Phosphate goethite

Fig. 11.11 Na" and Cl adsorption on pure and phosphated goethite (Nanzyo, Watanabe, 1982, with permission).

V.C. (1974) Surface structure of gibbsite, goethite and phosphated goethite. Nature 248 220-221... 

FeOOH, phosphate, goethite, from sulfate nitrate... 

Parfitt, L.R. (1979) The availability of P from phosphate-goethite bridging complexes desorption and uptake by ryegrass. Plant and Soil 53, 55-65. 

Parfitt, R.E., Russell, j.D. and Farmer, V.C. (1 976) Confirmation of the surface structure of goethite and phosphated goethite. Journal of Chemical Society Faraday Transactions 72, 1 082-1 087. 

Table 4.2. Infrared absorption band centers for goethite, phosphated goethites, phosphate minerals, and aqueous phosphate anions ... 

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). 

Rosso KM, Becker U, Hochella MF Jr (1999) The interaction of pyrite 100 surfaces with O2 and H2O Fundamental oxidation mechanisms. Am Mineral 84 1549-1561 Russell JD, Parfitt RL, Fraser AR, Farmer VC (1974) Surface structures of gibbsite, goethite and phosphated goethite. Nature 248 220-221... 

Even if the study by Honeyman and Santschi clearly showed the problems associated with solid-liquid separation, the solid-concentration effect still circulates in the recent literature [25]. In these latter studies, the authors studied metal ion sorption onto goethite in the presence of a phosphate buffer to control the pH phosphate strongly sorbs onto goethite itself, so that observed particle concentration effects should not be interpreted without considering the action of phosphate. It is highly probable that the metal ions were sorbed on a (more or less) phosphated goethite and not to a pure goethite. 

Galena, see Eead sulfite Glauber s salt, see Sodium sulfate 10-water Goethite, see Iron(II) hydroxide oxide Goslarite, see Zinc sulfate 7-water Graham s salt, see Sodium phosphate(l —) Graphite, see Carbon... 

Arsenate is readily adsorbed to Fe, Mn and Al hydrous oxides similarly to phosphorus. Arsenate adsorption is primarily chemisorption onto positively charged oxides. Sorption decreases with increasing pH. Phosphate competes with arsenate sorption, while Cl, N03 and S04 do not significantly suppress arsenate sorption. Hydroxide is the most effective extractant for desorption of As species (arsenate) from oxide (goethite and amorphous Fe oxide) surfaces, while 0.5 M P04 is an extractant for arsenite desorption at low pH (Jackson and Miller, 2000). 

O Reilly et al. (2001) studied the effect of sorption residence time on arsenate desorption by phosphate (phosphate/arsenate molar ratio of 3) from goethite at different pH values. Initially, desorption was very fast (35% arsenate desorbed at pH 6.0 within 24 hrs) and then slowed down. Total desorption increased with time reaching about 65% total desorption after 5 months. These authors found no measurable effect of aging on desorption of arsenate in the presence of phosphate. Furthermore, desorption results at pH 4.0 were similar to the desorption behaviour at pH 6.0. On the contrary, Arai and Sparks (2002) demonstrated that the longer the residence time (3 days-1 year), the greater was the decrease in arsenate desorption by phosphate from a bayerite. 

Desorption of arsenate, MMAs(V) and DMAs(V) from goethite and ferrihydrite by phosphate and sulfate was studied by Lafferty and Loeppert (2005). These arsenic compounds were desorbed more efficiently by phosphate than sulfate. In desorption envelopes, the amount of arsenate desorbed generally increased as the number of methyl groups increased... 

Liu F, De Cristofaro A, Violante A (2001) Effect of pH phosphate and oxalate on the adsorption/desorption of arsenate on/from goethite. Soil Sci 166 197-208 Livesey NT, Huang PM (1981) Adsorption of arsenate by soils and its relation to selected properties and anions. Soil Sci 131 88-94 Manceau A (1995) The mechanism of anion adsorption on iron oxides Evidence for the bonding of arsenate tetrahedra on free Fe(0, OH)6 edges. Geochim Cosmochim Acta 59 3647-3653. 

Shaw, S., Pepper, S.E., Bryan, N.D., Livens, F.R. 2005. The kinetics and mechanisms of goethite and hematite crystallization under alkaline conditions, and in the presence of phosphate. American Mineralogist, 90, 1852-1860. 

Anion Binding. This discussion illustrates how valuable information on enthalpy changes of surface reactions (either from temperature dependence or from direct calorimetric measurements) are. Zeltner et al. (1986) have studied calorimetrically the surface complex formation of phosphate and salicylate on goethite. They show that these reactions are exothermic (at pH = 4) with AHadS values at low coverage ( 10 %) of ca. -24 kJ mol 1, they argue tentatively that these values indicate biden-tate surface complex formation. They also show that -AH decreases with increasing surface coverage. 

A sharp decrease in adsorption enthalpy between 10 and 30% surface coverage of SAL can also be seen in Figure 2. This decrease may indicate that only a small number of surface sites are favorably oriented for SAL-goethite bond formation, although possible SAL-SAL interactions on the surface may also have an effect. Separate measurements of SAL adsorption on goethite, gave relatively small adsorption maxima (when compared to the phosphate and fluoride adsorption maxima discussed above) of 22 and 11 pmol/g at pH 4.8 and 6.3, respectively, in either 0.001 M NaN0 or 0.001 M KC1 06). J... 

Figure 2. Adsorption heat ( 1 SD) as a function of fractional surface coverage for phosphate ( ) and salicylate (x) at 10 g goethite/L in 0.05 M NaNO at pH 4.0.

ToF-SIMS, and AFM results, the formation of ordered monolayers of octade-cylphosphoric acid on a Ta205 surface involves both monodentate and bi-dentate phosphate species [135]. In the case of goethite, (y-AlOOH), it was found that methylphosphonic acid bound to the surface as a monodentate or a bidentate species depending on the pH and the concentration [163]. 

---