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SORPTION OF ARSENATE AND ARSENITE ON RUO2.XH2O: A SPECTROSCOPIC AND MACROSCOPIC STUDY
Citation:
Impellitteri**, C A., K G. Scheckel*, AND J A. Ryan*. SORPTION OF ARSENATE AND ARSENITE ON RUO2.XH2O: A SPECTROSCOPIC AND MACROSCOPIC STUDY. ENVIRONMENTAL SCIENCE & TECHNOLOGY 37(13):2936-2940, (2003).
Description:
The sorption of arsenate (As(V)) and arsenite (As(III)) on RuO2 xH2O was examined using macroscopic and microscopic techniques. Constant solid:solution ratio isotherms were constructed from batch sorption experiments to study the sorption of the inorganic arsenic species on RuO2 xH2O as a function of pH. Kinetic experiments were run using a pH stat titrator set at pH 7. Anion exchange cartridges were used to differentiate and quantify As(V) and As(III) in the batch sorption and kinetic experiments. X-ray Absorption Near Edge Spectroscopy (XANES) was employed to elucidate the solid state speciation of sorbed As. RuO2 xH2O showed a high affinity for As regardless of the initial As species present at all pH values studied (pH4-8). Sorption was also 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 within 5 seconds. As sorption on RuO2 xH2O follows 2nd order kinetics, thus the reaction rate is a function of the initial concentration of the sorbing species. XANES results show the presence of only As(V) on the RuO2 xH2O regardless of the initial oxidation state of the As. There was no change in the oxidation state for 4 weeks in both oxic and anoxic environments. The higher sorption capacity found when As(III) is the initial species could be attributed to structural changes in the framework of the RuO2 xH2O during the rapid oxidation of As(III) to As(V).