The influence of oxalic acid on release rates of metals from contaminated river sediment

Long term mining and smelting operations in the vicinity of the head waters of the Clark Fork River, Montana, USA, have led to extensive metal contamination of the river sediments. Discerning the relationship between the chemistry of these contaminants and the chemistry of naturally occurring iron and manganese oxyhydroxides is important for understanding this and other sediment/soil systems. The experimental results presented in this paper help define this relationship. Extraction solutions containing 0.00, 0.01 and 0.02 M oxalic acid at pH 1.85 were applied to samples of contaminated Clark Fork River sediment. Extraction of both matrix and contaminant metals was monitored as a function of time and correlations between iron, manganese, copper, zinc and arsenic extraction were studied. The data suggest that arsenic is associated with iron oxyhydroxides and zinc most closely associated with manganese oxyhydroxides.