Thermo-ecological and exergy replacement costs of nickel processing

In this paper, an exergy analysis of nickel processing is performed through the application of two methodologies: TEC (thermo-ecological cost) and ERC (exergy replacement cost). The merging of both methodologies allows to have a complete assessment of non-fuel mineral processing. TEC evaluates the cumulative consumption of non-renewable exergy required to produce a unit of useful product from the raw materials contained in natural deposits, i.e. from the cradle to the market. It further splits the results into the fuel, mineral and emission components so as to show the exergy consumption resulting from each part, thereby identifying the types of resources that are being consumed in each step of the overall production process. A problem detected with the TEC was that the exergy associated with the mineral component was small compared to that of fuels. This is because the TEC traditionally uses the chemical exergy of substances in their assessment and fossil fuels eclipse any other raw material. In order to overcome such issue, the TEC has been complemented with the ERC. The latter accounts for the exergy required to produce minerals from a completely dispersed state to the original conditions in which they were originally found in nature, i.e. the exergy that one would consume to restore minerals from the grave to the cradle. Through ERC, the aim is to account for the dispersion problem associated with minerals, because the scarcer a mineral, the more exergy is associated with its replacement. Results show that when ERC is embedded into the TEC infrastructure, the impacts associated with mineral consumption are significantly greater. Accordingly, the inclusion of ERC into TEC allows for a more comprehensive consumption of non-fuel mineral resources, thereby providing better indications as to the achievement of a more sustainable production.