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Alcoa World Alumina has implemented a wide range of Cleaner Production initiatives at its Western Australian bauxite mines and alumina refineries. For example, net savings through reduction in fine alumina waste are estimated at up to $14 million p.a.
Alcoa World Alumina Australia is a trading name of the unlisted public company, Alcoa of Australia Limited, whose principal shareholders are Alcoa Inc (60%) and WMC Limited (39.25%). Alcoa is a major Australian producer of aluminium from two smelters in Victoria, and is the world's biggest producer of alumina from three refineries in Western Australia. The company owns and operates alumina refineries at Kwinana, Pinjarra and Wagerup with a combined capacity of 7.3 million tonnes a year, equivalent to some 15 percent of world demand. Alumina is exported world-wide from shipping terminals at Kwinana and Bunbury.
Alcoa employs about 3700 people in Western Australia. Apart from refining, the company operates bauxite mines at Huntly and Willowdale in the Darling Range south of Perth, which supply the three refineries.
Environmental management is a high priority for Alcoa in all aspects of its operations. In 1990 the company's work on mine rehabilitation earned it listing on the United Nations Environment Programme's "Roll of Honour" for environmental achievement - the only mining company in the world to have been so recognised.
Alcoa mine area before and after rehabilitation
At Alcoa, cleaner production is a tool used within the "Alcoa Business System" (ABS) to assist the company to move towards sustainable aluminium production. Sustainable development is the basis for Alcoa's 2020 Global Environmental Strategy. Business units have adopted challenging waste reduction, cleaner production and cost improvement targets as well as strategies aimed at increasing community and social contribution. The ABS was initiated in 1996 and is being implemented throughout all 350 Alcoa locations in 37 countries.Processes and activities
Access to bauxite is the keystone of Alcoa's activities in Australia. Darling Range bauxite is a low-grade resource to which value is added through refining and smelting. Bauxite is defined as any ore in the lease which has a content of more than 27.5 percent aluminium oxide. Typically, it takes seven tonnes of Western Australian bauxite to yield one tonne of aluminium.
At current rates of alumina production, some 26 million tonnes of ore are mined each year from the Huntly and Willowdale mines. Darling Range bauxite is the lowest grade ore mined on a commercial scale anywhere in the world, and requires substantial investment in a fleet of loaders, excavators, trucks and crushing and conveying equipment.
At each new mining area, about half a metre of topsoil and overburden is removed and conserved for later rehabilitation, and the top one to two metres of cemented caprock bauxite is drilled and blasted so that it can be extracted along with the more friable bauxite below. Alcoa has developed a sophisticated computer-based blast acoustic model to ensure that blasting noise is kept below acceptable levels. Four Komatsu bulldozers - the world's biggest at 140 tonnes and 1050 horse-power - are successfully ripping caprock at pits near neighbours where blasting would be unacceptable. Once the ore has been broken, it is loaded onto haul trucks by excavators or front-end loaders and transported to primary crushers at the mines. Caterpillar and Komatsu mining machinery is used at the two bauxite mines, while the haul fleet comprises 85-tonne and 105-tonne trucks.
Bulldozer ripping caprock
Ore mined at Huntly is transported by conveyor to supply the Pinjarra refinery and the Kwinana railhead stockpile. From the stockpile, bauxite is railed to the Kwinana Refinery. Bauxite from the Willowdale mine is conveyed to the Wagerup refinery.
The Jarrahdale Mine was closed at the end of 1998. Over its lifetime it produced 168 million tonnes of bauxite for the Kwinana Refinery,
Alcoa operates a three-refinery system in Western Australia between the capital city, Perth, and the port of Bunbury 200 km to the south. The bauxite is fed via conveyors to the alumina refineries where it is subjected to the Bayer process to produce alumina. Alumina is a white granular material, a little less coarse than table salt, and is properly called aluminium oxide. Aluminium must first be refined from bauxite in its oxide form. The Bayer refining process used by alumina refineries worldwide involves four steps - digestion, clarification, precipitation and calcination.
Alcoa's Kwinana refinery, which began operating in 1963, has a current rated capacity of 1.9 million tonnes a year. The Pinjarra refinery is one of the world's biggest with a capacity of 3.2 million tonnes, and Wagerup has a capacity of 2.2 million tonnes.
Aerial view of the Kwinana Refinery
In 1992 Kwinana became the first alumina refinery in the world to achieve an ISO-9002 Quality Accreditation. Pinjarra and Wagerup, and the bauxite mining operations, achieved this standard in 1994. Similarly Kwinana refinery led the way in 1997 in achieving ISO 14001 environmental management certification, with Wagerup and Pinjarra planning to achieve certification by the end of 2001. Kwinana also achieved a Best Practice Environmental Licence in December 1998, the first industry in Western Australia to do so.Cleaner production initiatives
The Alcoa Cleaner Production programs primarily focus on:
Examples of initiatives include the following:
Improved vessel descaling practices
Explosives, jack hammers and high pressure water have traditionally been used to remove scale from inside large process tanks. These techniques are expensive, affect equipment availability, and impose serious injury and health risks. They produce large volumes of waste product with associated soil and groundwater contamination and waste disposal risks.
Today, in many situations, caustic and acid wash methods associated with changed operating and maintenance practices have now superseded the older techniques.
Improved heat exchanger maintenance
Heat exchangers in the process scale up and require regular maintenance. In the past, prior to descaling, the contents were emptied to the concrete floor resulting in temporary loss of process solutions (75kl each time) degradation of the concrete, safety issues and risks of soil and groundwater contamination.
Today, cool, lower concentration water is used to push the process solution through the heat exchangers prior to drain down. This saves costs and avoids the previous problems.
Improved bauxite quality
The contamination of the refinery liquor stream by organic compounds is a major constraint on production. The organics originate with the bauxite. During mining the top-soil and overburden are removed using heavy equipment. In the past , pockets of overburden were mined along with the bauxite. Research indicated that this was a significant source of organics.
Mining practices were modified to carefully remove all overburden, thereby reducing organic inputs and subsequent waste.
Removing overburden to reduce organic inputs
Reduction in fine alumina waste
Fine alumina is produced by uncontrolled precipitation and product breakdown during materials handling. It is captured in electrostatic precipitators in calcination. In the past, product quality specifications resulted in the recycling of over 200,000 tpa of fine alumina in three WA refineries. More than half of this was lost to residue.
Measuring alumina quality by electronic microscopy
Technology and product modifications led to waste reduction refinements in precipitation control and calciner design, as well as reuse of some of the superfines as liquor burning feed medium, have significantly reduced the waste. After discussions with customers, some relaxation in the product specification further reduced the superfines recycle. Further improvements in calcination are planned.
Sodium oxalate, an organic impurity, is removed from the liquor stream as a crystalline material. In the past, it was either treated with lime and disposed of to residue areas, or incinerated in a rotary kiln. While recovering some of the sodium value with the oxalate, these processes impose a range of health, safety and environmental risks.
The sodium oxalate has proved to be a useful reagent for vanadium processing - an example of industrial ecology - and it is being transported from Kwinana and Wagerup to Windamurra. Oxalate kilns at Kwinana and Wagerup have now been shut down resulting in cost avoidance, energy savings and reduced emissions. Other potential markets for these and other wastes are being examined.
Improved heat exchanger maintenance
Improved bauxite quality
Reduction in fine alumina waste
The incentives were reduced costs.
The barriers to the project were primarily that it was 'too hard' and that 'everything had already been tried'. In both cases the impetus by the team and backing by management led to a successful conclusion which has stimulated ongoing drivers for further improvements.
This and many other cleaner production projects implemented at Alcoa have resulted in a change in management approach form seeing environmental projects as being a necessary cost to awareness that such projects can result in significant financial savings as well as environmental improvements