Exergy analysis of mineral processing flow sheets: implications in process design

Exergy analysis can be used to assess and improve energy systems through more meaningful system analysis than a simple energy balance. Mineral processing operations including both physical and chemical pre-concentration stages have not generally been subjected to rigorous exergy analysis procedures. Standard thermodynamic software such as Factsage is used for easy estimation of exergy of a mineral resource. The methodology developed has been validated. Stream calculation procedures have been outlined. The application of the developed procedure is illustrated by two types of processing flow sheets, namely those applying standard crushing-grinding-beneficiation concepts (copper, iron and zinc) and those which deal with chemical beneficiation (alumina). Copper ore beneficiation flow sheets are more efficient than upstream processing of the concentrate. For iron ores, the processing flow sheets should be so designed to further increase the high exergetic efficiencies through waste stream reductions. Chemical beneficiation of alumina ores needs major improvement of exergy efficiencies. It is emphasized that in process dissipation exergy and the exergy discharge loss have different influences on the environment. This should be duly considered in flow sheet design in addition to development of exergy accounting procedures.