Tag Archives: mechanochemistry

Refining metals more sustainably

We don’t just extract and refine metals from the earth, increasingly, we extract and refine them from consumer goods. Researchers from McGill University (Montréal, Québec, Canada) have devised a ‘greener’ technique to do this. From a June 7, 2017 McGill University news release (received via email and also on EurekAlert),

A team of chemists in Canada has developed a way to process metals without using toxic solvents and reagents.

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.

“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,” says Jean-Philip Lumb, an associate professor in McGill University’s Department of Chemistry. “That’s what makes our advance so important.”

The discovery stems from a collaboration between Lumb and Tomislav Friscic at McGill in Montreal, and Kim Baines of Western University in London, Ont. In an article published recently in Science Advances, the researchers 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.

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.

“Applications of green chemistry lag far behind in the area of metals,” Lumb says. “Yet metals are just as important for sustainability as any organic compound. For example, electronic devices require numerous metals to function.”

Taking a page from biology

There is no single ore rich in germanium, so it is generally obtained from mining operations as a minor component in a mixture with many other materials. Through a series of processes, that blend of matter can be reduced to germanium and zinc.

“Currently, in order to isolate germanium from zinc, it’s a pretty nasty process,” Baines explains. The new approach developed by the McGill and Western chemists “enables you to get germanium from zinc, without those nasty processes.”

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.

Next step: industrial scale

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.

“This shows how collaborations naturally can lead to sustainability-oriented innovation,” Friscic says. “Combining elegant new chemistry with solvent-free mechanochemical techniques led us to a process that is cleaner by virtue of circumventing chlorine-based processing, but also eliminates the generation of toxic solvent waste”

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.”

Here’s a link to and a citation for the paper,

A chlorine-free protocol for processing germanium by Martin Glavinovic, Michael Krause, Linju Yang, John A. McLeod, Lijia Liu, Kim M. Baines, Tomislav Friščić, and Jean-Philip Lumb. Science Advances 05 May 2017: Vol. 3, no. 5, e1700149 DOI: 10.1126/sciadv.1700149

This paper is open access.

ETA June 9, 2017 at 1700 hours PDT: I have to give them marks for creativity. Here’s the image being used to illustrate the work,

Caption: Strategy for reducing the environmental impact of a refining process: replace hazardous chemicals with more benign and recyclable compounds. Credit: Michael J. Krause (Western University)

Concrete proof that materials at the nanoscale behave differently than materials at any other scale

I hadn’t realized this still needed to be proved but it’s always good to have your misconceptions adjusted. Here’s more about the work from the University of Cambridge in a Sept. 30, 2016 news item on phys.org,

Scientists have long suspected that the way materials behave on the nanoscale – that is when particles have dimensions of about 1–100 nanometres – is different from how they behave on any other scale. A new paper in the journal Chemical Science provides concrete proof that this is the case.

The laws of thermodynamics govern the behaviour of materials in the macro world, while quantum mechanics describes behaviour of particles at the other extreme, in the world of single atoms and electrons.

A Sept. 29, 2016 University of Cambridge press release, which originated the news item, hones in on the peculiarities of the nanoscale,

In the middle, on the order of around 10–100,000 molecules, something different is going on. Because it’s such a tiny scale, the particles have a really big surface-area-to-volume ratio. This means the energetics of what goes on at the surface become very important, much as they do on the atomic scale, where quantum mechanics is often applied.

Classical thermodynamics breaks down. But because there are so many particles, and there are many interactions between them, the quantum model doesn’t quite work either.

And because there are so many particles doing different things at the same time, it’s difficult to simulate all their interactions using a computer. It’s also hard to gather much experimental information, because we haven’t yet developed the capacity to measure behaviour on such a tiny scale.

This conundrum becomes particularly acute when we’re trying to understand crystallisation, the process by which particles, randomly distributed in a solution, can form highly ordered crystal structures, given the right conditions.

Chemists don’t really understand how this works. How do around 1018 molecules, moving around in solution at random, come together to form a micro- to millimetre size ordered crystal? Most remarkable perhaps is the fact that in most cases every crystal is ordered in the same way every time the crystal is formed.

However, it turns out that different conditions can sometimes yield different crystal structures. These are known as polymorphs, and they’re important in many branches of science including medicine – a drug can behave differently in the body depending on which polymorph it’s crystallised in.

What we do know so far about the process, at least according to one widely accepted model, is that particles in solution can come together to form a nucleus, and once a critical mass is reached we see crystal growth. The structure of the nucleus determines the structure of the final crystal, that is, which polymorph we get.

What we have not known until now is what determines the structure of the nucleus in the first place, and that happens on the nanoscale.

In this paper, the authors have used mechanochemistry – that is milling and grinding – to obtain nanosized particles, small enough that surface effects become significant. In other words, the chemistry of the nanoworld – which structures are the most stable at this scale, and what conditions affect their stability, has been studied for the first time with carefully controlled experiments.

And by changing the milling conditions, for example by adding a small amount of solvent, the authors have been able to control which polymorph is the most stable. Professor Jeremy Sanders of the University of Cambridge’s Department of Chemistry, who led the work, said “It is exciting that these simple experiments, when carried out with great care, can unexpectedly open a new door to understanding the fundamental question of how surface effects can control the stability of nanocrystals.”

Joel Bernstein, Global Distinguished Professor of Chemistry at NYU Abu Dhabi, and an expert in crystal growth and structure, explains: “The authors have elegantly shown how to experimentally measure and simulate situations where you have two possible nuclei, say A and B, and determine that A is more stable. And they can also show what conditions are necessary in order for these stabilities to invert, and for B to become more stable than A.”

“This is really news, because you can’t make those predictions using classical thermodynamics, and nor is this the quantum effect. But by doing these experiments, the authors have started to gain an understanding of how things do behave on this size regime, and how we can predict and thus control it. The elegant part of the experiment is that they have been able to nucleate A and B selectively and reversibly.”

One of the key words of chemical synthesis is ‘control’. Chemists are always trying to control the properties of materials, whether that’s to make a better dye or plastic, or a drug that’s more effective in the body. So if we can learn to control how molecules in a solution come together to form solids, we can gain a great deal. This work is a significant first step in gaining that control.

Nicely written!

Here’s a link to and a citation for the paper,

Solvation and surface effects on polymorph stabilities at the nanoscale by A. M. Belenguer, G. I. Lampronti, A. J. Cruz-Cabeza, C. A. Hunter, and J. K. M. Sanders. Chem. Sci., 2016, Advance Article DOI: 10.1039/C6SC03457H First published online 02 Sep 2016

This paper is open access.

Given that the news release mentions crystals, this lovely image illustrates the press release,

 Snow Crystal Landscape Credit: Peter Gorges

Snow Crystal Landscape Credit: Peter Gorges