Fascination: Lime

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Origin

Over millions of years, the creatures that once thrived in ancient seas have formed mighty limestone deposits.

 

Extraction

This valuable raw material is extracted with great care. A potential extraction site is researched in advance, with geophysical methods and core drilling providing information about the location and quality of the rock. The deposit is mapped, three-dimensional models are developed on the computer, and its economic extractability is examined. The licensing authorities weigh up all the interests involved before approving the site for mining. The operator must comply with a multitude of laws, regulations, and official requirements.

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Since almost all limestone deposits in Germany are covered by overburden, this must first be removed before the limestone can be mined. The spoil heaps are greened immediately after creation and serve as noise and visual barriers.

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Limestone is usually extracted in open-cast mines. The material is blasted out of the wall, forming stepped mining floors. To minimize vibrations in the surrounding area, the blasts are detonated at intervals of thousandths of a second. The blasted rock, known as waste rock, is picked up by heavy excavators or wheel loaders, loaded onto heavy-duty trucks as tall as houses, and transported to the crusher.

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The stone is crushed in a crusher. In most lime plants, impurities can be separated from the stone by screening, while in other plants the stones are washed. The wash water is fed into a settling pond, where the solids settle and the pure water is returned to the operating cycle.

 

The cleaned grain mixture is sorted into different grain sizes on screening plants. Some of the raw stone is ground. Part of the limestone is sold unburned and used directly as gravel, grit, sand, or powder.

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Refining​

For most applications, however, the limestone must be deacidified by burning. At temperatures between 900 and 1,200 °C, the limestone (CaCO3) is broken down into gaseous carbon dioxide (CO2) and calcium oxide (CaO = quicklime).​

 

Limestone (CaCO3) + energy > 900 °C = lime (CaO) + carbon dioxide (CO2)

 

There are basically two types of kilns: shaft kilns and rotary kilns. So-called GGR shaft kilns are particularly energy-efficient. Alternating firing usually takes place in two shafts connected by an overflow channel. The use of heat flows in the parallel shafts ensures maximum energy efficiency. The type of limestone used, the fuel, the firing temperature, and the dwell time in the kiln determine the quality.

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Transportation

Lime is produced close to where it is consumed. Transportation distances in Germany are short, as there are lime plants in almost all regions. Today, most products are transported as bulk goods (loose) by rail or truck. This means that no packaging material is required.

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This exhibition is on permanent loan from the Federal Association of the German Lime Industry (Bundesverband der Deutschen Kalkindustrie e.V.).

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