Sorption of Am3+ cations on suspended silicate: Effects of pH,ionic strength,complexing anions,humic acid and metal ions

Sorption of tracer Am³⁺ to silicate particles was studied as a function of pcH (4 to 9) and of ionic strength [0.20M to 1.50M (NaClO₄)] at 298 K. The sorption increased with increased pcH from 4 to 6 above which saturation was observed. The insensitivity of Am³⁺ sorption to increased ionic strength indicates inner-sphere complexation with the surface silicate sites. The effects of different complexing anions such as carbonate, acetate, oxalate, phosphate, citrate, EDTA and humic acid, on Am³⁺ sorption were investigated. Synergistic enhancement in Am³⁺ sorption was observed in the presence of phosphate (4≤pcH≤7) and acetate (4≤pcH≤5) ligands at 0.20M NaClO₄. The presence of the other ligands inhibited Am³⁺ sorption in the order: EDTA > citrate > oxalate > carbonate. Am³⁺ sorption in the presence of HA (25.00 mg/l) increased in the pcH range of 4.0 to 5.5, then decreased. Increased ionic strength enhanced Am³⁺ sorption in the presence of 25.00 mg/l HA for 4≤pcH≤9. The sorption increased in the presence of a mixture of HA (25.00 mg/l) and phosphate (1.00·10⁻³M) as compared to that of HA (25.00 mg/l) alone. The presence of Fe³⁺ (1.00·10⁻⁴M) enhanced Am³⁺ sorption at pcH∼4 but suppressed it from pcH of 5 to 9; 1.00·10⁻⁴M of Ca²⁺ and of UO₂²⁺ ions had no effect on the sorption profile. On leave from Radiochemistry Division, Bhabha Atomic Research Centre, Trombay, Mumbai -400 085, India.