Lime is a widely used reagent in drinking water treatment applications and as such, is vital for the wellbeing of millions of people. Hydrated lime and liquid lime products are typically used for water treatment.
Lime products are used to adjust pH, remove metals and precipitate solids. Treatment with lime reduces water hardness and lowers the deposition of scale in pipes, boilers and other appliances. Lime treatment can also limit the reabsorption of metals such as copper, zinc and lead which therefore minimises the corrosion of pipework and equipment.
Lime products used to produce drinking water must conform to standards for chemicals used for treatment of water intended for human consumption:
- BS EN 12518 - High calcium lime
- BS EN 16409 - Dolomitic lime
- BS EN 1017 - Half-burnt dolomite
BS EN 12485 specifies the methods used for the chemical analyses and the determination of physical properties of calcium carbonate, high-calcium lime, half-burnt dolomite, magnesium oxide, calcium magnesium carbonate and dolomitic lime used to treat water for human consumption.
All lime products used to treat drinking water are approved by either the Secretary of State for the Environment Food and Rural Affairs (England), the Welsh Ministers (Wales), the Northern Ireland Assembly (Northern Ireland) or the Scottish Ministers (Scotland). The approvals process is administered for the whole of the UK by the Drinking Water Inspectorate (DWI) in England and Wales. Details of approved products are available here.
Sugar manufacturers use lime to precipitate out impurities from beet and sugar cane extracts. Lime is also used to neutralise the odours which are generated by beet washing and transport.
In the UK, the locally grown and harvested beet is cut into thin strips and then the sugar is extracted after mixing with hot water. The raw juice obtained is then purified by adding a lime solution. The purified syrup is then filtered, heated and tiny sugar crystals are added which are allowed to grow to the required size for the desired product. The resulting sugar crystals are then washed, dried and cooled. The residual lime can be processed and used in agricultural liming.
More information on sugar manufacturing and the use of lime can be found on the British Sugar website.
The calcium ions in lime products help to boost soil fertility, as well as adjusting pH, both of which can improve crop yields and thus can help to reduce the amount of fertilisers required. Ensuring adequate calcium in the soil also boosts micro-organisms and earth worm activity. Lime products for agricultural liming are regulated in the UK under the ‘Fertiliser Regulations’.
An agricultural liming material has calcium and magnesium compounds capable of neutralising soil acidity and includes quicklime, hydrated lime, and dolomitic lime, as well as agricultural limes, such as limestones, chalks, marls and shells. Lime based by-products, such as slags from metal refining and residual limes from sugar manufacturing, are also used in agricultural liming.
More information on agricultural liming is available from the Agricultural Lime Association.
Lime products used for animal hygiene are typically used for the treatment of manure and sludges, bedding materials, as well as indoor and outdoor surfaces. The products applied can be quicklime, hydrated lime, dolomitic lime, lime blends with other materials, and liquid limes. Care should be exercised in choosing the appropriate product and applying it safely to avoid harm to the animals and the environment. Lime products for animal hygiene are regulated in the UK under the Biocidal Product Regulations (BPR) by the Health & Safety Executive (HSE) and controls the marketing and use of biocidal products. Biocidal products protect humans, animals, materials or articles against harmful organisms like pests or bacteria, by the action of the active substances contained in the biocidal product. The regulations approve the use of quicklime, hydrated lime, and dolomitic lime as active substances in biocidal products in two categories.
- Disinfectants and algaecides not intended for direct application to humans or animals
- Veterinary hygiene applications
Quicklime, hydrated lime and dolomitic lime are used to regulate pH and provide a source of calcium in aquaculture as well as to precipitate out fine particles for removal as sludge on a periodic basis. Lime is also thought to regulate the production of phytoplanktons. In a similar way to agricultural lime, limestones and chalks are also used. Lime can be used to control the pH of acidic ponds and lakes. In general terms this creates a more hospitable environment for all aquatic organisms, in particular fish. Lime is therefore used by fish farmers to maintain a suitable habitat for breeding fish. Care should be exercised in choosing the appropriate product and applying it safely to avoid harm to the animals and the environment.
Lime is used to extend shelf life of fruit in storage. As fruits ripen they emit carbon dioxide, which lowers the level of oxygen in the atmosphere and accelerates the rate of deterioration of the fruit. By circulating air around the fruit and over exposed lime, the lime absorbs the carbon dioxide and the fruit remains fresher for longer.
Residues from processing citrus fruits when mixed with lime can then be dried and used as cattle feed. In addition, lime can also be used to neutralise waste citric acid and to raise the pH of fruit juices to stabilise the flavour and colour.
Separation of cream from whole milk during butter production can include the addition of liquid lime to alter the pH before pasteurisation. To separate the casein, acid is added to the skimmed milk and the casein can be mixed with lime and sodium fluoride to produce calcium caseinate, which is a type of adhesive. When the remaining skimmed milk is fermented, lime can be added to form calcium lactate, which has medicinal properties or acid can be added to produce lactic acid.
Glue and Gelatin
Liquid lime can be used to treat the waste materials from rendering plants which causes the collagen to swell and this is known as alkaline hydrolysis. The process was developed when the use of rendering plant wastes in animal feed were banned. The treated waste is then cleansed, dried and the resulting product can be used as an adhesive or as gelatin in the manufacture of capsules, cosmetics and ointments
Lime can be used as an ingredient in the manufacture of a common baking powder called monocalcium phosphate when phosphoric acid is reacted with a high calcium lime.
Lime is also used in the following:
- Making corn tortillas – liquid lime is used to soak the corn before conversion to cornmeal.
- Calcium Tartrate / Tartaric acid precipitation by lime treatment of grape leaves from vineyards.
- Soils for growing Pak Choi can be treated with quicklime to raise the pH above 7.2 and reduce the susceptibility to club root, thus improving crop yields.
Lime is used in the manufacture of many inorganic salts such as calcium citrate a food and drink additive, and calcium phosphate, a toothpaste additive.