Guiomar Calvo

Decreasing ore grades in global metallic mining: A theoretical issue or a global reality?

Mining industry requires high amounts of energy to extract and process resources, including a variety of concentration and refining processes. Using energy consumption information, different sustainability issues can be addressed, such as the relationship with ore grade over the years, energy variations in electricity or fossil fuel use. A rigorous analysis and understanding of the energy intensity use in mining is the first step towards a more sustainable mining industry and, globally, better resource management. Numerous studies have focused on the energy consumption of mining projects, with analysis carried out primarily in one single country or one single region. This paper quantifies, on a global level, the relationship between ore grade and energy intensity. With the case of copper, the study has shown that the average copper ore grade is decreasing over time, while the energy consumption and the total material production in the mine increases. Analyzing only copper mines, the average ore grade has decreased approximately by 25% in just ten years. In that same period, the total energy consumption has increased at a higher rate than production (46% energy increase over 30% production increase).

Thermodynamic Approach to Evaluate the Criticality of Raw Materials and Its Application through a Material Flow Analysis in Europe

Summary This paper makes a review of current raw material criticality assessment methodologies and proposes a new approach based on the second law of thermodynamics. This is because conventional methods mostly focus on supply risk and economic importance leaving behind relevant factors, such as the physical quality of substances. The new approach is proposed as an additional dimension for the criticality assessment of raw materials through a variable denoted “thermodynamic rarity,” which accounts for the exergy cost required to obtain a mineral commodity from bare rock, using prevailing technology. Accordingly, a given raw material will be thermodynamically rare if it is: (1) currently energy intensive to obtain and (2) scarce in nature. If a given commodity presents a high risk in two of the three dimensions (economic importance, supply risk, and thermodynamic rarity), it is proposed to be critical. As a result, a new critical material list is presented, adding to the 2014 criticality list of the European Commission (EC) Li, Ta, Te, V, and Mo. With this new list and using Sankey diagrams, a material flow analysis has been carried out for Europe (EU-28) for 2014, comparing the results when using tonnage and thermodynamic rarity as units of measure. Through the latter, one can put emphasis on the quality and not only on the quantity of minerals traded and domestically produced in the region, thereby providing a tool for improving resource management.

Sankey and Grassmann Diagrams for Mineral Trade in the EU-28

Material flow analysis is a key tool to quantify and monitor natural resource use. A very visual way to undertake such analyses representing the mineral trade of a certain nation or continent is through the well-known Sankey diagrams, in which the mineral resources that are extracted, imported, exported, recycled and consumed within the given boundaries are represented with the arrows proportional to their respective quantities. Yet Sankey diagrams alone are not sensitive to the quality of the resources as they only reflect tonnage. This issue can lead to misleading conclusions and thereby ineffective resource policies. A way to overcome this deficiency is using Grassmann diagrams instead, in which instead of tonnage the flows are represented in exergy terms, thereby accounting for the physical value of minerals. In this chapter we use the exergoecology method to evaluate mineral trade and foreign dependency in EU-28 for the 1995–2012 period. Using the year 2011 as a case study, we can see that 45.8% of the total input tonnes of minerals are imported resulting in low values of self-sufficiency (Domestic Extraction to Domestic Material Consumption ratio). With data expressed in exergy replacement costs we can better reflect the real material dependency, 0.45 for minerals and 0.41 for fossil fuels, in contrast to 0.79 and 0.52 obtained respectively when using tonnes. Analyzing 10 of the 20 minerals considered critical by the European Commission, imports represent 6.74% of the total imports while extraction represents only 3.19% of the total extraction. This external dependency leaves Europe in a delicate situation regarding fossil fuels and non-fuel mineral supply and highlights the importance of recycling and the search for alternative sources.

Thermodynamic Methods to Evaluate Resources

Natural resources can be evaluated from different points of view. One of them, and perhaps the most commonly known is the economic point of view. Nevertheless, the price-fixing mechanisms, rarely take into account the concrete physical characteristics which make them valuable. But natural resources have at least two physical features which make minerals or fresh water for example unusual: a particular composition which differentiates them from the surrounding environment and a distribution which places them in a specific concentration. These intrinsic properties can be in fact evaluated from a thermodynamic point of view in terms of exergy. Chapter 6 presents in details how to evaluate resources quality applying exergy.

Resources. Production. Depletion

Any activity around the world as well as further development of humankind relies on natural resources. The primary deposits, which represent the work that nature offers us, are essential for current and future civilizations. There are several examples of ancient civilizations that collapsed due to the depletion of local natural resources; the most significant include depletion of the forests in Easter Islands, the depletion of fresh water in Central America or the depletion of the agricultural areas in South-East Asia [1]. Nowadays, these examples should not be underestimated and a rational resource management should be enhanced.