A novel utilization of ferronickel slag as a source of magnesium metal and ferroalloy production

Abstract

Processing laterite nickel ore by the pyrometallurgical route produces ferronickel slag as a byproduct. The main constituents of ferronickel slag are silicon oxide, magnesium oxide, and iron oxide. The amount of ferronickel slag has sharply increased in recent years as a result of the increasing demand for ferronickel and stainless steel. Some regions recognize ferronickel slag as hazardous waste, meaning that the handling of the slag requires special attention and treatment. A zero-waste ferronickel processing plant could be realized if most of the metallic components can be extracted from the slag. Based on FactSage calculations, it is thermodynamically possible to reduce ferronickel slag into magnesium and ferroalloy, leaving only a small amount of unreduced oxides. According to experiments conducted at 1500 °C and 1550 °C under an argon atmosphere and a vacuum environment, magnesium was evaporated and ferro-silicon-chromium was formed. Some magnesium cannot be evaporated and remains in the final slag together with silicon in the form of forsterite (Mg2SiO4). Further research is still needed to increase the degree of magnesium metal evaporation and to prevent reoxidation of magnesium metal by carbon monoxide and silicon oxide gases.