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12 April 2023

The Bayer process of refining bauxite ore to aluminium oxide (alumina) at a refinery causes a waste stream called “bauxite residue” or “red mud”. Bauxite residue is the aluminium sector’s largest waste stream by a long way: producing over 100 times as much, by mass, as the next largest waste stream, Spent Pot Lining.  On average it takes 4.5 tonnes of bauxite to produce 2 tonnes of alumina (and ultimately one tonne of aluminium).  Thus around 2.5 tonnes of dry bauxite residue is produced for every tonne of aluminium – globally between 150 and 200 million tonnes a year. The issues involved in the management of this significant volume waste are many and varied, with risks related to safe containment, high pH, dusting, land use, leachate treatment, security and monitoring all being relevant and with specificities per location. 

ASI’s Performance Standard includes criteria for the management of bauxite residue risks.  With around 25% of global alumina production from Entities with ASI Performance Standard certification, ASI seeks to ensure that companies are using good practice technologies in their operations.  Ultimately, the aim as per ASI’s Strategy is circularity and the production of zero wastes from the alumina refining processes, but this is a long way off.  In the meantime, appropriate management of this high volume material is both required and a condition of ASI certification.

This waste stream typically contains a number of minerals, the main ones being oxides of iron, silicona, titanium and calcium minerals and some residual alumina and caustic soda liquor (the chemical used in the Bayer process to break down the ore). Some other minerals are included at minor levels. The highly alkaline waste is typically stored in a bauxite residue storage area or impoundment. Whilst there have been some uses developed for bauxite residue, for the most part it needs to be contained until it dries and can be closed and rehabilitated into a safe and stable form. However, this process is time-consuming, requires often large areas of land and is limited in what the land can be ultimately used for. In many cases it prevents land being restored to pre-refining quality and use.

Pending technological and commercial breakthroughs in research and development projects to remove or minimise bauxite residue waste, the ASI Performance Standard V3 criterion 6.6 focuses essentially on dealing with the bauxite residue impoundment. In particular, this means to effectively prevent the release of residue and leachate to the environment and to perform regular checks and controls, including those conducted by third parties, to ensure the integrity of the storage area and control and neutralise water discharge. After closure of the refinery and its associated bauxite residue impoundments, the area must be remediated to a state that can adequately mitigate the risk of future environmental contamination. The main change from V2 is the addition of a requirement to assess the impact of water discharge from the storage area and mitigate any adverse actual or potential impacts to the environment. This applies to all alumina refinery audits from 1 June 2023.

Alongside ASI requirements, the industry continues to tackle this issue with novel technologies. There have been many years of projects, trials and development on alternative uses for bauxite residue, seeking to avoid or significantly reduce the volume required to be stored. However, there has not yet been a breakthrough that could apply across-the-board for the industry. There is potential for use as a bulk material for construction or raw material for other products, such as cement. Whilst projects are continuing, this is unlikely to lead to a universal solution, as not all areas where the refineries are located have a need for those materials. Some potential usage may be technically feasible, but not (yet) economically viable. This may include the potential sequestration of carbon dioxide in bauxite residue, which would bring a dual benefit of neutralization of the alkaline residue and capture and storage of greenhouse gases, but would still require management of large volumes of material. If there is a widespread and meaningful price on greenhouse gas emissions, there may be more research done in the area of carbon sequestration.

Press filtration has been a good technological development. This process produces a drier residue cake, which does not require as much room, is physically and environmentally safer to store and enables higher recovery of water and caustic soda. However, reasonably large volumes of residue are still produced from press filters.

Relatively recently, there have been a number of projects where the goal is to eliminate any residual waste as much as possible by separating out and extracting individual elements for sale or disposal. In the medium to long term, this should be the goal, where ideally there would be no waste left at all to store. This would be an excellent outcome from a safety, environmental, land use and circularity viewpoint. From a cost point of view, there would be savings in avoiding long term monitoring of residue and land holdings. The extraction and sale of precious metals or rare earth elements like scandium, cerium and neodymium, even in modest quantities, could provide good revenue streams or at the least cover the cost of extraction and dealing with red mud. Some of these elements could become increasingly sought after and valuable for electronic and electric systems.

Today more than 4 billion tonnes of bauxite residue is in storage around the world; by 2050 this number could reach 10 billion tonnes. The industry must continue to work towards some breakthrough solutions for bauxite residue.



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