This paper shows how thermodynamics and in particular the exergy analysis can help to assess the degradation degree of earth's mineral resources. The resources may be physically assessed as its exergy content as well as the exergy required for replacing them from a complete degraded state to the conditions in which they are currently presented in nature. In this paper, an analysis of the state of our mineral resources has been accomplished. For that purpose an exergy accounting of 51 minerals has been carried out throughout the 20th century. This has allowed estimating from geological data, when the peak of production of the main mineral commodities could be reached. The obtained Hubbert's bell-shaped curves of the mineral and fossil fuels commodities can now be represented in an all-together exergy-time representation here named as the “exergy countdown”. This shows in a very schematic way the amount of exergy resources available in the planet and the possible exhaustion behaviour. Our results show that the peak of production of the most important minerals might be reached before the end of the 21st century. This confirms the Hubbert trend curves for minerals obtained by other authors using a different methodology. These figures may change, as new discoveries are made. However, assuming that these discoveries double, most of the peaks would only displace our concern around 30 years. This is due to our exponential demand growth. The exergy analysis of minerals could constitute a universal and transparent tool for the management of the earth's physical stock.
keywords: Exergy; Hubbert peak; Scarcity; Fuel minerals; Non-fuel minerals』
2. Theoretical background
3. The exergy loss of world's mineral reserves in the 20th century
3.1. Non-fuel minerals
3.2. Fossil fuels
3.3. The exergy countdown
Fig. 1. The exergy replacement cost loss of the main non-fuel mineral commodities on earth in the 20th century.
Fig. 2. The exergy replacement cost loss of the main 15 non-fuel mineral commodities on earth in the 20th century, excluding iron and aluminium.
Fig. 3. Depletion degree in % of the main non-fuel mineral commodity reserves.
Fig. 4. The Hubbert peak applied to world iron, aluminium and copper production. Data in ktoe.
Fig. 5. The Hubbert peak model applied to the world exergy consumption of coal, oil and natural gas.
Fig. 6. The Hubbert peak model applied to the world conventional fossil fuel exergy
Fig. 7. The exergy countdown of the most extracted minerals in the 20th century.
Valero & Valero(2010)による『Physical geonomics: Combining the exergy and Hubbert peak analysis for predicting mineral resources depletion』から