Alumina and aluminium processing creates a range of waste products, the most significant being
- bauxite residue, a sand and mud (almost in equal parts) slurry that contains most of the iron and silicon impurities from the bauxite along with some residual caustic soda.
- mercury emissions, which occur through refining operations as mercury naturally occurs in bauxite though its intensity varies from one batch of bauxite to another. This variability adds to the challenge of finding a common solution to reducing emissions.
- spent pot lining (SPL), the waste produced from aluminium smelting process when the carbon and refractory lining of smelting pots reaches the end of its serviceable life.
Bauxite residue: Every metric tonne of alumina produced, results in approximately 1.5 metric tons of bauxite residue (depending on bauxite quality). Residue is stored in impoundments that are capped and re-vegetated when full. Elements of the ongoing bauxite residue management include:
- Managing bauxite residue storage to reduce size of storage (e.g. increase storage efficiency)
- Exploring reuse opportunities for residue (e.g. road construction or in building materials)
- Treating the residue to make it more benign for storage and reuse (e.g. carbonation and wash system to process the sand component, neutralizes any caustic)
- Rehabilitating bauxite storage areas for use (e.g. revegetation and natural resource laboratories).
In 2016 AWAC produced approximately 22.9 million tonnes of bauxite residue as a result of its global bauxite mining activities. This represents a marginal increase of 0.1 million tonnes compared to 2015.
Minimising waste through innovative processes and alternative uses for waste products are priorities that will reduce AWAC’s environmental footprint. In 2016 AWAC commissioned at its Kwinana alumina refinery in Western Australia, a residue filtration processes that uses very large filters to extract water from bauxite residue. The water obtained via the process is recycled back into the refinery process. Application of this technology has deferred the need to construct another 30-hectare residue storage area for at least 20 years compared to every five years previously. This technology reduces freshwater use by 1.2 gigalitres per annum and importantly, contributes to directly reducing the footprint of the residue storage areas.
In reducing the overall footprint, three long-term strategic targets for bauxite residue have been established:
- a 15% reduction in bauxite residue land requirements per tonne of alumina produced by 2020; 30% by 2030 from a 2005 baseline,
- rehabilitate 30% of total bauxite residue storage are by 2020; 40% by 2030, and
- reuse 15% of bauxite residue generated by 2020; 30% by 2030
Results and goals 2016
AWAC improved its bauxite residue storage efficiency (measured by square metres of land required per thousand tonnes of alumina produced) in 2016 by approximately 4 per cent compared to 2015 after achieving the 2020 goal of a 15% reduction in bauxite residue land requirements per unit of alumina 7 years ahead of schedule.
The bauxite residue storage rehabilitation rate as measured by percent of total area rehabilitated remained steady at 18 per cent.
The rehabilitation rate saw positive movement in the period however challenges remain in meeting the residue reuse goal.
Efforts to reuse bauxite residue have been slower than anticipated despite advancements we have made in modifying the residue—particularly decreasing its alkalinity—to enhance its prospects for reuse. One major impediment is that no regulatory framework exists to assess bauxite residue for reuse in many of the countries where we operate refineries. Work is continuing with various government bodies to create such a framework so innovations in the research pipeline can be approved much faster.
Despite that challenge, a number of products made from bauxite residue have been introduced. Alkaloam®, which is a fine-grained bauxite residue that is carbonated through a reaction with carbon dioxide, increases the pH of acidic soils almost instantly compared to years for agricultural lime. ReadyGritTM is a red-coloured crushed rock material that can be used for general fill, construction backfill, turf top dressing, bunker sand, and road bases. Bauxite residue is also used in our innovative Natural Engineered Wastewater Treatment (NEWT™) system.
Alcoa has long-term targets to reduce AWAC’s overall residue footprint (see table below).
Bauxite residue goals
|Bauxite residue land requirements per unit of alumina produced||15% reduction||30% reduction|
|Total storage areas rehabilitated||30%||40%|
|Residue recycle or reuse||15%||30%|
*From a 2005 baseline
Bauxite residue storage Efficiency*
Square metres of land required per thousand tonnes of alumina produced
As of 2016, a 23.9% improvement achieved towards the 2020 target of 30% reduction
*Although predominantly AWAC bauxite residue storage areas, the results against targets does include non-AWAC bauxite storage at Alcoa's Pocos de Caldas refinery in Brazil
Bauxite Residue Storage Area Rehabilitation
Percent of total area rehabilitated
Bauxite Residue Intensity
Metric tons per metric ton of alumina produced
The increase in bauxite residue intensity in 2016 was due to the curtailing of refineries that had lower residue-to-alumina ratios.
Bauxite Residue Reuse
Percentage of total residue generated
Due to the high volume of residue produced each year, the per cent recycled or reused is minimal.
Mercury is a naturally occurring element found in bauxite. Mercury concentrations vary along with bauxite quality and location, and this variability adds to the challenge of reducing emissions. Alcoa will continue to research technology and operational solutions to achieve AWAC’s strategic targets. In 2016, AWAC maintained intensity at 0.15 grams per metric ton of alumina produced.
Mercury Emissions Intensity
Grams per tonne of alumina produced
In 2016 mercury emissions intensity decreased by almost 12 per cent compared to 2015.
Spent Pot Lining (SPL)
Alcoa continued to make progress in reducing SPL waste from AWAC’s Portland aluminium smelter in Victoria.
The current focus is to increase the environmental credentials of the process.
Waste to landfill
AWAC operations have significantly reduced landfill waste. In 2014 we received for the first time, definitive data on the waste to landfill from all of AWAC's operations. A grand total of 15,441mt (metric tonnes) of waste was sent to landfill in 2014 (this excludes bauxite residue which is dealt with as a separate matter). The figure of 15,441mt of waste is contrasted against the total production tonnages from all of AWAC operational sites of 52,492,347mt of product.
In 2016 landfill waste amounted to 6,350mt. Reducing landfill waste is a significant environmental metric, demonstrates increasingly efficient production processes along with the increase of re-use and recycling. This has been the result of waste separation and recycling programs at site as well as initiatives that recycle printer toner cartridges, batteries and mobile phones.