ATR-FTIR Studies on the Nature of Surface Complexes and Desorption Efficiency of p-Arsanilic Acid on Iron (Oxyhydr)oxides

Abstract

The fate of organoarsenicals introduced to the environment through the application of arsenic-contaminated manure has attracted considerable attention after the recent implementation of the latest maximum contaminant level (MCL) of total arsenic in drinking water by the U.S. Environmental Protection Agency (EPA). We report herein detailed spectroscopic analysis of the surface structure of p-arsanilic acid (p-AsA) adsorbed on Fe−(oxyhydr)oxides using attenuated total internal reflectance Fourier transform infrared spectroscopy (ATR-FTIR). Spectra of p-AsA(ads) were collected in situ as a function of pH and ionic strength and using D₂O at 298 K in flow mode. Results indicate the formation of inner-sphere complexes, which are likely monodentate and become protonated under acidic pH(D). We also examined the desorption efficiency of p-AsA(ads) due to flowing electrolyte and phosphate solutions as low as 0.1 mol/m³ (3 ppm P) by collecting ATR-FTIR spectra as a function of time. Our results suggest that aqueous phosphate is an efficient desorbing anion of p-AsA(ads), which has implications on its bioavailability and mobility in geochemical environments.