Experimental Study On Carbon Dioxide Capture Characteristics Of Ca-based Materials Derived From Steel Slag Modification

With the rapid development of global industrialization,a large number of CO₂emissions from fossil fuel combustion cause global warming increasingly.High temperature Ca-based cycle is one of the most potential CO₂ capture technologies.Steel slag is a large amount of solid waste in the iron and steel industry.Its comprehensive utilization rate is low relatively.Steel slag contains up to 40-50%calcium element,which has the potential to capture CO₂ circularly as a Ca-based absorbent.However,the overall structure of steel slag is compact,most of calcium exists in the form of compound,and the direct absorption capacity of CO₂ is weak.Serious high temperature sintering is easy to occur in Ca-based absorbent after multiple cycles,which results in the rapid reduction of the capture capacity for the absorbent.These two aspects limit the comprehensive utilization of steel slag and the effect of CO₂ capture.In order to improve the reaction performance and cycle stability of steel slag absorbing CO₂,the following four aspects have been studied in this paper:（1）the Ca-based CO₂ absorbent derived from steel slag has been modified and prepared indirectly by using acetic acid leaching agent.The influence of the acetic acid indirect leaching parameters on the content of elements in the absorbent has been studied theoretically and experimentally,and the process of acetic acid leaching for steel slag and the mechanism of element regulation and control for the absorbent have been analyzed;（2）the ability of Ca-based absorbent prepared by acid leaching of steel slag to capture CO₂was investigated circularly in a fixed bed reactor;（3）mesoporous materials were introduced to modify the Ca-based absorbent derived from steel slag,and the influence of the modification on the capture of CO₂ by Ca-based absorbent derived from steel slag was studied,and the mechanism of improving the circulation stability of the absorbent was also studied.（4）The prediction model was used to predict the carbonation conversion of Ca-based absorbent derived form steel slag under long cycle.According to the thermodynamic calculation,most of the calcium containing phases in the slag can react with acetic acid spontaneously at room temperature.The results show that the acid concentration and liquid-solid ratio are the significant factors affecting the element content.Under the condition of low acid concentration and liquid-solid ratio,the acid leaching of steel slag is conducive to the increase of calcium content.It is shown that the amount of acid in the solution system can regulate the leaching of iron and silicon,and increase the content of calcium in the absorbent by analyzing the process of acetic acid leaching of steel slag.In the fixed bed reactor,the experimental study on the cyclic capture CO₂ by the Ca-based absorbent derived from steel slag was carried out.The content of elements except calcium in the Ca-based absorbent derived from steel slag will influence the absorption capacity of CO₂ by the absorbent.The elements such as aluminum and magnesium are conducive to the anti-sintering of the sorbent.The sintering of silicon and iron is accelerated.The carbon capture of the absorbent derived from steel slag can be improved by adjusting and controlling the process of acetic acid leaching modification.The initial carbon capture capacity of the sorbent is 0.61 g _CO2/g-absorbent under the optimized conditions,and the deactivation rate after 20 cycles is 52.46%,which is better than that of analytical reagent Ca O.In combination with the mesoporous molecular sieve technology,the modified steel slag derived absorbents were prepared by the non-aqueous synthesis evaporation induced self-assembly method,and better than optimized steel slag derived Ca-based absorbent.The uniform distributed amorphous Ti O₂ in the optimized steel slag derived Ca-based absorbent was resulted from the hydrolysis of tetrabutyl titanate,and a coating layer with mesoporous channels was formed on the surface of the absorbent particles.It can effectively reduce the sintering and fusion of Ca-based absorbent at high temperature due to the spacing of Ca Ti O₃ in the absorbers after calcination,and the activity attenuation of the absorbent is significantly reduced.The modification can effectively improve the cycle absorption performance of steel slag derived Ca-based absorbent,and significantly enhance the stability of Ca-based absorbent in the cyclic CO₂ absorbed process.After 20 cycles of CO₂ absorption,the best absorption amount is still 0.44 g _CO2/g-absorbent.The deactivation change of Ca-based absorbent under long cycle can be well predicted by the model X_N=（1/（1/（1-X_r）+kN）+X_r）×（1+k_D）of carbonation conversion rate decay in the Ca-based absorbent capture CO₂ process.It is found that the cycle stability of the Ca-based absorbent is better than that of the analytical reagent Ca O when it contains more Al,Mg,Mn and other elements.The carbonation conversion of the modified Ca-based absorbent changes little after 150 cycles,and the cycle stability of the absorbent is large amplitude increase.