Significant water resources are required for the production of alumina.
Water is used to produce the steam required in the digestion process; in the preparation of aqueous caustic soda, flocculants and lime; to wash the ore, residues and recycled caustic and for dust mitigation. There are also uses such as vehicle washing, sanitation and provision of drinking water which occur at a refinery.
The amount of water used in refineries is dependent on a variety of factors – bauxite quality, the design of the process facility, the extent to which water is recycled and the demand for non-process applications as well as the location of the facility and local water stress.
Many of these uses of water do not result in the “consumption” of water resources (i.e. volume of water with no changes in quality released back to the source of extraction is lower than the volume extracted). Recycling of water within the facility for certain processes also helps to reduce water use, where water resources are stressed. Large volumes of process water (an aqueous solution of caustic soda which contains dissolved aluminium and other impurities) can be reclaimed from the bauxite residue disposal area. Surface or storm water run-off can be collected in specially built ponds. All of this water can be treated and then reused.
Recognising that water is a precious resource, companies are investing in sustainable water management programmes, including increased use of recycled water, although non-recycled resources are still essential for some stages of the refining process.
The International Aluminium Institute (IAI) collects data on fresh water use, consumption and water stress indicators to track the industry’s impact on water resources. Aluminium for Future Generations sustainability objective:
“IAI Member Companies will seek to reduce their fresh water consumption per tonne alumina produced and concentrate efforts to minimise fresh water consumption where there are limited available fresh water resources.”