INCORPORATING PHYSICAL QUALITY IN THE ASSESSMENT OF CRITICAL RAW MATERIALS USING THERMODYNAMIC RARITY

Concern on the availability of raw materials has led to an increment in reports that assess the criticality of minerals. These classifications and lists vary between each country due to different approaches and targets, but... [ view full abstract ]

Concern on the availability of raw materials has led to an increment in reports that assess the criticality of minerals. These classifications and lists vary between each country due to different approaches and targets, but also according to domestic availability and demand and to predictable changes in technology and policies. Yet those approaches leave behind other relevant factors, such as the physical quality of substances. Therefore a new method based on the second law of thermodynamics is proposed as an additional dimension for the criticality assessment of raw materials.

This new variable denoted “Thermodynamic rarity”, accounts for the exergy cost required to obtain a mineral commodity from the bare rock, using the best available technology. Accordingly, a given raw material will be thermodynamically rare if: 1) it is currently costly to obtain and 2) if it is scarce in Nature. Combining these factors, a new critical material list is presented, including a total of 19 mineral substances: antimony, chromium, cobalt, gallium, germanium, indium, lithium, magnesite, molybdenum, nickel, niobium, PGM, phosphate rock, REE, silver, tantalum, tellurium, tungsten and vanadium. Some elements, such as gallium, germanium and indium are present, and are considered critical in the vast majority of the analyzed reports, but others such as lithium, chromium, molybdenum or vanadium are also included in this study as they are critical from a thermodynamic perspective.

With this new list and using Sankey diagrams, a material flow analysis (MFA) has been carried out for Europe (EU-28) for 2014. The main objective is to analyze the relevance of combining the thermodynamic approach with the conventional MFA analysis in mass terms to put emphasis on the quality and not only on the quantity of minerals traded and domestically produced in the region. For instance, the domestic production of magnesite in 2014 accounted for 63% of the total internal production when expressed in mass terms, but this number is reduced to only 15% when using thermodynamic rarity. Regarding imports, in mass terms it seems that the only material imported is phosphate rock, with a share of approximately 90%. Yet when analyzing the imports in rarity terms, phosphate rock only accounts for 1.4% and platinum group metals (PGM), tellurium, tantalum, nickel and niobium for 91.4%. Thus, using only mass as a yardstick in the assessment reports can generate incomplete results leaving behind other factors such as the physical quality of mineral resources. This way, minerals that were not considered in the critical raw material list but are indeed critical from a physical point of view can be taken into account. Combining both approaches, more accurate and robust resource efficiency policies could be implemented in the European Union putting the focus not only on supply risk and economic importance but also on the quality of the mineral resources that are being considered.