The Audi Environmental Foundation is working with the Freiberg University of Mining and Technology to research new ways of recovering raw materials through recycling. Elements such as indium, gallium, or even tin are both finite and essential for modern technologies such as fiber optics, photovoltaics, and semiconductors. Every electronic device is made up of parts that contain these elements.

A selective extraction process is planned that will recover these raw materials from incinerated waste. Currently, such materials are lost when the electronic parts that contain them are thrown away with household waste. The new process is designed to keep these valuable high-tech metals in the cycle.

In 2019, around 16 tons of primary raw materials were consumed per capita in Germany. This includes all raw materials extracted from natural sources, in addition to biomass and fossil fuels, as well as iron, copper, lead, and zinc ore. The latter currently have to be almost entirely imported to Germany for processing.

p>M>etallic raw materials are depletable resources and are often rare or found only in dispersed locations. The ores also contain large quantities of blind rock, meaning that the metals are not present in their pure form, but have to be extracted using complex chemical–thermal processes before they can be processed. Nevertheless, they are essential for many future technologies, including electromobility, telecommunications, and photovoltaics.

The United Nations World Resources Council, among others, predicts that demand for them will increase worldwide by 2030 because the demand for raw materials and metals, as well as the semiconductors made from them, is growing along with the number of electrical devices in use around the world. These devices rely on control electronics that are built with customized semiconductors, which in turn are useless without rare-earth elements.

Despite being rare and important elements, they are often lost unintentionally. Many people incorrectly throw away small electrical devices such as flashlights, USB sticks, charging plugs and cables, or even cell phones in their household waste instead of returning them to collection points. In Germany, household waste is usually incinerated. This process does not yield effective recovery of the valuable raw materials contained in the waste for industrial use. Instead, they remain in the slag or fly ash.

This in turn is landfilled, which means the technological elements leave the cycle and are lost for further use. This is where a research project on the selective extraction of indium, gallium, and tin, which is being funded by the Audi Environmental Foundation, comes in.

The project seeks to extract the metals contained in fly ash or slag after incineration of household waste for later use in new products. Through reuse and recycling, the raw materials do not have to be extracted from the earth in the first place, an approach which can reduce the environmental impact of mining and emissions from the international trade of ores and wrought materials (i.e., raw material equivalents).

Based on the selective extraction method, a recycling process is currently being developed in the laboratory by Betty Leibiger, a doctoral student in chemistry at the Freiberg University of Mining and Technology.

The challenge is to produce molecules that specifically bind the desired metal ions, Leibiger explains. Put simply, Leibiger has to develop a specially shaped “tweezer” that can pick out for separation the desired metal ions from a fly ash solution. Each custom-made “tweezer head”—a ligand—fits only one specific metal ion, such as indium. An acid then release the ions. This approach allows the individual metal ions to be gradually separated out from the mixture and rendered in a purity that makes them usable in technological applications.

At this stage of the project, the focus is on developing a number of suitable sligand, which will then be tested and further optimized on a small scale, Leibiger says. Once optimized, the process could be scaled up. In a further step, extraction experiments using real fly ash or leaching solutions from the reprocessing of fly ash will follow.

The project and associated doctoral thesis are scheduled to run for a total of three years and will initially be funded by the Audi Environmental Foundation until next year.