'Beyond tomorrow' molecular sorting for resource-efficient production
Most developed countries are “throwaway societies”, i.e. societies where people simply throw away defective articles and purchase new ones. However, our resources are finite. This is not only true for oil but also for many other raw materials such as precious metals or rare earths. Scientists from the Fraunhofer Institute for Interfacial Engineering and Biotechnology IGB in Stuttgart are working with researchers from other Fraunhofer institutes with the aim of developing technologies that enable raw materials to be sorted at the molecular level and returned to the production process. The ambitious project is focused on using specific separation technologies to extract any residual minute traces of valuable raw materials from waste streams.
Around 60 billion tonnes of raw materials – including precious metals or rare earths - are currently used worldwide each year. These quantities will continue to grow in the future. However, the end of our reserves is foreseeable and new technologies need to be developed in order to recycle valuable materials and maintain a sufficient supply of raw materials for the production of industrial and consumer goods in the future. The recycling of metals contained in waste is technically very complex, cost-intensive, environmentally harmful and not universally applicable.
Everyday items as raw materials reserves
Many everyday items including even wastewater, residues and ashes from combustion processes are a great store of precious raw materials. Electrical devices, batteries and catalysts consist of a complex mixture of precious metals or rare earth elements: copper, nickel and gold in computer chips or mobile phones, silver and cerium1 in catalysts, cobalt in batteries or neodymium in hard drives.
Up to 60 different raw materials are potentially built into mobile phones and other consumer goods. Until recently, electrical waste was usually sorted manually, a method that will not be affordable for much longer given the scarcity of resources. A 2013 EU report2 on the implementation of the Raw Materials Initiative already classified 14 of the raw materials on which the industry heavily depends as critical in terms of availability. The report highlighted the need to develop new separation technologies that will in future enable raw materials to be sorted on the molecular level and used for the production of new goods.
Molecular sorting: recycling at the molecular level
Seven Fraunhofer institutes are working together in the “Molecular Sorting for Resource Efficiency” project which is aimed at closing gaps in materials cycles by developing innovative methods that enable the separation and sorting of materials on the molecular level and the recycling of raw materials from used products. The researchers are seeking to develop a production system that requires no input of new, i.e. primary, raw materials. The idea is to develop processes that use secondary raw materials again and again and return them in cascades to the production process. However, such technologies must be efficient, easy to integrate and flexibly applicable to various groups of metals.
The “Molecular Sorting for Resource Efficiency” research consortium also involves scientists from the Fraunhofer IGB in Stuttgart. They are developing methods that enable the recycling of metals, including precious metals, rare earths and heavy metals. This involves using a set of different methods, starting with bioleaching to dissolve the metals. The concentration of the dissolved metal ions is subsequently increased by adsorption and membrane filtration. The process ends with electrophoretic separation, the fractionation of the ionic liquids and the galvanic deposition of the metals. The ultimate goal is to incorporate all methods into an integrated process. The feasibility of the concept is currently being validated in practice using a demonstrator sorting unit.
Bacteria dissolve metals from waste
Bioleaching involves the use of populations of various bacterial strains whose metabolic processes complement one another. These microorganisms convert metal from waste materials into water-soluble salts. A laboratory-scale bioleaching procedure has already been established at the Fraunhofer IGB. The IGB researchers have succeeded in making the bacteria form biofilms on metal or wood shavings and dissolve metal ions from the materials; considerable quantities of manganese, nickel, iron, copper, zinc and titanium were solubilised. The researchers also observed the precipitation of the metals in the suspension. They are currently working on upscaling the process and using it for other precious metals and rare earths.
Processing of the metals with polymers or keratin
The next step in the metal recovery process is aimed at increasing the concentration of the ions that are usually only present in trace amounts. The Fraunhofer researchers are developing special adsorbents from polymers and renewable raw materials and testing their suitability for use in membrane adsorbers. They have already succeeded in producing polymers with various functional groups. These polymers have a particularly high affinity to metals such as copper, neodymium, silver or lead, resulting in the highly selective enrichment of the metals. The modification of keratin from sheep’s wool has also been shown to efficiently adsorb silver ions. Moreover, the adsorption properties of the polymer materials are preserved when incorporated into the membrane adsorber.
The final step in the metal recovery process involves the fractionation and subsequent deposition of the metals, for which the IGB scientists are further developing electrophysical processes such as electrophoresis and galvanic deposition. The researchers have already developed a laboratory prototype that works according to the principle of free-flow electrophoresis. This procedure also permits the separation of metal ions which are very similar due to their chemical and physical properties and which can therefore only be separated to a limited extent using conventional technologies. The researchers have already been able to separate the metal ion mixtures copper-iron, neodymium-iron and the three-component mixture iron-copper-neodymium, and are working on adapting the procedure to other systems.
Recycling is also profitable beyond tomorrow
If integrated metal-recycling concepts one day become available, the issue as to whether the process will continue to be economically feasible in the future will also need to be addressed. The Fraunhofer research consortium is evaluating future recycling technology capabilities with three different scenarios that anticipate the situation in 2030: “Ideal - green new world”, “Catastrophic – after us, the deluge” and “Neutral – continue as before”. In this intellectual guessing game the aforementioned recycling technologies are all well placed to play a key economic role in any of the three rather different scenarios.
1 A silvery metal that belongs to the lanthanide group, most abundant of all rare earth elements.
2"Report from the Commission to the European Parliament, the Council, the European Economic and Social Committee and the Committee of the Regions on the Implementation of the Raw Materials Initiative", Brussels, 24th June 2013.
Dr. Thomas Schiestel
In charge of demonstrator sorting unit
Fraunhofer Institute for Interfacial Engineering and Biotechnology IGB
Tel.: +49 (0)711 970-4164