Salt is the common name for the substance sodium chloride (NaCI), which occurs in the form of transparent cubic crystals. Although salt is most familiar as a food supplement, less than 5% of the salt produced in the United States is used for that purpose. About 70% is used in the chemical industry, mostly as a source of chlorine. Salt is also used for countless other purposes, such as removing snow and ice from roads, softening water, preserving food, and stabilizing soils for construction.
The earliest humans obtained their salt from natural salt concentrations, called licks, and from meat. Those people who lived near the ocean may have also obtained it by chewing seaweed or from the natural evaporation of small pools of seawater. Meat became a more important source of salt as hunting was developed, as did milk when sheep, goats, horses, camels, reindeer, and cattle were domesticated. Even today, certain peoples—such as the Inuit of the far north, the Bedouin of the Middle Eastern deserts, and the Masai of east Africa—use no other form of salt.
As agriculture developed, leading to an increased population and a diet consisting mostly of plants, it became necessary to devise ways of obtaining salt in greater amounts. The earliest method of salt production was the evaporation of seawater by the heat of the sun. This method was particularly suited to hot, arid regions near the ocean or near salty lakes and is still used in those areas. Solar evaporation was soon followed by the quarrying of exposed masses of rock salt, which quickly developed into the mining of underground deposits of salt. Two thousand years ago the Chinese began using wells to reach underground pools of salt water, some of which were more than 0.6 miles (1.0 km) deep.
In areas where the climate did not allow solar evaporation, salt water was poured on burning wood or heated rocks to boil it. The salt left behind was then scraped off. During the time of the Roman empire, shallow lead pans were used to boil salt water over open fires. In the Middle Ages these were replaced with iron pans which were heated with coal. In the 1860s a procedure known as the Michigan process or the grainer process was invented, in which salt water was heated by steam running through pipes immersed in the water. This process is still used to produce certain types of salt. By the late 1880s open pans were replaced by a series of closed pans, in a device known as a multiple-effect vacuum evaporator, which had been used in the sugar industry for about 50 years.
Today the United States is the world's largest producer of salt, followed by China, Russia, Germany, the United Kingdom, India, and France.
Raw Materials
Salt is obtained from two sources: rock salt and brine. Rock salt is simply crystallized salt, also known as halite. It is the result of the evaporation of ancient oceans millions of years ago. Large deposits of rock salt are found in the United States, Canada, Germany, eastern Europe, and China. Sometimes pressure from deep inside the Earth forces up large masses of rock salt to form salt domes. In the United States, salt domes are found along the Gulf Coast of Texas and Louisiana.
Brine is water containing a high concentration of salt. The most obvious source of brine is the ocean, but it can also be obtained from salty lakes such as the Dead Sea and from underground pools of salt water. Large deposits of brine are found in Austria, France, Germany, India, the United States, and the United Kingdom. Brine may also be artificially produced by dissolving mined rock salt or by pumping water into wells drilled into rock salt.
Natural brines always contain other substances dissolved along with salt. The most' common of these are magnesium chloride, magnesium sulfate, calcium sulfate, potassium chloride, magnesium bromide, and calcium carbonate. These substances may be as commercially valuable as the salt itself. Rock salt may be quite pure, or it may contain various amounts of these substances along with rocky impurities such as shale and quartz.
For table salt, however, additives are usually mixed in. Most table salt is iodized in order to provide the trace element iodine to the diet. This helps to prevent goiter, a disease of the thyroid gland. To supply iodine, a small amount of potassium iodide is added. Table salt also contains a small amount of various chemicals used to keep the salt from absorbing water and caking. These chemicals include magnesium carbonate, calcium silicate, calcium phosphate, magnesium silicate, and calcium carbonate.
The Manufacturing
Process
Processing rock salt
- 1 Underground salt deposits are usually discovered by prospectors searching for water or oil. When salt is detected, a diamond-tipped, hollow drill is used to take several regularly spaced core samples throughout the area. These samples are analyzed to determine if salt mining would be profitable.
- 2 When a site is selected for mining, shafts are sunk into the center of the salt deposit. Then a machine that looks like a gigantic chain saw is used to cut a slot about 6.0 inches (15 cm) high, about 66 feet (20 m) wide, and about 10 feet (3 m) deep into the salt at floor level. This process is known as undercutting. A series of holes are drilled into the undercut salt with an electric drill containing a tungsten carbide bit. These holes are filled with an explosive such as dynamite or ammonium nitrate. Electric blasting caps connected to long wires are attached, and the explosive is detonated from a safe distance. Cutting and blasting are repeated in a pattern that leaves pillars of salt standing to support the roof of the mining area. This is known as the room-and-pillar method and is also used in coal mines.
- 3 Chunks of blasted rock salt are transported to an underground crushing area. Here they are passed over a grating known as a grizzly which collects pieces smaller than about 9 inches (23 cm). Larger pieces are crushed in a rotating cylinder between metal jaws with spiked teeth. The salt is then transported outside the mine to a secondary crushing area where a smaller grizzly and a smaller crusher reduce the particle size to about 3.2 inches (8 cm). At this point foreign matter is removed from the salt, a process known as picking. Metal is removed by magnets and other material by hand. Rocky material may also be removed in a Bradford breaker, a rotating metal drum with small holes in the bottom. Salt is dumped into the drum, breaks when it hits the bottom, and passes through the holes. Rocky matter is generally harder than salt, so it does not break and does not go through. The picked salt then goes to a tertiary crushing area, where an even smaller grizzly and crusher produce particles about 1.0 inch (2.5 cm) in size. If smaller particles are needed, the salt is passed through a grinder consisting of two metal cylinders rolling against each other. If purer salt is needed, rock salt is dissolved in water to form brine for further processing. Otherwise the crushed or ground salt is passed through screens to sort it by size, poured into bags, and shipped to the consumer.
Processing brine
- 4 The simplest method of evaporating brine is solar evaporation, but it can onlybe used in hot, dry, sunny places. The brine is collected into shallow ponds and allowed to evaporate in the sun. Insoluble impurities such as sand and clay and slightly soluble impurities such as calcium carbonate settle to the bottom as evaporation begins. The brine is pumped or moved by gravity flow to another pond where calcium sulfate settles out as evaporation continues. The remaining brine is moved to yet another pond where the salt settles out as evaporation proceeds. The brine is moved one more time before evaporation is complete to prevent highly soluble impurities such as magnesium chloride, magnesium sulfate, potassium chloride, and magnesium bromide from settling out with the salt. These substances may be collected separately for commercial use.
Rock salt is simply crystallized salt. It is the result of the evaporation of ancient oceans millions of years ago. Large deposits of rock salt are found in the United States, Canada, Germany, eastern Europe, and China. - 5 The salt is scooped up by machines running on temporary railroad tracks laid on top of the layer of salt. It is then washed with highly concentrated salt water. This water contains so much salt that it cannot hold any more, so the salt is washed free of any trace impurities without dissolving. The washed salt is removed from the salt water, rinsed with a small amount of fresh water, and piled into huge stacks to drain for two or three months. At this point the salt is about 99.4% pure and can be used for many industrial purposes. If purer salt is needed, it is rewashed in salt water and fresh water, allowed to drain for one or two days, then dried in a hot air oven at about 365°F (185°C). This salt is about 99.8% pure and can be used for food processing.
- 6 Most brine is processed by a multiple-effect vacuum evaporator. This device consists of three or more closed metal cylinders with conical bottoms. Brine is first treated chemically to remove calcium and magnesium compounds. It then fills the bottomof the cylinders. The brine in the first cylinder passes through tubes heated by steam. The brine boils and its steam enters the next cylinder, where it heats the brine there. The steam from this brine heats the brine in the next cylinder, and so on. In each cylinder the condensation of steam causes the pressure inside to drop, allowing the brine to boil at a lower temperature. Salt is removed from the bottom of the cylinders as a thick slurry. It is filtered to remove excess brine, dried, and passed through screens to sort the particles by size. Salt made this way is known as vacuum pan salt and consists of small cubic crystals.
Brine is water containing a high concentration of salt. The most obvious source of brine is the ocean, but it can also be obtained from salty lakes and underground pools of salt water. - 7 Brine may also be processed in a grainer. The brine is chemically purified and pumped into a long open pan heated by steam running through pipes immersed in the brine. The brine is heated to a temperature slightly below the boiling point and flakes of salt form on its surface as it evaporates. Usually a temperature of about 194°F (90°C) is used. Lower temperatures produce larger flakes and higher temperatures produce smaller flakes. The flakes grow until they sink to the bottom of the pan, where they are collected and dried. Grainer salt consists of small flakes rather than cubes and is preferred for certain uses in food processing. Sometimes the Alberger process is used, in which the brine is first partially evaporated in a vacuum evaporator then moved to a grainer. This process produces a mixture of flakes and cubes.
- 8 At this point salt used for most purposes is ready to be packaged in bags or boxes and shipped to consumers. To make iodized table salt, however, potassium iodide is added, then magnesium carbonate, calcium silicate, calcium phosphate, magnesium silicate, or calcium carbonate is added to make it free-flowing. The salt is then packaged and shipped to restaurants and grocery stores.
Quality Control
Specifications for salt vary widely according to the intended use. Salt intended for human consumption must be much purer than salt used for melting snow and ice, but salt used for certain scientific purposes may need to be even purer.For most purposes, rock salt is allowed to have a gray, pink, or brown tinge rather than being pure white. The impurities that cause these colors may make up as much as 4% of a test sample. To test solubility, a 0.7-ounce (20 g) sample is placed in 6.8 fluid ounces (200 ml) of water. It should completely dissolve in no more than 20 minutes.
Evaporated salt intended for food processing is very pure, containing as much as 99.99% sodium chloride before additives are mixed in. This is important not only for safety and good taste, but because certain impurities can cause problems with certain foods. For example, small amounts of calcium tend to toughen vegetables. Traces of copper or iron tend to destroy vitamin C and to increase the rate at which fatty foods become rancid. In addition, calcium and magnesium both tend to make salt absorb more water, causing it to cake.
Health Aspects
Salt intake—or more precisely, sodium intake—is a controversial topic in health care today. Healthy adults can safely consume 0.2-0.4 ounces (6-11 g) of salt daily, which is equivalent to 0.08-0.14 ounces (2400-4400 mg) of sodium. For some people with high blood pressure, salt intake should be reduced. About one-third to one-half of all hypertensive people are salt-sensitive and will benefit from a low-sodium diet. Since there is no way to tell who these people are, most hypertensives under medical care will be placed on such a diet to see if it helps. A low-sodium diet usually aims to reduce sodium intake to less than 0.08 ounces (2400 mg) per day. While some have suggested that everyone should reduce salt intake, others point out that there is no evidence that salt restriction is of any benefit to otherwise healthy individuals.Worth its Weight in Salt
Dietary changes, thought to have arisen during the transition from hunter-gathering to agriculture in the Neolithic period are believed to have prompted prehistoric people to artificially supplement salt in their diet, thereby creating demand for this new commodity (Casal, 1958; Gouletquer, 1974; Fawn et al., 1990). Dietary changes at this time included cooking (especially boiling) meat and vegetables and consuming salt deficient cereals.
The flavour-enhancing ability of salt is probably its best recognised quality today, and it is likely that this also played an important role in its addition to food from the Neolithic onwards (Gouletquer, 1974). Population expansion during the Neolithic may have prompted the development of salt harvesting technologies in order to meet greater demands for this mineral, which could no longer be adequately met from natural deposits alone.
Salt became a highly valued commodity from the Bronze Age, if not earlier, as its uses expanded to food preservation, leather tanning, cloth dyeing and medicine (Kurlansky, 2003). Early rulers were quick to see its economic and political value, and taxes were levied on salt as a means of maintaining control of its production and distribution. Haun K’uan’s “Discourse on Salt and Iron”, written in c. 80 BC, identifies taxation of salt by Chinese leaders, which continued until the early 20th Century (Tora and Vogel, 1993). The Romans were also quick to take control of the salt industry via taxation and state ownership during their political campaigns across Europe (Shotter, 2005). In addition to providing a source of revenue from taxation and leasing salterns, it was also an important resource for the Roman army (Shotter, 2005). This is due to their use of salt for tanning leather for uniforms and tents, food preservation, and the payment of soldiers (hence the term “salary”) (Kurlansky, 2003).
Advances in technology and salt processing techniques in the 18th and 19th Centuries have greatly increased salt production, whilst doing so at a reduced cost. Although salt still forms an essential and ubiquitous role in our daily lives (e.g. in the food we eat, and the manufacturing processes such as tanning and dyeing used to produce the clothes we wear), it is no longer such an expensive or exclusive commodity. It does however continue to generate large amounts of money for those involved in its production.
Salt through the Ages |
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| The first written reference to salt is found in the Book of Job, recorded about 2,250 BC. There are 31 other references to salt in the Bible, the most familiar probably being the story of Lot ’s wife who was turned into a pillar of salt when she disobeyed the angels and looked back at the wicked city of Sodom. From ancient times to the present, the importance of salt to humans and animals has been recognized. Thousands of years ago, animals created paths to salt licks, and men followed seeking game and salt. Their trails became roads and beside the roads; settlements grew. These settlements became cities and nations. Ancient Britons carried their crude salt by pack train from Cheshire to Southern England where they often were forced to delay their journey until the high tides of the Thames River subsided. A village known as Westminster grew up there and Westminster became London. Salt has greatly influenced the political and economic history of the world. Every civilization has had its salt lore - fascinating superstitions and legends that have been handed down, sometimes reverently and sometimes with tongue-in-cheek. The purifying quality of salt has made it a part of the rituals in some religious ceremonies. “He is not worth his salt”, is a common expression. It originated in ancient Greece where salt was traded for slaves. Roman soldiers were paid “salt money”, salarium argentum, from which we take our English word, “salary”. The early Greeks worshipped salt no less than the sun, and had a saying that “no one should trust a man without first eating a peck of salt with him” (the moral being that by the time one had shared a peck of salt with another person, they would no longer be strangers). The widespread superstition that spilling salt brings bad luck is believed to have originated with the overturned salt cellar in front of Judas Iscariot at the Last Supper, an incident immortalized in Leonardo Da Vinci’s famous painting. According to an old Norwegian superstition, a person will shed as many tears as will be necessary to dissolve the salt spilled. An old English belief has it that every grain of salt spilled represents future tears. The Germans believe that whoever spills salt arouses enmity, because it is thought to be the direct act of the devil, the peace disturber. The French throw a little spilled salt behind them in order to hit the devil in the eye, to temporarily prevent further mischief. In the United States, some people not only toss a pinch of spilled salt over the left shoulder, but crawl under the table and come out the opposite side. The United States has had its battles over salt. In 1777, Lord Howe made a successful attempt to capture General Washington's stock of salt. Many battles and treaties took place before Western salt licks were free to be used by settlers. During the War of 1812 with England, it became very difficult to obtain salt from abroad. Because of this, commercial production of salt began in Syracuse, New York. During the Civil War, Syracuse production freed the North of all salt problems, but by 1863, Southerners could not buy salt at any price. If the South had been able to protect its salt factories in Virginia and its salt deposits along the Louisiana gulf coast, the War between the States might have ended differently. Transporting salt has always been a problem because it is bulky and low priced. Syracuse salt was brought to Chicago by way of the old Erie Canal and the Great Lakes. As early as 1848, the canal was known as "the ditch that salt built." Today, Morton has solved many of the transportation problems by having salt plants located across North America |
Salt production method
Major salt concentrate production methods
Seaweed burning method (Moshio-yaki)
Details of the method are not clear and so there are various ideas
- ash salt was made by hardening the ash of burnt seaweed using seawater
- salt concentrate was produced by pouring seawater onto the ash salt
- salt concentrate produced by pouring seawater onto layers of seaweed was boiled down
The generally accepted view is that seaweed was used to produce salt concentrate (seaweed covered by seawater was dried under the sun, and the salt that crystallized on the surface of the seaweed was dissolved by pouring on seawater).
Banked salt-terrace method (Agehamashiki-enden)
Banked salt-terraces were located above sea level. The terraces were made by flattening the ground, hardening the base with clay and then applying a layer of sand. Seawater carried manually was sprayed over the sand. The sun and the wind evaporated the water, leaving salt-encrusted sand which was scooped up and put into a tank to concentrate the salt (the concentrator). Seawater was poured into the concentrator to produce a dense salt concentrate.This method could not be used in bad weather or during winter, so the operation period was spring through autumn. Salt is still produced using this method in Noto Peninsula in Ishikawa Prefecture.
- Banked salt-terrace structure
[ Work procedures at a banked salt-terrace ]
- Seawater was carried and sprayed onto the sand on the terrace.
- After the sand dried, it was scooped up and put into the concentrator.
- Seawater was poured into the concentrator to dissolve the salt crystallized on the sand.
- Salt concentrate drained from the bottom of the concentrator. [This was boiled down to crystallize the salt.]
- The sand was taken out of the concentrator and spread on the field again.
Channeled salt-terrace method (Irihamashiki-enden)
One major difference between the channeled salt-terrace method and the banked salt-terrace method was that seawater was not carried manually but poured into the field by exploiting the tidal differences in the sea level. Another difference was that the sand was wetted with seawater using capillary action. For the channeled salt-terrace method, a dyke was constructed on tidal flats which were shallow for a great distance, and terraces were made at a height midway between low tide and high tide.In the channeled salt-terrace method, seawater flowed into the channels and spread around the top of the sand by capillary action. The sun and the wind evaporated the water, leaving salt-encrusted sand which was scooped up and put into a tank to concentrate the salt (the concentrator). Seawater was poured onto the sand in the concentrator to produce salt concentrate.
This epoch-making method exploiting the tidal differences in the sea level was developed on the coast of the Setonaikai Sea in the mid-seventeenth century and remained in use until the 1960s.
- Channeled salt-terrace structure
[ Work procedures at a channeled salt-terrace ]
- Sand was spread onto the terrace.
- Seawater was sprayed onto the sand to enhance capillary action.
- The sand was churned to aid evaporation.
- After the sand dried, it was scooped up and put into the concentrator.
- Seawater was poured into the concentrator to dissolve the salt crystallized on the sand.
- Salt concentrate drained from the bottom of the concentrator. [This was boiled down to crystallize the salt.]
Sloping salt-terrace method (Ryukashiki-enden)
The sloping salt-terrace method replaced the channeled salt-terrace method and was used from the late 1960s to about 1970.This method used sloping terraces, covered with clay or a layer of plastic sheeting and then by a layer of fine gravel, and evaporation racks made of fine bamboo branches laid out in steps. Seawater was pumped up and flowed down over the first sloping terrace to a second sloping terrace and onto the evaporation racks where the sun and the wind evaporated the water. Salt concentrate was produced by repeating this cycle.
The evaporation racks improved wind evaporation of water because the seawater coated the bamboo branches in a thin film and cascaded down along the layers of branches. The evaporation racks allowed salt to be produced all year round and the sloping salt-terrace method obviated the need to carry heavy sand unlike the channeled salt-terrace method. The only requirement was a flow of seawater, so this method dramatically cut back on labor.
- Sloping salt-terrace structure
Ion-exchange membrane electrodialysis method
The ion-exchange membrane electrodialysis method produces salt concentrate from seawater using electrical power. This method is based on the principle that the salt in seawater exists as separated electrically-charged positive ions such as sodium, magnesium and calcium ions and electrically-charged negative ions such as chloride ions.
The salt concentration in seawater is about 3.5%. The ion-exchange membrane electrodialysis method is able to produce salt concentrate with a concentration of between about 15% and 20%. This concentrate is boiled down to crystallize the salt.
Other countries in addition to Japan that use the ion-exchange membrane electrodialysis method for salt production are Korea and Taiwan.
The salt concentration in seawater is about 3.5%. The ion-exchange membrane electrodialysis method is able to produce salt concentrate with a concentration of between about 15% and 20%. This concentrate is boiled down to crystallize the salt.
Other countries in addition to Japan that use the ion-exchange membrane electrodialysis method for salt production are Korea and Taiwan.
- The ion-exchanger has two electrodes at the two ends. Placed between these electrodes are a series of alternating positive and negative ion-exchange membranes. The positive ion-exchange membranes allow only positive ions to pass through and the negative ion-exchange membranes permit only negative ions to pass through.
- When a direct electric current flows between the two electrodes through the seawater-filled tank, positive sodium, magnesium and calcium ions migrate to the negative electrode, and similarly, but in reverse, negative ions, such as chloride ions, migrate to the positive electrode.
- Migrating positive ions such as sodium ions are stopped by the negative ion exchange membranes, and negative ions such as chloride ions are repelled by the positive ion-exchange membranes. As a result, highly saline brine (with a salt concentration of 15% to 20%) and low saline brine (with a salt concentration of approximately 2%) are trapped between alternating pairs of the membranes.
- The salt concentrate is transferred to a evaporation system and the low saline brine is returned to the sea.
Ion movements
Studies on the ion-exchange membrane electrodialysis method began around 1950. Compared with salt production using salt terraces, the ion-exchange membrane electrodialysis method realized remarkably higher productivity of both land and labor and is independent of the weather.
Ion-exchange membranes
The ion-exchange membranes are between 0.1mm and 0.2mm thick and have minute perforations (with a diameter of between 1 and 2 millionths of a millimeter). These membranes have useful properties of allowing the passage of ions such as Na+、Cl-、Ca2+ and Mg2+ and do not allow the passage of noxious substances such as PCB and organic mercury.
Ion-exchange membranes are widely used in the production of pharmaceuticals and foodstuffs, for example, to produce medical-use water (for injections), to produce drinking water from brine, to
Ion-exchange membranes are widely used in the production of pharmaceuticals and foodstuffs, for example, to produce medical-use water (for injections), to produce drinking water from brine, to
Major boiling-down methods
Earthenware vessel and salt kettle
To boil down salt concentrate, earthenware vessels were used from ancient times; salt kettles came into general use from the Middle Ages.
Types of salt kettles
- Shell kettle (clay salt-pan) (Kaigama)
Shell kettles were made from lime clay produced by kneading powdered shells with brine. - Bamboo kettle (Ajirogama)
Bamboo kettles were constructed in the form of a bamboo basket lined on both sides with clay composed of lime and sand. - Stone-lined kettle (Ishigama)
Stone-lined kettles were developed from earthenware vessels. The bottom was lined with stones and the gaps between the stones were filled in with mortar. - Open iron salt-kettle (Tetsugama,Hiragama)
Open iron salt-kettles were derivatives of Western models. They rapidly came into widespread use because they were more productive than the stone-lined kettles which had been used until then. Open iron salt-kettles were utilized at most of the salt terraces along the coast of the Setonaikai Sea by the beginning of the 1920s.
- <Process>
- The open iron salt-kettle system consisted of a rectangular salt crystal kettle (3m x 4m) and a small preliminary warming kettle. Steam was released into the air.
Salt kettle with steam heating
A salt kettle with a steam heating system was developed in 1922, based on sealed salt-kettles in use in Europe. From around this time producers started to perform the boiling down work in collaboration with each other and industrial cooperatives started to operate salt-kettles.
- <Process>
- Steam generated inside the sealed salt crystal kettle was used as the heat source for the preliminary warming kettle.
Pressurization evaporation
Salt shortages occurred during and after World War II leading to a strong demand to increase salt production in Japan.
Therefore, a salt production method that only needed seawater to be boiled, and which did away with the need for salt terraces, was investigated.
A pressurization evaporation system, which was cost effective if the system was reasonably large scale, was successfully developed.
This system came into operation in 1952 and produced 200,000 tons of salt a year during its most productive period.
Therefore, a salt production method that only needed seawater to be boiled, and which did away with the need for salt terraces, was investigated.
A pressurization evaporation system, which was cost effective if the system was reasonably large scale, was successfully developed.
This system came into operation in 1952 and produced 200,000 tons of salt a year during its most productive period.
- <Process>
- The boiler was used only to generate heat until evaporation started in the evaporation section and was not used at any other time. A compressor was used to compress the steam generated in the evaporation section which raised the temperature of the steam. This steam was then used as the heat source.
Vacuum evaporation
The first plant with a vacuum evaporation system was completed in 1931. Construction of plants with the present type of system began around the mid 1950s. The manual work required to boil kettles was replaced by inspection work such as monitoring and operating devices.
- <Process>
- The vacuum evaporation system is based on the principle that lowering the air pressure lowers the boiling point. The air pressure inside the evaporation system was lowered and steam generated from each of the evaporation sections was used as the heat source for the next evaporation section (for three or four sections). [Fuel consumption dropped to less than half of that required for open iron salt-kettles.]
Iodine is a vestige mineral which is very scarce in the human body and vital for the normal growth and development. The daily iodine amount to be taken daily is as much as a pin head. This amount is also very important for our lives. Iodine is taken into the body through the food, water and sea products consuming. The need of the body to iodine is at very little amount, but this amount is very important for the life. Iodine is necessary for the thyroid gland to produce hormones. Thyroid gland is in the butterfly shape and is located in the front part of the neck. The hormones synthesized in the thyroid gland pester into the blood and controls various functions in the body. The functions of the thyroid hormones are:| Provide the normal growth and development, Ensure the normal functioning of the brain, Arrange the functioning of the neural system, Control the body temperature, Control the body energy. The iodine deficiency diseases are seen in insufficient iodine intake. They are; abortion, dead birth-giving in fetus (baby in uterus Anomalies at birth Increase in the baby death |
Sun-normality, deafness, squinting, paralysis, dwarfishness,
Goiter in the newborns, Goiter with infants and youngsters Deficiency in the intelligence level Deficiency with the growth and development Goiter and its complications with the adults Not-functioning of the thyroid gland Not enough functioning of the memory Weakness |
Iodine deficiency diseases are mainly seen in the regions where there is lack of iodine especially in their land. The iodine available in the air settles in the earth and the plants growing in the earth intakes the iodine. The human beings and animals being fed with these plants utilize from the iodine. In the regions where there is plenty of rain and having no trees, the iodine on the surface of the soil is washed out by the rain and wind. The iodine deficiency diseases are often seen in these regions. The mostly seen symptoms of the iodine deficiency diseases are the simple goiter. Goiter is the enlargement of the thyroid gland on the neck. Goiter is seen with every 31 people out of every 100 people. Goiter is seen with the women most commonly. Goiter with 1 man in comparison to 3 with women is seen. We do not know the absolute frequency of the growth deficiency, sub-normality, deafness and dumbness connected to iodine in our country.The children who are of iodine deficiency:
understands more difficultly
being educated harder are less productive in their works |
---Coal-burning blast Furnace
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----Vibrating Blast Drier
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---Fixed Fluidizing-Bed Drier
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---GWC Series Belt-type Air-through Dryer
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-----FG Series Air Circulation Dryer
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---Model THJ-1300 Horizontal Frying Cylinder Dryer
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---Coal-fired Clean Hot-Air Circulation Drying
|  ---Rotating Cylinder Sieve |
-----Salt Washing, Iodizing and Refining Plant
|  ----Vibrating Grading Sieve |
 ----Opposite Roller Pulverizer |  ---Screw Salt-Washer |
-----Tank Salt-Washer
|  -----Sprinkling Dust Remover |
 ----Cyclone Seperator | 
---Countercurrent Washer
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 ----Intermittent Inclined Plate Settler |  ----Screw Conveyer |
----Screw Constant-weight Feeder
