Limestone

Limestone is the most abundant of all commercially used sedimentary rocks. It is formed in marine, and sometimes freshwater environments by the accumulation of CaCO3 shells and skeletons in layered beds. In some cases, limestone is formed by direct precipitation from seawater, partly triggered by biogenic activity. Direct precipitation by chemical changes is responsible for limestone formed as stalactites, stalagmites, oolitic limestones, and travertine.

Limestone commonly contains three minerals: calcite (CaCO3), its polymorph aragonite (CaCO3), and dolomite (CaMg(CO3)2, with calcite the most abundant.

As an industrial mineral, limestone probably has more uses than any other mineral commodity. The uses of limestone can be broadly subdivided into those based on its chemical composition and others based on its physical properties. The chemical uses are those where calcium carbonate is converted to other calcium compounds with silicates and aluminates to make cement, oxides to make quicklime and hydroxides to make hydrated (slaked) lime. Other chemical uses are where limestone is used as a reactant in metallurgical processes, glass manufacture, agricultural lime, water purification, and sewage treatment. Physical properties of limestone, such as colour, reflectivity, crystal size, particle size, density, absorption characteristics and hardness, all are significant factors for uses in various fillers.

Limestone and lime are generally abundant but the high quality materials required by industry standards are uncommon. In terms of total tonnage, limestone ranks among the top four of all mineral commodities, and lime is the second most used chemical after silica in most countries. Limestone is generally used for making portland cement and lime, as a flux in steel making, in copper and lead smelting, and as a raw material in glass.

Other uses are: aggregates; agriculture; as a filler in paper, paint, rubber; in plastics extrusion, and as stone dust in coal mines.

Calcined limestone (lime) is used in many industries: steel, alumina, sugar, building, water treatment, road stabilisation, and gold extraction.

Many manufactured objects require limestone or lime in some phase of their production, either as a primary or incidental processing material. Although the strategic importance of limestone is frequently overlooked, limestone is essential for future industrial development. The trend in limestone production indicates a steady increase as demonstrated over the last decade.

Since so much of the limestone is used for cement, future growth will depend on the development of major projects and the local building industry. However, potential limestone resources along the coastal regions are being threatened by possible development of land required for urban and industrial purposes and reserves for water catchment and storage reservoirs. Other threats include international discussions on reducing greenhouse gas emissions which are being monitored very closely by the lime and cement industries. Any program regulating carbon dioxide emissions would have a direct impact on these industries.
With the recent 4.6% rise in the total value of construction commencements in commercial and engineering projects the cement industry is set to improve in the near future. The industrial growth is expected to continue and limestone seems assured of an expanding market.