ABx Group has installed a pilot-scale bath reactor and an associated support system at its Alcore Technology Centre in NSW to trial the production of hydrogen fluoride from aluminium smelter waste.
The chemicals research and manufacturing company has developed a world-first process to produce hydrogen fluoride from a fluoride-rich waste product known as “bath", which is often produced in excess from the electrolytic process of alumina smelting to produce aluminium metal. ABx has an 83 per cent stake in Alcore, which will commission the reactor this week.
ABx Group managing director and chief executive officer Dr Mark Cooksey said: “The commissioning of this state-of-the-art reactor will be a major milestone in the development of the Alcore process, as it will demonstrate that sufficient fluorine yield can be achieved using commercial reactor designs and process conditions. This significantly increases confidence in the overall process scale-up and commercialisation.”
Electrolytic aluminium smelting is the process of extracting aluminium from its oxide (alumina), generally by what is known as the Hall-Heroult process.
Bath material is the electrolyte used in the Hall-Héroult process and is also commonly known as secondary cryolite, crushed bath, bath cryolite, pure bath, bath and tapped bath material.
During an aluminium smelting process, surplus liquid bath material can be generated, often because of high sodium content in the alumina. The surplus is tapped off and is often crushed for re-use to start new smelting pots to compensate for electrolyte losses or for use in aluminium scrap recycling and in several other processes, such as in the manufacture of glass, enamel, ceramics and more.
Typically, a smelter generating a surplus of bath material will have to crush it to certain technical specifications and then bag it in order to reuse it.
The smelting process produces several fluoride waste products, including per-fluorocarbons and hydrogen fluoride as gases, in addition to sodium and aluminium fluorides and unused cyrolite as particulates. The waste can be as little as 0.5kg per tonne of aluminium in the best plants and up to 4kg per tonne of aluminium in older designs from as far back as 1974.
And this is where the Alcore technology comes in.
Its pilot plant is designed to recover fluorine from some or all of the “excess bath” waste product to produce hydrogen fluoride. A later-stage commercial plant is proposed to further react the hydrogen fluoride to produce aluminium fluoride, which can then be returned and used in aluminium smelting.
Recent development work by Alcore indicates that achieving a high fluorine yield from the aluminium smelter waste is feasible, but management says it depends on achieving sufficient process mixing, which was difficult using its previous laboratory reactor.
ABx says that the overall yield is important to maximise the amount of hydrogen fluoride and aluminium fluoride produced and to minimise the amount of fluorine that reports to other unwanted metal sulphate co-products.
The company’s new reactor features state-of-the-art technology to enhance process mixing and has a process capacity 10 times larger than its previous reactor.
Management believes that if the pilot batch reactor achieves the high fluorine yields from aluminium smelter waste, it will provide confidence that the first commercial plant will perform as designed and enable further development work on processing and market potential evaluation of metal sulphate co-products.
Any system that can recycle toxic fluoride products back into an Australian industry where related fluoride salts are of critical value has to be a good thing – especially when the nation has no significant fluorine production and obtains most of its fluorine-based compounds from the United States and Canada.
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By Doug Bright
