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Guiomar Calvo (2016)

Exergy assessment of mineral extraction, trade and depletion

PhD thesis, Universidad de Zaragoza.

Natural resources, especially minerals, are present in all products and are a vital component of society. Mineral consumption is experiencing an exponential increase and hence future availability is now playing a major role in resources efficiency policies. For this reason it is fundamental to have the best possible tools, objective and rigorous, that can help to properly account for this loss of resources. Studies cannot only be centered in analyzing current consumption patterns and reserves as it is happening now, but they need to take into account the gradual loss of future availability of resources due to mineral dispersion and the criticality of each of the materials. By means of the Second Law of Thermodynamics, through property exergy and with a so-called Physical Geonomics approach, mineral extraction and dispersion can be assessed. Exergy, traditionally used to assess energy resources, can be also used to account for non-energy minerals. The advantage of this approach over other conventional ones is that it takes into account not only the quantity but also the quality of the given resource. Moreover, it is totally independent of monetary variations, thereby providing more accurate and objective information. Additionally, using this approach, one can easily cross over from the physical to the economic level, linking Thermodynamics with Economics, something that has been largely sought by the school of Ecological Economics. As the basis of Physical Geonomics model was already established in previous studies, the first task of this PhD Dissertation has consisted on improving the available data. For this endeavor, an analysis on real data on energy consumption from different mining industries was performed to obtain new and more accurate data on energy consumption as a function of ore grade. Additionally, using the available information of fossil fuel and electricity consumption over the years, several energy intensity factors have been calculated. The general trend observed is that average ore grade slowly diminishes over time while energy consumption and production increases. Moreover, new data of exergy replacement costs for several mineral substances, meaning the exergy required restoring a resource from a complete dispersed state where no deposits exist to the physical and chemical conditions found in Nature with the available technology, has been calculated and has been added to the initial model. The second task of this PhD Dissertation has been to propose a new indicator (GDP/DMD) that can be used at global level and that can evaluate natural resource efficiency. This new indicator takes into account not only the quantities of materials that are consumed within a region but also the quality of those materials, being able to put the focus on scarcer and critical substances. With GDP/DMD we can have a better and more accurate assessment of mineral depletion and it can be used to enhance more effective actions in the policy making process. The third task has been to include Physical Geonomics into the Ecological Economics approach, which can be extremely helpful to evaluate natural resource efficiency use. One aspect that can be calculated using exergy replacement costs are the mineral market prices and the monetary loss associated to mineral extraction and depletion. Starting from the current mineral market prices, a new mineral price has been estimated considering that scarcity and not only economic factors are being taken into account. This allows seeing the distance between situations in which resources are treated as ordinary goods and situations in which they are treated as physical assets that need to be replaced. Last, this new approach has been applied to several case studies. Spain, the European Union (EU-28) and Colombia have been chosen as examples of regions where mineral extraction and trade is substantial. Different factors, such as mineral depletion, foreign dependency, trade deficit and monetary loss associated to mineral depletion, have been calculated for each case. As demonstrated by all the case studies, carrying out a conventional material flow analysis to study mineral depletion is not enough, as material flow analysis and conventional indicators are usually related to monetary valuation and usually put together substances that are very different from each other, comparing “apples with oranges”. To complement this model and to obtain more realistic and accurate values, an exergy approach is needed, as using exergy replacement costs instead of tonnage as a yardstick we can place focus on the quality of the minerals and have a better overall picture of mineral depletion.

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