Transparency on greenhouse gas emissions from mining to enable climate change mitigation

Carbon dioxide (CO2) capture and sequestration includes a portfolio of technologies that can potentially sequester billions of tonnes of CO2 per year. Mineral carbonation (MC) is emerging as a potential CCS technology solution to sequester CO2 from smaller/medium emitters, where geological sequestration is not a viable option. In MC processes, CO2 is chemically reacted with calcium- and/or magnesium-containing materials to form stable carbonates. This work investigates the current advancement in the proposed MC technologies and the role they can play in decreasing the overall cost of this CO2 sequestration route. In situ mineral carbonation is a very promising option in terms of resources available and enhanced security, but the technology is still in its infancy and transport and storage costs are still higher than geological storage in sedimentary basins ($17 instead of $8 per tCO2). Ex situ mineral carbonation has been demonstrated on pilot and demonstration scales. However, its application is currently limited by its high costs, which range from $50 to $300 per tCO2 sequestered. Energy use, the reaction rate and material handling are the key factors hindering the success of this technology. The value of the products seems central to render MC economically viable in the same way as conventional CCS seems profitable only when combined with EOR. Large scale projects such as the Skyonic process can help in reducing the knowledge gaps on MC fundamentals and provide accurate costing and data on processes integration and comparison. The literature to date indicates that in the coming decades MC can play an important role in decarbonising the power and industrial sector.

We have assembled extensive information on the cradle-to-gate environmental burdens of 63 metals in their major use forms, and illustrated the interconnectedness of metal production systems. Related cumulative energy use, global warming potential, human health implications and ecosystem damage are estimated by metal life cycle stage (i.e., mining, purification, and refining). For some elements, these are the first life cycle estimates of environmental impacts reported in the literature. We show that, if compared on a per kilogram basis, the platinum group metals and gold display the highest environmental burdens, while many of the major industrial metals (e.g., iron, manganese, titanium) are found at the lower end of the environmental impacts scale. If compared on the basis of their global annual production in 2008, iron and aluminum display the largest impacts, and thallium and tellurium the lowest. With the exception of a few metals, environmental impacts of the majority of elements are dominated by the purification and refining stages in which metals are transformed from a concentrate into their metallic form. Out of the 63 metals investigated, 42 metals are obtained as co-products in multi output processes. We test the sensitivity of varying allocation rationales, in which the environmental burden are allocated to the various metal and mineral products, on the overall results. Monte-Carlo simulation is applied to further investigate the stability of our results. This analysis is the most comprehensive life cycle comparison of metals to date and allows for the first time a complete bottom-up estimate of life cycle impacts of the metals and mining sector globally. We estimate global direct and indirect greenhouse gas emissions in 2008 at 3.4 Gt CO2-eq per year and primary energy use at 49 EJ per year (9.5% of global use), and report the shares for all metals to both impact categories.