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 (eg increase storage efficiency)
- Exploring reuse opportunities for residue (eg. road construction or in building materials)
- Treating the residue to make it more benign for storage and reuse (eg carbonation and wash system to process the sand component, neutralizes any caustic)
- Rehabilitating bauxite storage areas for use (eg. revegetation and natural resource laboratories).
In 2015 AWAC produced approximately 22.8 million tonnes of bauxite residue as a result of its global bauxite mining activities. This represents a decrease of 3.2 million tonnes compared to 2014 due to the sale of the Jamaican refinery and the 2015 second-half curtailment of the Suralco refinery in Suriname. Minimising waste through innovative processes and alternative uses for waste products are priorities that will reduce AWAC’s environmental footprint.
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 unit 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 2015
AWAC improved its bauxite residue storage efficiency in 2015 by approximately 5 per cent compared to 2014 after achieving the 2020 goal of a 15% reduction in bauxite residue land requirements per unit of alumina 7 years ahead of schedule. 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-colored 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.
Residue filtration, an innovative technology has been commissioned at AWAC's Kwinana refinery in Australia. With this technology, bauxite residue is forced through very large filters that squeeze the water from the mud, with the water being recycled in the refining processes. Because of the technology, the refinery will not need to construct another 30 hectare residue storage area for around 20 years compared to every five years previously. The system is also expected to reduce freshwater use by 1.2 gigalitres annually. We anticipate deploying this technology at other refineries around the world.
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
Goal: 15% reduction. Progress as of December 2015: 20.9%
Bauxite Residue Storage Area Rehabilitation*
Percent of total area rehabilitated
As of 2015, a 20.9% 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
The December 2015 progress towards the goal of 30% storage rehabilitation before 2020 was 18%.
Opportunities to reuse bauxite residue are being continually researched. To-date Alcoa’s Technology Delivery Group based in Western Australia have developed a re-crushed rock material suitable for construction back fill, general fill, use in road base construction or golf bunker sand. Demonstration trials continued in 2012 from the Kwinana refinery. Due to the high volume of residue produced each year, the percent 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 2015, AWAC maintained intensity at 0.17 grams per metric ton of alumina produced (2014: 0.20 grams per tonne of alumina produced). Absolute mercury emissions decreased due to lower alumina production.
Mercury emission goals
|Mercury emission intensity||80% reduction||90% reduction|
Spent Pot Lining (SPL)
Alcoa continued to make progress in reducing SPL waste from AWAC’s aluminium smelters in Victoria. Collaborating with a cement manufacturer, the SPL is being converted into mineral products and a fuel that has reduced emissions for the cement industry at the Point Henry Operations. SPL waste (per tonne) has been dropping continuously since 2007.
The current focus is to increase the environmental credentials of the process.
Waste to landfill
In 2014 we received for the first time, definitive data on the waste to landfill from all of AWAC's operations. In 2015 a grand total of 13,420mt (metric tonnes) (2014: 15,441mt) of waste was sent to landfill in 2015 (this excludes bauxite residue which is dealt with as a separate matter). The figure of 13,420mt of waste is contrasted against the total production tonnages from all of AWAC operational sites of 57,219,084mt of product. Reducing landfill waste is a significant environmental metric, demonstrates increasingly efficient production processes along with the increase of re-use and recycling. Since 2011 the amount of waste from operations ending up in landfill has reduced by a significant 34.6 per cent. 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.
AWAC landfill waste (thousands of metric tons)