LIME BASICS

What is Lime?

The generic term, lime includes quicklime and slaked lime.

Quicklime is produced by the thermal dissociation of limestone. Its principal component is calcium oxide. Its quality depends on many factors including physical properties, reactivity to water and chemical composition. As the most readily available and cost-effective alkali, quicklime plays an essential part in a wide range of industrial processes.

Slaked lime is produced by reacting, or “slaking” quicklime with water, and consists mainly of calcium hydroxide. The term includes hydrated lime (dry calcium hydroxide powder), milk of lime and lime putty (dispersions of calcium hydroxide particles in water). Slaked lime is widely used in aqueous systems as a low-cost alkali.

Lime is the least expensive and most widely-used alkali. It is one of the most heavily used chemicals. In most industrialized countries, the major uses of lime products are in steel making and the construction industry.

HISTORY OF LIME

Some of the earliest evidence for the use of lime dates back some 10,000 years. Excavations in Cajenu in Eastern Turkey, uncovered a Terrazzo floor, which had been laid with lime mortar. That site dated from 7,000 to 14,000 years ago. Lime stabilisation of clay was used in Tibet, over 5000 years ago, in the construction of the pyramids of Shersi. It was also used in conjunction with limestone by the Egyptians in the construction of the pyramids and by the Chinese when building the Great Wall.

Perhaps the earliest excavated lime kiln was at Khafaje in Mesopotamia which was dated at about 2450 B.C. A battery of six lime kilns, excavated at Iversheim, Germany, showed that the Romans produced lime in quantity on military sites. The production of lime in kilns was mentioned by Cato in 184 B.C.

Lime was also well known to the Romans as a chemical reagent. In 350 B.C. Xenophon referred to the use of lime for bleaching linen. Almost all of the Mediterranean peoples were familiar with lime as paint. Lime was used for tanning leather, and was mixed with organic substances to produce putty and glue.

In the 1700s Joseph Black gave the first sound technical explanation of the calcination of limestone including the evolution of carbon dioxide. Lavoisier confirmed and developed Black’s explanation. In 1766 De Ramecourt published a detailed account of “the art of the lime burner”, which described the design, operation and economic aspects of limestone quarrying and lime burning. The first exact measurements of the dissociation pressure were made by Le Chatelier in 1886.