Understanding ferronickel smelting from laterites through computational thermodynamics modelling

The smelting of nickel laterite ores to ferronickel alloy is unique in extractive metallurgy. It treats feed that is very low grade with respect to the target metal and, as a result, produces much more waste slag than valuable metal product. The energy consumption per tonne of product is therefore high and requires sustained research and design development in an effort to improve the economics of laterite smelting. In this work, the main characteristics of nickel laterite smelting are reviewed, and then a simple and transparent computational thermodynamics model of the electric furnace smelting step is developed. This model predicts the nickel grade, nickel recovery and FeO content of the slag as functions of the iron recovery to ferronickel satisfactorily. It correctly predicts that the carbon and silicon contents in ferronickel increase sharply at high iron recoveries. However, in common with more sophisticated models, it incorrectly predicts the iron recovery at which this increase is observed in practice. It is concluded that the model provides an accessible and a satisfactorily accurate vehicle for understanding the relationships between process variables and process outcomes during nickel laterite smelting.