salt solution

Description

A salt mine is a mining operation involved in the extraction of rock salt or halite from evaporite deposits. Salt is the most humble and precious of minerals. In Roman times, soldiers were sometimes paid with it. In the Middle Ages, it was called "White Gold." Today, we collect 146 million tons of salt annually, and it is used in over 14,000 ways. MODERN MARVELSTM journeys beneath the earth to tell the extraordinary story of how we collect this essential mineral--and of the awesome caverns salt mining creates. Visit a 700-year-old mine in Poland that has three chapels and a soccer field among its underground chambers. Sea salt has been collected over the millennia, from dehydrating sea water to scratching it out of underground chambers. And take a fascinating step-by-step trip backwards from the salt shaker on your dinner table to the strange, subterranean world of a modern salt mines. From a Manhattan-sized mine near Cleveland to the world's largest underground storage facility, SALT MINES tells the story of the staff of life and the amazing places created by its collection. Before the advent of the internal combustion engine and earth moving equipment, mining salt was one of the most expensive and dangerous of operations. Why?. While salt is now plentiful, until the Industrial Revolution it was difficult to come by, and salt mining was often done by slave or prison labor. In ancient Rome, salt on the table was a mark of a rich patron (and those who sat nearer the host were above the salt, and those less favored were "below the salt"). Roman prisoners were given the task of salt mining, and life expectancy among those so sentenced was low. The Roman historian Pliny the Elder stated as an aside in his Natural History's discussion of sea water, that "In Rome ... the soldier's pay was originally salt and the word salary derives from it ..." Modern rock salt mine near Mount Morris, New York Even as recently as the 20th century, salt mining in the Soviet Union and Nazi Germany was performed by people being punished. Today salt mines are private operated or by large multi-national companies like AkzoNobel, Cargill and Compass Minerals. Salt Mining In 2006, more than 200 million tons of salt were produced in the world. China is the largest producer, with 48 million tons, followed closely by the United States, with 46 million tons [source: Salt Institute]. Salt is generally produced one of three ways: deep-shaft mining, solution mining or solar evaporation. Deep-shaft mining is much like mining for any other mineral. Typically, the salt exists as deposits in ancient underground seabeds, which became buried through tectonic changes over thousands of years. Many salt mines use the "room and pillar" system of mining. Shafts are sunk down to the floor of the mine, and rooms are carefully constructed by drilling, cutting and blasting between the shafts, creating a checkerboard pattern. After the salt is removed and crushed, a conveyor belt hauls it to the surface. Most salt produced this way is used as rock salt. In solution mining, wells are erected over salt beds or domes (deposits of salt forced up out of the earth by tectonic pressure) and water is injected to dissolve the salt. Then the salt solution, or brine, is pumped out and taken to a plant for evaporation. At the plant, the brine is treated to remove minerals and pumped into vacuum pans, sealed containers in which the brine is boiled and then evaporated until the salt is left behind. Then it is dried and refined. Depending on the type of salt it will be, iodine and an anti-clumping agent are added to the salt. Most table salt is produced this way. When solution mines are located near chemical plants, they are called brine wells, and the salt is used for chemical production. After the salt is removed from a salt mine, the empty room often stores other substances, like natural gas or industrial wastes. Salt is harvested through solar evaporation from seawater or salt l...