Solubility ferrous phosphate

Fig. 6-23. Experimental data on solubility product of ferrous phosphate. From P. C. Singer, /. Wafer Pollution Control Fed., 44 663 (1972). 1972 Water Pollution Control Federation, reprinted with permission.

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. 

Sequential reduction of electron acceptors can have a significant effect on soluble phosphorus release. After a soil is flooded, it is expected that the amount of soluble P will increase. This is attributed to the anaerobic conditions occurring in the flooded soil and the various mechanisms of releasing phosphorus under those conditions. As shown in Figure 9.58, the amount of soluble phosphorus starts increasing after the third day of inundation, when almost the entire nitrate pool has been reduced, and consequently the reduction of manganese and iron contained in oxide minerals is already in process. On reduction of ferric oxide minerals, water-soluble and exchangeable concentrations of ferrous iron increase markedly. Thus, the dissolution of iron minerals is accompanied by increases in concentrations of both adsorbed and water-soluble phosphorus. Some of the ferrous ions react with the released phosphorus and precipitate to form new ferrous phosphate minerals. As the soil continues to be under anaerobic conditions, ferric ions are soon depleted and the reduction... 

Schematic of key chemical transformations that may occur on the addition of iron-based coagulant to a MBR (Wang and Waite, 2010). Addition of inorganic Fe(lll) salts will result in either precipitation as amorphous ferric oxide (AFO) (reaction b), complexation by soluble microbial products (SMPs) (reaction c) or reduction to Fe(ll) (reaction j). Fe(lll) in both inorganic (as AFO) and SMP-bound forms (as Fe(lll)SMP) may undergo reduction (especially in the low Eh (<-0.2 mV) anoxic region (reactions e, a and j). Any Fe(ll) present may be oxidized (especially in the aerated oxic compartment) (reactions i and f). Fe(ll) may form insoluble precipitates such as ferrous phosphate or vivianite (reaction k). 

Iron absorption occurs predominantly in the duodenum and upper jejunum. The physical state of iron entering the duodenum greatly influences its absorption. At physiological pH, ferrous iron is rapidly oxidized to the insoluble ferric form. Gastric acid lowers the pH in the proximal duodenum, enhancing the solubility and uptake of ferric iron. When gastric acid production is impaired, iron absorption is reduced substantially. Ascorbic acid enhances iron absorption. Ascorbic acid mobilizes iron from iron-binding proteins in vivo, which in turn could catalyze lipid peroxidation. Iron absorption is inhibited by antacids, phytates, phosphates and tetracyclines. 

When a ferrous alloy is immersed in phosphoric acid, il initially forms a soluble phosphate. As the pH rises at the mclal/solutiun interface, the phosphate becomes insoluble and crystallizes epitaxially on Ihe substrate metal. The phosphate coating thus produced consists of a nonconduciivc layer nf crysinlx that insulates the metal from any subsequently applied film and provides a topography with enhanced tooth" for increased adhesion. The cry stals insulate microanode and microcathode centers caused by stress or imperfections in the metal surface. This greatly reduces Ihe severity of electrochemical corrosion. 

In subsequent experiments, using other crystal systems, such as ferrous sulfate and sodium hydrogen phosphate, it was similarly observed that the first crystallization product to form was the one most closely resembling the structure of the solvent (Nyvlt, 1995). For the case of citric acid, this is the monohydrate, which more closely resembles the aqueous structure. As the temperature of the solution is increased, the structure of the solvent, as well as the solubility of the crystal, changes, resulting in a more thermodynamically stable anhydrous product. This conversion between the kinetic and thermodynamic product occurs at a critical transition temperature, below which the structure of the solution favors the formation of the hydrated product. As the transition temperature is surpassed, the anhydrous product becomes favored. 

Iron absorption takes place predominantly in the duodenum where the acid environment enhances solubility, but also throughout the gut, allowing sustained-release preparations to be used. Most iron in food is present as ferric hydroxide, ferric-protein complexes or haem-protein complexes. Ferrous (Fe " ) iron is more readily absorbed than ferric (Fe ). Thus the simultaneous ingestion of a reducing agent, such as ascorbic acid, increases the amount of the ferrous form ascorbic acid 50 mg increases iron absorption from a meal by 2-3 times. Food reduces iron absorption due to inhibition by phytates, taimates and phosphates. 

Iron bioavailability is affected by valence state, form, solubility, particle size, and com-plexation which in turn may be affected by the food matrix. Complexation of iron has been found to have either a positive or negative effect on availability, with such compounds as ascorbic acid and fructose increasing availability and oxalates, phytates, phosphates and food fibers perhaps decreasing availability. Availability has also been shown to be directly correlated to acid solubility. We have found that acidity tends to increase ionization as well as favoring the ferrous state which has greater solubility at... 

Under well drained conditions, iron in soil, unless chelated, is insoluble and tends to be concentrated through weathering as the more soluble ions are removed. In poorly drained soils, iron is reduced to the soluble ferrous state and is either removed from the soil or precipitated as sulfide, phosphate, or carbonate minerals. Other processes, such as chelation, are also effective in mobilizing the iron in the soil profile. The bulk of secondary iron in soils is in the oxide forms. 

CCRIS 4661 EINECS 248-848-2 HSDB 6795 Isopropylphenyl diphenyl phosphate Kronitex 100 Phosflex 41P Phosphoric acid, (l-methylethyl)phenyl diphenyl ester Syn-O-Ad 8460, Antiwear and EP agents in non-crankcase lubricants ferrous metal passivator fluid base stock where inhibition of flame propagation is desired. Insoluble in H2O, soluble in organic solvents, Akzo Chemie. 

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