Precipitates iron oxide

The fixed-bed catalyst is a siUca-based extmdate containing precipitated iron oxide promoted with potassium and copper. The catalyst is activated by hydrogen reduction of most of the iron cataly2ed by small amounts of copper. As the catalyst is used, additional reduction occurs and Hagg carbide [12127 5-6] Fe C2, is formed. 

Pretreatment For most membrane applications, particularly for RO and NF, pretreatment of the feed is essential. If pretreatment is inadequate, success will be transient. For most applications, pretreatment is location specific. Well water is easier to treat than surface water and that is particularly true for sea wells. A reducing (anaerobic) environment is preferred. If heavy metals are present in the feed even in small amounts, they may catalyze membrane degradation. If surface sources are treated, chlorination followed by thorough dechlorination is required for high-performance membranes [Riley in Baker et al., op. cit., p. 5-29]. It is normal to adjust pH and add antisealants to prevent deposition of carbonates and siillates on the membrane. Iron can be a major problem, and equipment selection to avoid iron contamination is required. Freshly precipitated iron oxide fouls membranes and reqiiires an expensive cleaning procedure to remove. Humic acid is another foulant, and if it is present, conventional flocculation and filtration are normally used to remove it. The same treatment is appropriate for other colloidal materials. Ultrafiltration or microfiltration are excellent pretreatments, but in general they are... 

Second, oxygen attacks the metal directly by precipitating iron oxide at the anode, thus, preventing anodic polarization by Fe ions. 

How organisms induce oxide formation depends upon the degree to which iron participates in their physiological processes. Organisms which precipitate iron oxides extracellularly are either autotrophic or heterotrophic. Autotrophic organisms obtain energy for metabolism by oxidation of Fe . This biotic oxidation reaction is... 

Dixon, J.B. (1997) Seasonally precipitated iron oxides in a vertisol of Southeast Texas. Soil Sci. Soc. Am. J. 61 958-964... 

Henry prepared sodium and potassium bromides by boiling ferrous bromide respectively with potassium or sodium carbonate until the precipitate is brown the clear liquid was then filtered and evaporated. J. Knobloch recommended treating a mixture of ferrous bromide with milk of lime, and then with potassium sulphate if potassium bromide is desired, or with Glauber s salt if sodium bromide is to be made. The mixture is then to be boiled, the precipitated iron oxide filtered off, and the soln. evaporated, for cubic crystals of potassium bromide. This is the principle of the method employed for manufacturing potassium bromide on a large scale ... 

Figure 19.3 Synthesis gas conversion as a function of time for the precipitated iron oxide catalyst pretreated with CO (weight = 72.7 g, Sg = 32 m2 g ). O, CO , H2 O, CO + H2.

The catalytic activity for Fischer-Tropsch synthesis of the Fe-carbides (Fe2C and Fe7C3) produced by laser pyrolysis has been evaluated and compared to that of a precipitated iron oxide catalyst. Details of the results of these studies are the subject of chapter 19 of this book.35... 

Figure 19.5 XRD results for the precipitated iron oxide catalyst at various times of the CO pretreatment and Fischer-Tropsch Synthesis (1-Fe304, 2-x-Fe5C2, 3-e -Fe22C).

The oxides of iron, bismuth, copper, cerium, and magnesium are capable of exerting an appreciable influence on the rate of decomposition,7 but much depends on the physical condition of the solid, freshly precipitated iron oxide, for example, being more effective than the ignited substance 8 aluminium hydroxide is rather exceptional in behaving as a negative catalyst and retarding the decomposition. 

The rapid precipitation of iron oxides close to the vents has a strong effect on the behavior of REE. The freshly precipitated iron oxides exhibit a very strong absorption of the REE, so that, despite the fact that vent fluids have perhaps 10 times the REE content of seawater, these are all removed close to the vents and the hydrothermal emission actually produces a net removal of REE from seawater (Mitra et al., 1994). Thus, at least in today s high-02 oceans, the REE signature of the seawater-hydrothermal systems is not transferred to the bulk seawater. The hydrothermal signature... 

Various explanations have been offered for the mechanism of the formation of the carbon dioxide and of the ethane which has also been obtained in certain cases. None of these are entirely free from objections. Aldehydes are known to condense to esters under certain conditions and the decarboxylation of such has been offered as one explanation. However, the presence of carbon dioxide by this mechanism has not been supported by the evidence of other products of ester decomposition. Methane formation has not been reported in all cases where carbon dioxide has been found and this, together with the fact that entirely inadequate amounts of carbon have been found, seems to point that the rupture of acetaldehyde to C -+- C02 instead of carbon monoxide does not occur. The decomposition of aldehyde alone in the presence of precipitated iron oxide at 400° C. gave 40 per cent carbon dioxide and a large quantity of resinous matter.70 In the presence of reduced nickel, however, no carbon dioxide was formed and no resinous matter or oil resulted although nickel is an active catalyst for aldehyde decomposition. 

Procedure To 5 ml of dilute aqueous ethanol solution four drops of hydrogen peroxide (12%) and 0.5 ml of 4% ferrous ammonium sulfate are added and allowed to stand for 10 min. A few drops of piperidine are then added and the solution is filtered to get rid of the precipitated iron oxides. Three drops of the 3% sodium nitroprusside solution are added to the filtrate to give a blue color (39). 

---