Speciation and adsorption of arsenic on diagenetic iron oxyhydroxides

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Abstract
Diagenetic Fe and As samples have been obtained from 12 lakes on the Canadian Shield by deposition on Teflon collectors inserted vertically in the surficial sediments. Dissolution of the deposits showed that only arsenate was present, i.e. arsenite concentrations were undetectable. Laboratory batch experiments indicated that As(III) is oxidized rapidly by Fe oxyhydroxides. Apparent equilibrium constants for the absorption of As have been calculated from the Fe and As concentrations dissolved from the deposit of diagenetic material and As concentration in the water overlying the lake sediments. These field‐derived equilibrium constants agree well with laboratory‐derived equilibrium constants for the absorption of arsenate on amorphous Fe oxyhydroxides; the results taken together suggest that the latter laboratory constants can be used for modeling adsorption of inorganic As on Fe oxyhydroxides in natural waters.
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