2 August 2012
A new technique to treat the hazardous ‘red mud’ waste from aluminium manufacturing could help protect the environment and aid industry.
A Canadian company claims to have trialled a commercially viable technique for neutralising the highly alkali substance while extracting valuable materials from it, using a process originally designed for extracting alumina (aluminium oxide) from clay.
Red mud is usually left untreated in reservoirs, which is cheaper than treating it with acid but can cause great damage to the environment if it leaks out, as happened in Hungary in 2010 when a spill of around one million cubic metres killed several people and injured many more.
`It’s an environmental nightmare,’ said Richard Boudreault, president and chief executive officer of Orbite Aluminae, the company behind the new technique. ‘This technology allows the red mud to disappear and the materials to be extracted and does it economically.’
These reservoirs have also become a big issue for the aluminium industry, he added.
‘In Germany and in Turkey, there are plants that are essentially slated to be abandoned because their red-mud ponds have been filled and the governments won’t give them authorisation to build additional ponds.’
Orbite’s answer is to treat the mud with hydrochloric acid and extract the alumina, iron, rare-earth elements and other valuable materials as the solution reaches different pHs and temperatures.
This relies on a fast-switching pH technique that uses equipment lined with glass to protect it from the acid and a computerised system that carefully controls the changing pH so different materials can be extracted at different stages.
The final residue left after Orbite’s treatment process has roughly 10 per cent of the volume of the original red mud.
The remaining liquids are circulated through an acid recovery loop that the company claims recovers 99.75 per cent of the acid, helping to make the process economic while the extracted materials provide an extra revenue stream.
‘It pays back [its capital costs] in a year and a half to two years,’ said Boudreault. ‘This is not something you do to recover the red mud only — you make money out of it.’
Orbite has been operating a pilot plant in Quebec for around 18 months producing between one and five tonnes of the different product materials a day and now hopes to license the technology to aluminium refineries.
Red mud is a waste product of the Bayer process, which is used to refine bauxite aluminium ore into alumina before it is electrolysed to produce the pure metal, but leaves up to 25 per cent of the alumina in the mud.
If spilled, as happened in China in May this year and in India in 2011, the mud is dangerous not just for its caustic properties but because it can contain heavy metals and radiation that contaminate the environment.
Researchers at Glasgow University are currently working on a lab-scale technique whereby the red mud is used as a catalyst to crack methane and the hydrogen and carbon released help extract the iron within and neutralise the mud without acid.