Efficient separation of iron elements from steel slag based on magnetic separation process

Abstract

Steel slag is the main industrial solid waste generated from the steelmaking process. It can be returned to the steelmaking process for reuse due to its chemical composition and structural properties. For the structure of steel slag components, the combination of high temperature holding and slow cooling operation with magnetic separation can efficiently improve the recovery efficiency of valuable elements from the converter slag. In this study, chemical analysis, X-ray diffraction, and scanning electron microscopy were used to analyze the changes in phase composition and morphology during high-temperature holding and slow cooling. In addition, the reasonable magnetic separation process conditions suitable for converter slag were experimentally studied. The results showed that the RO phase in the slag significantly grew under the conditions of holding at 1500 °C for 90 min, cooling at 1 °C/min to 1100 °C, and holding for 90 min. The high temperature insulation allows the steel slag to be fully melted and uniformly mixed, and the slow cooling process applied to the slag provides enough time to grow for RO phase. The multi-stage wet weak magnetic separation method is suitable for steel slag, with a best magnetic separation intensity of 100 mT in the laboratory range and a single magnetic separation time of 1 min. The steel slag concentrate rate is 30.54% and the T.Fe content is 54.10%. It can replace part of the sintered ore to return to the iron making process. Moreover, the tailings can be used to produce high value-added materials such as subgrade and phosphate fertilizer. Therefore, the current technological route can transform the industrial solid waste into a useable resource and achieve efficient and low consumption recycling of steel slag.