Salt

From Cargo Handbook - the world's largest cargo transport guidelines website
Revision as of 13:40, 10 July 2012 by DeBeer (talk | contribs)
(diff) ← Older revision | Latest revision (diff) | Newer revision → (diff)
Jump to: navigation, search
Infobox on Salt
Example of Salt
Salt.jpg
Facts
Origin Salt is produced extensively over all continents.
Stowage factor (in m3/t)
  • 1.25 m3/t (paper bags, 5-ply with plastic lining, 50 kg)
  • 1.47 m3/t (wooden barrels)
  • 1.06 - 1.11 m3/t (bags)
  • 0.98 - 1.11 m3/t (bulk)
Humidity / moisture
  • Relative humidity: 55 - 65%
  • Water content 0.05 - 0.5%
  • Maximum equilibrium moisture content: 65%
Oil content -
Ventilation Salt requires particular humidity/moisture and possibly ventilation conditions (storage climate conditions).

As bagged salt is protected from water vapor exchange by a plastic lining, it does not normally need to be ventilated.

However, if it is transported as bulk cargo, note should be taken of the behavior of a cargo block in the event of temperature changes:

* transport from temperate latitudes to the tropics = travel from cold to hot: the cargo block is heated from the outside, resulting in water vapor transport from the outside to the cold core, which causes caking of the outer layers while the inner layers display wetting phenomena (syrup formation).

* transport from the tropics to temperate latitudes = travel from hot to cold: if the cargo block cools down from the outside, resulting in water vapor transport from the warm core to the outside, wetness and mold may occur there while inside the release of water vapor by the warm core results in caking phenomena (loss of flowability).
Risk factors Salt is sensitive to unpleasant or pungent odors.

Salt is sensitive to contamination and moisture damage.
Salt solutions and salt dust have a highly corrosive action on metals.

Weight losses of approx. 5% due to water vapor release are deemed normal. To these must be added trickle losses, which arise during cargo handling.

Description

Salt, also known as table salt, or rock salt, is a crystalline mineral that is composed primarily of sodium chloride (NaCl), a chemical compound belonging to the larger class of ionic salts. It is essential for animal life in small quantities, but is harmful to animals and plants in excess. Salt is one of the oldest, most ubiquitous food seasonings and salting is an important method of food preservation. The taste of salt (saltiness) is one of the basic human tastes.

Salt for human consumption is produced in different forms: unrefined salt (such as sea salt), refined salt (table salt), and iodized salt. It is a crystalline solid, white, pale pink or light gray in color, normally obtained from sea water or rock deposits. Edible rock salts may be slightly grayish in color because of mineral content.

Chloride and sodium ions, the two major components of salt, are needed by all known living creatures in small quantities. Salt is involved in regulating the water content (fluid balance) of the body. The sodium ion itself is used for electrical signaling in the nervous system. Because of its importance to survival, salt has often been considered a valuable commodity during human history. However, as salt consumption has increased during modern times, scientists have become aware of the health risks associated with too much salt intake, including high blood pressure. Therefore health authorities have recommended limitations of dietary sodium.

Different natural salts have different mineralities, giving each one a unique flavor. Fleur de sel, a natural sea salt from the surface of evaporating brine in salt pans, has a unique flavor varying from region to region. Completely raw sea salt is bitter because of magnesium and calcium compounds, and thus is rarely eaten. Unrefined sea salts are also commonly used as ingredients in bathing additives and cosmetic products.

Food grade salt accounts for only a small part of salt production in industrialized countries although worldwide, food uses account for 17.5 percent of salt production. The majority is sold for industrial use. Salt has great commercial value because it is a necessary ingredient in many manufacturing processes. A few common examples include: the production of pulp and paper, setting dyes in textiles and fabrics, and the making of soaps and detergents.

The manufacture and use of salt is one of the oldest chemical industries. Salt can be obtained by evaporation of sea water, usually in shallow basins warmed by sunlight; salt so obtained was formerly called bay salt, and is now often called sea salt or solar salt. Rock salt deposits are formed by the evaporation of ancient salt lakes, and may be mined conventionally or through the injection of water. Injected water dissolves the salt, and the brine solution can be pumped to the surface where the salt is collected.

Table salt is refined salt, which contains about 97 to 99 percent sodium chloride. It usually contains substances that make it free-flowing (ant-caking agents) such as sodium silicoaluminate or magnesium carbonate.

Most table salt sold for consumption contains a variety of additives, which address a variety of health concerns, especially in the developing world. The amounts of additives vary widely from country to country.

Applications

Salt is produced by evaporation of seawater or brine from other sources, such as brine wells and salt lakes, and by mining rock salt, called halite. Apart from its use in table salt in the diet, sodium chloride is a major industrial chemical. It occurs widely, being the main saline component of the oceans, and plays a role in formation of clouds.

Shipment / storage / usage

When stowed in containers a high standard of container preparation is required, ensuring the interior of the container is absolutely dry and clean. It is important the bags are of good quality and not stowed with goods that might emit moisture. As protection for the container, it is recommended that an innerliner is fitted.

Salt corrodes steelwork, therefore for breakbulk shipments all steel structures in the holds are given two coats of whitewash. Cracks in ceilings and planking must be effectively stopped up. Salt is not to be loaded together with cargoes emitting/attracting moisture. During the voyage, salt may loose 5% in weight by evaporation. A bulk liner bag is fitted inside the container and the cargo can be either blown into a zip up bag or brought in by bob cat shovel to an enveloping liner bag. In both cases a door bulkhead must be created and this can be done either by bars fitted into the doorway recess or by bagging a portion of the cargo to hold the liner in position across the doorway.

Common salt is shipped in bags or in bulk. Subject to loss of weight due to evaporation. On a long voyage this may be 5% or more. When shipped in jute bags contact with iron results in rusting of the metal, which stains and rusts the bags, with subsequent bursting on handling and loss of contents. Should sacks be repaired, careful attention should be paid to the re-sewn portions, as this loss might be confused with loss due to ‘normal tearing’. The salt nearest to the torn portion of the bag is usually rust stained. Damaged salt, if unfit for the purpose of which it was intended, may attract a reasonable figure for agricultural purposes. With bulk cargoes holds should be limewashed before loading.

If allowed to absorb too much water vapor, salt begins to flow. If the water vapor is released again, lumps form. Depending on its intended use, care should be taken to ensure that salt remains pourable and does not tend towards lump formation. This may be achieved by adding appropriate additives (anti-caking agents). If salt is stored in suitably dry and warm conditions, it may be stored for several years.

Risk factors

  • Odor
  • Moisture
  • Contamination
  • Mechanical influences
  • Toxicity / Hazards to health
  • Shrinkage/Shortage