Study of arsenate adsorption on iron oxide by in situ ATR-FTIR spectroscopy

• Main Author: Carabante, Ivan
• Format: Master Thesis
• Language: English
• Published: Luleå tekniska universitet, Industriell miljö- och processteknik 2009
• Subjects: Chemical Process Engineering; Kemiska processer; Luleå
• Online Access: http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-26159

Stabilization of arsenic contaminated soils by iron oxides has been proposed as a remediation technique to prevent leaching of arsenate into the environment. However, fundamental studies are needed to establish under which conditions the complexes formed are stable. A new method based on ATR-FTIR spectroscopy was adapted to study the adsorption of arsenate species on iron oxides. The measurements required the use of D2O as solvent. The amount of arsenate complexes adsorbed on the iron oxide increased with decreasing pD in the range studied, viz. pD 4-12. Arsenate complexes adsorbed at pD 4 desorbed from the film to some extent as the pD was increased to 8.5 or 12. The stability of arsenate complexes adsorbed on the iron oxide evidently changed with the change in pD, most likely due to the electrostatic repulsion between the negatively charged oxoanion and the more negatively charged iron oxide as the pD increased. From competitive adsorption experiments it was found that arsenate species were more strongly bonded to the iron oxide than phosphate species. Furthermore, it was found that two different phosphate complexes formed on the iron surface at pD 4, one deuterated and the other one de-deuterated. The complexes showed very different stability. The deuterated phosphate complex was desorbed easily from the iron oxide film as arsenate was added to the system whereas the de-deuterated phosphate complex only desorbed slightly from the film upon adding arsenate.This work has increased the fundamental knowledge of the iron oxide/arsenate/phosphate system, which will be of importance for the development of more effective soil remediation techniques. Godkänd; 2009; 20090905 (ivacar); LICENTIATSEMINARIUM Ämnesområde: Kemisk teknologi/Chemical Technology Examinator: Professor Jonas Hedlund, Luleå tekniska universitet Tid: Fredag den 2 oktober 2009 kl 10.00 Plats: C 305, Luleå tekniska universitet