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…What is limestone?
…Where does limestone come from?
…How is limestone formed?
…How is limestone mined?
…How is limestone processed?
…How is limestone treated?
…What is limestone used for?
…How are limestone quarries rehabilitated?
…Photographic flowchart of limestone quarrying
…McDonald's Lime - 'Shunning the Limelight'
Limestone is a sedimentary rock. 'Lime' is a general term often used to describe limestone, quicklime, or hydrated lime. 'Limestone' refers to the naturally occurring calcium carbonate.
Where does limestone come from?……
Limestone is found in several areas in both the North and South Islands of New Zealand.
Limestone consists mainly of calcium carbonate (CaCO3) and forms on the bed of the sea from the remains of sea shells and other marine organisms. Fish, shellfish, coral and marine micro-organisms extract calcium and dissolved carbon dioxide from seawater to make calcium carbonate. Their remains settle on the sea bed where they may later be buried by other sediments. Heat and pressure causes these animal remains to form hard beds rich in calcium carbonate. The remains of shells and other fossils can often be seen in limestone.
If limestone is very deeply buried, heat and pressure will cause the calcium carbonate to recrystallize, forming marble. The largest deposits of marble in New Zealand are found in the northwest Nelson region.
At the McDonald's Lime quarry just south of Otorohanga the company mines a 67 hectare property. Underneath the topsoil, ash, and siltstone is an exceptionally high grade limestone, much of it with a purity exceeding 95%. Limestone is mined in a quarry . It is then transported by truck to a crushing plant . The limestone in its natural block form is fed into a closed circuit primary impactor until it has been reduced to the required size. Different sized limestone has different applications. Different treatments produce different products from the raw material.
To view a photographic flow chart of limestone quarrying at the McDonald's Lime quarry click here.
McDonald's Lime quarry and limeworks south of Otorohanga produce a range of lime products for use in a wide variety of applications.
At Omya's plant near Te Kuiti a high purity limestone is processed through crushing and milling circuits to produce a range of finely milled limestone powder (whiting) for use by New Zealand industries.
A major use of this high purity limestone powder is as a filler in paper and fibreboard. In addition it is a vital ingredient in the production of paint, plastics, rubber inks, adhesives, glass, putty, and ceramics. Visit the Omya website at www.omya.co.nz
At Omya's research centre, Calcium Carbonates are tested in paper manufacture.
Burnt Lime (calcium oxide CaO) is manufactured by calcining high quality limestone at very high temperatures. nearly half the limestone's weight is volatilized off as carbon dioxide to produce calcium oxide or burnt lime. This product is commonly known as quicklime, roach lime, or unslaked lime.
Hydrated Lime (calcium hydroxide Ca(OH)2) is a derivative of burnt lime. It is treated with water in continuous hydrators then dried. The micron-sized particles are then classified by air separators. The final product appears as a fine white powder. Hydrated lime is also known as slaked lime, and is the most widely used alkali in the world.
Agricultural Lime (calcium carbonate CaCO3) is commonly known as lime and ground limestone. It is produced by grinding limestone to less than 2mm.
Limestone Chip is calcium carbonate that has been crushed and screened. It is used for decorative driveways, in steel manufacturing, and in coal desulphurisation.
Lime is one of man's oldest materials and is also known as the world's most versatile chemical. Lime was used in the building of Egyptian pyramids and by the Chinese as far back as 3000BC for the stabilisation of clay soils. The ancient Romans used lime to reduce the need for vast quantities of expensive foundation metal. The Romans knew that lime would react with volcanic ash to produce a type of concrete - still seen today on the Appian Way.
Thousands of years later and on the other side of the world lime is still used on roads. Burnt Lime and Hydrated Lime are used to stabilise roads, airport runways, irrigation canals, earth dams and building foundations. The lime agglomerates clay particles into coarser particles through base ion exchange as well as producing a cementing or hardening action. The reaction products are permanent, producing a durable stabilising layer. Benefits of lime use in road construction include: improved structural quality, greater load bearing capacity, reduced maintenance costs and extended life.
In New Zealand large quantities of lime are consumed in steel making where it serves as a flux for removing impurities such as silica, phosphorous and sulphur. In the construction industry lime fulfills a crucial role as a soil stabiliser for roads, airfields, building foundations and earth dams. Lime is used to chemically treat and strengthen clay soils to form satisfactory base and subbase material. Many New Zealand buildings from last century are constructed from limestone or use it for door and window surrounds.
In paper making lime is used as a causticizing agent and for bleaching.
In non-ferrous metallurgy lime is used to beneficiate copper ore, make alumina and magnesia for use in aluminium and magnesium manufacture, extract uranium and recover gold, silver and other precious metals.
The chemical industry requires lime to make such chemical as sodium alkalies, calcium carbide, calcium hypochlorite, citric acids and petro-chemicals.
The traditional use of lime in mortar and plaster for construction is still important. Limestone is the primary ingedient of cement, and so is vital in the construction and roading industires. In addition lime is used in refractories, sugar refining, glass making, leather tanning. plastics, and pigments.
Being non-toxic, lime is also vitally important as an environmental clean-up chemical. Lime is used to: clarify and soften drinking water; treat sewage in waste water by removing phosphorous and nitrogen, assisting clarification and killing bacteria; neutralise acid mine and industrial wastewater discharges; absorb and neutralise sulphur oxides and industrial chimney gases and to stabilise solid wastes for safe land disposal.
Lime also has a vital role to play in New Zealand's farming industry as an agricultural fertiliser, fungicide and insecticide.. Agricultural lime has a range of uses and benefits, it: neutralises soil acidity, is a direct source of plant nutrients, increases the supply of other nutrients, increases organic matter, increases soil micro organisms, improves soil tilth, provides a source of trace elements, and increases the efficiency of fertilisers.
New Zealand pastures rely on lime to increase soil health and increase productivity.
All these products rely on lime.
How are limestone quarries rehabilitated?……
Topsoil and overburden removed to gain access to the limestone deposit is stockpiled for future use. Unwanted materials are used as fill in gully areas. The larger material is placed the base of the gullies to preserve existing water pathways. Clay and topsoil are layered over the rock fill and the area is reseeded and returned to productive pasture.
Unwanted material is used as fill. The rock fragments in the gully in the background are larger than the material in the foreground. This easily allows rainfall to flow through and so preserves the natural waterways.
Overburden and topsoil are returned and rehabilitation is completed. This flat area is now a hay paddock.
This information has been compiled with the help of McDonald's Lime Limited and OMYA New Zealand Ltd.
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