Iron 3 , solubility

In the absence of sufficient hydrogen, the solubility of magnetite is markedly temperature dependent, which provides an explanation for some of the problems in high-temperature circuits. Most studies in boilers relate to high temperatures. Thus the work of Bloom " and of Potter and Mann has reproduced the types of corrosion found in high-pressure boilers. The relationship between corrosion rates and iron solubility and pH are given in Fig. 17.2. Note that the pH range about the neutral point (relative to 300 C... 

We were quite elated, and it appeared that it was a rich field. Now, fifty years later, I must say that it wasn t as rich as we thought. But we have over the years discovered half a dozen natural radioactive elements, and two of these, the samarium-147 with its decay to neodymium-143 and rhenium-187 with its decay to osmium-187, prove to be of use in Nuclear Dating. The importance of rhenium is that it is iron soluble while the other radioactivities are insoluble in metallic iron. In fact, the best half life we have for rhenium-187 was obtained by measuring the osmium-187 to rhenium-187 ratio in iron meteorites which had been dated by other methods. This work was started many years ago by Dr. Herr and others in Germany. The half life is 43,000,000,000 years. 

Oxide/hydroxide minerals of Mn(III,IV), Fe(III), Co(III), and Pb(IV) are thermodynamically stable in oxygenated solutions at neutral pH, but are reduced to divalent metal ions under anoxic conditions in the presence of reducing agents. Changes in oxidation state dramatically alter their solubility. Reduction of Fe(III) to Fe(II), for example, increases iron solubility with respect to oxide/ hydroxide phases by as much as eight orders of magnitude (1). 

Although the details of the equilibrium model are still uncertain, the general trends are likely reliable. As shown in Figme 5.16, most of the Fe(III) in seawater is predicted to be in the form of the FeL complex. The equilibrium model also predicts that this degree of complexation should enhance iron solubility such that 10 to 50% of the iron delivered to the ocean as dust will eventually become dissolved if equilibrimn is attained. If this model is a reasonable representation for iron speciation in seawater, uptake of [Fe(III)]jQjgj by phytoplankton should induce a spontaneous dissolution of additional particulate iron so as to drive the dissolved iron concentrations back toward their equilibrium values. 

Diakonov, G.G. Schott, J. Martin, F. Harri-chourry, J.-C. Escalier, J. (1999) Iron solubility and separation in aqueous solutions. Ex-... 

The availability of iron as a nutrient for phytoplankton growth is dependent on its chemical speciation (Wells et al., 1995). Thus processes which alter iron solubility in the atmospheric aerosols have the potential to influence bioavailability... 

Iron-nickel alloys are known to dissolve in the aluminium melts non-selectively. " As seen from Table 5.3, during dissolution of a 50 mass % Fe-50 mass % Ni alloy the ratio, cFe cNi, of iron to nickel concentrations in the melt is 1.00 0.05, i.e. it is equal to that in the initial solid material. The same applies to other alloys over the whole range of compositions. Respective saturation concentrations are presented in Table 5.4. The data obtained display a strong mutual influence of the elements on their solubilities in liquid aluminium because in its absence the solubility diagram for a constant temperature would be like that shown by the dotted lines in Fig. 5.5, with the eutonic point, E, at 2.5 mass % Fe and 10.0 mass % Ni. The effect of iron on the nickel solubility is seen to be more pronounced than that of nickel on the iron solubility. 

Iron solubility is an obvious factor in Fenton oxidation because the rate of hydroxyl radical formation is directly proportional to [Fe2+]. At elevated pH values, iron hydroxides and oxides form and precipitate, causing a dramatic decrease in hydroxyl radical formation rate. Iron chelators can be used to offset this factor. A related issue is the rate of Fe3 + reduction to Fe2+, which, if insufficient, can result in Fe2+ concentrations that are too low to... 

Iron speciation is a major factor in Fenton chemistry. As previously discussed, iron solubility, redox potentials, and concentrations of Fe2+ and Fe3+ are all dependent on the ligands that coordinate iron. In order to produce hydroxyl radical, there must be a readily accessible coordination site for H202 to bind to [9,10]. Very strong iron chelators, therefore, inhibit the formation of hydroxyl radical. Iron ligands can also act as hydroxyl radical scavengers. Because the radical is always formed in close proximity to these ligands, they are more likely to react with hydroxyl radical than pollutants that are not in close proximity to the iron. 

Ferric mycobactin T obtained as an amorphous solid containing 5.8% iron. Soluble in chloroform and extractable with ether. Absorption maxi-... 

Copper ferrites have been included in the model, but have as yet not been found to be equilibrium controls on copper or iron solubility. The calculated activity products for the two minerals, cuprous ferrite and cupric ferrite, are characteristically several orders of magnitude oversaturated when compared to their respective equilibrium constants in a wide variety of surface waters. 

Properties (free acid) Liquid. Bp 185-190C (760 mm Hg), 90-92C (14 mm Hg), d 1.389 (22.8 4C). Very soluble in water and alcohol soluble in ether, (sodium salt) Crystals salty taste. Decomposes 174—176C. Corrosive to iron. Soluble in water aqueous solutions hydrolyze above 70C. 

Properties Crystals characteristic odor hygroscopic discolors on exposure to air or iron. Soluble in water slightly soluble in alcohol. Combustible. 

This pattern of complexation and precipitation behavior is qualitatively similar for all metal ions that complex readily with humus and hydrolyze to form insoluble hydroxides or oxides. For example, Fe complexed by humus at very low pH is probably bonded by polyphenols but as the pH is raised, precipitation of Fe(OH)3 reduces iron solubility and strips Fe from organic matter complexes. 

Anaerobic organisms are able to use oxidized chemical species such as nitrate (NO ) as electron acceptors in place of molecular oxygen. Consequently, microbial reduction of nitrate to N2 (a process termed denitrification ) occurs in the early stages of soil reduction, as does Mn oxide reduction to Mn. Reduced species such as nitrite (NO ) and Mn then appear in solution. As more extreme reducing conditions develop, ammonium (NH ) accumulates from nitrogen reduction reactions, and iron solubility increases in the form of Fe. The elevated iron and manganese solubility is ultimately limited by precipitation of the rather insoluble carbonates of Fe (siderite) and Mn (rhodochrosite) if the soil pH is not too low ... 

Consistent with the role of iron as a limiting nutrient in EINLC systems is the notion that organisms may have evolved competitive mechanisms to increase iron solubility and uptake. In terrestrial systems this is accomplished using extracellularly excreted or membrane-bound siderophores. Similar compounds have been shown to exist in sea water where the competition for iron may be as fierce as it is on land. In open ocean systems where it has been measured, iron-binding ligand production increases with the... 

Wells should not be located in the zone where iron solubility is governed by FeC03(s). since they will produce a water that is unacceptably high in iron. 

Emulsion droplet charge can be an important factor in l id oxidation rates in oil-in-water emulsions, as well as in other lipid dispersions. When com oil-in-water emulsions are prepared with anionic (sodium dodecyl sulfate SDS), cationic (dodecyltrimethylammonium bromide DTAB) or nomonic (Brij 35) surfactants, iron-promoted lipid oxidation is in tiie order of SDS>Brij 35>DTAB (13). The prooxidant activity of iron in the SDS-stabilized emulsions increased at low pH (3.0) where iron solubility increases. The high... 

Efflorescence. Pitting and spalling of clay products and natural stones is associated with efflorescence, a phenomenon in which salts percolate through the member and crystallize on the surface of a brick, stone, or mortar joint. These salts may be the sulfates of calcium, magnesium, sodium, potassium, and, in some cases, iron. Soluble salts may be present in the clay, or they may be formed by the firing process (oxidation of pyrites, or reaction of sulfurous fuel gases with carbonates in the clay). 

Depending on the prior coal treatment, the sulfur value from the ultimate analysis may include all three of them. Various methods are available for ultimate sulfur determination (e.g., ASTM D-4239 [38], ISO 334 [39]). All are based on the combustion of the sulfur to produce a sulfete, which is measured gravi-metrically or volumetrically. Even x-ray fluorescence can be used to determine the total sulfur. To differentiate between the types of sulfur (ASTM D-2492 [40], ISO 157 [41]), the coal sample is treated with dilute HCl solution in which only sulfete sulfur is soluble. The pyrite sulfur is determined by subtracting the amount of soluble iron in dilute HCl from the amount of iron soluble in HNO3. From this difference, the quantity of FeS2 can be calculated. Together with the total sulfur, the organic sulfur can be determined by difference. Also x-ray spectroscopy can proof the chemical state of the sulfur in the coal. 

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