Cours project by discipline «basic technological processes and devices» content

2. Description of supplied products.
Sodium chloride is an essential nutrient and is used in healthcare to help prevent patients from becoming dehydrated.
It is used as a food preservative and as a seasoning to enhance flavor.
Sodium chloride is also used in manufacturing to make plastics and other products, and it is used to de-ice roads and sidewalks.
Salt is regulated by the FDA (food and drug administration) as a “generally recognized as safe” (GRAS) ingredient. A GRAS substance is one that has a long history of safe, common use in foods, or that is determined to be safe, for the intended use, based on proven science.
Uses & Benefits
Sodium chloride is an essential nutrient and is used in healthcare to help prevent patients from becoming dehydrated. It is used as a food preservative and as a seasoning to enhance flavor. Sodium chloride is also used in manufacturing to make plastics and other products. It is also used to de-ice roads and sidewalks.
Medical and Health
Hospitals use an intravenous sodium chloride solution to supply water and salt to patients to alleviate dehydration. Sodium chloride is essential to maintain the electrolyte balance of fluids in a person’s body. If levels of electrolytes become too low or too high, a person can become dehydrated or over hydrated, according to U.S. National Library of Medicine
Food Flavoring and Preservative
Sodium chloride has been used to flavor and preserve foods for thousands of years. As a preservative, salt helps to prevent spoilage and helps to keep foods like ready-to-eat meats and cheeses safe to eat.3 Salt is also used in fermenting processes for foods like sauerkraut, pickles and kefir.
Manufacturing
Large quantities of sodium chloride are used in industrial manufacturing settings to make a range of products. Plastic, paper, rubber, glass, chlorine, polyester, household bleach, soaps, detergents and dyes are made using sodium chloride^.
Limestone (calcium carbonate CaCO₃) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of CaCO₃. Limestone forms when these minerals precipitate out of water containing dissolved calcium. This can take place through both biological and nonbiological processes, though biological processes, such as the accumulation of corals and shells in the sea, have likely been more important for the last 540 million years. Limestone often contains fossils which provide scientists with information on ancient environments and on the evolution of life.
About 20% to 25% of sedimentary rock is carbonate rock, and most of this is limestone. The remaining carbonate rock is mostly dolomite, a closely related rock, which contains a high percentage of the mineral dolomite, CaMg(CO₃)₂. Magnesian limestone is an obsolete and poorly-defined term used variously for dolomite, for limestone containing significant dolomite (dolomitic limestone), or for any other limestone containing a significant percentage of magnesium. Most limestone was formed in shallow marine environments, such as continental shelves or platforms, though smaller amounts were formed in many other environments. Much dolomite is secondary dolomite, formed by chemical alteration of limestone. Limestone is exposed over large regions of the Earth's surface, and because limestone is slightly soluble in rainwater, these exposures often are eroded to become karst landscapes. Most cave systems are found in limestone bedrock.

Limestone has numerous uses: as a chemical feedstock for the production of lime used for cement (an essential component of concrete), as aggregate for the base of roads, as white pigment or filler in products such as toothpaste or paints, as a soil conditioner, and as a popular decorative addition to rock gardens. Limestone formations contain about 30% of the world's petroleum reservoirs.^[1]

Limestone is composed mostly of the minerals calcite and aragonite, which are different crystal forms of calcium carbonate (CaCO₃). Dolomite, CaMg(CO₃)₂, is an uncommon mineral in limestone, and siderite or other carbonate minerals are rare. However, the calcite in limestone often contains a few percent of magnesium. Calcite in limestone is divided into low-magnesium and high-magnesium calcite, with the dividing line placed at a composition of 4% magnesium. High-magnesium calcite retains the calcite mineral structure, which is distinct from dolomite. Aragonite does not usually contain significant magnesium. Most limestone is otherwise chemically fairly pure, with clastic sediments (mainly fine-grained quartz and clay minerals) making up less than 5% to 10% of the composition. Organic matter typically makes up around 0.2% of a limestone and rarely exceeds 1%.

Limestone often contains variable amounts of silica in the form of chert or siliceous skeletal fragments (such as sponge spicules, diatoms, or radiolarians). Fossils are also common in limestone.

Limestone is commonly white to gray in color. Limestone that is unusually rich in organic matter can be almost black in color, while traces of iron or manganese can give limestone off-white to yellow to red color. The density of limestone depends on its porosity, which varies from 0.1% for the densest limestone to 40% for chalk. The density correspondingly ranges from 1.5 to 2.7 g/cm³. Although relatively soft, with a Mohs hardness of 2 to 4, dense limestone can have a crushing strength of up to 180 MPa. For comparison, concrete typically has a crushing strength of about 40 MPa.

Although limestones show little variability in mineral composition, they show great diversity in texture. However, most limestone consists of sand-sized grains in a carbonate mud matrix. Because limestones are often of biological origin and are usually composed of sediment that is deposited close to where it formed, classification of limestone is usually based on its grain type and mud content.

Grains.
Most grains in limestone are skeletal fragments of marine organisms such as coral or foraminifera. These organisms secrete structures made of aragonite or calcite, and leave these structures behind when they die. Other carbonate grains composing limestones are ooids, peloids, and limeclasts (intraclasts and extraclasts).

Skeletal grains have a composition reflecting the organisms that produced them and the environment in which they were produced. Low-magnesium calcite skeletal grains are typical of articulate brachiopods, planktonic (free-floating) foraminifera, and coccoliths. High-magnesium calcite skeletal grains are typical of benthic (bottom-dwelling) foraminifera, echinoderms, and coralline algae. Aragonite skeletal grains are typical of molluscs, calcareous green algae, stromatoporoids, corals, and tube worms. The skeletal grains also reflect specific geological periods and environments. For example, coral grains are more common in high-energy environments (characterized by strong currents and turbulence) while bryozoan grains are more common in low-energy environments (characterized by quiet water).

Ooids (sometimes called ooliths) are sand-sized grains (less than 2mm in diameter) consisting of one or more layers of calcite or aragonite around a central quartz grain or carbonate mineral fragment. These likely form by direct precipitation of calcium carbonate onto the ooid. Pisoliths are similar to ooids, but they are larger than 2 mm in diameter and tend to be more irregular in shape. Limestone composed mostly of ooids is called an oolite or sometimes an oolitic limestone. Ooids form in high-energy environments, such as the Bahama platform, and oolites typically show crossbedding and other features associated with deposition in strong currents.

Oncoliths resemble ooids but show a radial rather than layered internal structure, indicating that they were formed by algae in a normal marine environment.

Peloids are structureless grains of microcrystalline carbonate likely produced by a variety of processes. Many are thought to be fecal pellets produced by marine organisms. Others may be produced by endolithic (boring) algae or other microorganisms or through breakdown of mollusc shells. They are difficult to see in a limestone sample except in thin section and are less common in ancient limestones, possibly because compaction of carbonate sediments disrupts them.

Limeclast are fragments of existing limestone or partially lithified carbonate sediments. Intraclasts are limeclasts that originate close to where they are deposited in limestone, while extraclasts come from outside the depositional area. Intraclasts include grapestone, which is clusters of peloids cemented together by organic material or mineral cement. Extraclasts are uncommon, are usually accompanied by other clastic sediments, and indicate deposition in a tectonically active area or as part of turbidity current.

Mud
The grains of most limestones are embedded in a matrix of carbonate mud. This is typically the largest fraction of an ancient carbonate rock. Mud consisting of individual crystals less than 5 microns in length is described as micrite. In fresh carbonate mud, micrite is mostly small aragonite needles, which may precipitate directly from seawater, be secreted by algae, or be produced by abrasion of carbonate grains in a high-energy environment.[30] This is converted to calcite within a few million years of deposition. Further recrystallization of micrite produces microspar, with grains from 5 to 15 microns in diameter.

Limestone often contains larger crystals of calcite, ranging in size from 0.02 to 0.1 mm, that are described as sparry calcite or sparite. Sparite is distinguished from micrite by a grain size of over 20 microns and because sparite stands out under a hand lens or in thin section as white or transparent crystals. Sparite is distinguished from carbonate grains by its lack of internal structure and its characteristic crystal shapes.