Synergistic calcium leaching and iron enrichment by indirect carbonation of thermally modified steel slag

Abstract

Indirect carbonation of steel slag is an effective CO2 sequestration strategy, which is of great significance for reducing CO2 emissions of the iron and steel industry and achieving its green and low-carbon development. This paper proposed a process for high-temperature modification followed by indirect carbonation of steel slag, which enabled the separation and synergistic utilization of calcium and iron elements of the slag. The reactivity of various minerals in steel slag was initially studied at the level of ion coordination utilizing crystal structure theory. The results indicated that the O2- valence of β-Ca2SiO4 was unsaturated, resulting in high reactivity. In contrast, the O2- valence of Ca2Fe2O5 was relatively saturated, resulting in poor reactivity. The results of high-temperature modification and leaching experiments demonstrated that as the basicity of the steel slag decreased, the calcium component transformed into Ca2SiO4, while the iron component transformed into spinel minerals. When the basicity was too low, the Ca and Fe components recombined to form the poorly reactive Ca3Fe2(SiO4)3. As the basicity of the steel slag decreased, the Ca2+ leaching rate and the total iron content of leaching residue initially increased and then decreased. At a basicity of 2, both the Ca2+ leaching rate and the total iron content of leaching residue reached their maximum of 84.46% and 48.39%, respectively. This study significantly improved the Ca2+ leaching rate and the total iron content of leaching residue through high-temperature modification, thereby enhancing the CO2 sequestration capacity of the steel slag and the recovery level of iron resources The above strategy would be of great significance for promoting the green and low-carbon development of the iron and steel industry.