| Steel slag,as a by-product produced in the production process of mining and metallurgy,has significant characteristics such as huge output and low utilization rate.And its performance and compositions are quite different due to varieties in raw materials and smelting processes.Among all industries in China,iron and steel metallurgical industry CO2 emissions are second only to the power industry.Under the background of the "Double Carbon" policy,China’s steel and metallurgical industry is facing huge environmental,economic and social pressures.How to achieve reasonable and efficient use of steel slag and reduce CO2 emissions in the industry is an industry transformation problem that the traditional heavy industry must face.CO2 curing steel slag to prepare building materials is expected to achieve efficient use of steel slag and carbon emission reduction.At the same time,carbonization potential evaluation on various types of steel slag,steel slag carbonization and cementation mechanism research,and the rational design of solid waste carbonized building materials are key theoretical and technical problems that must be solved in the process of carbon neutralization in China’s mining,metallurgy,and building materials industries.This study takes eight kinds of steel slag as the research object,based on the analysis of QXRD,XRF and other raw materials analysis,combined with the carbonization flow test,the carbonization leaching test,and the high-humidity carbonization curing test,to quantify the carbonization potential of the steel slag under the normal temperature and pressure environment,and determine Carbonization activity of various minerals in steel slag.In addition,through the organic combination of various physical and chemical analysis methods such as QXRD,XPS,SEM,TG,MIP,etc.,the influence of desulfurized gypsum on the carbonization and cementation properties of four steel slags with different aluminum content and different alkalinity was studied.Synergy mechanism of steel slag-desulfurized gypsum system in the hydration and carbonized environment was established.Orthogonal experiment and single factor analysis were used to study the influence of molding method,gypsum content,liquid-tosolid mass ratio and curing environment on the strength and CO2 uptake of steel slag carbonized building materials,and optimize the production process parameters of steel slag carbonized building materials.The main rsults are as follows:(1)It was found that calcium-containing minerals in steel slag,except for brownmillerite,have high carbonization activity.Based on this fact,a method for evaluating the carbonization potential of steel slag and determining the content of active calcium in steel slag based on the composition of raw materials was proposed.And the feasibility of the method is verified by the carbonization leaching test results.The leaching mechanism of the main ions of steel slag in the carbonization environment is revealed.The results show that in the calcium of ordinary converter steel slag,active calcium accounts for 74%to 90%.This result intuitively proves that steel slag has very high carbonization activity.(2)Using comprehensive methods including X-ray diffraction quantitative phase analysis,X-ray photoelectron spectroscopy,thermal analysis,and pore structure analysis,it revealed the changes in mineral composition during the hydration and carbonization process of steel slag,and revealed the catalytic mechanism of gypsum on the hydration-carbonization of steel slag.It was found that gypsum can stimulate the activity of aluminate minerals in steel slag.The ettringite and hemicarboaluminate formed are important intermediate products,which were further carbonated into calcite and monocarboaluminate in the carbonization environment.Carbonation products such as calcium carboaluminate,aragonite and vaterite.The hydrated and carbonated products intersperse and wrap each other to fill the pores and promote the increase of the strength of the sample.The higher the aluminum content in the steel slag,the stronger the stimulating effect of gypsum on the carbonization of the steel slag.After adding gypsum,the highest increasing rates of carbonated calcium content in low-aluminum,mediumaluminum and high-aluminum steel slag were 13.62%,41.40%and 71.46%,respectively.(3)The technological parameters of different types of steel slag carbonization curing were optimized.Steel slag-desulfurized gypsum carbonized building materials with high strength,short curing period and high CO2 uptake were prepared.When the liquid-solid mass ratio is 1:5,gypsum/Anshan converter slag is 1:16,and the molding pressure is 27MPa,the compressive strength can reach 30MPa and the CO2 uptake can reach 10.39%after 6 hours of carbonization curing.Besides,when the carbonization curing duration is 1 day,carbonized building materials samples have a compressive strength of 55MPa and CO2 uptake of 12.36%.(4)The decisive effects of water on the mechanical properties and carbon fixation performance of the sample were revealed.The implementation of hydration pre-curing,the selection of an appropriate liquid-to-solid ratio and the curing environment humidity have a great impact on the strength and CO2 uptake of the samples.The main reasons is that the products such as ettringite and C-S-H gel,formed by hydration reactions,lay a matrix for strength growth and provide a material and space basis for the subsequent carbonization reactions.The prehydration curing of the press-molded sample for 1 day before carbonization curing can promote the strength of the sample and CO2 uptake of steel slag to increase by 25.24%and 3.91%,respectively.For the cast-moled samples,increasing 1 day hydration curing before carbonization to 9 days,the compressive strength and CO2 uptake of steel slag increased by 126.43%and 9.57%,respectively.The research results of this paper have further improved the theoretical basis of steel slag carbonization and cementation.A more scientific production method of steel slag carbonation-cured building materials was obtained,which can provide technical guidance for the industrialization and large-scale high-efficiency production of metallurgical slag carbonated building materials.It is of great significance to achieve carbon peak and carbon neutrality as soon as possible,and to achieve an organic combination of economic,environmental,social and technological benefits. |
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