Effects of Na₂O on Crystallization of Converter Slag

This study investigated the influence of Na₂O content on the crystallization behavior of converter slag. Various analytical techniques such as SEM, XRD, FTIR, and Raman spectroscopy, were used to clarify the impact of Na₂O on crystalline phase formation within the slag matrix. Na₂O addition facilitated crystallization, changing the slag morphology and composition notably. Initially, without Na₂O, the slag primarily comprised Ca₂SiO₄ and Ca₂Fe₂O₅ phases. Upon 2.5 wt% Na₂O addition into the slag, the morphology changed, revealing a new phase, (MgO)_0.239(FeO)_0.761. There was no distinct separation of MgO and FeO due to their uniform distribution. Moreover, a clear phase separation occurred at 5 wt% Na₂O, increasing calcium ferrite concentration. With 7.5 wt% Na₂O, a non-magnetic NaFe₂O₃ phase emerged, which could possibly cause a loss of valuables during magnetic separation. Additionally, Na₂O addition introduced O²⁻ ions, facilitating a non-bridging oxygens' formation and leading to an increased Q_Si⁰ and Q_Si¹ units, and a decreasing Q_Si², Q_Si³, and Q_Si⁴ units, resulting in an increased depolymerization degree of silicate structure. The depolymerized silicate network, enhanced slag crystallization and aiding metal precipitation and aggregation.