Nearly every aspect of modern society relies on materials of limited supply on Earth. To live within the limits set by our planet, we need to figure out how to make the most of what we gain and reuse what we’ve won. A new study released this week examines how close we are to reaching that ideal for 61 different metals.
Along the way, the authors figure out how long different metals remain in circulation before they are lost and identify the stage at which those losses occur. While a lack of recycling is a major roadblock to a circular economy, it is by no means the only one. For many metals, including some critically important, we discard huge amounts that are present in the ores we mine for various elements.
Watch your metals
Tracking so many metals throughout their life cycle is a daunting task, but the authors were able to build on previous work by Japanese researchers who developed a software model called MaTrace. The model is designed to track material flow from production to loss, estimating losses at each stage of the material life cycle based on empirical data.
Losses are tracked at a number of points in the life cycle of a material. For metals, these include the production of a raw material from ores, the use of the metal in the manufacture of products, and its loss during the use of the product. Finally, at the end of a product’s life, the metal is recycled or disposed of as waste. MaTrace can also track the flow of the material through the recycling process (with the inevitable losses) and back to additional products.
To make this concrete, we can turn to something as simple as iron, which is extracted from ores that are then processed. Both steps involve some loss of iron and other metals contained in the same ore. The iron is eventually made into products, a process that can again introduce losses as foreign matter is cut away – some of the excess is also sent into the recycling process here. There is also loss during use, which can be as simple as a fraction of the iron that rusts away in the environment. Ultimately, a fraction of iron-based products will be recycled, with the rest ending up in the environment.
Some of the numbers needed to track the fate of metals, such as the efficiency of converting ore to metal, are easy to find. Others, such as the percentage of indium entering electronics, are necessarily rougher estimates, and the researchers caution against taking any number here as a definitive estimate.
For their analysis, the researchers start with a kilogram of material and send it through MaTrace for 1,000 years or until all the metal is lost — whichever comes first. The authors performed individual analyzes for each of the 61 metals and aggregated them into a number of groups: ferrous metals (iron and its derivatives), non-ferrous metals, specialty metals, and precious metals. This allowed the researchers to pick up general trends for materials commonly used in specialized industries.
