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Arai, Y. and D. L. Sparks. 2001. ATR-FTIR spectroscopic investigation on phosphate adsorption mechanisms at the ferrihydrite-water interface. J. Colloid Interf. Sci. 241:317-326.

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ATR-FTIR Spectroscopic Investigation on Phosphate Adsorption Mechanisms at the Ferrihydrite-Water Interface

Yuji Arai*,  D. L. Sparks  

Department of Plant and Soil Sciences, University of Delaware, Newark, 19717-1303, Delaware

Abstract

We investigated the phosphate (P) adsorption mechanisms at the ferrihydrite-water interface as a function of pH, ionic strength (I), and loading level, using a combination of adsorption envelopes, electrophoretic mobility (EM) measurements, and attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy. The P adsorption envelopes show that: (1) adsorption decreases with increasing pH 3.5-9.5 and (2) adsorption is insensitive to changes in I at pH 4-7.5, but it slightly increases with increasing I from 0.01 to 0.8 at pH>7.5. The EM in 0.1 M NaCl decreases with increasing P concentration from 0 to 50 µmol L^-1 at pH 3-9. The results of these macroscopic studies suggest the formation of inner-sphere complexes. The ATR-FTIR investigation shows that inner-sphere surface complexes are nonprotonated, bidentate binuclear species (=Fe₂PO₄) at pH >7.5 and could be associated with Na⁺ ions at P loading levels of 0.38 µmol m^-2. At pH 4-6, protonated inner- sphere complexes are proposed at the loading levels between 0.38 and 2.69 µmol m^-2. Copyright 2001 Academic Press.

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