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It is no longer unheard of for people to throw away expensive computers in order to have the latest model. Your mobile phone may be functioning perfectly, but if it doesn’t take pictures or have the latest advanced features it has got to be replaced. As a consequence, there is a growing tide of obsolete computers and other electronic products finding its way into landfill sites throughout the UK and Europe.
Electronic Waste Initiatives
From 2004, the EU Waste Electrical and Electronic Equipment (WEEE) directive will tackle the increasing waste streams of electrical and electronic equipment by requiring manufacturers to take back equipment for recycling. Responding to the need for an environmentally acceptable solution to deal with the huge problem of redundant computers and other electronic equipment, funding from the UK Government’s programme for Waste Minimisation through Recycling, Recovery and Reuse in Industry (WMR3) has helped scientists to pioneer the development of two novel methods s for recycling components and valuable metals in printed circuit boards (PCBs).
New Technology for Processing Printed Circuit Boards
Researchers at Cambridge University have collaborated with colleagues from with Alpha-Fry Ltd and EA Technology to develop a patented process that employs a specially developed chemical leaching agent to release all the valuable electronic components such as chips or condensers for recycling, and to recover valuable metals and other materials from shredded boards.
Recycling Printed Circuit Boards
Around 60 million PCBs are produced each year. Each circuit board has a metal content of up to 30% by weight. The metals present in the majority of cases are gold, silver, copper, tin and lead. Many of the processes used to recover non-precious metals are based on mechanical, pyrometallurgical and hydrometallurgical techniques, in which the value of the electronic component is totally lost and maximum metal recovery is not possible. The integrated approach developed at Cambridge enables the components to be separated and resold, the solder leached and re-deposited as a solder alloy and the shredded boards to be reused as a binder in aggregate use.
How the Process Works
The key to the new process is the development of a selective leaching agent that is highly effective at dissolving solder used in the circuit boards yet has no effect on the performance of the electronic components. The selective leachant that has been developed is composed of fluoroboric acid containing a titanium redox couple. The leachant dissolves the lead and tin content in exactly the same ratio as the solder, leaving the copper content of the boards intact. The same process can also be applied to shredded boards after they have been treated to remove aluminium and ferrous scrap. The solder is then electroplated from the leaching agent, which is then regenerated.
Impetus for the New Technology
‘Our initial idea was to develop a leachant that would release all the electronic components for reuse,’ says Professor Derek Fray Head of the Department of Materials Science and Metallurgy at Cambridge University. ‘Unlike thermal processes, our technique does not degrade their performance in any way. You should be able to get everything back, and you can then sort the components in a range of different ways depending on their market value, type or toxicity.’ The next step for Professor Fray is applying the technology on an industrial scale.
Recovery of Precious Metals
The disposal of electronic scrap in landfill sites has become increasingly restricted over recent years. In the UK, electronic waste is now being shipped to copper smelting plants in Sweden and Belgium. However, copper smelters will only take material above a certain metal concentration, which leaves industry with the problem of how to dispose of low-level material. Research work at Imperial College in London has resulted in a process that not only recovers copper, tin and lead, but also recovers low-level metals such as gold, silver and palladium. ‘We have developed a clean process for recovering nearly all precious metals and heavy metals from electronic waste,’ explains Professor Geoff Kelsall from the Department of Chemical Engineering and Chemical Technology at Imperial College. ‘The essence of the process is its ability to dissolve all these metals non-selectively and then recover them selectively or non-selectively. Unfortunately we can’t recover everything but we can recover a wide range of metals.’
How the Process Works
The process uses two reactors, a leach reactor and an electrochemical reactor. Using anodically generated chlorine, the leach reactor dissolves the metals, while the electrochemical reactor has two functions. It not only generates the reagent for dissolving the metals, but also recovers, from solution, the metals dissolved in the leach reactor. The overall process involves inputting electrical energy to move the metals from the scrap to the reactor’s cathode, which produces only de-metallised waste. ‘Essentially you are just moving materials from one place to another,’ says Kelsall. ‘Chlorine is a nonselective oxidant. We deliberately developed a system involving non-selective oxidation with the possibility of selective recovery.’
Feasibility of the Process
Using a small-scale pilot system capable of processing 10kg of waste per day, Kelsall and his research team have demonstrated the feasibility of the process to selectively recover metals from electronic scrap. The next step is to increase this by a factor of 10. ‘I have an industrial partner willing to host and run a pilot plant to treat 100kgs of scrap per day, ‘says Kelsall, ‘but we are not able to quantitatively design it yet.’
The Future for the Technology
Funding permitting, within two years Kelsall believes he will be able to develop a model from which he can design a full-scale pilot plant. ‘There are several basic science and engineering issues to be addressed before we can design such a plant,’ says Kelsall. ‘We know that there are some metals we cannot recover, which was entirely predictable. Metals such as aluminium cannot be electrodeposited from aqueous solutions and so will require an additional unit process to prevent the accumulation of Al (111) in the solution, which will increase the overall cost of the process.'
Summary
The industry is aware of the problems it faces, and from 2004, producers will be responsible for taking back and recycling electrical and electronic equipment. As the tide of electronic scrap continues to rise and environmental regulations are tightened, innovative work currently going on at UK universities is likely to become an increasingly attractive proposition for getting most of the materials back from obsolete electronics.
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