Arsenite and arsenate adsorption on ferrihydrite: Surface charge reduction and net OH{sup {minus}} release stoichiometry
- Texas A and M Univ., College Station, TX (United States). Dept. of Soil and Crop Sciences
Arsenite [As(III)] and arsenate [As(V)] are highly toxic inorganic arsenic species that represent a potential threat to the environment and human health. Iron oxides including poorly crystalline oxides, e.g., ferrihydrite, play a significant role in controlling dissolved As concentration and limit the mobility and bioavailability of As(III) and As(V). Adsorption occurs by ligand exchange of the As species for OH{sub 2} and OH{sup {minus}} in the coordination spheres of surface structural Fe atoms. The objective of this study was to evaluate H{sup +}/OH{+-}{sup {minus}} release stoichiometry and changes in surface charge properties of the adsorbent during the adsorption of arsenite and arsenate on ferrihydrite in the pH range of 4--10. This information, which is not directly accessible through spectroscopic studies, provides important clues to bonding mechanism. While arsenate adsorption resulted in the net release of OH{sup {minus}} at pH 4.6 and 9.2, arsenite adsorption resulted in net OH{sup {minus}} release at pH 9.2 and net H{sup +} release at pH 4.6. The amount of H{sup +} or OH{sup {minus}} release per mole of adsorbed As varied with the As surface coverage, indicating that different mechanisms of arsenic adsorption predominate at low versus high coverage. The experimentally observed surface charge reduction and net OH{sup {minus}} release stoichiometry were compared with the theoretical stoichiometry of the surface adsorption reactions that might occur. A better understanding of these aspects of the adsorption process is helpful to elucidate the reaction mechanism and eventually to optimize strategies for the removal of arsenic from contaminated water and the management of arsenic contaminated soil.
- OSTI ID:
- 355517
- Journal Information:
- Environmental Science and Technology, Journal Name: Environmental Science and Technology Journal Issue: 8 Vol. 33; ISSN ESTHAG; ISSN 0013-936X
- Country of Publication:
- United States
- Language:
- English
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