Industrial use of Lime and Limestone

Lime is a basic inorganic mineral which contains calcium and is primarily made up of hydroxides and oxides. The etymology of the word lime comes from its use as building mortar and its sense of sticking. Limestone is a carbonated sedimentary rock which is predominantly found on the seafloor. The main component found in limestones is calcium carbonate.

In the lime industry, limestone is a term which is used to refer to stones that are composed of 80% or more calcium or magnesium carbonate. Mines or quarries are where the limestones are extracted from and part of the stones which are extracted, based on their chemical composition and optical granulometry (measuring the grain sizes in a granular material), are then calcined at about 1,000 °C (1,830 °F) in various forms of lime kilns to form calcium oxide or quicklime according to the reaction :

After the production of quicklime and before it’s use, quicklime is hydrated which means it is combined with water, this is referred to as slaking. So, lime which is hydrated is known as slaked lime. It is produced according to this reaction :

CaO + H2O → CaO + Ca(OH)2                               

There are other forms of slaking as well :

Dry slaking includes slaking lime with just enough water to hydrate it but keep it powdery. The lime produced using this is known as hydrated lime. Wet slaking, as the name suggests, includes adding a slight excess of water to turn the lime into a putty form known as lime putty. 

Because of lime’s property to stick to bricks and stones, it is very commonly used as material to bind things in masonry works. 

Lime and Limestone : Industrial Uses

Sugar Refining 

Hydrated lime, which is produced by dry slaking, is an important part of production of sugar regardless of whether the sugar is produced from sugar cane or sugar beets. Hydrated lime is also used in the process of purifying sugar from other sources, mainly maple or sorghum. 

Sugar canes and sugar beets are harvested and then processed with the use of water so that they form raw juice but this raw juice has low pH and has dissolved impurities. Hydrated lime is mixed into this raw juice so that it not only raises the pH of the juice but also reacts with the impurities and turns them into insoluble calcium organic compounds. This in turn helps with an easy removal of the impurities. After this process, excess lime from the juice is extracted by carbonation or by adding phosphoric acid to the juice. 

Refractory Products 

Dolomite of high-purity refractory and Dead Burned Dolomite or DBD of lower purity fettling grade are both manufactured by calcining dolomitic limestone. The production of these materials is similar to the production of an ordinary lime, the only difference is the increase in burning time and temperature. 

Higher purity dolomas are fired at the upper end of the temperature range in a rotary kiln and without any addition of impurities. High purity dolomas are also used in the production of refractory bricks which are utilized in cement and lime rotary kiln linings, refining vessels and steel ladles. 

Lower purity DBDs are fired at the lower end of the temperature range with the addition of iron oxides during the process of calcination to stabilize the hard burned quicklime from decomposing from the moisture. This produced DBD is used in the manufacturing of monolithic patchings and repairing materials for steel furnaces. 

Large amounts of dolomitic lime which are lightly burned are put to use in the production of magnesium oxide (MgO). This is done by slaking the quicklime in magnesium chloride brines where it precipitates magnesium hydroxide. This magnesium hydroxide is calcined and fired to turn into a thicker, higher purity of magnesium oxide. Refractory magnesia is used to produce linings for cement and lime kilns as well as steel ladles and furnaces.

3% lime is added to stabilized zirconium oxide during the process of fusion or sintering. Zirconium oxide is predominantly used for thermocouple tubes and analysis crucibles.

Food Industry

Lime is used for various parts of the food industry, including tortilla and corn-chip making, as well as fruit and vegetable storage and the process used for producing sugar.

Dairy Industry

When butter is produced, cream is separated from whole milk and during this process, lime water is added to the separated cream. This reduced acidity in the milk before the process of pasteurization. This skimmed milk is then later acidified to separate casein. This separated casein is mixed with lime and a small amount of sodium fluoride. This mixture produces a form of glue, calcium caseinate. The fermentation of the remaining milk and then the addition of lime to it produces calcium lactate which forms lactic acid if acidified. 

Baking Industry

Lime is an essential in the production of monocalcium phosphate, a common type of baking powder. To produce this, a high calcium lime is reacted with pure phosphoric acid.

Fruits and Vegetables

Bags of hydrated limes are placed in the storage room where fruits and vegetables are stored in a controlled atmosphere. By doing so, the bags absorb the CO2 produced by the ripening of the fruits and vegetables, keeping the atmosphere controlled. This also helps keep a higher ratio of oxygen to CO2 which in turn helps in keeping the fruits and vegetables fresh for a longer period of time. 

Building and decorative stones

Since ancient times, limestones have been an integral part of the building and construction process. One such example is that of the Pyramids of Giza, Egypt. 

Lime Burning

The process of lime burning or calcining requires limestone. When heated, limestone breaks down to form lime. Thus, it can be considered a raw material in the production of lime.

Conclusion

Lime and Limestone have both long fascinated scientists because of their rich fossil content. Fun fact but a lot of knowledge about the Earth’s chronology and development has been derived from the fossils that have been embedded in these limestones. As we already learnt, lime and limestones both have considerable commercial importance and are used for not only industrial purposes but household, construction and other purposes as well. Limestones, when heated to temperatures of 900 to 1000°C, will separate calcium carbonate and produce carbon dioxide and lime. Limes are majorly used in the manufacture of glass and in agriculture. Limestones also serve for building purposes.