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Article No : a24_317 Article with Color Figures Sodium Chloride GISBERT WESTPHAL, Solvay Salz GmbH, Solingen, Federal GERHARD KRISTEN, Solvay Salz GmbH, Solingen, Federal WILHELM WEGENER, Sudwestdeutsche€ Salzwerke AG, Heilbronn, Germany PETER AMBATIELLO, Salzbergwerk Berchtesgaden, Germany HELMUT GEYER, Salzgewinnungsgesellschaft Westfalen mbH, Ahaus, Germany BERNARD EPRON, Compagnie des Salins du Midi et des Salines de l’Est, Paris, France CHRISTIAN BONAL, Compagnie des Salins du Midi et des Salines de l’Est, Paris, France ¨ GEORG STEINHAUSER, Atominstitut der Osterreichischen Universit€aten, Vienna University of Technology, Austria FRANZ Go€TZFRIED, Sudsalz€ GmbH, Heilbronn, Germany 1. History ..........................319 4.3.6. Other Process Steps ...................343 2. Properties ........................320 4.3.7. Evaluation of the Different Processes ......344 3. Formation and Occurrence of 4.3.8. Vacuum Salt based on Seawater as Raw Salt Deposits ......................322 Material . ........................345 4. Production ........................324 4.4. Production of Solar Salt...............346 4.1. Mining of Rock Salt from Underground 4.4.1. Production from Sea Water . ...........346 and Surface Deposits .................324 4.4.1.1. The Main Factors Governing Production of 4.1.1. Mining by Drilling and Blasting..........325 Sea Salt . ........................347 4.1.2. Continuous Mining ...................327 4.4.1.2. Production Stages in a Modern Salt Field . .349 4.1.3. Upgrading of Rock Salt . ...............327 4.4.2. Crystallization from Mined Brine . ......351 4.1.4. Utilization of the Chambers . ...........329 4.4.3. Extraction from Salt Lakes. ...........351 4.2. Brine Production ....................330 4.4.4. Seawater Desalination . ...............352 4.2.1. Natural Brine Extraction ...............330 5. Salt Standards .....................352 4.2.2. Solution Mining . ....................330 6. Analytical Methods .................352 4.2.2.1. Drilling and Construction of the Borehole. .331 7. Uses .............................353 4.2.2.2. The Process of Solution Mining ..........331 7.1. Table Salt and Food Processing.........353 4.2.2.3. Planning of the Extraction Process . ......332 7.2. Agriculture ........................355 4.2.2.4. Other Systems . ....................332 7.3. Water Treatment....................355 4.2.2.5. Equipment. ........................333 7.4. Chemical Uses ......................355 4.2.2.6. Storage Caverns . ....................333 7.5. De-icing and Anti-icing ...............356 4.2.3. Combined Dry and Solution Mining . ......334 7.6. Other Industrial Uses ................357 4.3. Vacuum Salt .......................335 8. Anticaking and Free-Flow Additives ....357 4.3.1. Brine Purification ....................336 9. Health Aspects .....................357 4.3.2. Open-Pan Evaporation . ...............340 10. Environmental Aspects ..............359 4.3.3. Multiple-Effect Process . ...............340 11. Economic Aspects ..................360 4.3.4. Mechanical Vapor Recompression (MVR) References ........................361 Process . ........................341 4.3.5. Recrystallization Process ...............342 1. History [1–7] LIEBIG appreciated the importance of sodium chloride for human life: ‘‘Among all precious In the Odyssey, HOMER wrote: ‘‘travel ... until stones salt is the most precious’’. you meet mortals who do not know the sea and Sodium chloride was used almost exclusively who never eat food seasoned with salt’’. Else- as a food and preserving substance for millennia. where he refers to salt as ‘‘holy’’. JUSTUS VON Presumably, human salt consumption became Ó 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim DOI: 10.1002/14356007.a24_317.pub4 320 Sodium Chloride Vol. 33 necessary with the change from nomadic hunters French Revolution. Similarly, the Russians to settled farmers. Before this, eating meat Czars’ salt taxes were an important revenue covered human salt demand. source. In Germany a tax of 60 e/t was levied Finds at Hallstatt in the Austrian Salzkammer- on all salt used in food. This tax was discontinued gut,atSchw€abisch Hall in Germany, and in many at the beginning of 1993, following the establish- other places prove that salt was already extracted ment of the Common Market in the European in prehistoric times. As early as 1000 B.C. salt Union. In Europe two salt monopolies estab- was extracted in Hallstatt, perhaps the oldest salt lished by the Cantons in the 19th century exist mine in the world, and in Schw€abisch Hall from in Switzerland today still. ca. 500 B.C. A series of finds in Wieliczka and Salt was of crucial importance economically. Bochnia in Poland indicate that extensive salt A far-flung trade in ancient Greece involving production existed already before 1000 A.C., using exchange of salt for slaves gave rise to the brine springs emergent at the earth’s surface as expression ‘‘not worth his salt’’. Special salt raw material. The salt mine in Wieliczka has been rations given to early Roman soldiers were a world cultural heritage site since 1978. In known as ‘‘salarium argentum’’, the forerunner Egyptian grave paintings salt production was of the English word ‘‘salary’’. Possession of the already described in 1450 B.C. In ancient China precious materia salt meant wealth and power the majority of the salt was obtained evaporation over centuries. Cities such as Salzburg in Austria of seawater. Inland brine sources were opened and Luneburg€ in Germany blossomed with salt up by boring. Around 2700 B.C. the Peng-Tzao- production and the salt trade. The value of salt Kan-Mu, probably the earliest known treatise on diminished with the industrial revolution in the pharmacology, was published in China. A major 1800s. Since salt was needed as a raw material in portion of this writing was devoted to a discussion the emergent chemical industry, salt deposits of more than 40 kinds of salts, including descrip- were opened up by dry mining and exploited tions of two methods of extracting salt and putting with improved drilling technology, and saturated it in usable form that are amazingly similar to brine from boreholes was increasingly used in processes used today. CONFUCIUS reported borings salt works. with a depth of more than 500 m in ca. 600 B.C. In many museums, e.g., the German Museum Indian history recalls the prominent role of salt. in Munich, the Musee du Marsal in France, the There was even a caste of salt diggers. During Salt Museum of Northwich in the UK, the British colonial days, salt motivated the Great Zigong Salt Museum of Sichuan in China, the Hedge of India and its role in the British salt Salt Palace, Grand Saline, Texas in the USA, starvation policy and GHANDI’s resistance to and in the Salt and Tobacco Museum in Tokyo, British colonial rule. salt history is presented vividly. Today, visitors Salt also had military significance. For in- can take tours through salt mines such as those stance, it is recorded that thousands of in Wieliczka/Poland, Berchtesgaden/Germany, Napoleon’s troops died during his retreat from Hallstatt/Austria, Bex/Switzerland, and the Moscow because their wounds would not heal as 19th century Khewra Salt mines in Pakistan. a result of a lack of salt. In 1777, the British Lord HOWE was jubilant when he succeeded in captur- ing General Washington’s salt supply. 2. Properties [8] Throughout history the essentiality of salt has made it subject to governmental monopoly and Sodium chloride, NaCl, Mr 58.443, is a colorless special taxes. The Chinese, like many other salt with good solubility in water. Chemically governments over time, realizing that everyone pure NaCl crystallizes from aqueous solutions in needed to consume salt, created a government well-formed cubes, which under the influence of salt monopoly, and made salt taxes a major surface tension often grow together into funnel- revenue source. French kings developed a salt shaped, hollow, square-based pyramids. In the monopoly by selling exclusive rights to produce presence of impurities, octahedra or dodecahedra it to a favored few who exploited that right to the are sometimes formed. Crystallization from point where the scarcity of salt, and the gabelle, hydrochloric acid solution gives long, fibrous, the salt tax, was a major contributing cause of the needle-shaped crystals. Vol. 33 Sodium Chloride 321 During crystallization, small amounts of wa- Table 1. Solubility of NaCl in water ter can be trapped in holes in the crystals. When Density of NaCl content this vaporizes on heating, it causes the crystals to Temperature, g NaCl/100 g NaCl, solution, of solution, 3 explode with audible decrepitation. In salt from C H2O wt % g/cm g/L natural deposits, inclusions of gases such as 0 35.76 26.34 1.2093 318.5 methane, carbon dioxide, and hydrogen sulfide 20 35.92 26.43 1.1999 317.1 can occur. 40 36.46 26.71 1.1914 318.2 In the crystal, the Na and Cl ions alternate. The 60 37.16 27.09 1.1830 320.5 80 37.99 27.53 1.1745 323.3 ions of each type form a face-centered cubic 100 39.12 28.12 1.1660 327.9 lattice, in which each ion is surrounded octahe- 180 44.9 30.99 drally by six ions of the other type at a distance of a/2 (lattice constant a ¼ 0.56273 nm). The mod- ulus of elasticity perpendicular to the surface of the cube is 41 074 MPa. Under high pressure, Table 2. Density of aqueous solutions of NaCl slow flow takes place. Sodium chloride is highly 3 transparent to light of wavelength between Density, g/cm 200 nm (ultraviolet) and 15 mm (infrared). Ion- NaCl, wt % 0 C20C40C60C80C izing radiation causes lattice defects (color cen- 4 1.03038 1.02680 1.01977 1.0103 0.9988 ters) which give the salt a blue color. On heating 8 1.06121 1.05589 1.04798 1.0381 1.0264 to ca. 250 C, this color disappears. 12 1.09244 1.08566 1.07699 1.0667 1.0549 Some important physical properties are listed 16 1.12419 1.11621 1.10688 1.0962 1.0842 below and also in Tables 1–3.