Selective Leaching of Steelmaking Slag for Indirect CO2 Mineral Sequestration

Indirect CO2 mineral sequestration, which could make CO2 fixate into precipitated calcium carbonate (PCC) of value-added products, is an important technology that is used to reduce greenhouse gas emissions economically. It can be conducted in two steps, one of which has been investigated in the previous paper. In this work, extraction of calcium ions from steelmaking slag using it novel leaching medium, which involves organic solvent tributyl phosphate (TBP), acetic acid, and ultrapure water, was studied. Several operating variables, including stirring speed, phase-volume ratio, organic solvent-to-solid ratio, initial acetic acid concentration, acid-to-slag ratio, reaction temperature, and reaction time were investigated. It was found that the leaching process could be divided into three regions according to the acid-to-slag ratio. The first region below 0.5 g/g was characterized by the acid-to-solid ratio; the second region above 0.5 g/g but below 1.0 g/g was characterized by the acid-to-solid ration and the third region above 1.0 g/g was characterized by the acid-to-solid ratio. When the acid-to-solid ratio was below 1.0 g/g, only Ca and Mo could be leached with the maximum leached ratios of 75% and 35%, respectively. Moreover, the leaching behaviors of Ca Mg, Fe, Al, and Si were greatly affected by reaction temperature and reaction time. Results show that the Calcium ions can be effectively and selectively extracted from the steelmaking slag and that the reaction medium can be recovered and recycled with high efficiency. These are the keys to indirect CO2 mineral sequestration.