How is rock salt extracted



    Rock salt, obsolete as Sal gemmae, sometimes misleadingly also referred to as salt stone, is an evaporite and sedimentary rock (salt rock), which is created by chemical sedimentation from seawater or evaporation of mineral-rich groundwater.

Rock salt is monomineral, which means that apart from small admixtures of other minerals such as anhydrite, sylvine, gypsum and others, it is composed almost exclusively of the mineral halite.

Education and Locations

Due to the constant continental drift, changes in sea level and climate, it happened that marine areas or salt lakes were cut off and isolated from their inflows. These dried out completely and often left behind layers of salt that were kilometers thick. Due to further sedimentation, these were covered with other rocks and partly or completely sunk under the earth's surface due to continental drift.

The salt domes created by the plasticity of the salts at high pressure were used by people for salt production early on (Wieliczka / Poland, 3500 BC).

Well-known rock salt deposits in Austria include Hallstatt and near Hallein, where rock salt has been mined since the time of the Celts. One of the oldest salt mines in Europe is located near Wieliczka in Poland.

A large part of the world production of rock salt (estimated up to 70%) comes from the region known as the Salt Range in the hill country of northeastern Pakistan, the Pakistani Punjab. This part of Pakistan borders the Karakoram in the north. This salt is mined and often wrongly brought onto the market in Europe as Himalayan or Karakorum salt. Both mountain ranges are, however, as folded mountains, geologically a low-salt area.

Extraction

Mining mining

Rock salt is mined underground by breaking the rock salt into blocks. The mining is very economical. In the USA in 1975 the cost ranged from $ 0.80 to $ 1.60 per ton extracted.

Salt pans

The vast majority, around two thirds of the world's salt production, is obtained in salt pans. The salt deposits are drilled in several places. Water is pumped into some of the boreholes to dissolve the salt; Through the other boreholes, brine (with a salt content of up to 35%) comes back to the surface as an almost saturated saline solution. During the subsequent evaporation, an extremely pure and therefore high-quality table salt with a purity of 98 percent and more is left over. This type of rock salt extraction is even more cost-saving than mining, despite the high energy requirements for evaporation. As a result, caverns are formed in the salt dome, which can cause damage to the earth's surface if they collapse.

use

Rock salt is processed into table salt after chemical and physical cleaning, which also results in other salts such as potash salt. The vast majority (around 85%) is processed in industry. The rest of the rock salt obtained is divided between the production of table salt (around 3%), de-icing salt (around 5%) and industrial salt (around 7%).

literature

  • Martin Okrusch, Siegfried Matthes: mineralogy. 7th edition. Springer Verlag, Berlin 2005, ISBN 3-540-23812-3

Categories: Sedimentary Rock | salt