accelerated the hydration rate of cement during the first 24 hours,mainly due to the presence of a greater calcite content in the aqueous carbonation.However,the strength results showed that the replacing cement with 10%～30%of either dry or aqueous carbonated BOFS decreased the compressive strength of blended cement paste due to less hydraulic binder for cement hydration.4.The carbonated slurry reduce the flowability,increase the porosity and decrease the compressive strength of all paste samples,as compared to pure cement.However,this should be noted that the use of slurry increased the strength with a maximum 28-day compressive strength of 96.6%of OPC(replacement ratio of 10%),as compared to fresh BOFS.