Metal phosphate salts

The chemistry of phosphate complexation in inorganic systems is important in agriculture and soil science and more recently in remediation technology because of the low solubility product of many of the metal phosphate salts. A large number of inorganic phosphate phases have been identified [1,2]. In the area of catalysis the aluminophosphates have been investigated both as catalysts and catalyst supports due to their surface acidity and thermal stability. Re-... 

NPE, water, some impurities Sucrose and alkali metal phosphate salts... 

Orthophosphate salts are generally prepared by the partial or total neutralization of orthophosphoric acid. Phase equiUbrium diagrams are particularly usehil in identifying conditions for the preparation of particular phosphate salts. The solution properties of orthophosphate salts of monovalent cations are distincdy different from those of the polyvalent cations, the latter exhibiting incongment solubiUty in most cases. The commercial phosphates include alkah metal, alkaline-earth, heavy metal, mixed metal, and ammonium salts of phosphoric acid. Sodium phosphates are the most important, followed by calcium, ammonium, and potassium salts. 

Zinc phosphate, Zn2(P0 2> forms the basis of a group of dental cements. Chromium and zinc phosphates are utilized in some metal-treating appHcations to provide corrosion protection and improved paint adhesion. Cobalt(II) phosphate octahydrate [10294-50-5] Co2(P0 2 8H20, is a lavender-colored substance used as a pigment in certain paints and ceramics. Copper phosphates exhibit bioactivity and are used as insecticides and fungicides. Zinc, lead, and silver phosphates are utilized in the production of specialty glasses. The phosphate salts of heavy metals such as Pb, Cr, and Cu, are extremely water insoluble. 

The tertiary metal phosphates are of the general formula MPO where M is B, Al, Ga, Fe, Mn, etc. The metal—oxygen bonds of these materials have considerable covalent character. The anhydrous salts are continuous three-dimensional networks analogous to the various polymorphic forms of siHca. Of limited commercial interest are the alurninum, boron, and iron phosphates. Boron phosphate [13308-51 -5] BPO, is produced by heating the reaction product of boric acid and phosphoric acid or by a dding H BO to H PO at room temperature, foUowed by crystallization from a solution containing >48% P205- Boron phosphate has limited use as a catalyst support, in ceramics, and in refractories. 

Alkali Meta.IPhospha.tes, A significant proportion of the phosphoric acid consumed in the manufacture of industrial, food, and pharmaceutical phosphates in the United States is used for the production of sodium salts. Alkali metal orthophosphates generally exhibit congment solubility and are therefore usually manufactured by either crystallisation from solution or drying of the entire reaction mass. Alkaline-earth and other phosphate salts of polyvalent cations typically exhibit incongment solubility and are prepared either by precipitation from solution having a metal oxide/P20 ratio considerably lower than that of the product, or by drying a solution or slurry with the proper metal oxide/P20 ratio. 

Multilayers of Diphosphates. One way to find surface reactions that may lead to the formation of SAMs is to look for reactions that result in an insoluble salt. This is the case for phosphate monolayers, based on their highly insoluble salts with tetravalent transition metal ions. In these salts, the phosphates form layer stmctures, one OH group sticking to either side. Thus, replacing the OH with an alkyl chain to form the alkyl phosphonic acid was expected to result in a bilayer stmcture with alkyl chains extending from both sides of the metal phosphate sheet (335). When zirconium (TV) is used the distance between next neighbor alkyl chains is - 0.53 nm, which forces either chain disorder or chain tilt so that VDW attractive interactions can be reestablished. 

The pH of a medium also impacts the formation of metal-phosphate precipitates. For example, divalent ionic cadmium (Cd2+) concentrations rapidly decline as both phosphate concentration and pH increase. Sandrin and Hoffman121 determined that when no phosphate is present in a commonly used mineral salts medium, the concentration of divalent ionic cadmium remains relatively constant until an abrupt decline above pH 8. When 15 mM inorganic phosphate is added to the medium, divalent cadmium ion concentrations rapidly decline at pH values above only 6. 

Herbicides, insecticides, fungicides, nitrates, phosphates, potassium, BOD, nutrients, heavy metals, inorganic salts, pathogens, surfactants organic solvents used in cleaning... 

It is the divalent metal cation Ca + that is absolutely critical in human physiology. It is important both structurally and functionally. I noted above that hydroxyapatite, a phosphate salt of calcium, is an integral component of bone. As a component of bone, calcium is quantitatively one of the most abundant elements in higher organisms, such as humans. 

The physical and chemical properties of elemental thorium and a few representative water soluble and insoluble thorium compounds are presented in Table 3-2. Water soluble thorium compounds include the chloride, fluoride, nitrate, and sulfate salts (Weast 1983). These compounds dissolve fairly readily in water. Soluble thorium compounds, as a class, have greater bioavailability than the insoluble thorium compounds. Water insoluble thorium compounds include the dioxide, carbonate, hydroxide, oxalate, and phosphate salts. Thorium carbonate is soluble in concentrated sodium carbonate (Weast 1983). Thorium metal and several of its compounds are commercially available. No general specifications for commercially prepared thorium metal or compounds have been established. Manufacturers prepare thorium products according to contractual specifications (Hedrick 1985). 

Phosphorus is one of the most widely distributed elements on earth. It is found as phosphate salts in nearly all igneous rocks and in sedimentary deposits and sea beds. Phosphorus occurs in more than three hundred minerals, usually associated with Ca, Mg, Fe, Sr, Al, Na, and several other metals, and with anions such as silicates, sulfates, oxides, hydroxides, and hahdes. 

Na2HP04), and tribasic salts (Na3P04). The addition of various metal ions to solutions dissolving these salts precipitates monobasic, dibasic, and tribasic metal phosphates as shown in the boxes. As described next, these precipitation reactions are widely used for preparation of different kinds of metal phosphate particles. 

The hydrothermal method has been employed in recent years to synthesize a variety of solids that include aluminium phosphates (ALPOs) and other microporous transition-metal phosphates and transition-metal polychalcogenides (Davis Lobo, 1992 Haushalter Mundi, 1992 Liao Kanatzidis, 1990, 1992). Unlike zeolites, synthesis of ALPOs requires acidic or mildly basic conditions and no alkali metal cations. A typical synthetic mixture for making ALPO consists of alumina, H3PO4, water and an organic material such as a quaternary ammonium salt or an amine. The hydrothermal reaction occurs around 373-573 K. The use of fluoride ions, instead of hydroxide ions as mineralizer, allows synthesis of novel microporous materials under acidic conditions (Estermann et al, 1991 Ferey et ai, 1994). 

Pharmacopeial compendia establish a couple of tests that should be carried out with raw material batches to determine their level of impurities. Concomitants usually detected are heavy metals, chloride, or sulfated ash. The presence of byproducts varies from raw material to raw material. Examples can be both innocuous substances such as monohydrogen phosphate, which is an impurity in dihydrogen phosphate salts and glycine, which is an impurity in alanine, and toxic substances, such as the classical enantiomer S of thalidomide. 

Another diagnostic method for determining the effect of the nature of the catalyst on the mechanism is the observation of the stereoselectivity of elimination [68,121,132]. It has been found, using the reaction of threo- and erythro-3-deutero-2-butanol, that, in a series of salt catalysts, only the phosphates Ca3(P04)2, CaHP04, Ba3(P04)2 and A1P04 preferred the E2 mechanism while on other metal phosphates and all carbonates, the El mechanism predominated [ 132]. 

If vitamins are added to a product to make a nutritional claim, it is critical that shelf-life studies are undertaken to prove that the overages added are sufficient to ensure that the label claims can be met at the end of product shelf life. This is important as none of the vitamins are fully stable in a soft drink environment and some, for instance vitamin C, are very quickly lost in the presence of oxygen. The addition of the fat-soluble vitamins to a soft drink also offers a formulation challenge to ensure that they are fully dispersed and that there are no problems with neck ringing during storage. Trace metals, particularly the transition elements, can also have a deleterious effect on vitamin shelf life, and sometimes metal scavengers, such as EDTA or phosphate salts, are added to improve the shelf life. 

Another preparative method in which the rate of precipitation is slow involves slow decomposition of zirconium fluoro complexes [14], These are first prepared by adding an appropriate amount of hydrofluoric acid (HF) to the zirconyl salt and these complexes are decomposed in the presence of phosphoric acid, with a slow stream of nitrogen or water vapor passing through the system. The rate of precipitation of zirconium phosphate is controlled by the rate of removal of HF from the system, and when this is very slow, a highly crystalline a-ZrP is obtained. The gamma form of the metal phosphate differs significantly from the alpha and current discussion will be concerned with the latter phase. 

Crude phosphoric acid is often black and contains dissolved metals and fluorine, and dissolved and colloidal organic compounds. Suspended solid impurities are usually removed by settling and solvent extraction (using a partially miscible solvent, such as n-butanol, /.so-butanol, or n-heptanol), or solvent precipitation is used to remove the dissolved impurities. The phosphoric acid is extracted, and the impurities are left behind. Back-extraction with water recovers the purified phosphoric acid. Solvent precipitation uses a completely miscible solvent plus alkalis or ammonia to precipitate the impurities as phosphate salts. After filtration, the solvent is separated by distillation and recycled. 

When an alkaline oxide such as MgO is stirred in phosphoric acid, the pH of the solution rises slowly due to the neutralization of this acid. Initially, the phosphoric acid has pH 0, but initial dissolution of the oxide and reaction with phosphate anions precipitate phosphate salts. This neutralization of the acid raises the pH of the solution to >2. Even in this pH range, the acid dissolves sufficiently, and protons and H2PO4 anions are readily available to react with the ions produced by the dissolution of metal oxides. Subsequently, consolidation of the precipitate in the neutral solution leads to the formation of ceramics. 

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