Smelter savings

A barrier coating developed by researchers at the Australian Commonwealth Scientific and Industrial Research Organisation (CSIRO) offers significant annual savings to aluminium smelters.

Smelter trials indicate that the low-cost coating prevents air burn oxidation and extends the operational life of carbon anodes used in high-temperature electrolytic cells.

Use of the coating was shown to produce a net reduction in carbon usage of 0.02kg carbon per kilogram of aluminium produced.

Dr Mahnaz Jahedi of CSIRO Materials Science and Engineering said: 'Our coating can provide considerable savings for the companies operating the more than 100 smelters that produce aluminium at present.'

Jahedi presented the results of the project at a recent meeting of The Minerals, Metals and Materials Society in San Francisco.

Carbon anodes are made from petroleum coke and, in the extreme heat of aluminium electrolysis cells, the exposed top and sides of the anodes can oxidise spontaneously owing to air burn.

Air burn can spread rapidly between anodes and necessitates more frequent interruptions to the smelting process to replace anodes.

The CSIRO coating performed significantly better than the conventional aluminium spray coating.

Jahedi said: 'The trials demonstrated that the coated anodes don’t develop air burn and last longer in the smelter cells as a result.'

The trials were designed to test the efficacy of the coating by placing coated anodes in positions in the electrolytic cells found to be particularly prone to air burn. 'None of the coated anodes had to be removed due to air burn during the trials,' Jahedi said.

Uncoated anodes placed in similar positions needed to be replaced more frequently as a result of severe air burn.

The coating also proved durable during trials, remaining undamaged during transport of anodes to the smelter and during in-plant handling.

'The coating did not melt or crack while the anodes were in use,' added Jahedi. 'The trials showed no safety issues with application or use of the coating in smelters.'

The coating is said to be simple to apply and adheres well to the carbon anode.

The next stage of in-plant trials will use several hundred coated anodes and is expected to provide a complete assessment of the productivity improvements offered by the coating.

CSIRO plans to license the coating technology to smelters.

CSIRO project officer Enzo Gulizia and Dr Mahnaz Jahedi inspect the surface of a freshly coated carbon anode, intended for use in a trial at an aluminium smelter