Sustainable and high-efficiency recycling of valuable metals from oily honing ferroalloy scrap via de-oiling and smelting separation

Oily ferroalloy scraps generated from machinery honing enterprises are typical hazardous municipal materials that release benzene-series volatile organic compounds (VOC), which endanger human physical and mental health. Therefore, harmless treatment and resource reuse for these hazardous materials is urgent. In this study, the VOC emission, and pyrolysis and de-oiling behaviors of oily honing scrap was first characterized to evaluate the environmental risks. Smelting separation was then proposed to economically and eco-friendly recover valuable metals from the de-oiled ferroalloy scraps. The thermodynamics of Al2O3-SiO2 and CaO-Al2O3-SiO2 systems was calculated to optimize the slag formation. Results showed that after de-oiling and smelting with CaO addition, the hazardous VOC are removed, and the valuable metals are recovered in ferroalloy state. Under optimum conditions, a crude Fe-Mo-Cu alloy with Fe, Mo and Cu recoveries of 98.5 wt%, 97.9 wt%, and 98.4 wt % were obtained. In addition, the slag containing few toxic elements and VOC can be used for silicate cement production. Pyrolysis, de-oiling behaviors and mechanism for slagging and growth of Fe-Mo-Cu alloy during smelting were discussed via various testing techniques, and leaching toxicity of the cleaned slag was also characterized in this work. This process is also applicative to recover metals from various honing ferroalloy scraps.