Innovative methodology for co-treatment of mill scale scrap and manganese ore via oxidization roasting-magnetic separation for preparation of ferrite materials

Abstract

Mill scale scrap, which contains vast amounts of valuable metals, is a solid waste produced in the iron and steel industry. Conventional mill scale scrap treatment methods for metal extraction are characterized by high energy consumption and low value addition. In this study, co-treatment of mill scale scrap and manganese ore via the oxidization roasting-magnetic separation process was investigated for the synchronous preparation of higher-value materials and recovery of valuable metals. Thermodynamic and magnetism analyses indicated that a higher temperature (>1100 °C) and a MnO2/Fe2O3 molar ratio of 0.75–1 are essential for the preparation of manganese ferrite. The experimental validation revealed that soft magnetic manganese ferrite powders with a purity of 97.5 wt% were obtained when the test was conducted at 1300 °C for 120 min, followed by a two-stage grinding and magnetic separation process; the corresponding yield and the Mn and Fe recoveries were 78.99 wt%, 86.14 wt%, and 84.60 wt%, respectively. During the oxidization process, [Fe2+]O was initially oxidized to the anti-form spinel-type structure of [Fe3+][Fe2+Fe3+]O4, and thereafter, it reacted with the decomposition product of [Mn3+][Mn2+Mn3+]O4 to form a hybrid spinel-type structure [Me2+xMe3+l-x][Me2+1-xMe3+1+x]O4 (Me refers to Mn and Fe) via the Mn2+/Fe2+/Mn3+/Fe3+ ions exchange at the tetrahedral and octahedral sites. Moreover, the as-purified ferrite can be used as an ingredient for the preparation of high-performance MnZn ferrite.