Abstract:
Biotite and albite grains having a size range from 20 to 124 μm were suspended in Be-bearing solutions at pH 2 to 9 for periods of 30 min to 20 days. The amount of Be sorbed onto biotite is up to 40 times higher than onto albite under the same conditions and pH≤7. At pH≤6, the distribution of Be between solution and solids is related to sorption but at pH>6, the solute concentration is strongly controlled by solubility of Be(OH)2-solid. Because of this solubility control, the calculation of a distribution coefficient (Kd=S/C, where S is Be sorbed at equilibrium per mass or specific surface area of sorbent, and C is the Be concentration in solution at equilibrium) seems to be valid only at pH≤6. The Kd increases with decreasing suspended particle concentration (from 0.2 to 2.0 g l−1) for both minerals. For biotite the Kd also increases with the fine (20–63 μm) relative to the coarse (63–124 μm) size fraction even upon normalization to specific surface area. The relatively small amount of Be sorbed onto albite at pH 2 and 4 limited extensive evaluation and comparison. The rate of Be sorption onto biotite follows a logarithmic function and ranges from 0.8 to 1.0×10−11 mol cm−2 s−1 in pH 2 and 6 solutions, respectively. The time-variation of sorbed Be onto albite was insignificant with increasing pH. The sorption of Be onto biotite partly relates to the kinetics of cation release. The results of experiments are discussed with respect to some examples of the distribution of Be isotopes in continental aquatic systems.