Mining the scrapheap: Sustainable chemical methods to save critical elements from e-waste

In brief:

• The world’s ever-increasing supply of waste electronics is a crucial source of technologically critical metals such as gold, copper and palladium.
• Chemist have a crucial role to play in developing processes and technologies to recover this valuable resource – securing continued provision as supplies in nature become scarce, and reducing the damaging environmental and societal footprint of traditional mining.  
• School of Chemistry researchers are developing new methods for metal recovery from waster electronics, drawing on advanced metal separations chemistry and insight from computational modelling.
• With collaborators, the team have developed a new chemical reagent that can precipitate gold selectively from electronic waste that is dissolved in acid. Their method avoids the hazards of organic solvent used in other metal separations, can be tuned to separate other valuable metals, and provides an attractively simple process which could be incorporated into a variety of metal extraction and recycling processes.
• In the next step in the development of their technology towards real-world use, the team collaborated with environmental remediation company SEM Ltd and e-waste collectors WEEE Scotland to show that SEM’s ‘Dram’ biological filtration system, manufactured using co-products from the distillation of malt whisky, can be used to recover other metals such as aluminium, tin, and zinc from the effluent of the chemical separation process – maximising metal recovery and rendering the discharge from the extraction process environmentally benign.

Read more below.

The challenge: Urban mining for sustainable recovery of critical technological elements

E-waste is the fastest growing waste stream worldwide. And contained in the ever-increasing supply of waste electrical and electronic equipment (WEEE) – mobile phones, computers, smart TVs, MP3 players and e-readers, amongst other things – are critical metals such as gold, copper and palladium in significantly higher abundance than in the original ores. The gold content of WEEE, for example, is approximately 80 times that found in primary mining deposits – perhaps as much as seven per cent of all the world’s gold.

These metals are critical to global technological advances, not least the technologies which will underpin a decarbonising society and low-carbon energy. In the face of increasingly scarce supplies of these critical metals in nature, as well as the damaging environmental and societal footprint of obtaining them through traditional mining, it has become crucial that we develop processes and technologies that enable us to repurpose the supply we already have. The recycling strategies needed to recover metals from waste electronics have become known as urban mining.

Conventional metal recovery approaches have typically used harsh chemicals, generated damaging waste, and required large amounts of energy. High efficiency, low waste and zero emission technologies are urgently required to replace these methods and help us transition to a circular economy. In this, chemists and chemical scientists have a crucial role to play.

The chemistry solution: Advancing metal separations chemistry for new and sustainable metal extraction and recycling processes

The recovery of metals from their ores and secondary sources such as WEEE relies on reagents that recognize one metal from another. The School of Chemistry’s Professor Jason Love and his group are developing new reagents based on advances in fundamental coordination and supramolecular chemistries that can recover selectively base, platinum-group, or rare-earth metals from a variety of sources, including e-waste. These new reagents include anion receptors that promote the selective and tailored precipitation of metals from acidic solutions and pre-organised receptors for the highly selective separation and precipitation of rare-earth and actinide anionic compounds.

The Love Group work closely with Professor Carole Morrison and group, who use computational modelling to both fill in the gaps left by experiment and guide new experimental research in critical metals recovery. By simulating the interactions between metals and various chemicals, the Morrison Group have been able to gain valuable insights into the efficiency of metal recovery. This information is then used to inform the development of improved extraction methods which are not only more efficient but also more sustainable and environmentally friendly.

With collaborator Professor Bryne Ngwenya from the School of Geosciences, an expert in microbial geochemistry, this team recently described a new chemical reagent that can precipitate gold selectively from electronic waste that is dissolved in acid. The reagent is not only highly selective towards gold, but the acid concentration can be tuned such that different metals such as tin, gallium and platinum can be targeted and separated in the precipitation process. Their precipitation process overcomes hazards associated with the use of organic solvents in other precious-metal separations, and provides an attractively simple process which could be incorporated into a variety of metal extraction and recycling processes due to its selectivity, recyclability, and relevance to various metal dissolution processes. 

Partnering towards real-world solutions for metal circularity and net zero

In the next step in the development of their technology towards real-world use, the team collaborated with environmental remediation company SEM Ltd and e-waste collectors WEEE Scotland to show that SEM’s ‘Dram’ biological filtration system, manufactured using co-products from the distillation of malt whisky, can be used to recover other metals such as aluminium, tin, and zinc from the effluent of the chemical separation process. These metals can be recovered by microbes in the form of metallic nanoparticles and then purified for reuse. By integrating the chemical separation with this next stage of environmentally friendly biology-based processing, the discharge from the extraction process is rendered environmentally benign, the recovery of metal is maximised, and a sustainable holistic recycling process is created.

Brick, Bread and Biscuit: The Chemical Recycling of Precious Metals from E-Waste for Jewellery Design in India

Professor Jason Love has also delivered the EPSRC-Global Challenges Research Fund project “Chemical recycling of electronic waste for sustainable livelihoods and material consumption in India”. This highly collaborative project involving jewellers, designers and metallurgists from the Duncan of Jordanstone College of Art & Design in Dundee, the National Institute of Design in India and the Indian Institute of Technology at Banaras Hindu University developed ways to exploit chemical recycling techniques to separate gold and copper from e-waste to provide female artisanal jewellers in India with an alternative and sustainable supply of recycled metals. These artisanal jewellers play an important role in maintaining cultural heritage, but are subject to exploitative middlemen and poor wages and conditions. India is an enormous collector of e-waste, much of which ends up being recycled informally and hazardously, so the re-use of e-waste would have significant environmental, health and societal benefits.

The team worked with rural artisanal jewellers to determine their needs, delivered workshops to develop the techniques required to fabricate high-value jewellery from e-waste metals, and provided provenance for these materials through the creation of a chain of custody mark. Exhibition pieces were generated and displayed in India and the UK to promote the work and highlight the advantages of this approach.

The project team published a book, Brick Bread and Biscuit, containing stories of the journey of accessing gold from e-waste, the chemistry being developed to recover the precious metals, and how this endangered material can help revitalise Indian craft techniques such as meenakari, koftgari, and metal patination. The book’s name refers to the sizes of gold ingots in India – brick is 5 kg, bread is 1 kg and biscuit 100 g – while also commenting on more local scale hydrometallurgical refining compared with industrial scale pyrometallurgy.

Read the full book here Brick Bread and Biscuit.pdf

Find out more about the technology

https://edinburgh-innovations.ed.ac.uk/technology/metal-refining-and-recycling