Phosphate adsorption kinetics

Y.-S.R. Chen, J. N. Butler, and W. Stumm, Kinetic study of phosphate reaction with aluminum oxide and kaolinite, Env. Sci. Technol. 7 327 (1973). D. N. Munns and R. L. Fox, The slow reaction which continues after phosphate adsorption Kinetics and equilibrium in some tropical soils. Soil Sci. Soc. Am. J. 40 46 (1976). 

Phosphate adsorption kinetics for both of these oxide sur ces were studied by immersing the oxide sanq>le in a -19 ""C solution containing 3.5 mMCaOb, 119 pg P mT as KH2PO4, a pH adjusted to 6.5 with NaOH, and an ionic strength of 0.01 A/, using Nad as the background electrol e. 

Adsorption kinetics of phosphate on soils or soil minerals... 

Luengo, C., Brigante, M. and Avena, M. (2007) Adsorption kinetics of phosphate and arsenate on goethite. A comparative study. Journal of Colloid and Interface Science, 311(2), 354-60. 

Figure 13.4. Adsorption kinetics of phosphate on soils or soil minerals plot of Elov-ich equation. (From Chien and Clayton, 1980.)...

Phosphate behavior is also described by Langmuir and Freundlich adsorption equations, although these models may be too simple to accurately explain soil phosphate behavior. Kinetic models of phosphate retention by soils are also being employed. Although kinetics can suggest retention mechanisms, the complexity of soil-phosphate behavior makes this prospect difficult to achieve. 

Figure 7. Adsorption kinetics for mucin (Mu) and collagen (Col) on polyethylene (PE) and mica (Mi). Protein solution concentration 0.05 mg/ml. Temp. 20 C. Collagen adsorption from 0.2 M NaCl - 0.1 M CH3COOH buffer at pH = 2.75. Mucin adsorption from 10 3 M phosphate buffer with 0.15 M NaCl at pH = 7.2. Dotted lines and arrows indicate desorption and the amount after desorption.

Adsorption of organic phosphorus on soil minerals initially proceeds by a fast reaction that is often considered to reach an equilibrium value. However, a true equilibrium is not found for phosphate ions within a very long period. For example, one study showed that phosphate adsorption on to soils had not reached equilibrium after 1000 days at 25°C (Barrow and Shaw, 1975). The longterm adsorption processes for organic phosphorus compounds on to soils and oxides have not been well studied. Shang et al. (1990) compared the kinetics of adsorption of phosphate and selected organic phosphates on aluminium precipitates. They found that adsorption obeyed first-order... 

Arsenate adsorption on ferrihydrite consisted of a period of rapid uptake followed by slow adsorption for at least 8 days 43). The rate of the slow adsorption reaction is considered to be limited by diffusion into the ferrihydrite aggregates. Slow adsorption kinetics similar to those for phosphate are expected for arsenate because of the similar chemistry of these two anions. Arsenate adsorption data adhere to the Elovich kinetic model indicating a diffusion limited reaction. Arsenate desorption rates were much slower than arsenate adsorption rates, also consistent with a diffusion limited process. A model was developed that assumes that 63% of adsorbing sites are located at the exteriors of aggregates and reach arsenate equilibrium rapidly, while 37% of adsorbing sites are located in the interiors of aggregates with access being diffusion limited. 

Previous experience indicates that the long-term (over a period of several weeks) kinetics of phosphate adsorption and desorption on goethite is rather complex. Some of the variations in measured properties, both pH and mobility, may be attribiited to the complicated kinetic behavior of these systems. 

Mukerjee, S., Koel, B., and Chen, S. (2010) Influence of phosphate adsorption on the kinetics of oxygen electroreduction on low index Pt hU] single crystals. Phys. Chem. Chem. Phys., 12, 12544-12555. 

Phosphate Adsorption on Hematite. The presence of P as PO4 at the surface was confirmed in AES by princ al minima occurring near 94 and 110 eV kinetic energy (32). hi addition, the minima occurring at -43 and 52 eV demonstrate that the Fe203 stoichiometry of the thin film oxide was maintained after solution e q)osure. To determine the accumulation of phosphate at the surfece, AES P/Fe intensity ratios were calcmlated fi om measurements of the P(LMM) transition at 110 eV and the Fe(LMM) transition at 651 eV. A plot of this ratio with reaction time (Figure 1) shows that phosphate accumulates rapidly at the sur ce of thin film Fe203 during the first 10 min. 

Figure 26 shows the redox potential of 40 monolayers of cytochrome P450scc on ITO glass plate in 0.1 KCl containing 10 mM phosphate buffer. It can be seen that when the cholesterol dissolved in X-triton 100 was added 50 pi at a time, the redox peaks were well distinguishable, and the cathodic peak at -90 mV was developed in addition to the anodic peak at 16 mV. When the potential was scanned from 400 to 400 mV, there could have been reaction of cholesterol. It is possible that the electrochemical process donated electrons to the cytochrome P450scc that reacted with the cholesterol. The kinetics of adsorption and the reduction process could have been the ion-diffusion-controlled process. 

Rhaman and coworkers [112,113] studied the adsorption of lipase on [MgAl] LDH and its biocatalytic activity for butyl oleate synthesis. They demonstrated that up to 277 and 531 mgg-1 of lipase were adsorbed on [MgAl-N03] and [MgAl-Dodecylsulfate] LDH, respectively, showing the highest adsorption capacity of the anionic clays compared to smectite or inorganic phosphate. Recently, we reported the adsorption isotherms of urease on [ZnRAl] LDH under various experimental conditions (pH, buffer) [117]. The kinetic study showed the fast adsorption process (less than 60 min) (Figure 15.3). 

Pigna M, Colombo C, Violante A (2003) Competitive sorption of arsenate and phosphate on synthetic hematites (in Italian). Proceedings XXI Congress of Societa Italiana Chimica Agraria SICA (Ancona), pp 70-76 Quirk JP (1955) Significance of surface area calculated from water vapour sorption isotherms by use of the B. E. T. equation. Soil Sci 80 423-430 Rancourt DG, Fortin D, Pichler T, Lamarche G (2001) Mineralogical characterization of a natural As-rich hydrous ferric oxide coprecipitate formed by mining hydrothermal fluids and seawater. Am Mineral 86 834-851 Raven K, Jain A, Loeppert, RH (1998) Arsenite and arsenate adsorption on ferrihydrite kinetics, equilibrium, and adsorption envelopes. Environ Sci Technol 32 344-349... 

Relaxation studies have shown that the attachment of an ion to a surface is very fast, but the establishment of equilibrium in wel1-dispersed suspensions of colloidal particles is much slower. Adsorption of cations by hydrous oxides may approach equilibrium within a matter of minutes in some systems (39-40). However, cation and anion sorption processes often exhibit a rapid initial stage of adsorption that is followed by a much slower rate of uptake (24,41-43). Several studies of short-term isotopic exchange of phosphate ions between aqueous solutions and oxide surfaces have demonstrated that the kinetics of phosphate desorption are very slow (43-45). Numerous hypotheses have been suggested for this slow attainment of equilibrium including 1) the formation of binuclear complexes on the surface (44) 2) dynamic particle-particle interactions in which an adsorbing ion enhances contact adhesion between particles (43,45-46) 3) diffusion of ions into adsorbents (47) and 4) surface precipitation (48-50). 

Analyses of enzyme reaction rates continued to support the formulations of Henri and Michaelis-Menten and the idea of an enzyme-substrate complex, although the kinetics would still be consistent with adsorption catalysis. Direct evidence for the participation of the enzyme in the catalyzed reaction came from a number of approaches. From the 1930s analysis of the mode of inhibition of thiol enzymes—especially glyceraldehyde-phosphate dehydrogenase—by iodoacetate and heavy metals established that cysteinyl groups within the enzyme were essential for its catalytic function. The mechanism by which the SH group participated in the reaction was finally shown when sufficient quantities of purified G-3-PDH became available (Chapter 4). 

H. A.-Kozlowska, J. Klinger, and B. E. Conway, /. Electroanal. Chem. 75, 45 (1911). Fukuda and A. Aramata, The kinetic study of adsorption processes of the phosphate species on platinum)111) in aqueous acidic solutions, J. Electroanal. Chem., in press (1997). 

Feldspar, among many natural substances such as termite mount-clay, saw dust, kaolinite, and dolomite, offers significant removal ability for phosphate, sulfate, and color colloids. Optimization laboratory tests of parameters such as solution pH and flow rate, resulted in a maximum efficiency for removal of phosphate (42%), sulfate (52%), and color colloids (73%), x-ray diffraction, adsorption isotherms test, and recovery studies suggest that the removal process of anions occurs via ion exchange in conjunction with surface adsorption. Furthermore, reaction rate studies indicated that the removal of these pollutants by feldspar follows first-order kinetics. Percent removal efficiencies, even under optimized conditions, will be expected to be somewhat less for industrial effluents in actual operations due to the effects of interfering substances [58]. 

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