The thermodynamic rarity concept for the evaluation of mineral resources

Abstract

This chapter provides the thermodynamic tools required to assess mineral depletion. Specifically, as mineral depletion is closely linked with declining ore grades in the crust, concentration exergy is the most relevant parameter for its assessment. To this endeavour, the reference baseline to obtain concentration exergies is shown. This reference baseline is assimilated to a resource depleted Earth coined Thanatia, where no concentrated mineral depostis are found and all minerals are at the current average crustal concentration. Minerals are then assessed through exergy replacement costs, calculated as the exergy required to concentrate a substance from Thanatia, to the initial state of concentration found in the original mines. with prevailing technologies. This can be seen thus as a “grave to cradle” approach and accounts for the "mineral bonus" lost through extraction. If one adds to the exergy replacement costs the real exergy costs associated to extract, beneficiate and refine a given mineral, the so-called thermodynamic rarity values are obtained. A certain element of the periodic table is thermodynamically rare if it is scarce in the crust and/or difficult to obtain. Thermodynamic rarity values for different elements is shown and several examples illustrate how these numbers have been obtained. A final example shows how the methodology can be used to assess the thermodynamic criticality of for instace electronic appliances.