Hydrous ferrous oxide

Pure Fe(OH)2 can be obtained only in the total absence of oxygen in highly reducing conditions. It is a bulky white precipitate which oxidizes rapidly in air to red-brown Fe(OH)3 the intermediate products of oxidation are of a dirty green hue. The rare mineral amakinite occurs in nature, and formation of Fe(OH)2 has been noted in bottom sediments (Stashchuk, 1968). 

Comparison of the solubility of hydrous ferrous oxide made in the summary work by Feitknecht and Schindler (1963) makes it possible to calculate the values of the isobaric potentials of formation of precipitates (AGf298 kcal/mol)  

Thermodynamic analysis shows that amakinite is a stable phase with respect to iron oxides and liquid water. The low solubility of Fe(OH)2 in nature is explained by its replacement by siderite, iron silicates and sulfides, and also by extreme ease of oxidation in the presence of traces of free oxygen. 

Approximate values of Gf 29 of iron carbonate sediments are (in kcal/mol)  

The constants of fayalite that we recommended earlier, based on experimental investigations of low-temperature equilibria (Teruo and Yukiyoshi, 1962), have been slightly revised in connection with refinement of the constants of Fe, Oj and SiOj. The values obtained for the isobaric potentials are close to the tabulated vdues (Robie and Waldbaum, 1968). 

---

More reduced forms of oxide are present beneath the rust layer. Hydrous ferrous oxide (Fe0 nH20), that is, ferrous hydroxide [Fe(OH)2l... 

HELP HEU HFO HFR HLW HREE HRL HT HTGR HWR Hydrological evaluation of landfill performance Highly enriched uranium Hydrous ferrous oxide or ferric hydroxide Hot fractured-rock High-level nuclear waste Heavy rare earth elements (Gd-Lu) Hard rock laboratory High temperature High-temperature gas-cooled reactor Heavy water reactor... 

Since the rate of the oxide reduction is usually greater than the rate of the oxygen reduction on metallic iron, the corrosion rate of iron in the presence of the redox oxide is greater than that in the absence of the redox oxide. It is in fact an accepted understanding that the presence of hydrous ferric oxide accelerates the corrosion of mild steels forming hydrous ferrous oxide. The ferrous oxide thus formed is then oxidized to ferric oxide again by atmospheric oxygen. 

Hydrous ferrous oxide (Fe0 nH20) or ferrous hydroxide [Fe(OH)2] composes the diffusion-barrier layer next to the iron surface through which O2 must diffuse. The pH of saturated Fe(OH)2 is about 9.5, so that the surface of iron corroding in aerated pure water is always alkaline. The color of Fe(OH)2, although white when the substance is pure, is normally green to greenish black because of incipient oxidation by air. At the outer surface of the oxide film, access to dissolved oxygen converts ferrous oxide to hydrous ferric oxide or ferric hydroxide, in accord with... 

Within the range of about pH 4-10, the corrosion rate is independent of pH and depends only on how rapidly oxygen diffuses to the metal surface. The major diffusion barrier of hydrous ferrous oxide is continuously renewed by the corrosion process. Regardless of the observed pH of water within this range, the... 

On the other hand, some investigators, using different natural waters and different chemicals to control pH, have observed that the corrosion rate does change with pH in the pH range 6-9. This behavior has been attributed to reduced buffer capacity of HCOi (an inhibitor) as pH increases, causing a pH at local sites that is lower than the pH that would otherwise exist in a solution of saturated hydrous ferrous oxide. The reader may wish to consult the review by Matsushima on this matter... 

Fe203 H20 or hydrous ferrous oxide, sometimes written as Fe(OH)3, is the principal component of red-brown rust. It can form a mineral called hematite, the most common iron ore. 

Rusting (rust) corrosion of iron or ferrous alloys resulting in a corrosion product which consists largely of hydrous ferric oxide. 

Reactions between Fe(ll) in contaminated groundwater (5.8 mg/L) and oxic sediment also affected As mobility. Ferrous iron was oxidized by manganese oxides to ferric iron which precipitated as hydrous ferric oxide, creating additional sorption sites. Evidence for this reaction included an increase in ferric oxide concentrations in reacted column sediments and manganese concentrations in leachate that were greater than in the initial eluent. 

Charlet, L. Manceau, A.A. (1992a) X-ray absorption spectioscopic study of the sorption of Cr(III) at the oxide/water interface. II. Adsorption, coprecpitation, and surface precipitation on hydrous ferric oxide. J. Colloid Interface Sd. 148 443-458 Charlet, L. Manceau, A.A. (1992) X-ray absorption spectroscopic study of the sorption of Cr(III) at the oxide-water interface. J. Colloid Interface Sd. 148 425-442 Chatellier, X. Fortin, D. West, M.M. Leppard, G.G. Ferris, F.G. (2001) Effect of the presence of bacterial surfaces during the synthesis of Fe oxides by oxidation of ferrous ions. Fur. J. Mineral. 13 705-714 Cheetham, A.K. Fender, B.E.F. Taylor, R.I. (1971) High temperature neutron diffraction study of Fei. O. J. Phys. C4 2160-2165 Chemical Week (1988) Glidderfs anti rust secret is out." 15 10... 

Ferrous Oxide (Hydrous) A hydrated, jet black product of iron corrosion, FeO nH20. 

Metal hydroxides in general are anion-selective in acid solution and turn to be cation-selective beyond a certain pH, called the point of the iso-selectivity, pHpjS it is pHpjS = 10.3 for ferric oxide and pHpis = 5.8 for ferric-ferrous oxide [72]. Adsorption of multivalent ions may also control the ion selectivity of hydrous metal oxides because of its effect on the fixed charge in the oxides. For instance, hydrous ferric oxide, which is anion-selective in neutral sodium chloride solution, turns to be cation-selective by the adsorption of such ions as divalent sulfate ions, divalent molybdate ions, and trivalent phosphate ions [70,73]. It is worth emphasizing that such an ion-selectivity change due to the adsorption of multivalent ions frequently plays a decisive role in the corrosion of metals. 

Let us consider a hydrous ferric-ferrous oxide layer, which is sensitive to the reduction-oxidation reaction on the surface of corroding metallic iron ... 

Rusting (13c) v. Corrosion on the surface of iron or ferrous metals resulting in the formation of products consisting largely of hydrous ferric oxide. 

The aqueous chemistry of iron is also important in a number of other settings. Iron can be the dominant cation released in acid rock drainage, due to the oxidation of pyrite (FeS2(s)) when it becomes exposed to air and water. This process is catalysed by bacteria which cycle ferrous iron back to ferric iron which, in turn, can oxidise further pyrite. Thus, the rate of oxidation will depend on the aqueous concentration of ferric iron. If insufficient iron (and acid) is produced or the iron is removed by the inherent neutralisation capacity of the material, the rate of oxidation will be substantially reduced. The precipitation of iron oxyhydroxide phases and their ability to adsorb other aqueous elements have also been studied in detail (Dzombak and Morel, 1990). The removal of arsenic from drinking water by hydrous iron oxides is one example of these adsorption reactions. 

After the water was collected in the reaction vessel, 288 ppm ferrous sulfate was added. Addition of a stoichiometric quantity (100 ppm) of potassium permanganate thus resulted in formation of hydrous ferric and manganese oxides. Scavenging eflBciencies for this precipitation reaction have been reported previously (5, 6). The resulting suspension was agitated for 10-20 min and allowed to settle for 12-24 hr, after which the supernatant hquid was siphoned. The precipitate was removed and... 

---