Exergoecology: A thermodynamic approach for accounting the Earth's mineral capital. The case of bauxite–aluminium and limestone–lime chains

As man extracts minerals, the natural deposits become depleted in quantity and concentration, and hence the mineral wealth of the Earth decreases. This paper explains the exergoecological method used for calculating the mineral exergy bonus that Nature gives us for free for providing minerals concentrated in mines and not dispersed in the Earth's crust. The method is based on two concepts: Exergy and the Exergy cost. Exergy measures the minimum (reversible) work required to extract and concentrate the materials from a Reference Environment (RE) to the conditions found in Nature. This RE can be approximated to a completely degraded crepuscular planet with the absence of fossil fuels and mineral deposits. And the exergy cost accounts for the actual exergy required for accomplishing the same process with available technologies. These costs are complementary to the conventional extraction, land-recovering, processing and refining costs. The case studies of two industrial chains: bauxite–alumina–aluminium, and limestone–calcite–lime are presented and discussed. As the method provides values in energy units, the annual exergy decrease in the mineral endowment of the planet due to the extraction of minerals can now take into account the fossil fuel's exergy as well as the non-fuel mineral exergy costs.