“Protecting is a core value at Emirates Global Aluminium. Acknowledging the importance of preserving precious natural resources, EGA endeavours to act responsibly to protect the environment wherever the business operates. Optimising raw material and energy consumption, minimising harmful emissions and implementing a 'reduce, reuse, recycle' waste philosophy are fundamental to this approach.”

Abdulla Kalban
Managing Director & CEO
Emirates Global Aluminium

Campaign Website

Spent potlining treatment plant in Jonquiere, Quebec, Canada (Rio Tinto Alcan)

A key feature of the smelting process is the enclosed nature of the electrolytic pots.

Fugitive emissions from point fed prebake cells, which produce almost 90% of the world’s primary aluminium, are very low – less than 2% of the generated emissions. The balance of the emissions is collected inside the cell itself and carried away to very efficient scrubbing systems, which remove particulates and gases. Computer technology controls the process down to the finest detail, which means that occurrence of the anode effect – the condition that causes small quantities of perfluorocarbons (PFCs) to be produced – can be minimised. All new plants and most plant expansions are based on prebake technology.

Fluorides

For many decades fluoride emissions (as gases and particulates) were considered to be the single most important pollutant from aluminium smelters. Depending on local conditions, fluorides could have a serious environmental impact on the local flora and fauna. Fluorides accumulate in vegetation and can cause damage to coniferous trees. They also accumulate in the teeth and bones of ruminants eating fluoride-contaminated forage.

Plants with modern control systems to remove and recycle the fluorides today do not generate local concerns. Optimum fume collection from the electrolytic cells and specific workplace training on minimisation of fugitive fluoride emissions, as well as improvements in cell technology have driven a 50% reduction in total fluoride emissions per tonne of aluminium production between 1990 and 2010 (around 80% since the 1960s. The industry has committed to a further reduction of at least 35% between 2006 and 2020.

Fluoride “scrubbing systems” use alumina to extract gaseous fluoride from pot gases. This “activated” alumina, which contains the residual fluoride is then used as a feed for the reduction process; in fact, it has a positive impact on cell chemistry and process efficiency over non-activated alumina. Thus the fluoride is recycled through in a closed loop system. Around xxxx% of smelters worldwide employ such scrubbing systems.

Bauxite Residue

Bauxite residue is the industry’s single largest solid waste stream, a by-product of the Bayer Process. It is primarily composed of the insoluble fraction of the bauxite ore that remains after extraction of the aluminium-containing components. Iron oxides (10 – 30%), titanium dioxide (2– 15%), silicon oxide (5 – 20%) and undissolved alumina (0 – 20%) make up the residue, together with a wide range of other oxides which will vary according to the initial bauxite source. The high concentration of iron compounds in the bauxite gives the by-product its characteristic red colour, and hence its common name “Red Mud”. The pH level of the residue is generally up to 13 or higher in some cases, due to the presence of alkaline sodium compounds, such as sodium carbonate and sodium hydroxide.

After washing, the residue is contained in special facilities known as Bauxite Residue Disposal Areas (BRDA) or Residue Storage Areas (RSA). The type of disposal employed by alumina refineries varies across the world, depending on factors such as land availability, technology availability, climatic & geographic conditions, logistics and regulatory requirements.

Companies are required to ensure that BRDAs comply with the respective environmental standards. Modern BRDA guidelines will include both general and location-specific design criteria such as soil conditions, earthquake risk, long term stability and management of storm events. Careful monitoring ensures structural integrity is maintained.

Further information on bauxite residue, along with case studies from around the world, can be found here.

Spent Pot Lining

Spent pot lining (SPL) is an unavoidable by-product of the aluminium smelting process. On average, 15-35 kg of SPL is produced per tonne of aluminium. Reporting plants have increased from 51 to 73 plants increasing the reported production from 13 to 16 million tonnes. In 2007, 27% of SPL output was recycled externally out of a total reported output of 406 thousand tonnes of SPL. About 58% of the SPL output was deposited in form of treated deposition or stored pending final deposition or recycling.

The industry has systematically worked to minimize the amount of SPL produced, by extending the lifetime of the lining in the smelter pots. Since the 1970s, SPL has been recognised as a valuable resource for other industries, including as a feedstock in the cement, mineral wool and steel production processes. However, the main barrier to supply of SPL as a feedstock has been economics. Individual smelters do not produce enough SPL to provide a continuous supply of feedstock for a cement plant to justify their conversion to receiving this material.

Through collaboration with potential customers, and between companies to increase regional supply, the recycling of this material has become more viable and widespread.