Infrared Spectra of Phosphate Sorbed on Iron Hydroxide Gel and the Sorption Products

Abstract

Infrared absorption spectra of phosphate sorbed on iron hydroxide gel were obtained by applying the differential diffuse reflectance method. Absorption bands due to P-O stretching vibration were observed at 1,110 and 1,010 cm-1 at pH 12.3. With decreasing pH, these absorption bands gradually shifted to 1,100 and 1,020 cm-I at pH 4.9. At pH 2.3, they became a broad single absorption band at 1,060 cm-I. At pH 11 or above, the difference in the Na+ adsorption between phosphated iron hydroxide gel and iron hydroxide gel was almost equal to the amount of phosphate sorption. This finding shows that phosphate was retained on the iron hydroxide gel surface as a bidentate ligand at a high pH.It was concluded that at a high pH phosphate was sorbed on iron hydroxide gel as a binuclear surface complex similar to that on goethite; the change in spectra for P-O stretching vibration with decreasing pH value was mainly caused by an increase in the fraction of amorphous iron phosphate; at pH 2.3, the phosphate sorption product consisted of amorphous iron phosphate.

Measuring Surface Chemical Properties of Soil Using Flow Calorimetry 1

“…This slow uptake is thought to be the result of one or more of the following processes: i) diffusion to less accessible sites within pores of solid aggregates (Willet et al, 1988;Cabrera et al, 1981;Parfitt, 1989;Madrid and de Arambarri, 1985;Lookman et al, 1994); ii) penetration into the amorphous Fe and/or Al oxides by solid state diffusion (van Riemsdijk and de Haan, 1981;van Riemsdijk et al, 1984;Barrow, 1983); and iii) pre cipitation with metals derived by dissolution of the soil matrix (Aulenbach and Meisheng, 1988;Lookman et al, 1994;Martin et al, 1988;Nanzyo, 1984Nanzyo, , 1986Pierzynski et al, 1990). Malati et al (1993) reported that phosphate sorption on kaolinite, mica, and anatase at pH Ͻ 5 was endothermic and generally in the range of ϩ10 to ϩ15 kJ mol Ϫ1 .…”

Effect of organic reducing agents on the p sorption product formed on noncrystalline hydrous fe oxide

“…Within this pH range, the amount of P retention increased with decreasing pH (Nanzyo 1986). Though the pH value decreased with the increase in the amount of ascorbic acid added, the amount of P dissolved increased.…”

“…The absorption band at 1,060cm -1 was close to that of noncrystalline iron phosphate. The P sorption product which consists of a mixture of noncrystalline iron phosphate and binuclear surface complex (Nanzyo 1986) was converted to noncrystalline iron phosphate through treatments with the agents-A followed by H202. No X-ray diffraction peaks were detected after these treatments.…”

“…Fe gel was prepared by the method described previously (Nanzyo 1986). To 4.00g of the Fe gel, 400ml of0.01M NaC1 was added and shaken for 16h at 25_+ Ioc.…”

“…After air-drying, these Fe gels were then treated with 5 ml of 10% H202 for 2 h without heating followed by washing with 0.01 M NaC1 twice. IR spectra of P retained on the Fe gels were obtained by the differential diffuse reflectance method (Nanzyo, 1986).…”