Phase transition and dissolution behavior of Ca/Mg-bearing silicates of steel slag in acidic solutions for integration with carbon sequestration

Abstract

Steel slag (SS) and carbon dioxide are two major waste products of the iron- and steelmaking process. Indirect aqueous carbonation of SS using Ca/Mg is a promising way for carbon capture, utilization, and storage (CCUS). However, it is generally accepted that the Si-rich layer produced during the leaching of silicates in SS has serious implications for the Ca/Mg recovery. Therefore, understanding the phase transition and dissolution behavior of Ca/Mg-bearing silicates of SS in acidic solutions is of vital importance for SS-based CCUS. In this work, three synthetic Ca/Mg-bearing silicates (Ca3MgSi2O8, Ca2MgSi2O7, and γ-Ca2SiO4) of SS were prepared and studied by leaching tests. Experiments were carried out with leaching silicate powder in 0.1 mol· L−1 HCl solution for various reaction time at room temperature. Results show γ-Ca2SiO4 and Ca3MgSi2O8 dissolved rapidly during the early leaching stages, giving more silica gel towards the end. Phases of Ca3MgSi2O8 and Ca2MgSi2O7 dissolved to yield Ca2+ and Mg2+ in solution in a similar ratio as in the original mineral. The Ca2MgSi2O7 phase was transformed into diopside (CaMgSi2O6) and silica gel during the acid leaching. Thus, the difference in phase transition of the studied Ca/Mg-bearing silicates is primarily related to the dissolution of the Si group in the crystal.