Analysis of dominant phases inhibiting dissociation of smelting slags and the alkali depolymerization mechanism

Abstract

This study analyzed the prevalent physicochemical phases of smelting slag from the perspective of data science and chemistry. Findings delineated the silicate phase as the pivotal and predominant constraining phase for the resource utilization of smelting slag. An intricate correlation between metallic elements and dominant phases was constructed. Typical silicate phase olivine (OL) was synthesized as a paradigm to examine alkali depolymerization, unveiling the optimal conditions for such depolymerization to be an alkali to olivine molar ratio of 1:5, a reaction temperature of 700 °C, and a duration of 3 h. The underlying mechanism of alkali depolymerization within silicate phases was elucidated under these parameters. The reaction mechanism of alkali depolymerization within silicate phases can be encapsulated in three sequential steps: (1) NaOH dissociation and subsequent adsorption of OH⁻ to cationic (Mg or Fe) sites; (2) disruption of cation-oxygen bonds, leading to the formation of hydroxide compounds, which then underwent oxidation; (3) Na⁺ occupied the resultant cation vacancy sites, instigating further depolymerization of the intermediate Na₂(Mg,Fe)SiO₄. The articulated mechanism is anticipated to furnish theoretical underpinnings for the efficacious recuperation of metals from smelting slags.

Graphical abstract