Drinking water

Lime is widely used in the production of water for human consumption, in fact in terms of quantity, it even competes with chlorine as the major chemical used in water treatment.

Water treatment is comprised of several basic processes, depending on the impurities that need to be reduced. They are as follows:

• The removal of suspended/colloidal matter (helping to reduce tase, odours and colouration).
• Reducing hardness.
• Reducing the concentrations of dissolved metals.
• Disinfection.
• pH adjustment.

Overall a wide range of chemicals are used in water treatment. lime is used both as an alkali and as a source of calcium ions.

Flue Gas Treatment

In order to minimise pollutants produced by industrial combustion processes such as energy from waste plants lime is used to ‘scrub’ acid pollutants such as HCL and SO₂ from the exhaust gases.

Desulphurisation

Flue gases produced when burning fossil fuels that contain sulphur result in emissions to the atmospheres that are the principal cause of acid rain.  Acid gases containing oxides of sulphur can be treated by introducing limestone, chalk, quicklime or hydrated lime as a powder or slurry, promoting a reaction to form insoluble calcium sulphate or gypsum which can then be collected. If carried out under the correct conditions this process can produce a saleable gypsum co-product.

Energy from Waste

In recent years there has been an increase in the number of energy from waste plants all of which could be sources of acid rain whether they burn municipal or industrial waste, clinical waste, animal carcasses or natural fuels. Almost all incinerators around the world have utilised lime as a means of removing harmful gases for many years and proved lime to be cost-effective, efficient and sustainable.

Lime is sprayed into the flue gas stream in the form of a dry powder or as a suspension in water. It then reacts with the pollutants to form an insoluble salt which is easy to dispose of. In the case of desulphurisation, it is possible to produce quality gypsum (calcium sulphate) which can be used as a raw material in plaster or plasterboard.

Flue Gas Treatment

Lime, being the most cost-effective alkali, is widely used in the removal of acidic gases emitted by power stations.

Lime based techniques for the abatement of acidic gases can be divided into 5 groups:

• Wet scrubbing – where gases are treated with milk lime to remove SO₂ (Sulphur Dioxide) and neutralisation products are removed as a suspension.
• Semi-dry scrubbing – where milk of lime is sprayed onto the gases to remove SO₂ (Sulphur Dioxide) and reaction products are removed with a dust collector.
• High temperature (over 850°C) dry injection of hydrated lime – where the hydrated lime calcines and the resulting calcium oxides reacts with the acid gases (SO₂). Reaction products are also removed using a dust collector.
• Low temperature (below 300°C) dry injection of hydrated lime – removes HCl, HF and SO₂. Similarly, reaction products are removed using a dust collector.
• Low temperature (below 300°C) absorption by hydrated lime – in a fixed bed used to remove Hafnium from kilns calcining ceramic products.-