Salt
| Infobox on Salt | |
|---|---|
| Example of Salt |  |
| Facts | |
| Origin | Salt is produced extensively over all continents. |
| Stowage factor (in m3/t) |
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| Humidity / moisture |
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| 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. |
Salt
Contents
Description
"Salt" is the colloquial term for the chemical compound sodium chloride (NaCl). It is principally obtained by four processes:
- by mining of rock salt. In Germany, approx. 90% of all NaCl is obtained in this way.
- by the evaporation of natural or artificial saturated aqueous NaCl solutions. This may proceed with the aid of brines, which are obtained by pumping water into underground salt beds or from salt works ("boiled salt").
- by evaporation of saline seawater collected in large ponds or of water from salt lakes in hot countries (such as Spain or Southern France). This salt is also called sea salt.
- as a by-product of seawater desalination for obtaining drinking or process water.
Salt has a solid, crystalline structure and is very hygroscopic. It attacks metals when combined with moisture.
Applications
Salt is used, among other things, as:
- cooking salt or table salt, as a seasoning for human consumption,
- curing salt, for salt meat and fish,
- cattle lick (dyed with iron oxide) in animal husbandry.
- industrial salt for freezing mixtures (denatured with kerosene or marked with dyes),
- salt grit for clearing roads in winter,
- pit salt for combatting coal dust in mining,
- hide salt for curing hides.
Storage/Transport
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 (e.g. cooking salt), 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. Salt producers therefore use sodium ferrocyanide, which prevents salt crystals from agglomerating (sticking together).
If salt is stored in suitably dry and warm conditions, it may be stored for several years. Salt is transported as bulk cargo as well as in barrels and bags (e.g. 3 - 5-ply paper bags with single plastic lining, 50 kg). The plastic lining prevents water vapor exchange between product and hold or container air. Smaller amounts may also be packaged in cartons or cans ready for retail sale.
Standard containers and bulk containers may be used, subject to compliance with lower limits for water content of goods, packaging and container flooring. In damp weather (rain, snow), the cargo must be protected from moisture. Stow dry. Because of their impact- and pressure-sensitivity, the packaging containers must be secured in such a way that damage is prevented. Bags must not develop tears and barrels must not break apart. Spaces between packages or pallets must be filled, to prevent slippage or tipping. Pallets must be loaded flush with their edges as protruding packages may readily result in damage.
Temperature
Favorable travel temperature range: no lower limit - 25°C. If salt is transported into the subtropics and tropics, the temperature of the cargo of salt on unloading in the port of destination must be higher than the dew point temperature of the outside air, so as to prevent sweat from forming on the cargo.
If salt is loaded in Europe in the winter months, the consignor should ensure that the temperature of the salt is not below freezing point, as it is difficult to heat the product up during the voyage to tropical ports of destination. The most favorable cargo temperature is 15 - 20°C. Such salt (even in containers) may be stowed in the lower holds, as there is sufficient time for slow heating of the cargo given the relatively slight temperature difference between the port of loading and the port of discharge. However, if the temperature of the salt at the port of loading is 0 - 10°C, it should preferably be stowed in holds above the water line, so as to achieve faster heating of the cargo.
| Designation | Humidity/water content |
| Relative Humidity | 55 - 65% |
| Water content | 0.05 - 0.5% |
| Maximum equilibrium moisture content | 65% |
At up to 74% relative humidity and 20°C, salt does not absorb any appreciable quantities of water vapor. The critical water content of sodium chloride (NaCl) is 0.5% at 74% relative humidity, which is the flow moisture point at which salt begins readily to absorb water vapor, and increases such that, at 75% relative humidity, the salt dissolves (hygroscopicity). If salt is loaded as bulk cargo, it is at risk from direct exposure to moisture, such as rain, snow or condensation water, during both cargo handling and transport.
The water vapor absorption of the salt is particularly critical when its temperature is below the dew point temperature of the hold or container air (see RF Temperature). In this case, the condensation zone spreads throughout the entire cargo and the salt becomes thoroughly wet. It is not possible to dry the wettened cargo of salt by ventilation, as it hardens and cakes when it releases water vapor due to recrystallization, so leaving monolithic surfaces. The utility value of the product is reduced considerably by the loss of flowability and the unloading process is rendered more difficult.
Hygroscopicity is increased by the addition of companion salts, such as KCl and MgCl2. If the product is packaged in paper bags with plastic linings, a higher relative humidity than that indicated above is feasible. However, a higher relative humidity makes the paper packaging damp, so that it may be damaged during cargo handling.
Ventilation
Salt requires particular humidity/moisture and possibly ventilated 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).
Biotic activity
Salt displays zero order biotic activity. Salt is a nonliving product and does not therefore display any biotic activity.
Gases
Salt does not normally evolve any gases. However, contact with acids leads to the liberation of chlorine, which has an asphyxiating action and is toxic.
Risk factors
Self-heating / Spontaneous combustion
No risk.
Odor
Active behavior: Salt does not release any odor.
Passive behavior: Salt is sensitive to unpleasant or pungent odors. It must not be loaded in holds or containers which were previously used to transport living animals or other odor-tainting goods. To prevent spoilage of salt, it must not be stored together with sugar, hides, tobacco, fish products and other goods with an intense odor.
Contamination
Active behavior: Salt creates dust. Goods at risk of rusting, such as iron, sheet metal, wire coils, engines, machinery or motor vehicles, may be rapidly corroded by salt dust in conjunction with moisture.
Passive behavior Salt is sensitive to dust, dirt, fats and oils. The holds or containers must accordingly be clean and in a thoroughly hygienic condition before loading.
If the product is transported in linen cloth bags, anyone entering the holds or containers must do so only in soft, clean footwear, as salt is very sensitive to contamination. Salt solutions and salt dust have a highly corrosive action on metals.
Mechanical influences
Because of the impact- and pressure-sensitivity of the bags and barrels, they must be handled with appropriate care during cargo handling, transport and storage. No hooks of any kind may be used during handling of bagged goods, as they cause the salt to trickle out of the bags. Where plastic packaging is damaged, humidity and temperature fluctuations may lead to agglomeration, so rendering the surface monolithic (particularly in the case of fine-grained salt).
Toxicity / Hazards to health
There is normally no risk. Storage together with acids results in the formation of chlorine, which is asphyxiating and toxic.
Shrinkage/Shortage
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.
Additional information
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 usts 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.
Note:(Source including Transport Information Service of the GDV)