A team of chemists in Canada has developed a way to process metals without using toxic solvents and oxidants. The system, which also consumes far less energy than conventional techniques, could greatly shrink the environmental impact of producing metals from raw materials or from post-consumer electronics.
In an article “A chlorine-free protocol for processing germanium,” published recently in Science Advances, researchers from Western University and McGill University outline an approach that uses organic molecules — instead of chlorine and hydrochloric acid —to help purify germanium, a metal used widely in electronic devices. Laboratory experiments by the researchers have shown that the same technique can be used with other metals, including zinc, copper, manganese and cobalt – metals that are resource-intensive and can be environmentally costly.
The research could mark an important milestone for the “green chemistry” movement, which seeks to replace toxic reagents used in conventional industrial manufacturing with more environmentally friendly alternatives. Most advances in this area have involved organic chemistry – the synthesis of carbon-based compounds used in pharmaceuticals and plastics, for example.
“Currently, in order to isolate germanium from zinc, it’s a pretty nasty process,” said Western University chemistry professor Kim Baines. “This new approach enables you to get germanium from zinc, without those nasty processes.”
The discovery stems from a collaboration among Jean-Philip Lumb, an associate professor in McGill University’s Department of Chemistry and Tomislav Friscic at McGill in Montreal, and Baines at Western.
“At a time when natural deposits of metals are on the decline, there is a great deal of interest in improving the efficiency of metal refinement and recycling, but few disruptive technologies are being put forth,” said Lumb. “That’s what makes our advance so important.”
Lumb said applications of green chemistry in metals “lag far behind” other areas, Lumb says. “Yet metals are just as important for sustainability as any organic compound.”
There is no single ore rich in germanium and so it is generally obtained from mining operations as a minor component in a mixture with other materials. Through a series of processes, that blend of matter can be reduced to germanium and zinc.
To accomplish this, the researchers took a page from biology. Lumb’s lab for years has conducted research into the chemistry of melanin, the molecule in human tissue that gives skin and hair their color. Melanin also has the ability to bind to metals. “We asked the question: ‘Here’s this biomaterial with exquisite function, would it be possible to use it as a blueprint for new, more efficient technologies?’”
The scientists teamed up to synthesize a molecule that mimics some of the qualities of melanin. In particular, this “organic co-factor” acts as a mediator that helps to extract germanium at room temperature, without using solvents.
The system also taps into Friscic’s expertise in mechanochemistry, an emerging branch of chemistry that relies on mechanical force – rather than solvents and heat – to promote chemical reactions. Milling jars containing stainless-steel balls are shaken at high speeds to help purify the metal.
The next step in developing the technology will be to show that it can be deployed economically on industrial scales, for a range of metals.
“There’s a tremendous amount of work that needs to be done to get from where we are now to where we need to go,” Lumb says. “But the platform works on many different kinds of metals and metal oxides, and we think that it could become a technology adopted by industry. We are looking for stakeholders with whom we can partner to move this technology forward.”
Funding for the research was provided by the Natural Sciences Engineering Research Council of Canada, the National Natural Science Foundation of China, the Soochow University-Western University Center for Synchrotron Radiation Research, and the Collaborative Innovation Center of Suzhou Nano Science and Technology, Soochow University.
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