Assessing the energy and greenhouse gas footprints of nickel laterite processing

The energy and greenhouse gas footprints of some of the various technologies that are used for processing nickel laterite ores have been assessed using life cycle assessment methodology based largely on publicly reported inventory data. The results of the study were used to identify opportunities to improve the energy and greenhouse gas impacts of the various processes and to examine how they might be affected under different future scenarios such as falling laterite ore grades and the possible imposition of a carbon tax. The opportunities identified included the use of biochar as a fuel and reductant, along with slag waste heat recovery in ferronickel smelting, and the use of the emerging bath smelting technology for ferronickel production instead of the rotary kiln/electric furnace process. As a significant amount of the life cycle-based greenhouse gas emissions from the hydrometallurgical acid leaching processes are generated by acid neutralisation with lime or limestone, there may be opportunities to reduce these emissions by utilising other neutralising agents or possibly by considering non-acid leaching systems. Improving the energy efficiency of the electrowinning stage used to recovery nickel metal from the leach liquor is another possible way in which the sustainability of hydrometallurgical production of nickel from laterite ores could be improved.