Exergy Evolution of the Mineral Capital on Earth

Dr. Alicia Valero is a lecturer in the Department of Mechanical Engineering at the University of Zaragoza and works in the Centre of Research for Energy Resources and Consumption (CIRCE).

Her main scientific research areas are exergoecology and energy efficiency. In particular, she has had extensive involvement in the application of the exergy analysis in the global assessment of mineral resources on earth.

Download her PhD thesis (English): Exergy Evolution of the mineral capital on Earth

Abstract

The 20th century has been characterized by the economic growth of many industrialized countries. This growth was mainly sustained by the massive extraction and use of the earth’s mineral resources. The tendency observed worldwide in the present, is that consumption will continue increasing, especially due to the rapid development of Asia, the desire for a higher living standard of the developing world and the technological progress. But the physical limitations of our planet might seriously restrain world economies. In fact, many mineral commodities such as oil or copper are already showing signs of scarcity problems, and consequently their prices are increasing sharply.

Our society is based on an inefficient use of energy and materials, since there is a lack of awareness of the limit. If resources are limited, their management must be carefully planned. But it is impossible to manage efficiently the resources on earth, if we do not know what is available and at which rate it is being depleted.

Therefore, the aim of this PhD has been the assessment of the physical stock on earth and the degradation velocity of our mineral resources due to human action. This has been accomplished through the exergy analysis under the exergoecological approach. This way, the resources are physically assessed as the energy required to replace them from a complete degraded state to the conditions in which they are currently presented in nature. The main advantage of its use with respect to other physical indicators is that in a single property, all the physical features of a resource are accounted for. Furthermore, exergy has the capability of aggregating heterogeneous energy and material assets. Unlike standard economic valuations, the exergy analysis gives objective information since it is not subject to monetary policy, or currency speculation.

Examples of scientific contributions

With the relative abundance of the substances in each of the earth’s outer spheres obtained in this PhD, and the thermochemical information, we were able to calculate for the first time, the average Gibbs free energy, enthalpy of formation and chemical exergy of the atmosphere, hydrosphere and upper continental crust. Furthermore, since the mass of each layer of the earth is well known, we have obtained the first estimation of the earth’s specific chemical exergy: 1,22E9 Gtoe.

This study has obtained an inventory of the most important renewable and non-renewable resources on earth measured in exergy terms. The main novelty introduced in the inventory is the combined assessment of energy resources with non-fuel minerals. Since exergy is an additive property, we have been able to obtain the total exergy of the non renewable energy resources, including nuclear, fossil fuels and non-fuel mineral reserves. Furthermore we could estimate for all renewable resources, the rate of current consumption with respect to the available potential use.

Similarly, for non-renewables, we estimated the resource to production ratio. We came to the important conclusion that vast amounts of energy resources are available on earth, especially of renewable nature. However, we are currently using less than 2% of its potential. On the other hand, we have estimated that the reserves of concentrated fuel and non fuel minerals, which can be practically used by man, represent only 0,01% of the chemical exergy of the earth. Furthermore, their global R/P ratio excluding nuclear materials, is less than 100 years. Hence, humankind is not facing an energy crisis, as many claim, but rather a material’s scarcity.

This PhD has applied for the first time the Hubbert model to non-fuel minerals, with the aim of estimating the year were the peak of production is reached. It has been stated that the bell-shape curve is better suited to non-fuel minerals if it is fitted with exergy over time, instead of mass over time. This way, we take into account the concentration factor, which is very important for the case of solid minerals. Consequently, we have developed the required equations for estimating the Hubbert’s peak for all kinds of minerals in exergy terms.

With the available information about world mineral historic statistics and available reserves, we have carried out the first diagnosis of the state of non-renewable minerals on earth. This PhD has estimated through the exergy analysis, the degradation degree of the mineral commodities, detecting the ones being degraded at the highest rates, and the ones facing important scarcity problems.

We have stated that iron and aluminium are the most extracted commodities but not the most depleted ones, due to their crustal abundance. On the contrary, copper, which is also being extracted at very high rates, is already suffering scarcity problems, with more than 50% of its world reserves depleted. Other commodities such as mercury, silver, gold, tin, arsenic, antimony or lead are even more degraded, with more than 70% of their reserves depleted.