The Greening of Gold: AuTEK explores gold's potential to clean the environment

If you imagine a particle of gold the size or a speck of dust, you're thinking too big. Think much smaller - one thousand millionth of a metre small.

While a speck of dust may contain up to 100,000 atoms, a nanometer-sized particle of gold is measured in tens of atoms - perhaps 20, 30, 40 atoms in size. That's the size gold needs to be to act as a catalyst. While PGMs are also broken down into minuscule particles to act as catalysts, with gold, the particles would need to be one-tenth the PGM size. A unique feature of gold is that it can accomplish its catalytic action at room temperature and in the presence of moisture, whereas other catalysts require higher temperatures and dry air streams.

Researching gold's potential as a catalyst is the primary focus of Project AuTEK, a 50:50 joint venture launched by AngloGold, the world's largest gold producer, and Mintek, South Africa's national metallurgical research organisation. Mintek has a long ­standing involvement in the extraction, processing and application of precious metals and their alloys and compounds.

Forming part of AngloGold 's international marketing activities, Project AuTEK is the company's first foray into research and development in areas other than the traditional mining, engineering and metallurgical disciplines. Commenting on the initiative, Dave Hodgson, the executive officer responsible for the project, said, "Project AuTEK draws strength from the fact that gold has unique properties that can be utilised optimally and profitably in applications over and above jewellery production, especially in environmentally-sensitive areas."

How it could work

"AU metallic surfaces attract gas molecules to a greater or lesser extent - in the case of gold, very much the lesser because it is so inert," says Dr Mike Cortie, manager of the project 's research division at Mintek. Usually, the surface of metal gets completely coated with a layer of the gas molecules, which stay there. But in the case of a metallic catalyst, the various kinds of gas molecules absorbed on its surface can react to form a new kind of gas molecule - which doesn't stick to the surface as readily as the original reactant molecules did. So these molecules float off again and are replaced by fresh reactant molecules.

AuTEK's research has started by targeting how gold might catalyse pollutants such as carbon monoxide. "The concept is that individual molecules or carbon monoxide and individual molecules of' oxygen settle onto the 'surface' of the gold and then because they suddenly Find themselves cheek-by-jowl they will react to form molecules of harmless carbon dioxide, which then float off again."

Computer graphics visualisation of nanoscale gold particles with absorbed oxygen atoms.

But why should the carbon dioxide molecules float off while other ones stick? "Chemists are still rather hazy on precise details," says Dr Cortie. "Ostensibly, the reason is that the affinity of gold surfaces for carbon dioxide molecules is rather weaker than For the carbon monoxide or oxygen molecules."

A catalytic conversion - to gold

Work in the field has traditionally been fragmented, and researchers have rarely had the opportunity to interact. That's set to change at Catalytic Gold 2001, an international conference on the industrial applications of gold. Being held in Cape Town on 3-5 April 2001, the conference is open to both researchers and possible commercial users of products. Topics will include carbon monoxide oxidation, environmental applications, automobile exhaust purification, the chemical industry and electrocatalysts for fuel cells.

The interesting catalytic properties of gold have only been known for about a decade in this business, a relatively short time - and scientists are still rather unsure about how it works. "

We can only speculate what exciting applications might be unlocked in the future once a fuller understanding of the scientific issues has been achieved," Dr Cortie explained. "Such catalysts might someday find application in office buildings, in the purification of air for the occupants of passenger aircraft and as a general solution to air pollution. There is also evidence that gold has potential application in certain types of fuel cells that provide environmentally-friendly power and that it might serve as a useful catalyst in heavy industry chemical synthesis ."

If successful Project AuTEK will produce positive results not just for AngloGold and Mintek, but for South Africa, the global gold mining industry and, ultimately, for the environment.