Aluminium could easily be the poster child for recycling. Reusing scrap aluminium to produce new aluminium requires only 5 per cent of the energy needed to extract aluminium from bauxite ore. However, aluminium recycling, technically referred to as secondary aluminium production, is not without its environmental problems.
The aluminium recycling and production process causes the emission of pollutants such as dioxides and furans, hydrogen chloride, and particulate matter.
Dioxides and furans accumulate in high concentrations in fish and other fatty foods and affect brain development and hormone systems, particularly in foetuses. Hydrogen chloride is corrosive to eyes, skin and mucous membranes. Short- and long-term exposure to hydrogen chloride are both linked to respiratory and other health effects. Exposure to particulate matter is linked to asthma and other respiratory problems.
To control these emissions, aluminium recyclers are required to comply with the National Emission Standards for Hazardous Air Pollutants for Secondary Aluminum Production. Aluminum recyclers are required, among other things, to design, install and use systems to capture emissions, demonstrate compliance and establish and monitor operating parameters.
The process of refining aluminium creates a waste product known as dross. This dross consists of metals, salts, oxides and other substances. Black, or dry, dross is granular like sand and has a low metal but high salt content. White, or wet, dross has a high metal content and forms large clumps. If aluminium dross or salt cake is not properly handled or disposed of, it can pose serious threats to human health and cause serious environmental problems.
Salt cake, or salt slag, is a hazardous waste produced when aluminium waste is melted under a layer of salt. Salt cake is essentially a combination of dross and salt. It contains oxides, carbides and sulphites, as well as trapped metallic aluminium and the pollutants PCDD and PCDF. When put in contact with water, salt cake emits flammable gases like acetylene and can give off toxic chemicals, like ammonia, in dangerous quantities.