Am(III) and Eu(III) uptake on hematite in the presence of humic acid

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Abstract
Summary: The uptake of Am(III) and Eu(III) on hematite (1.0 g/L) in the presence of humic acid (HA; 4.7×10-5M) was investigated at ionic strengths of 0.05 to 0.5 M (NaClO4) in the pH range of 4 to 10. The sorption behavior of Am(III) was similar to that of Eu(III). The Am(III) and Eu(III) exhibited 100% retention on the solid in the entire pH region studied at high ionic strength (0.5 M). As the ionic strength was decreased below 0.1 M, Am(III) and Eu(III) sorption which was complete at low pH values decreased stepwise with increasing pH from 5 to 7. In order to test the additivity and to understand the solid–water interface reactions for Am(III) sorption in ternary systems, binary interactions between Am(III), HA, and hematite were also examined under identical conditions. The additive results reproduced the stepwise decreases of sorption up to a pH of about 6 for lower ionic strengths, which can be ascribed to HA adsorption behavior. However, inconsistencies in additivity from experimental results were found in the pH regions above 7 at low ionic strengths and in the entire pH region at an ionic strength of 0.5 M. Some non-additive effects are discussed in this paper.