Hoopes process
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The Hoopes process is a metallurgical process, used to obtain aluminium metal of very high purity (about 99.99% pure). The process was patented by William Hoopes, a chemist of the Aluminum Company of America (ALCOA), in 1925.[1]
Introduction
[edit]It is a method used to obtain aluminium of very high purity. The metal obtained in the Hall–Héroult process is about 99.5% pure, and for most purposes it is taken as pure metal. However, further purification of aluminium can be carried out by the Hoopes process. This is an electrolytic process.
The process
[edit]A Hoopes cell consists of an iron tank lined with carbon at the bottom, containing three layers of molten metal; an alloy of copper, crude aluminium and silicon on the bottom (serving as the anode), a mixture of fluorides of sodium, aluminium and barium (cryolite + BaF2) in the middle, and pure aluminium at the top. A set of graphite rods dipped in molten aluminium serve as the cathode. During electrolysis, aluminium is oxidised to Al3+ ions in the bottom layer. These ions migrate up through the middle layer before being reduced back to aluminium at the top layer, where it can be tapped off.
References
[edit]- ^ John E. Hatch (1 January 1984). Aluminum: Properties and Physical Metallurgy. ASM International. p. 1. ISBN 978-0-87170-176-3. Retrieved 13 May 2017.
Further reading
[edit]- Schwarz, V.; Wendt, H. (1995). "Electrorefining of aluminium scrap from chloride melts". Journal of Applied Electrochemistry. 25. doi:10.1007/BF00251262. S2CID 94160544.