The release of arsenic from contaminated sediments and muds
Titel:
The release of arsenic from contaminated sediments and muds
Auteur:
Clement, William H. Faust, Samuel D.
Verschenen in:
Journal of environmental science and health. Part A, Toxic/hazardous substances & environmental engineering
Paginering:
Jaargang 16 (1981) nr. 1 pagina's 87-122
Jaar:
1981
Inhoud:
Stream muds and sediments, contaminated with arsenic from an industrial waste water, have been studied, under laboratory conditions, for release of this contaminant to overlying waters. The arsenic content of the muds was determined initially whereupon simulated reservoirs were prepared from these muds and natural stream water. The systems studied were: anaerobic conditions at 25o, 20o, 15°, 10°, and 4°C, aerobic conditions at 20°and 10°C with dissolved oxygen (DO) levels of 100%, 50%, 25%, and 10% saturation. Distribution coefficients, the dimensionless ratio of AS /AS ,, were determined. In both the water mud aerobic and anaerboic systems, lower temperatures produced smaller distribution coefficients (those in the 4-10oC range were about 40% of the coefficients at the higher 20-25°C range). Very little difference was found in the distribution coefficients at a given temperature between reservoirs having either 10%, 25%, 50%, or 100% of saturation of dissolved oxygen. Anaerobic conditions led to levels of arsenic, principally as As (+III), about ten times higher than concentrations reached with aerobic conditions. The ratio of anaerobic As level/aerobic As level in reservoir waters was decreased also with decreasing temperature (8.3 at 25°C, and 5.6 at 10°C). The arsenic in the aerobic reservoirs was found to be about 70% arsenate, and 20% organic-arsenic. Little pH effect was observed over a pH range of 6.0 to 8.5. Both iron and phosphate concentrations present in the systems were found to be significant factors in establishing the arsenic levels. Release of the arsenic is highly dependent on the reduction of ferric iron (+III) to ferrous iron (+II), however, the level of arsenic reached in solution was found to be controlled by more complicated phenomena than simple dissolution. The results of this investigation indicate that adsorption-desorption equilibria as well as the amount of “available”; arsenic present in these muds and sediments greatly influences the soluble arsenic concentration found in the aqueous phase.
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