Quantitative Analysis of Fe(II) Adsorption on Iron Hydroxide  Goethite (α-FeOOH)

Iron (Fe) is an essential element for plants, animals, and human. The chemistry of iron in natural systems like soils, particularly in the anaerobic and flooded paddy soils, strongly influences the bioavailability and transformation of various elements and, therefore, plays an important role in bio- and geo-chemical cycles. Mobility and availability of iron in the natural systems is controlled by the adsorption-desorption and dissolution-precipitation reactions. These reactions are strongly affected by environmental conditions especially proton (pH) and electron (pe) activities. Considering the importance of the adsorption process in controlling equilibrium concentration of Fe(II), we investigated Fe(II) adsorption process on goethite over a wide range of pH and ionic strength. The goethite charging behavior was calculated from acid-base titration at different levels of ionic strength. Titration data revealed pHpzc=9.1 for the goethite. The Fe(II) adsorption isotherms data were analyzed with the CD-MUSIC surface complexation model. Adsorption data were successfully described using two inner-sphere surface complexes, i.e. and. The calculated CD values indicated some charge transfer to the surface plane. Total Fe(II) adsorption was increased with increasing pH in response to drop in the surface potential. Mole fraction calculation showed that was the dominant surface species in the studied pH range. Furthermore, experimental data and model calculations revealed that ionic strength had no considerable effect on Fe(II) adsorption, possibly due to the type of adsorption mechanism. Almost full recovery of the adsorbed Fe(II) rejected possible precipitation of Fe(II), i.e. the dominance of adsorption process.