Red sludge is the by-product of a process used during aluminium production (production of alumina as an intermediate product). When materials with aluminium content are extracted with the use of alkali from the raw material – bauxite -, red sludge is formed from the remaining residue and the sodium hydroxide solution. The name is taken from its muddy texture and distinctive colour, which is due to the ferrous oxide content of bauxite. Ferrous oxide is used for many purposes, for example as a colourant in red paints.
Usually around 24-45 percent of red sludge is ferrous oxide (responsible for its reddish-brown colour), but it also contains other metallic compounds (aluminium oxide, titanium dioxide, silicon dioxide, sodium oxide and calcium oxide). It contains gallium-, vanadium- and rare earth metal oxides in less than 1 percent. There is also sodium hydroxide in the sludge, which is a caustic base. The heavy metal content of red sludge is seven times higher that in normal soil.
Red sludge is not poisonous, but it is a hazardous material, due to its sodium hydroxide content. It becomes hazardous when, during processing, sodium hydroxide (lye) is added to it. The sodium hydroxide content of red sludge stored in Ajka is around 5-8%. Sodium hydroxide is a highly alkaline material, which is widely used in large quantities in the paper and textile industries, during the production of soaps and detergents, as well as in bauxite processing. It is a fact that dried red sludge, which is a very fine powder, irritates the airways when inhaled and its alkalinity causes stronger irritation than in the case of normal dusts. The adverse effect – irritation – is the same as with the inhalation of normal fine dust.
Lye (sodium hydroxide) is a highly alkaline material. Solid or concentrated lye causes burns and may damage the eyes on contact. The reason for these burns is that when lye gets in contact with water (such as water in the skin), it produces heat. The generated heat may cause burn injuries. The severity of the thermal effect (and the resulting burn injury) depends on the length of the contact and the concentration of the lye. Burns or eye injuries may be prevented by immediately washing the affected skin surface or eye with plenty of water. Longer exposure to red sludge and lye requires medical treatment.
Alkali poisoning: the caustic material causes the inflammation of the skin and the mucosa, followed by necrosis and ulceration. When this poisonous material is ingested, it causes the same effects in the oesophagus and the stomach. Tissues become oedematous and lubricious. On direct contact with lye, veins are burnt and together with blood this material forms a reddish-brown alkaline haematocrit. The burnt mucosa is swollen; depending on the concentration of the lye, its discolouration may vary from reddish to even black and it is covered with a white, sometimes fragmented coating, which is susceptible to bleeding. Scarring starts on week 3 or 4 and finishes on week 8 or 9.
Detoxification: skin may be washed with plenty of water or the toxic effect may be neutralised with vinegar, lemon, boric acid, milk and eggs. Having been in contact with this alkaline material, eyes may also be cleaned with plenty of water, boric acid or paraffin oil. Apart from milk, water and vinegar, ÁNTSZ (National Public Health and Medical Officer Service) also recommends ammonium chloride, sugary solutions and bicarbonate soda.
Vomiting should not be induced in cases when the sludge is swallowed and poisoning occurs through the mouth.
Protective equipment, boots, suitable protective clothing, goggles and rubber gloves must be worn during all activities where there is a danger of alkaline materials getting in contact with the skin or the eyes. After these activities, protective equipment and clothing must be washed while being worn, then the person must take a thorough bath or shower.
Cleaning: According to experts, the material should be collected in containers or on plastic sheets, ready for transport. During this work goggles and a mask must be worn in order to prevent contact with the eyes or the airways, in case the material is splashed on the person. Rubber boots and protective clothing over normal clothes are also recommended. In most areas neutralisation, cleaning up the sludge and ploughing in the residue (to avoid dusting) may be sufficient. Where the upper layers of the soil are heavily soaked through with the material, the affected soil must be replaced. Experts will assess which areas should be replaced and to what extent.