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.
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.
Results and goals 2018
In 2018 AWAC produced approximately 22.8 million tonnes of bauxite residue as a result of its global bauxite mining activities. This equivalent to 2017.
AWAC improved its bauxite residue storage requirements (measured by square metres of land required per thousand tonnes of alumina produced) in 2017 by approximately 2 per cent compared to 2017 and 12.5% compared to 2014.
In reducing the overall footprint, three long-term strategic targets for bauxite residue had been established:
- a 15% reduction in bauxite residue land storage requirements per tonne of alumina produced by 2030 from a 2015 baseline, A reduction of 5.8 per cent from the baseline was achieved.
|Bauxite residue land requirements per unit of alumina produced||15% reduction|
*From a 2015 baseline
2020 Target 57m2
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
2020 target 30%
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 2017, AWAC maintained intensity at 0.12 grams per metric ton of alumina produced.
In 2016 mercury emissions intensity decreased by almost 12 per cent compared to 2015.
|2017 AWAC total (metric tons)||10,879||11,186||1,819|
AWAC operations have significantly reduced landfill waste.