Aluminium waste headache solved
31 May 2002
An Australian research team claims to have solved one of the world's big industrial waste headaches - what to do with spent pot lining (SPL) from aluminium smelters.
In an advance for sustainable mineral production, the 'Alcoa Portland SPL Process' developed jointly by Portland Aluminium, Alcoa, Ausmelt and the Commonwealth Scientific and Industrial Research Organisation (CSIRO) renders the hazardous waste harmless and at the same time produces two commercial by-products.
According to the CSIRO, aluminium smelters worldwide produce about half a million tones a year of SPL which, in many cases, simply has to be stored on site because local regulations prevent its disposal in landfill.
Aluminium fluoride produced by the process will directly replace a portion of the expensive imported aluminium fluoride used in the smelting process - significantly reducing purchase costs for this material.
Another product, 'synthetic sand', has received Australian Environment Protection Authority approval for unrestricted use and is expected to be used road-making and concrete production.
'Treating SPL is a costly process, but achieving such an environmental breakthrough, where the by-products partially offset the processing costs, is an outstanding result,' said SPL project manager, Mr Ken Mansfield.
Mr Mansfield said Portland Aluminium had 75,000 tonnes of SPL stored safely in secure containers and specially ventilated buildings. 'But we couldn't go on storing it for ever, so in 1989 we started seeking suitable treatment options. That was when we approached CSIRO, to comb the world for a process that would meet our environmental, technical and economic goals'.
'When it became clear there wasn't anything suitable worldwide, we began our own joint research, which led in 1992 to our trialling the Ausmelt technology.'
Ausmelt Limited was established in the early 1980s by a former CSIRO researcher Dr John Floyd to commercialise his submerged-lance smelting technology - SIROSMELT.
SIROSMELT is said to be a fast and efficient method of processing non-ferrous metals based on a submerged combustion process. Fuel and gases are injected through a lance, the tip of which is submerged into the molten material in the furnace. The fuel combusts at the tip, heating and melting the incoming feed materials, and the injected gases cause vigorous agitation and rapid reactions.
Globally there are now 30 smelting plants using the core SIROSMELT technology which are used primarily for copper, zinc, lead and tin smelting which process more than 3 million tonnes per year of metallic concentrates.
In the processing of spent pot lining, typically operating at around 1250 degrees Celsius, the submerged lance technology has proved ideal for releasing the fluorine contained in the spent pot lining for conversion to other products. The process also destroys any cyanide that may be present.
The Portland Aluminium SPL team had to overcome many technical challenges, including finding a way to produce aluminium fluoride from the gases liberated by the process. Later, when the pilot reprocessing plant began operating, problems had to be solved in handling the gases and by-products.
