Sorption of arsenate and arsenite on RuO2 x xH2O: a spectroscopic and macroscopic study.
The sorption reactions of arsenate (As(V)) and arsenite (As(III)) on RuO2 x xH2O were examined using macroscopic and spectroscopic techniques. Constant solid:solution isotherms were constructed from batch sorption experiments and sorption kinetics assessed at pH 7. X-ray absorption near edge spectroscopy (XANES) was employed to elucidate the solid-state speciation of sorbed As. At all pH values studied (pH 4-8), RuO2 x xH2O showed a high affinity for As regardless of the initial As species present. Sorption was higher at all pH values when the initial As species was As(III). Oxidation of As(III) (250 mg/L solution) to As(V) was virtually complete (98-100%) within 5 s. XANES results showed the presence of only As(V) on the RuO2 x xH2O regardless of the initial As oxidation state. There was no change in the As oxidation state on the solid phase for 4 weeks in both oxic and anoxic environments. It is speculated that changes in the RuO2 x xH2O structure, due to oxidation reactions, caused the higher total As sorption capacity when As(III) was the initial species. The As sorption capacity of RuO2 x xH2O is greater than that of other metal oxides reviewed in this study. The ability of RuO2 x xH2O to rapidly oxidize As(III) is much greater than other oxides, such as MnO2.
Impellitteri
Christopher A
CA
U.S. EPA, ORD, LRPCD, RCB, 5995 Center Hill Avenue, Cincinnati, Ohio 45224, USA. Impellitteri.christopher@epa.gov
Scheckel
Kirk G
KG
Ryan
James A
JA
D015502:Absorptiometry, Photon; D000327:Adsorption; D001149:Arsenates / Q000737:chemistry*; D018053:Arsenites / Q000737:chemistry*; D007700:Kinetics; D010084:Oxidation-Reduction; D017975:Ruthenium Compounds / Q000737:chemistry*; D014867:Water / Q000737:chemistry*
D001149:Arsenates; D018053:Arsenites; D017975:Ruthenium Compounds; D014867:Water; C029017:ruthenium dioxide; C015001:arsenite; C025657:arsenic acid