Laboratory studies have been performed on the uptake of uranium by the chief secondary minerals identified on fracture surfaces in groundwater flow systems of the Canadian Shield. The extent of adsorption from prepared solutions onto these materials, i.e. ferric oxyhydroxide uptake > chlorite uptake > calcite uptake, was similar to that previously observed in place on field samples.Although adsorption on the oxyhydroxide proceeds rapidly to near equilibrium in about 3 weeks, slower, two-stage processes have been postulated for uranium uptake by both chlorite and calcite. In some cases the times required to reach equilibrium are greater than 1 year.

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