Sodium Chloride

Sodium Chloride or salt is found from two sources: brine and rock salt. Rock salt is only crystallized salt, also called halite. It is the outcome of the evaporation of prehistoric oceans millions of years ago. Large deposits of rock salt are found in Canada, Eastern Europe, the United States, Germany, and China. Occasionally pressure from deep inside the Earth pushes up large masses of rock salt to produce salt domes. In the U.S, salt domes are seen along with the Louisiana and Gulf Coast of Texas.

Brine is water comprising of a high concentration of salt. The clearest source of brine is the ocean, but it can also be found from salty lakes such as the Dead Sea and also from underground pools of salt water. Large heaps of brine are found in France, Austria, India, Germany, the United States, and. Brine may also be artificially manufactured by melting mined rock salt or by pumping water into wells bored into rock salt.

Natural brines always have other materials dissolved along with salt. The most common is magnesium chloride (MgCl), magnesium sulfate, potassium chloride, calcium sulfate, calcium carbonate, and magnesium bromide. These materials may be as commercially appreciated as the salt itself. Rock salt may be fairly pure, or it may hold several amounts of these materials along with rocky impurities like quartz and shale.

For table salt, however, additives are typically mixed in. Most table salt is iodized to deliver the trace element iodine for nourishment. This helps to avoid goiter, a sickness of the thyroid gland. To supply iodine, a certain amount of potassium iodide is added. Table salt also comprises a small amount of several chemicals used to keep the salt from absorbing water and caking. These chemicals contain magnesium silicate, magnesium carbonate, calcium phosphate, calcium silicate, and calcium carbonate. NaCl is made naturally by mining and also from the ocean. 

Processing  Rock Salt

1. When the mining site is selected, shafts are drilled into the center of the salt deposit. Then a machine that looks like an enormous chain saw is used to cut a slot of about 15 cm high (6.0 inches), about 20 m (66 feet) wide, and about 3 m (10 feet) deep into the salt at floor level. This procedure is called undercutting. 

2. A chain of holes is drilled into the undercut salt with the help of an electric drill comprising a tungsten carbide tip. These holes are then filled with an explosive like ammonium nitrate or dynamite. Electric blasting caps linked to long wires are attached, and the explosive is ignited from a safe distance. Blasting and Cutting are frequent in a pattern that leaves pillars of salt standing to support the roof of the mining area. This is called the room-and-pillar technique.

3. Lumps of blasted rock salt are conveyed to an underground breaking area. Here, they are shifted over a rough ground known as a grizzly which collects pieces smaller than about 23 cm (9 inches). Bigger pieces are crushed in a spinning cylinder; it also has metal jaws with spiked teeth. The salt is then conveyed outside the mining to a secondary crushing area where a smaller fractious and a smaller crusher decrease the size of the particle to about 8 cm (3.2 inches). 

4. At this point, foreign impurities are removed from the salt, by a process known as picking. Metal is removed by magnets and other substances by hand. Rocky material may also be removed with the help of the Bradford breaker; it is a rotating metal drum with small holes in the bottom. Salt is dumped into the barrel, breaks when it hits the bottom, and goes through the holes. The rocky matter is usually harder than salt, therefore it does not break and does not pass through. 

5. The picked salt then passes to a tertiary crushing area, where an even smaller crusher yields particles about 1.0 inch (2.5 cm) in size. If lesser particles are needed, the salt goes through a grinder containing two metal containers rolling against each other. If cleaner salt is required, rock salt is dissolved in water to produce brine for further processing. Then the crushed or ground salt is passed along screens to type it by poured into bags, size, and shipped to the customer.

Processing Brine

1. The common method of evaporating brine is solar evaporation, but it can only be used in hot, dry, sunny places. Shallow ponds are used to collect brine and allowed to vaporize in the sun. Impurities that are not soluble such as sand and clay and marginally soluble impurities like calcium carbonate settle down to the bottom as vaporization begins. 

2. The brine is moved or pumped by gravity flow to another pond where calcium sulfate settles out as vaporization continues. The leftover brine is passed to another pond where the salt settles down out as vaporization proceeds. The brine is moved one more time before vaporization is complete to avoid highly soluble impurities such as magnesium sulfate, magnesium chloride, magnesium bromide and potassium chloride from settling down out along with salt. These materials may be collected separately for commercial uses.

3. The salt is lifted up by machines running on short-term railroad tracks placed on top of the layer of salt. It then washes away with very high concentrated saltwater. This water has so much salt that it cannot contain anymore, so the salt is washed and it is free of any trace impurities without dissolving in the salts. The washed salt is then removed from the saltwater, washed with a small amount of freshwater, and heaped into huge stacks to drain for two or three months. 

4. At this stage, the salt is about 99.4% clean and pure and can be used for several industrial purposes. If cleaner salt is required, it is rewashed in salt water and fresh water, allowed to drain for one or two days more, and then salt is dried in a hot air oven at about 366°F (188°C). This salt is about 99.9% pure and can be used for food industries.

5. Maximum brine is treated by a multiple-effect vaccum evaporator. This device contains three or more closed metal drums with a conical base. Brine is first processed chemically to remove calcium and magnesium compounds which are impurities. It then fills the bottom of the drums. 

6. The brine in the first cylinder passes through tubes heated by vapour. The brine boils and its steam comes in the next drum, where it heats the brine present there. The steam from this brine heats the brine in the next drum, and so on the process goes on. In each cylinder the condensation of steam makes the pressure inside the drop, permitting the brine to boil at a much lower temperature. 

7. Salt is removed from the bottom of the drums as the dense slurry. It is filtered to eliminate excess brine, dried, and distributed through screens to sort the particles by size.

8. Brine may also be treated in a grainer. The brine is also chemically purified and pushed into a long open pan heated by steam running along pipes immersed in the brine. The brine is heated to a temperature partially below the boiling point and flakes of salt develop on its surface as it vaporizes. Typically, a temperature of about 196°F (95°C) is used. Lower temperatures create larger flakes and higher temperatures create smaller flakes. 

9. The flakes grow till they sink to the bottom of the pan, where they are collected and dried in the sun. Grainer salt contains small flakes rather than cut into cubes and is preferred for some uses in food processing. Sometimes the Alberger procedure is used, in which the brine is first moderately evaporated in a vacuum evaporator then passed to a grainer. This method gives rise to a mixture of flakes and cubes.

10. At this point salt used for most purposes is prepared to be packaged in bags or boxes and transported to consumers. To make iodized table salt, yet, potassium iodide is added, then calcium silicate, magnesium carbonate, magnesium silicate, calcium phosphate, or calcium carbonate is added to make it free-flowing, which is one of the properties of salt. The salt is then boxed and shipped to restaurants and grocery supplies.

Properties of Sodium Chloride  

• Physical Description: A white crystalline solid. The market grade usually contains some chlorides of calcium and magnesium which absorb moisture and cause caking.

•  Colour: Colorless, transparent crystals or white, crystalline powder

• Taste: Salty

• Boiling point: 2575° F at 760 mm Hg

• Melting point: 1474.0  F 800.7 deg

• Solubility: It is greater than or equal to 100 mg/mL at 68° F and it is easily soluble in water and partially soluble or insoluble in other liquids.

• Density: 2.165 at 77° F

• Vapour pressure: 1 mm Hg at 1589° F

• Stability: Stable under recommended storage conditions.

• Decomposition: When heated to decomposition it emits toxic fumes of /hydrochloric acid and disodium oxide.

• Viscosity: Viscosity of saturated aqueous solution = 1.93 mPa-s

• Corrosivity: Sodium chloride solutions are corrosive to base metals.

• pH: pH = 6.7 to 7.3; its aqueous solution is neutral

• Surface tension: 110 mN/m at 850 deg C /Molten sodium chloride

• Index of refraction: 1.5442

Uses of Sodium Chloride

There are a number of uses of sodium chloride in everyday life and in industries as well:

• Salt is invariably used as a taste enhancer in almost every kind of food product.

• Salt also works as a food preservative.

• Numerous chemicals like sodium hydrogen carbonate and sodium carbonate can be extracted or processed by industrial methods using sodium chloride.

• Salt is used in manufacturing products of glass.

• Salt has a life-saving advantage. It prevents ice from piling up on the road, thus, ensuring public safety on the roads.