Novel materialization and harmless treatment of copper smelting slag (CSS): Composite ferrite formation and nonferrous metals doping mechanisms

Abstract

The composite ferrite materialization conversion of copper smelting slag (CSS) is an alternative approach for the value-added utilization of high-Fe-content industrial byproduct. Various Fe-bearing minerals and secondary resources, including the Fe2O3-type, Fe3O4-type, and FeO-type, have been successfully used to prepare high-performance composite ferrite materials. In this work, a more refractory Fe2SiO4-type CSS was attempted to prepare composite ferrite through oxidizing roasting process. Firstly, the thermodynamics analysis of the Fe2SiO4-MnO2 system in oxidization atmosphere was conducted to determine the main reactions for composite ferrite formation. Then, the phase transformation, microstructure evolution, and interface element migration were investigated to determine the oxidation reconstruction of fayalite and the Cu/Zn doping behaviors in composite ferrite. The oxidized products of fayalite react with decomposed oxides of MnO2 to form composite ferrite. Importantly, it’s found that Cu and Zn in CSS occupy the original Mn (II) at the tetrahedral site within the spinel structure. The Cu/Zn doping can improve the comprehensive electromagnetic wave absorption property, and reduce the risk of heavy metal pollution through solidification within the stable composite ferrite structure. On the other hand, the released SiO2 after oxidization of fayalite combines with CaO, Al2O3, and seldom Mn oxide to form silicate phase of (Mn, Ca, Al) SiO3. Eventually, this work proposes an alternative method for the materialization and safe disposal of CSS, which realize the dual effect of composite ferrite transformation and simultaneous immobilization of heavy metals of Cu and Zn into the spinel structure. This work establishes the theoretical basis for the composite ferrite preparation from refractory Fe2SiO4-type iron resources.