Phosphates and Superphosphates
|Infobox on Phosphates and Superphosphates|
|Example of Phosphates and Superphosphates|
|Stowage factor (in m3/t)|
|Humidity / moisture||0% to 2%|
|Ventilation||No special requirements|
|Risk factors||See text|
Phosphate, salt or ester of phosphoric acid, H3PO4. Because phosphoric acid is tribasic (having three replaceable hydrogen atoms), it forms monophosphate, diphosphate, and triphosphate salts in which one, two, or three of the hydrogens of the acid are replaced, respectively. Because replaceable hydrogens remain in monophosphates and diphosphates, they are sometimes called acid phosphates. The most important inorganic phosphate is calcium phosphate, Ca3(PO4)2. It makes up the larger part of phosphate rock, a mineral that is abundantly distributed throughout the world. Since calcium phosphate is only slightly soluble in water, it is not very suitable as a source of the phosphorus necessary for plant life; however, by treating it with sulfuric acid the soluble calcium acid phosphate known as superphosphate of lime is formed. Other important inorganic phosphates include ammonium phosphate, important as a fertilizer; trisodium phosphate, used in detergents and for softening water; and disodium phosphate, used to some extent in medicine and in preparing baking powders. Various acid phosphates, e.g., those of calcium, magnesium, and sodium, are sometimes present in carbonated beverages. Microcosmic salt, used in certain bead tests in chemical analysis, is sodium ammonium phosphate. Organic phosphates play an important role in metabolism. For example, in the metabolism of sugars (which have hydroxyl groups, -OH, in their molecules), phosphate esters are often formed as an intermediate compound. Formation of these esters is called phosphorylation. Nucleotides are phosphate esters that play an important role in the conservation and use of the energy released in the metabolism of foods in the body; adenosine triphosphate is an important nucleotide. DNA and RNA (see nucleic acid) are complex polymeric organic phosphates.
Phosphates are the naturally occurring form of the element phosphorus, found in many phosphate minerals. In mineralogy and geology, phosphate refers to a rock or ore containing phosphate ions. Inorganic phosphates are mined to obtain phosphorus for use in agriculture and industry.
In ecological terms, because of its important role in biological systems, phosphate is a highly sought after resource. Once used, it is often a limiting nutrient in environments, and its availability may govern the rate of growth of organisms. This is generally true of freshwater environments, whereas nitrogen is more often the limiting nutrient in marine (seawater) environments. Addition of high levels of phosphate to environments and to micro-environments in which it is typically rare can have significant ecological consequences. For example, blooms in the populations of some organisms at the expense of others, and the collapse of populations deprived of resources such as oxygen can occur. In the context of pollution, phosphates are one component of total dissolved solids, a major indicator of water quality, but not all phosphorus is in a molecular form which algae can break down and consume.
Phosphate deposits can contain significant amounts of naturally occurring heavy metals. Mining operations processing phosphate rock can leave tailings piles containing elevated levels of cadmium, lead, nickel, copper, chromium, and uranium. Unless carefully managed, these waste products can leach heavy metals into groundwater or nearby estuaries. Uptake of these substances by plants and marine life can lead to concentration of toxic heavy metals in food products.
Shipment / Storage / Risk factors
Phosphates and superphospates
A phosphate, an inorganic chemical, is a salt of phosphoric acid. In organic chemistry, a phosphate, or organophosphate, is an ester of phosphoric acid. Organic phosphates are important in biochemistry and biogeochemistry or ecology. Inorganic phosphates are mined to obtain phosphorus for use in agriculture and industry. At elevated temperatures in the solid state, phosphates can condense to form pyrophosphates.
Bulk shipping is the usual transport for these commodities. Single and triple superphosphate tend to be shipped in granular form. Are highly corrosive if packed too fresh or if humidity is encountered. Subject to loss in weight following seepage from containers.
Phosphate rock and/or fines
A light brown to white rock which is sometimes crushed to make the phosphate fines. Varies in texture from a sandy powder to a lumpy material containing a large proportion of dust, and due to its free-flowing properties considerable loss may arise in course of handling. If the material is not perfectly free-flowing it cannot be used easily in the machinery set up for the manufacture of the acid phosphate and, although moisture contact does little of no damage, the commodity must be dried before it can be processed.
Rock phosphate is a rock form of naturally occurring phosphate fertilizer which is formed from sea floor sediments of ancient and current day seas. It is reported as a percentage of phosphorus pentoxide (P2O5). Phosphates can be deposited in a wide range of marine depositional environments. Normally phosphates are deposited in very shallow, near shore marine or low energy environments. Rock phosphate can be wet-processed to produce phosphoric acid or smelted to produce phosphorus. Phosphoric acid is reacted with phosphate rock to produce superphosphate or with anhydrous ammonia to produce ammonium phosphate.
A rock phosphate treated with sulphuric acid: usually in granular form. A dry, free-running fertilizer, slightly acid in character. Moisture damage will render the commodity sticky and pasty and reduce both the fertilizer and material value. The commodity may be dried by hot air, but this may be an expensive matter.
Unduly high temperatures may cause the reversion of the soluble phosphate to the insoluble form, with consequent reduction in the value.
Generally superphosphates are liable to become wet in the vessel’s hold and if this occurs considerable difficulty may be experienced in discharge. On occasions the commodity may be hardened to such an extent that mechanical equipment is necessary to break it up before discharge takes place.
Triple superphosphates (TSP) are made from phosphate rock treated with phosphoric acid and are not always three times more concentrated than single superphosphate (SSP).
Note: For overseas carriage of phosphates, consult the IMSBC Code (International Maritime Solid Bulk Cargoes Code). The cargo has no special hazards and is non-combustible resp. has a low fire-risk. The cargo is hygroscopic and will cake if wet.