Background

Quicklime in India

The manufacturing process & application of quicklime in India

The Lime Cycle

The lime cycle shows the steps from entering the limestone through to the creation of mortars and plasters for our buildings and how it continuously, through the re-absorption of Carbon Dioxide, goes back to its original chemical form (Calcium Carbonate) in the wall.

Burning of lime

Limestone i.e. Calcium Carbonate – CaCO3 is burnt in a furnace giving off Carbon Dioxide (CO2) gas and forming Calcium Oxide (CaO) which is commonly recognised as Quicklime or lymphoma.

It needs to be burnt at 900°C to guarantee a good material is produced. The temperature at which it is burnt will influence its reactivity in all other stages of the lime cycle–slaking and carbonating. The resulting lime is at its most volatile and dangerous at this step.

Slaking Lime

The Burnt Lime or Quicklime is then mixed with water (slaked) as quickly as possible. From the time it is burnt the material starts to degrade by ‘air-slaking’. Mixing Quicklime (CaO) and water (H20) produces Calcium Hydroxide (Ca(OH)2 - slaked lime and heat. There are three major ways of slaking the Quicklime:

  • In an oversupply of water to produce a putty;( Krishna mines a quicklime manufacturer in India uses the same method)
  • In a shortage of water to produce a powder - hydrated or bag lime;
  • In wet sand to produce a hot mix.

Carbonisation of time

Lime sets by absorbing water-soluble Carbon Dioxide directly from the air. This process is termed carbonation. The ‘set’ or carbonation must occur gradually – the slower the set the better (it is not a case of simply drying), therefore direct heaters or dehumidifiers do not help and may produce failures – since it is vitally important that the circumstances are right to enable the water-borne Carbon Dioxide (CO2) to be absorbed. In our Lime Handbook, we describe specific conditions to control the carbonation process. Failing to properly control carbonation will lead to problems and potential crash on site. It is, therefore, an important process to understand.

Application of Quick Lime in India

Sugar industries

Hydrated lime is required for the creation of sugar from both sugar cane and sugar beets. They also apply it to purify sugar from other sources, such as maple, although these are produced in much fewer quantities.

Sugar cane and sugar beets are harvested and handled with water to form raw juice, which has low pH and includes dissolved dirt. Hydrated lime is added to the juice to increase the pH and to react with the dirt to form insoluble calcium organic compounds that can be separated. Excess lime is removed by carbonation process. This process may be repeated multiple times depending on the purity of the final product required.

High-purity refractory “dolomite” (frequently called Doloma) and lower purity fettling category “dead-burned dolomite” (usually referred to as DBD) are both produced by calcining dolomitic limestone. The production method is similar to the production of ordinary lime, except that the burning time is more extended and temperatures considerably higher (in the range of 1600 – 1850º C). High purity dolomite is burned in rotary kilns to the upper end of the temperature range and without the addition of dirt. High purity dolomite is used to manufacture refractory bricks employed in cement and lime rotary kiln linings, and in steel vessels and refining vessels. The lower-purity DBD is fired in revolving kilns to the lower end of the temperature range, and iron oxides are combined during calcination to stabilize the resulting hard-burned quicklime against decomposition from moisture. DBD is used for the manufacture of solid patching and repair materials for steel furnaces.

Vast quantities of light-burned dolomitic lime are used in the creation of synthetic refractory grade magnesia (MgO). The quicklime is slaked in magnesium chloride brine and precipitating magnesium hydroxide. The mag-hydroxide is calcined and burned into dense, high-purity magnesium oxide. Refractory magnesia is used in the production of linings for cement and lime kilns, besides steel vessels and furnaces.

Food Industry

Quick Lime in India serves a myriad of uses in the food industry.

Dairy Industry

When the cream is isolated from whole milk during the production of butter, lime water is often added to the cream to decrease acidity prior to pasteurization. The skimmed milk is next acidified to isolate casein. The casein is mixed with lime and a little amount of sodium fluoride to produce calcium caseinate, a form of glue. Fermentation of the dwelling skimmed milk (whey) and the addition of lime forms calcium lactate, which is exchanged as medicinal or acidified to produce lactic acid.

Glue and Gelatin

Waste materials from administering plants are treated with lime in slurry form. This process swells the collagen, facilitating after hydrolysis. Afterwards, the treated stock is cleaned to remove lime, albumin, and mucin. The washed stock is dried, and the final result is sold as glue or gelatin.

Baking Industry

In the preparation of a standard type of baking powder, mono-calcium phosphate, lime is required as a component. This baking powder is made by reacting purified phosphoric acid with a high calcium lime.

Fruit and Vegetables

In the measured atmospheric storage of fruit and vegetables, bags of hydrated lime are placed on shelves in the storage room to absorb CO2 that exudes from maturing fresh produce. The co-location of hydrated lime in the storage room has a higher ratio of oxygen to CO2, allowing vegetables and fruit to be collected fresh for much longer periods. When placed near the produce, carbon dioxide enters easily through the multi-wall paper bags into the lime. For apples, lime using averages about 1 to 1.5 lb./bushel. Pears, plums, and tomatoes, in appreciation of apples, have been stored this way in India.

Miscellaneous

All quality tortillas are indulged with lime. Corn is first dipped in milk-of-lime before its conversion to cornmeal. Lime is also employed in the corn chip business. Grape leaves from wineries are operated with lime to precipitate calcium tartrate, which is sold as such or turned to tartaric acid. Several recipes for preparing watermelon pickles require the melon rind to be soaked in milk-of-lime. In such ways, quick lime in India is applied to food industries.