Iron phosphate adsorption

Brewer and Spencer [428] have described a method for the determination of manganese in anoxic seawaters based on the formulation of a chromophor with formaldoxine to produce a complex with an adsorption maximum at 450 nm. Sulfide (50 xg/l), iron, phosphate (8 ig/l), and silicate (100pg/l) do not interfere in this procedure. The detection limit is 10 pg/1 manganese. 

Magnetic separation (after precipitation as iron phosphate or after adsorption to magnetite)... 

Atkinson, R.J. (1976) The formation of iron(III) oxide hydroxides from iron(III) oxalate. Aust. J. Chem. 29 2149-2158 Atkinson, R.J. Parfitt, R.L. Smart, R.S.C. (1974) Infrared study of phosphate adsorption on goethite. J. Chem. Soc. Earaday Trans. I. 70 1472-1479... 

Borggaard, O.K. (1983) Effect of surface area and mineralogy of iron oxides on their surface charge and anion-adsorption properties. Clays Clay Min. 31 230-232 Borggaard, O.K. (1983 a) The influence of iron oxides on phosphate adsorption by soil. J. 

Raben-Lange, B. (1990) Influence of organic matter on phosphate adsorption by aluminium and iron oxides in sandy soils. J. Soil Sci. 41 443-449... 

J. Electrochem. Soc. 114 994-1000 Fontes, M.P.F. Weed, S.B. (1991) Iron oxides in selected Brazilian oxisols I. Mineralogy. Soil Sd. Soc. Am. J. 55 1143-1149 Fontes, M.P.F. Weed, S.B. (1996) Phosphate adsorption by days from Brazilian oxisols relationships with specific surface area and mineralogy. Geoderma 72 37-51 Fontes, M.P.F. Bowen, L.H. Weed, S.B. 

M.C. (1991) Relationship between zinc and phosphate adsorption on montmorillonite and an iron oxyhydroxide. Aust. J. Soil Res. 29 239-247... 

The content and type of iron oxide affects soil chemistry. Several workers (e.g., Scheinost and Schwertmann 1995) have shown that phosphate adsorption maxima increase from red (hematitic) to yellow (goethite-rich) soils. Consequently, because yellow soils in some regions are closely correlated to soil P sorption, soil color has been used to predict the likely need for phosphate applications. 

Bouwman et al. demonstrated that Pt can be used in the ionic form (Pt" and Pt") by dispersing it in a matrix of hydrous iron phosphate (FePO) via a sol-gel process (Pt-FePO)." The hydrous FePO possesses micropores of approximately 2 nm. It has 3 H2O molecules per Fe atom and is thought to also serve as a proton transport medium. The Pt-FePO catalyst exhibited a higher ORR activity than Pt/C catalysts. This catalyst was also found to be less sensitive to CO poisoning because CO did not adsorb onto the catalyst surface. The ORR catalytic activity was attributed to the adsorption and storage of oxygen on the FePO, presumably as Fe-hydroperoxides. However, these catalysts have poor electrical conductivity. There is no published data on the long-term stability of these catalysts in fuel cell environments. 

When oxides in soils or sediments dissolve, substances adsorbed to the oxide surfaces will also be released into solution. Thus, for example, phosphate release into sediment pore waters accompanies the reductive dissolution of iron oxides in anoxic sediments. Release of phosphate into the overlying (oxic) water column is limited by phosphate adsorption on freshly precipitated amorphous iron oxides at the oxic-anoxic interface (9, 10). A similarly coupled cycle of phosphate and iron is observed in surface waters where photochemical reductive dissolution of iron oxides results in increased dissolved concentrations of ferrous iron and phosphate during the day (11). 

Other publications postulate specific adsorption between the surface and the /3-plane. For example Barrow and Bowden [69] interpreted adsorption of anions on goethite in terms of the mentioned above four layer model. The four layers are (in order of increasing distance from the surface) surface layer (H" and OH ions), the layer of specifically adsorbed anions, the first layer of inert electrolyte counterions (analogous to the /3-layer in TLM). and diffuse layer. This model requires an additional adjustable parameter, namely, the capacitance between the surface and the layer of specifically adsorbed anions. Barrow and Bowden report 2.99 F m for phosphate and 60,000 F m ( ) for silicate. The fit in the four layer model was substantially better than with simpler models for fluoride adsorption, but for other anions equally good fit could be obtained without introducing the additional electrostatic plane. In another paper of this series the capacitance of 3-5 F was used in model calculations of phosphate adsorption on aluminum and iron oxides [92]. Similar approach was used by Venema et al. [93] who applied the 1-pK model to interpret the Cd binding by goethite. The ions were assumed to... 

Prasad, B., Characteristics and phosphate adsorption on ferruginous soils and synthetic iron oxides, Ph.D. Thesis, University of Minnesota, St. Paul, 1976, cited after [10]. 

Kreller, D.L et al.. Chemical force microscopy investigation of phosphate adsorption on the surface of iron(III) oxyhydroxide particles, J. Colloid Interf. Sci., 254, 205, 2002. 

Cations and anions that adsorb by forming short directional bonds with the surface cannot be considered to be indifferent in character. These ions actually alter the surface charge by the very process of adsorption, and their bonding is classified as chemical adsorption (or chemisorption) in this text. Examples of chemisorption include copper and phosphate adsorption on iron oxides ... 

In section 7.4.2.1 the theoretical significance of phosphate adsorption onto iron oxides was illustrated. Numerous studies on natural sediments suggest that iron oxides control phosphate pore water and solid phase concentrations, as well as the overall sedimentary phosphate cycle (Krom and Berner 1980 Froelich et al. 1982 Sundby et al. 1992 Jensen et al. 1995 Slomp et al. 1996a,b). A generalized representation of the sedimentary phosphorus cycle is shown in Fig. 6.11. Apart from the Fe-bound P, organic P and authigenic carbonate fluorapatite are the principal carriers of solid phase P. HPO/ is the predominant dissolved P species under sea water conditions (Kester and Pytkowicz 1967). 

The method developed here for the description of chemical equilibria including adsorption on charged surfaces was applied to interpret phosphate adsorption on iron oxide (9), and to study electrical double-layer properties in simple electrolytes (6), and adsorption of metal ions on iron oxide (10). The mathematical formulation was combined with a procedure for determining constants from experimental data in a comparison of four different models for the surface/solution interface a constant-capacitance double-layer model, a diffuse double-layer model, the triplelayer model described here, and the Stem model (11). The reader is referred to the Literature Cited for an elaboration on the applications. 

Baldwin et al. (1995) surveyed the effect of various mineral phases on the rate of hydrolysis of the model organophosphate ester p-nitrophenyl phosphate. They found that, normalized for the number of independently determined phosphate adsorption sites, the manganese oxides were most effective in catalysing the hydrolysis reaction, followed by iron and titanium oxides, with a small effect for alumina. No effect was... 

R. L. Parfitt, J. D. Russell, and V. C. Farmer, Confirmation of the surface structures of goethite (a-FeOOH) and phosphated goethite by infrared spectroscopy, J.C.S. Faraday I 72 1082 (1976). R. L. Parfitt, Phosphate adsorption on an oxisol. Soil Sci. Soc. Am. J. 41 1065 (1977). R. L. Parfitt, R. J. Atkinson, and R. St. C. Smart, The mechanism of phosphate fixation on iron oxides. Soil Sci. Soc. Am. J. 39 837 (1975). R. L. Parfitt, The nature of the phosphate-goethite (a-FeOOH) complex formed with Ca(H2P04)2 at different surface coverage. Soil Sci. Soc. Am. J. 43 623 (1979). J. B. Harrison and V. E. Berkheiser, Anion interactions with freshly prepared hydrous iron oxides. Clays and Clay Minerals 30 97 (1982). 

The results presented here suggest that in the non-contact area, only physical adsorption of ZnDTP takes place on the existing oxide layer. In the contact region, a reaction occurs due to the tribostress and a thin tribofilm is formed. The tribofilm contains iron phosphate and other reaction products, such as sulfides and... 

The same authors studied the thermal films produced by triphenyl phosphorothionate (TPPT) at 423 K. Also, in this case, the formation of short-chain ironfll) polyphosphate with a low amount of iron snlfafe was suggested [22]. In the tribotracks, short-chain ironfll) polyphosphate, iron sulfides, and sulfates were defected. Increasing sliding time induced an increase in the amormt of iron snUate. After 6 h, comparable amounts of iron snlfafe and phosphates were observed. These findings were explained by the authors with a decomposition temperature for triphenyl phoshoro-thionate of around 423 K. Following the adsorption, the thermal oxidative process took place after the breakage of the P=S bond, the formation of iron phosphate and sulfate was proposed to occur. 

WADA K. and GUNJIGAKI N. 1979. Active aluminium and iron and phosphate adsorption in Ando soils. Soil Science,... 

Color None Decaying organic material and metallic ions causing color may cause foaming in boilers hinders precipitation methods such as iron removal, hot phosphate softening can stain product in process use Coagulation, filtration, chlorination, adsorption by activated carbon... 

Early studies on oxide films stripped from iron showed the presence of chromium after inhibition in chromate solutionand of crystals of ferric phosphate after inhibition in phosphate solutions. More recently, radio-tracer studies using labelled anions have provided more detailed information on the uptake of anions. These measurements of irreversible uptake have shown that some inhibitive anions, e.g. chromateand phosphate are taken up to a considerable extent on the oxide film. However, other equally effective inhibitive anions, e.g. benzoate" pertechnetate and azelate , are taken up to a comparatively small extent. Anions may be adsorbed on the oxide surface by interactions similar to those described above in connection with adsorption on oxide-free metal surfaces. On the oxide surface there is the additional possibility that the adsorbed anions may undergo a process of ion exchange whereby... 

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