Freeze-dried preparations of Chlorella vulgaris will accumulate U(VI) from alkaline, bicarbonate-containing waters collected from uranium mill process streams, provided that the pH is pre-adjusted to between 4.0 and 6.0. Bicarbonate ion complexes the uranyl ion in these waters and seriously interferes with the binding of U(VI) to the algal cells at pH values above 6.0. No binding of U(VI) to the algae occurred at the natural pH of 8.0 when Chlorella vulgaris was suspended in untreated mill-waters containing up to 2.5 x 10-4M U(VI). However, when the pH of these waters was lowered from 8.0 to near 5.0, with nitric acid, nearly quantitative binding of U(VI) to the alga was achieved. Binding is rapid and largely unaffected by ions including Na', CI-, NOT, -OAc, and SO:-. Our results indicate that provided steps are taken to eliminate bicarbonate interference, such as adjustment of the pH to near 5.0, dried algal biomass could prove useful for the removal and recovery of U(VI) from high carbonatecontaining waters.
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