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Highlights in Chemical Technology

Chemical technology news from across RSC Publishing.

Metals without the meltdown

13 February 2008

Scientists have found a practical, cheap and environmentally friendly way of producing the industrially important metal niobium.

Electron micrograph of niobium metal

Niobium is used in a variety of applications, from superalloys to optics, and total world production is nearly 23,000 tonnes per year. But, like many industrially important metals, it is mainly produced using pyrometallurgical extraction, a relatively high cost process.

In the late 1990s, Fray, Farthing and Chen invented a method that is much simpler and less energy consuming than conventional pyrometallurgical processes, and has the advantage of being carbon-free. Known as the FFC Cambridge Process, metals and alloys are extracted directly from their solid oxides using electrolysis in molten calcium chloride. Now one of these scientists - George Zheng Chen from the University of Nottingham, UK, and his colleagues at Wuhan University, China - have improved the process and reduced energy consumption by a third.

There is an urgent call for increased use of renewable energy, which is most likely to be converted to electricity in large scales, said Chen. 'Consequently, new, efficient and green electro-technologies are a necessity,' he said.

"The system provides an attractive and direct route to the formation of speciality alloys"
- Frank Walsh, University of Southampton, UK
Frank Walsh, an expert on industrial electrochemistry from the University of Southampton, UK, agreed. 'Alternative processes are essential to provide environmentally acceptable and energy efficient routes to metal extraction,' he said. 'In particular, minimising the number of steps in a production route and achieving direct transformation of minerals to metals is a critical subject area.'

Chen and co-workers found that electrolysing niobium oxide in a three-electrode cell using a variable voltage uses significantly less energy than the constant voltage two-electrode system of the FFC Cambridge Process. However, the set-up is more complicated and so impractical in large scale operations. To get around this problem the scientists mimicked the cell voltage variation using computer-aided control (CAC) of the two-electrode cell voltage. And modifying the FFC Cambridge Process in this way results in a 'more than 37 per cent saving in energy consumption,' said the team.

'CAC is demonstrated in principle for niobium extraction, but it is perfectly suitable for other reactive metals such as tantalum, titanium, zirconium and many rare earths,' said Chen. Also, said Walsh, 'the system described provides an attractive and direct route to the formation of speciality alloys.'

The FFC Cambridge Process is being commercialised by a spin-out company - Metalysis. 'Metalysis has won very strong support from investors,' said Chen. It has also formed strategic partnerships with important industrial players BHP Billiton and Rolls-Royce. According to Chen, this new energy-saving modification is very simple in principle and would not require any changes to be made to the cells used by Metalysis.

Freya Mearns

Link to journal article

Computer-aided control of electrolysis of solid Nb2O5 in molten CaCl2
Tian Wu, Wei Xiao, Xianbo Jin, Chao Liu, Dihua Wang and George Z. Chen, Phys. Chem. Chem. Phys., 2008, 10, 1809
DOI: 10.1039/b719369f

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