Recovery of calcium and magnesium bearing phases from iron– and steelmaking slag for CO2 sequestration

[Display omitted] •Orders of solubility of Ca/Mg–bearing phases are investigated and proposed.•CaO and MgO exhibited a relatively higher solubility than Ca/Mg–bearing silicates.•Minerals showed higher solubility in acidic solutions than ammonium salt solutions.•Transformation mechanism of silicates in leaching process is illustrated. Large amounts of iron– and steelmaking slag and greenhouse gas are annually produced by the steel industry worldwide. Using Ca/Mg in the slag to capture and store the CO2 via mineral carbonation is a promising approach to the reduction of waste emissions. Since iron– and steelmaking slags are a mixture of numerous types of minerals, understanding the dissolution behavior of various phases in solution system is of critical importance for Ca/Mg recovery. In this work, seven Ca/Mg–bearing phases and four typical solutions were prepared and studied. Theoretical results indicated that the order of mineral solubility in aqueous solution is as follows: (CaO and Ca2SiO4) > (Ca3MgSi2O8, Ca2MgSi2O7, and MgO) > Ca2Al2SiO7 > MgCr2O4. A batch of leaching tests was conducted at room temperature, and the recovery yield of Ca/Mg was investigated. It was found that minerals show different dissolution behavior in various systems, and the metallic oxide phases exhibited a relatively higher solubility than silicate phases. The solubility of minerals in various systems was illustrated by radar plots. Moreover, leaching tests for silicate briquettes were performed to investigate the transformation mechanism. On the basis of the results, it was proposed that a silicic acid layer generated on the surface of briquettes in the leaching process, and could transform into porous silica phase via dehydration process. The formed Si–rich layer obstructed the dissolution of inner mineral leading to a low recovery efficiency of Ca/Mg.