Phosphate, 440 adsorption

Since properties of both arsenate and phosphate species are very close, the adsorption of phosphate species was studied prior to that of arsenate. The phosphate adsorption was tested by the following two methods (i) and (ii). Hereafter, flow rate and volume of feed are given in space velocity (SV, h 1)... 

Goldberg, S., and G. Sposito (1984), "A Chemical Model of Phosphate Adsorption by Soils I. Reference Oxide Minerals II. Noncalcareous Soils", Soil Sd. Soc. Am. 48, 772-783. 

Figure 3 shows the pH dependence for phosphate adsorption on YAI2O3 for a phosphate concentration of 8 x 10 3 mol dm-3, at 1= 1.5xlO-2M, [P] = 30 g dm-3, and 25°C. It is well known that below the pHZpC in the absence of phosphate, both the surface- and C-potential in the -y—AI2O3 suspension are positive however in the presence of phosphate, the surface is negatively charged at pH values below the zpc (pH = 8.5 indicating specific adsorption of phosphate (see Figure 4). A mechanism to explain phosphate adsorption based on pressure-jump studies has been postulated by Mikami et al. (15)...

The retention of Cu by allophane is enhanced by phosphate regardless of the sequence of Cu and phosphate adsorption, although Cu has been found to have no effect on the simultaneous and subsequent adsorption of phosphate on surface bound Cu (32) ESR results suggest that the Cu binds to surface A10H groups of the allophane irrespective of the presence of phosphate and it was proposed that the enhanced Cu retention was the result of the formation of a ternary complex by the binding of phosphate to the axial position of the surface-bound Cu ion. 

Muller B, Stierli R, Wiiest A (2006) Phosphate adsorption by mineral weathering particles in oligotrophic waters of high particle content. Water Resour Res 42 doi 10.1029/ 2005WR004778... 

Adsorption of phosphate on Fe oxides involves a ligand exchange mechanism (Par-fitt and Russell, 1977 Sigg and Stumm, 1981) and appears to be promoted by increasing the ionic strength (Bowden et al., 1980). Spectroscopic studies have not provided an entirely consistent picture of the mode of phosphate adsorption, but the consensus from studies with a range of techniques is, that phosphate adsorbs on Fe oxides predominantly as a binuclear, bidentate complex. 

The practical significance of such competition evolves from the experience that silicate and (anionic) humics can increase the efficiency of phosphate fertiliser because these compounds occupy sites suitable for phosphate adsorption (Kingston et ak, 1968 Schwertmann, 1995). Hydroxyl is another anion that competes effectively with adsorbing anions, owing to its location in the inner Helmholz layer. The release of adsorbed phosphate after liming a soil or after inflow of acidic surface soil into weakly alkaline surface waters due to erosion, can be considered as the result of competition between OH and phosphate ions. 

Fig. 16.15 Phosphate adsorption curves of three low moor soils with different goethite content as a function of contact time (1 -238 h) (Schwertmann Schieck, 1980 with permission).

Arai,Y. Sparks, D.L. (2001) ATR-ETIR spectroscopic investigation on phosphate adsorption mechanisms at the ferrihydrite-water interface. J. Coll. Int. Sd. 241 317—326 Araki, S. Hirai, H. Kyuma, K. (1986) Phosphate absorption of red and/or yellow colored soil materials in relation to the characteristics of free oxides. Soil Sd. Plant Nutr. 32 609-616... 

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... 

Barron,V. Herruzo, M. Torrent, J. (1988) Phosphate adsorption by aluminous hematites of different shapes. Soil Sci. Soc. Am. J. 52 647-651... 

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... 

Colombo, C. Barron,V. Torrent, J. (1994) Phosphate adsorption and desorption in relation to morphology and crystal properties of synthetic hematites. Geochim. Cosmochim. Acta 58 1261-1269... 

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. 

Gerke, J. (1993) Phosphate adsorption by hu-mic/Ee-oxide mixtures aged at pH 4 and 7 and by poorly ordered Ee-oxide. Geoderma 59 279-288... 

Goldberg, S. Sposito, G. (1984) A chemical model of phosphate adsorption by soils. I. Reference oxide minerals. Soil Sci. Soc. Am. J. 48 772-778... 

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

Parfitt, R.L. Atkinson, R.J. (1976) Phosphate adsorption on goethite (a-FeOOH). Nature 264 740-742... 

Phosphate adsorption and desorption by goethites differing in crystal morphology. Soil Sd. Soc. Am. J. 54 1007-1012 Torrent, J. Guzman, R. Parra, M.A. (1982) Influence of relative humidity on the crystallization of Fe(III) oxides from ferrihydrite. Clays Clay Min. 30 337-340 Torrent, J. Schwertmann, U. Barron,V. 

Rhoton, F.E. and Bigham, J.M. (2005) Phosphate adsorption by ferrihydrite-amended soils. Journal of Environmental Quality, 34(3), 890-96. 

Haussmann, D.D. and Anderson, M.A., 1985. Using electrophoresis in modelling sulfate, salinity and phosphate adsorption on to goethite. Environmental Science and Technology, 19 544-551. 

Barrow, N. J, and Shaw, T. C. (1979). Effects of solution Soil ratio and vigour of shaking on the rate of phosphate adsorption by soil. J. Soil Sci. 30, 67-76. 

Table 5.8 SCM input parameters for ferric hydroxide surfaces used for the calculation of phosphate adsorption using the CCM and the adsorption of Pb, Cu, Zn and Cd using the DDLM...

Using the equations and input parameters in Table 5.8 the results of a calculation involving phosphate adsorption on a goethite are shown in Fig. 5.6. 

CCM to calculate phosphate adsorption by a hydrous ferric oxide as a function of pH. The proportion of added [H3P04]t adsorbed (a,) is given by the sum of the surface phosphate species divided by [H3P04]t. The different surface phosphate species are shown as proportions of the total number of surface sites [=SOH°]t. 

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