Industrial and Dried Minerals – Useful Information

Limestone is used as a flux in the extraction of iron from iron ore. Iron is extracted from ore by heating in a furnace. Limestone is added so that the silicon in the ore forms a calcium silicate (with the calcium carbonate that is limestone) otherwise it would form an iron silicate and thus reduce the quantity of metallic iron produced. The calcium silicate, together with other impurities, forms the ’slag’ and this substance can be used as a lightweight secondary aggregate. Includes by-product mineral waste, synthetic materials and soft rock (shale) used with or without processing as a secondary aggregate.

Sand, usually silica sand, is used to make moulds in a foundry. These are the hollow containers into which molten metal is poured to produce a casting of a particular shape. The exact type of sand used depends on the particular metal or alloy that is to be cast, but it usually contains clay and/or some other material to bind it together.

The burning of coal at power stations produces sulphur dioxide, one of the main gases that causes acid rain. Rather than simply emit this gas along with their other flue gases, most coal fired power stations today use limestone in a process known as ‘flue-gas desulphurisation’. Limestone is finely crushed and mixed with water to form a slurry. It is then sprayed into the absorber tower of the power station where a chemical process converts the limestone and sulphur into gypsum. This ‘artificial’ gypsum is then recovered and sold for the manufacture of plasterboard. Limestone, or calcium carbonate, also has many other uses.

Ground to a fine powder it is used as a whitening agent or filler in paper, adhesives, paint, plastics, PVC, toothpaste, medical tablets and cleaning products. It is also used to provide additional calcium in vitamin and mineral supplements, flour and animal feed.

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