Solubility ferric phosphate

Variable results have been reported with this pigment and an examination of its inhibitive action has led to the conclusion that under rural and marine conditions, where the pH of the rain-water is above 5, it behaves as an inert pigment owing to its limited solubility. However, in industrial and urban areas, where the pH of the rain-water may be in the region of 4 or lower, it is converted into the more soluble monohydrogen phosphate. This reacts in the presence of oxygen, with the steel surface to form a mixture of tribasic zinc and ferric phosphates, which being insoluble protects the steel from further attack. 

Determination of the Solubility of Ferric Phosphate in Phosphating Solutions Using Radioiron , US Department of Commerce, Office of Technical Services, Rep. No. PB 111, 399 (1953)... 

Patented proposals have been made to heat sodium chloride with phosphoric acid (A. Delhaye) zinc or lead pyrophosphate (L. J. F. Margueritte) or ferric phosphate (A. R. Arrott). The resulting soluble sodium phosphate is decomposed by boiling with lime to form sodium hydroxide, which, if needed, can be converted into carbonate by a current of carbon dioxide. These methods are quite impracticable. In 1809, J. L. Gay Lussac and L. J. Thenard proposed to make soda by the action of steam on a mixture of sodium chloride and silica If these two compounds are melted together there is very little action, for the salt volatilizes before anything but a superficial combination takes place, and the action of salt in the glazing of pottery is probably made possible by the aq. vapour in the furnace gases. The sodium silicate formed by the joint action of sodium and... 

Ferric Phosphate occurs as a yellow-white to buff colored powder. It contains from one to four molecules of water of hydration. It is insoluble in water and in glacial acetic acid, but is soluble in mineral acids. 

The resulting salt, whilst readily soluble in dilute mineral acids, is insoluble in cold acetic acid, phosphoric acid, and sodium phosphate. It is slightly soluble in citric and tartaric acid solutions, and readily dissolves m neutral aqueous ammonium citrate, yielding a green solution with a brownish tint.3 The salt is insoluble in water, but hot water hydrolyses it, and boiling with excess of ammonia solution converts it into a mixture of ferric hydroxide 4 and ferric phosphate, or if the ammonia is present in great excess the ferric phosphate may be entirely decomposed. Thus —... 

Thus in contact with aluminium and ferric phosphates, the aluminium and ferric ion concentrations are reduced and so the phosphate ion concentration is increased to maintain the solubility product at their constant levels. AIPO4 represents various hydrated and hydroxyl phosphates of aluminium, including any adsorbed or precipitated surface layers on oxides and alumino-silicates. FePO similarly, represents various hydrated and hydroxyl phosphates of iron including adsorbed or precipitated surface layers on iron oxide. 

Ferric Phosphate—(Pe,)(PO,),—301.8—is produced by the action of an alkaline phosphate on ferric chloride. It is soluble in HCI, HNO, citric and tartaric acids, insoluble in phosphoric acid an[Pg.129]

Phosphates.—Triferrous Phosphate—Fes(P04)3—857.7.—A white precipitate, formed by adding disodic phosphate to a solution of a ferrous salt, in presence of sodium acetate. By exposure to air it turns blue a part being converted into ferric phosphate. The ferri phosphas (Sr.) is such a mixture of the two salts. It is insoluble in HsO sparingly soluble in HsO containing carbonic or acetic acid. 

HiS levels in pore waters. In these locations, Fe phosphate minerals may control Fe solubility. The combination of laboratory equilibration studies and pore water solute concentration measurements led Martens et al., for example, to conclude that deep pore waters were in equilibrium with vivianite -F63P04 8H2O - in a coastal sediment. Hyacinthe et al. found that iron was sequestered as an Fe(iii) phosphate in low-salinity, estuarine sediments. This ferric phosphate may have been formed in surface sediments (see below) or in the water column. 

Ferric casse is also affected by pH. Indeed, iron has a degree of oxidation of three and prodnces soluble complexes with molecules such as citric acid. These complexes are destabilized by increasing pH to prodnce insolnble salts, snch as ferric phosphates (see white casse ) or even ferric hydroxide, Fe(OH)3. 

Phosphorus solubility is also directly affected by the changes in redox potential (Patrick, 1964). In well-drained mineral soils, some of the inorganic P is bound to oxidized forms of iron such as iron oxyhydroxides. Ferric phosphate is a common phosphate compound in these systems. Similarly, in oxidized portions of mineral wetland soils, some of the inorganic phosphorus is also present as ferric phosphate. The mineral form of FeP04 is called strengite. 

Under oxidized conditions in mineral wetland soils, the coating of hydrated ferric oxides on silt or clay particles have occluded in them several forms of phosphate including ferric phosphate, aluminum phosphate, and calcium phosphate (Figure 9.32). As a result of anaerobic conditions, reduction of hydrated ferric oxide to more soluble ferrous hydroxide results in the release of these occluded phosphates. Calcium phosphate released in this manner is available to wetland plants, whereas the occluded ferric phosphate is probably not available to the plants until it has been reduced to more soluble ferrous phosphate. 

It is well established that iron reduction is coupled to soluble phosphorous release in soils dominated by iron redox couples (Figure 10.32) (see Chapter 9 for details). Although phosphorous itself is not normally involved in redox reactions, it does undergo reactions that have a pronounced effect on its reactivity. Most of this change in the reactivity of phosphorous in wetland soils and aquatic sediments is associated with the oxidation-reduction of iron and manganese. The reduction of ferric phosphate compounds results in the release of phosphorous, a major solubility mechanism in wetlands and aquatic systems. 

Ferric salts form brown compounds with nitrosonaphthol and thus interfere with the test for cobalt. Although iron nitrosonaphthol is soluble in acids, the precipitate dissolves quite slowly when it has been deposited in the pores of filter paper. In the presence of iron, it is best to precipitate the phosphates on filter paper and then to add the reagent. The yeUow-white ferric phosphate does not react with the nitrosonaphthol, whereas cobalt phosphate reacts instantaneously. 

Just as in the case of difficultly soluble metals, sulfides, and oxides, almost all other insoluble bodies may be obtained in the colloidal form. Of importance are the colloidal salts, which may be prepared either as hydrosols or hydrogels. Graham obtained colloidal copper ferrocyanide by dissolving the brown precipitate in ammonium oxalate, and subsequent dialysis. He also prepared colloidal Prussian blue by a similar method. Schneider f obtained a hydrosol of ferric phosphate, Lottermoser and E. v. Meyer J colloidal silver halides, while Lotter-moser has made a whole series of hydrosols of difficultly soluble salts. Recently the number of these hydrosols has been greatly increased by the work of von Weimam. ... 

Inorganic and (possible but unlikely) organic phosphorus that is absorbed onto particles or is otherwise out of solution in sea water but which becomes soluble and reacts with acid molybdate in 5 min. Such material includes calcium and ferric phosphates and any phosphate from plant cells. It can be appreciable in sea water. 

In the double-neutralization process, Na2SiFg is precipitated and removed by filtration at a pH of 3—4 (9). Upon raising the pH to 7—9, insoluble phosphates of Fe, Al, Ca, and Mg form and separate. Iron can be precipitated as hydrous ferric oxide, reducing the phosphate loss at the second filter cake. Both the fluorosihcate and metal phosphate filter residues tend to be voluminous cakes that shrink when dewatered recovery of soluble phosphates trapped within the cakes is difficult. 

Typically, mammalian ferritins can store up to 4500 atoms of iron in a water-soluble, nontoxic, bioavailable form as a hydrated ferric oxide mineral core with variable amounts of phosphate. The iron cores of mammalian ferritins are ferrihydrite-like (5Fe203 -9H20) with varying degrees of crystallinity, whereas those from bacterioferritins are amorphous due to their high phosphate content. The Fe/phosphate ratio in bacterioferritins can range from 1 1 to 1 2, while the corresponding ratio in mammalian ferritins is approximately 1 0.1. 

---