Hydrous ferric oxide hydroxide

As an example of an equilibrium calculation accounting for surface complexation, we consider the sorption of mercury, lead, and sulfate onto hydrous ferric oxide at pH 4 and 8. We use ferric hydroxide [Fe(OH)3] precipitate from the LLNL database to represent in the calculation hydrous ferric oxide (FeOOH /1H2O). Following Dzombak and Morel (1990), we assume a sorbing surface area of 600 m2 g-1 and site densities for the weakly and strongly binding sites, respectively, of 0.2 and 0.005 mol (mol FeOOH)-1. We choose a system containing 1 kg of solvent water (the default) in contact with 1 g of ferric hydroxide. 

As pH rises, the metal content of drainage water tends to decrease. Some metals precipitate directly from solution to form oxide, hydroxide, and oxy-hydroxide phases. Iron and aluminum are notable is this regard. They initially form colloidal and suspended phases known as hydrous ferric oxide (hfo, FeOOH n O) and hydrous aluminum oxide (HAO, AlOOH nH.2O), both of which are highly soluble under acidic conditions but nearly insoluble at near-neutral pH. 

In surface precipitation cations (or anions) which adsorb to the surface of a mineral may form at high surface coverage a precipitate of the cation (anion) with the constituent ions of the mineral. Fig. 6.9 shows schematically the surface precipitation of a cation M2+ to hydrous ferric oxide. This model, suggested by Farley et al. (1985), allows for a continuum between surface complex formation and bulk solution precipitation of the sorbing ion, i.e., as the cation is complexed at the surface, a new hydroxide surface is formed. In the model cations at the solid (oxide) water interface are treated as surface species, while those not in contact with the solution phase are treated as solid species forming a solid solution (see Appendix 6.2). The formation of a solid solution implies isomorphic substitution. At low sorbate cation concentrations, surface complexation is the dominant mechanism. As the sorbate concentration increases, the surface complex concentration and the mole fraction of the surface precipitate both increase until the surface sites become saturated. Surface precipitation then becomes the dominant "sorption" (= metal ion incorporation) mechanism. As bulk solution precipitation is approached, the mol fraction of the surface precipitate becomes large. 

Me, metal cation HFO, hydrous ferric oxide or ferric hydroxide am, amorphous. 

In laboratory conditions hydrolysis usually is carried out as follows a solution of FeClj is added drop by drop to distilled water heated to boiling, stirring constantly. The whole liquid quickly takes on the red-brown color characteristic of hydrous ferric oxide, but remains transparent. If the solution is allowed to cool, the color fades somewhat, as some of the Fe(OH)3 changes back into FeCl3. To prevent the reverse reaction, the solution is boiled for a few minutes to remove HCl with water vapor, or it is removed by dialysis. In this way one obtains stable colloidal solutions of iron hydroxide containing from 5 to 5000 mg/1 of iron. 

Kuma, K., Nakabayashi, S., Suzuki, Y., and Matsunaga, K. (1992). Dissolution rate and solubihty of colloidal hydrous ferric oxide in seawater. Mar. Chem. 38, 133-143. Kuma, K., Nishioka, J., and Matsunaga, K. (1996). Controls on iron(III) hydroxide sol-... 

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. 

Hence, we see that iron hydroxide precipitate in acid solution, when the pH just exceeds 1.8 When you prepare a solution of FeCla in water, it will slowly hydrolyze to form ion hydroxide (hydrous ferric oxide), a rust-colored gelatinous precipitate. To stabilize the iron(III) solution, you must acidify the solution with, for example, hydrochloric acid. 

There is no evidence that any definite hydroxide, Fe(OH)3, exists, and the red-brown precipitate commonly called ferric hydroxide is best described as hydrous ferric oxide, Fe203 nH20. At least a part of such precipitates seems to be the FeO(OH) noted above. 

The common method for preparing a colloidal solution of hydrous ferric oxide, for example, has been to hydrolyze ferric chloride in solution by heat, and remove the hydrochloric acid by dialysis. Colloidal silica can be made in a similar way, that is, by dialyzing a solution of sodium silicate. One hydrolysis product—hydrochloric acid or sodium hydroxide—can pass through the membrane used for dialysis, whereas the colloidal particles of hydrous oxide cannot. The process is rather tedious and takes hours or even days. A much simpler method is to take out the acid or alkali with one of the solid ion exchangers or acid absorbers used in water purification. ... 

Column experiments were conducted to simulate the transport of oxoanion aquifers containing iron hydroxides. The Riedel de Haen Hfo material used in these column experiments exhibits a low specific surface area and contains a significant proportion of goethite. PHREEQC2 is equipped to model surface complexation of oxoanions onto iron hydroxides but a consistent data set of surface complexation constants is only available for amorphous hydrous ferric oxides. Tests were conducted to determine whether it is possible to use PHREEQC2 with this data set to model the oxoanion transport in the columns. If the data set of surface complexation constants is also suitable for the Riedel de Haen Hfo material than it should be sufficient to adjust the site density of the iron hydroxide surface in the model. 

Aggregation (non-crystalline) and orientation (crystalline) are both influenced by supersaturation and temperature, but the type of species is also very important. For example, strongly polar salts, such as lead iodide, silver chloride and barium sulphate, invariably precipitate in crystalline form. Carbonates of calcium and barium and hydroxides of magnesium and zinc do likewise, but there is evidence in some of these cases of the prior precipitation of hydrated short-lived precursor phases (Mullin et al., 1989 Brecevic and Nielsen, 1990). Hydrous oxides like hydrous ferric oxide (o-ferric hydroxide) are generally amorphous, especially when precipitated from cold solution. 

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... 

The almost specific test for aluminum with Chrome Fast Pure Blue B (see page 100) can be used for the rapid detection of traces of this element in water. Only 25-50 ml is required. After adding one drop of a 1 % solution of iron i chloride or sulfate, ammonium hydroxide is added and the suspension is centrifuged in portions and the precipitate thus gathered in a conical centrifuge tube. The hydrous ferric oxide acts as collector for the hydrous alumina. The precipitate on the bottom of the tube is dissolved in a drop or two of a mixture of equal volumes of 2 iV hydrochloric acid and 80 % thioglycolic acid. One drop of a 5 % water solution of the dye is added and the mixture then made basic with ammonium hydroxide. Finally, the system is acidified with 1 1 hydrochloric acid and shaken with ether. The ether layer is pink if the response is positive. 

Ferrihydrite (Fe50Hg.4H20) is common in young soil deposits but readily transforms to more stable iron hydroxides and oxides such as goethite and hematite (qq.v.). Ferrihydrite is also called amorphous iron oxide or hydrous ferric oxide, due to its disordered crystal structure the precise structure or formula of this mineral is not yet known (Schwertmann and Cornell, 2000). Ferrihydrite may be present in samples of naturally occurring raw ochres and sieimas (qq.v.) but identifications in works of art have not yet been made. 

Hydrous ferric hydroxide (HFO), for arsenic removal, 3 279, 283-285 Hydrous manganese dioxide, 15 581 Hydrous manganese oxides, 15 585... 

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... 

Manganese dioxide, sodium nickel hexacynaoferrate, hydrous titanium oxide, zirconium phosphate, ferric hydroxide, different commercial sorbents... 

Hydrous manganese oxides and amorphous iron oxides were prepared in the laboratory according to the methods described by Oakley et al 3). The addition of manganese sulfate solution to a slightly basic potassium permanganate solution produces a suspension of hydrous MnO. A suspension of Fe(0H)2 is produced by simply adjusting a ferric nitrate solution to a pH of 8.0 with a dilute sodium hydroxide solution. Both suspensions were washed repeatedly with seawater and stored in seawater for several days. 

Mixed gels of hydrous ferric and chromic oxides were prepared by the addition of an equivalent amount of ammonium hydroxide to mixtures of the solutions of ferric nitrate (0.5M with respect to Fe20j) and chromic nitrate (0.5M with respect to Cr203). The dual gels were washed free of nitrate ions and air- or oven-dried. A series of mixtures corresponding to 20, 40, 60, and 80% Fe203 was prepared. 

Materials. Colloid Particles. The ferric hydrous oxide sol was prepared by acid hydrolysis of 0.019 M FeCla solutions containing 10 M HCl over a period of three weeks at room temperature. This yielded the p form of the oxide-hydroxide (7-8), Free Fe ions were removed by repeated centrifugation. In some instances, dialysis of the sol against deionized water was also done to obtain the sol free of Fe " " ions. The structure of jSFeOOH is of hollandite type. The method of preparation gives ellipsoidal shaped particles uniform in shape and of narrow size distribution - Figure 1. The morphology was studied extensively and needs... 

Oil and hydrocarbon leaks that return with the condensate coat heat-exchange surfaces and cause FW system fouling and deposit binding. These materials must be removed or they will reenter the boiler to produce nonwettable boiler surfaces, and create serious problems. Oil in condensate should be removed by the use of an inline pre-coat filter. The pre-coating should be either aluminum hydroxide ox ferric hydroxide becaue both these hydrous oxide gels have an affinity for oil. 

Most of the zinc introduced into aquatic environments is sorbed onto hydrous iron and manganese oxides, clay minerals, and organic materials, and eventually is partitioned into the sediments (USEPA 1987). Zinc is present in sediments as precipitated zinc hydroxide, ferric and manganic... 

---