Iron ferric

It is essential to use an excess of sodium, otherwise if sulphur and nitrogen are both present sodium thiocyanate, NaCNS, may be produced in the test for nitrogen it may give a red coloration with ferric iron but no Prussian blue since there will be no free cyanide ions. With excess of sodium the thiocyanate, if formed, will be decomposed ... 

Organosulfur Compounds. These compounds, Hsted in Table 8, are used in a variety of appHcations, including cooling water, paint, and metalworking. Methylenebisthiocyanate hydroly2es rapidly at a pH above 8 to cyanate ion which complexes with ferric iron to poison the cytochrome systems (36). 

Hydrogenis prevented from forming a passivating layer on the surface by an oxidant additive which also oxidizes ferrous iron to ferric iron. Ferric phosphate then precipitates as sludge away from the metal surface. Depending on bath parameters, tertiary iron phosphate may also deposit and ferrous iron can be incorporated into the crystal lattice. When other metals are included in the bath, these are also incorporated at distinct levels to generate species that can be written as Zn2Me(P0 2> where Me can represent Ni, Mn, Ca, Mg, or Fe. 

Sulfosahcyhc acid is prepared by heating 10 parts of sahcyhc acid with 50 parts of concentrated sulfuric acid, by chlorosulfonation of sahcyhc acid and subsequent hydrolysis of the acid chloride, or by sulfonation with hquid sulfur trioxide in tetrachloroethylene. It is used as an intermediate in the production of dyestuffs, grease additives, catalysts, and surfactants. It is also useful as a colorimetric reagent for ferric iron and as a reagent for albumin. Table 9 shows the physical properties of sahcyhc acid derivatives. 

Dithionite is a stronger reducing agent than sulfite. Many metal ions, eg, Cu", Ag", Pb ", Sb ", and Bi ", are reduced to the metal, whereas TiO " is reduced to (346). Dithionite readily reduces iodine, peroxides, ferric salts, and oxygen. Some of the decolorizing appHcations of dithionite, eg, in clay bleaching, are based on the reduction of ferric iron. 

Thiocyanates are rather stable to air, oxidation, and dilute nitric acid. Of considerable practical importance are the reactions of thiocyanate with metal cations. Silver, mercury, lead, and cuprous thiocyanates precipitate. Many metals form complexes. The deep red complex of ferric iron with thiocyanate, [Fe(SCN)g] , is an effective iadicator for either ion. Various metal thiocyanate complexes with transition metals can be extracted iato organic solvents. 

Iron Absorption. A very important effect of ascorbic acid is the enhancement of absorption of nonheme iron from foods. Ascorbic acid also enhances the reduction of ferric iron to ferrous iron. This is important both in increasing iron absorption and in its function in many hydroxylation reactions (140,141). In addition, ascorbic acid is involved in iron metaboHsm. It serves to transfer iron to the Hver and to incorporate it into ferritin. 

With aluminum sulfate, optimum coagulation efficiency and minimum floe solubiUty normally occur at pH 6.0—7.0. Iron coagulants can be used successfully over the much broader pH range of 5.0—11.0. If ferrous compounds are used, oxidation to ferric iron is needed for complete precipitation. This may require either chlorine addition or pH adjustment. 

Foulants enter a cooling system with makeup water, airborne contamination, process leaks, and corrosion. Most potential foulants enter with makeup water as particulate matter, such as clay, sdt, and iron oxides. Insoluble aluminum and iron hydroxides enter a system from makeup water pretreatment operations. Some well waters contain high levels of soluble ferrous iron that is later oxidized to ferric iron by dissolved oxygen in the recirculating cooling water. Because it is insoluble, the ferric iron precipitates. The steel corrosion process is also a source of ferrous iron and, consequendy, contributes to fouling. 

Reagents similai to those used in the analysis of chloiine are commonly employed in the quantitation of gaseous and aqueous chloiine dioxide as well as its reaction coproducts chlorine, chlorite, and chlorate. The volatihty of the gas from aqueous solutions as well as its reactivity to light must be considered for accurate analysis. Other interferences that must be taken into account include other oxidizers such as chloramine, hydrogen peroxide, permanganate, and metal impurities such as ferrous and ferric iron. 

Talc and Pyrophyllite. Talc (qv) and pyrophjlhte are 2 1 layer clay minerals having no substitution in either the tetrahedral or octahedral layer. These are electrostatically neutral particles (x = 0) and may be considered ideal 2 1 layer hydrous phyUosiHcates. The stmctural formula of talc, the trioctahedral form, is Mg3Si402Q(0H)2 and the stmctural formula of pyrophylUte, the dioctahedral form, is Al2Si402Q (OH)2 (106). Ferripyrophyllite has the same stmcture as pyrophylUte, but has ferric iron instead of aluminum in the octahedral layer. Because these are electrostatically neutral they do not contain interlayer materials. These minerals are important in clay mineralogy because they can be thought of as pure 2 1 layer minerals (106). 

Glauconite. Glauconite [1317-57-3] (123—126) is a green, dioctahedral, micaceous clay rich in ferric iron and potassium. The generally accepted formula for glauconite is (Na,K)Q yg(Fe " oi o 45 o 65 35) io( )2 Glauconite has many characteristics common to iUite, but much... 

Calcium ion enters the system not ordy in the form of water hardness but also in the form of calcium salts contained in the sod. Other heavy-metal ions such as aluminum and ferric iron may also be present in the sod, and must be removed by an appropriate budder to achieve good sod removal. Effective budders for cotton washing are those for which the calcium dissociation constant, expressed as or —logif -, is >4 and preferably >7 (33). 

Metal depositors. Metal-depositing bacteria oxidize ferrous iron (Fe ) to ferric iron (Fe ). Ferric hydroxide is the result. Some bacteria oxidize manganese and other metals. Gallionella bacteria, in particular, have been associated with the accumulation of iron oxides in tubercles. In fact, up to 90% of the dry weight of the cell mass can be iron hydroxide. These bacteria appear filamentous. The oxide accumulates along very fine tails or excretion stalks generated by these organisms. 

In hydrochloric acid at temperatures up to 100°C, the corrosion rate decreases with time and ferric iron concentration . The presence of air does not affect the general corrosion rate but in IOn acid it promotes pitting attack, which also arises in chloride-containing methanolic solutions in the absence of sufficient water to effect passivation . Alloying niobium with 2.5% or more of tantalum significantly decreases corrosion rates in hydrochloric acid . 

Where a stable, passivated magnetite film exists, there is little risk of corrosion when using these products, and under normal alkaline boiler conditions (above a pH of 10.0), the chelation of ferric iron [Fe(OH)3, Fe203, Fe304] does not take place (so the protective magnetite film is not disrupted). 

NOTE Although control over transported iron is critical in larger power boilers, as discussed earlier, control by the chelation of ferric iron is not possible (because of the competing anion effect). Consequently, Fe203 and Fef04 are essentially unaffected by chelants. However, it is well known that where an iron chelate (chelonate) is formed, it is stable and will not be destroyed by hydrolysis at high temperature. 

Enterocytes in the proximal duodenum are responsible for absorption of iron. Incoming iron in the Fe " state is reduced to Fe " by a ferrireductase present on the surface of enterocytes. Vitamin C in food also favors reduction of ferric iron to ferrous iron. The transfer of iron from the apical surfaces of enterocytes into their interiors is performed by a proton-coupled divalent metal transporter (DMTl). This protein is not specific for iron, as it can transport a wide variety of divalent cations. 

The iron of Hb must be maintained in the ferrous state ferric iron is reduced to the ferrous state by the action of an NADH-dependent methemoglobin reductase system involving cytochrome reductase and cytochrome b. ... 

The quadrupole doublet has an isomer shift corresponding to iron in the ferric or Fe " state. After reduction in H2 at 675 K the catalyst consists mainly of metallic iron, as evidenced by the sextet, along with some unreduced iron, which gives rise to two doublet contributions of Fe " and Fe " in the centre. The overall degree of iron reduction, as reflected by the relative area under the bcc ion sextet, is high. Fischer-Tropsch synthesis at 575 K in CO and FI2 converts the metallic iron into the Flagg carbide, Fe5C2. The unreduced iron is mainly present as Fe ". Exposure of the carburized catalyst to the air at room temperature leaves most of the carbide phase unaltered but oxidizes the ferrous to ferric iron. 

Silverman and Dodson made the first detailed isotopic study of this exchange system using the separation afforded by the addition of 2,2 -dipyridyl at pH 5, followed by the precipitation of the ferric iron with either ammonia or 8-hydro-xyquinoline. Dodson , using this separation method, had previously obtained an overall rate coefficient of 16 l.mole" sec at 23 °C for 0.4 M perchloric acid media. The exchange in perchlorate and perchlorate-chloride media was found to conform to a rate law, first order with respect to both total ferrous and ferric ion concentrations, with an observed rate constant (k bs) dependent on the hydrogen-ion concentration, viz. 

Studies on carotenoid autoxidation have been performed with metals. Gao and Kispert proposed a mechanism by which P-carotene is transformed into 5,8-per-oxide-P Carotene, identified by LC-MS and H NMR, when it is in presence of ferric iron (0.2 eq) and air in methylene chloride. The P-carotene disappeared after 10 min of reaction and the mechanism implies oxidation of the carotenoid with ferric iron to produce the carotenoid radical cation and ferrous iron followed by the reaction of molecular oxygen on the carotenoid radical cation. Radical-initiated autoxidations of carotenoids have also been studied using either radical generators like or NBS.35... 

Wang Q, EM Scherer, AT Lemley (2004) Metribuzin degradation by membrane anodic Fenton treatment and its interaction with ferric iron. Environ Sci Technol 38 1221-1227. 

Seeliger S, R Cord-Ruwisch B Schink (1998) A periplasmic and extracellular c-type cytochrome of Geobacter sulfurreducens acts as a ferric iron reductase and as an electron carried to other acceptors or to partner bacteria. J Bacteriol 180 3686-3691. 

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