Effect of unmelted lime on the element distribution behavior on a CaO–SiO(2)–MgO–Al(2)O(3)–FeO–CaF(2)(–Cr(2)O(3)) slag

In this study, a CaO–SiO(2)–Al(2)O(3)–MgO–FeO–CaF(2)(–Cr(2)O(3)) slag was chosen according to the compositions of the stainless steel slag for industrial production, and a CaO block was added to the molten slag after the synthetic slag was fully melted. The influences of unmelted lime on the distribution of elements and the structure of product layers at the lime/slag boundary, particularly the existing state of chromium oxide in the chromium-bearing stainless steel slag, were deeply discussed by scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) and FactSage 7.1. The experiment results indicated that when the unmelted lime existed in the CaO–SiO(2)–Al(2)O(3)–MgO–FeO–CaF(2) slag system, two product layers of periclase (MgO) and dicalcium silicate (Ca(2)SiO(4)) at the boundary of the CaO block were formed. However, when the CaO block was added in the CaO–SiO(2)–Al(2)O(3)–MgO–FeO–CaF(2)–Cr(2)O(3) stainless steel slag, besides MgO and Ca(2)SiO(4) product layers, needle-shaped calcium chromite (CaCr(2)O(4)) was also precipitated around the CaO block. Moreover, a small amount of Cr dissolved in the periclase phase. Eh–pH diagrams showed that the CaCr(2)O(4) and MgO phase unstably existed in a weak acid aqueous solution. Therefore, the existence of unmelted lime in the stainless steel slag could enhance the leachability of chromium.