Abstract
Copper slag, which contains Fe-rich fayalite (Fe2SiO4), is a valuable solid waste that warrants further research in order to recover iron. Calcium oxide (CaO) can significantly enhance iron recovery from copper slag; however, the associated mechanism has not yet been explored. In this study, we investigated the interaction between CaO and Fe2SiO4 to obtain detailed understanding of the role of CaO in enhancing iron recovery. The presence of CaO was found to accelerate the decomposition of Fe2SiO4 via an ion-exchange-like process. Specifically, CaO dissociated into Ca(II) and a Ca-deficient Ca1-yO species at high temperatures. The Fe(II) ion at the M2 site of Fe2SiO4 was substituted by the released Ca(II) ion, resulting in the formation of [(Fe(2-x)Cax)SiO4]∙xFe(II). Subsequently, the substituted Fe(II) occupied the Ca vacancy in Ca1-yO to form (Ca(1-y)Fe(II)y)O. The disproportionation of Fe(II) and the combination reaction between CaO and the SiO2 separated from Fe2SiO4 led to the generation of the final products, viz. Fe2O3, Fe3O4, and CaSiO3. This study explains the specific role of CaO in decomposing Fe2SiO4. It would not only provide theoretical guidance for iron recovery from copper slag but also present a new perspective on the recycling of valuable resources from many other smelting slags (e.g., iron slag, lead slag, and nickel slag).
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