title: Sorption of curium by silica colloids: effect of humic acid.
abstract: Sorption of curium by silica colloids has been studied as a function of pH and ionic strength using (244)Cm as a tracer. The sorption was found to increase with increasing pH and reach a saturation value of ∼95% at pH beyond 5.3. The effect of humic acid on the sorption of (244)Cm onto silica was studied by changing the order of addition of the metal ion and humic acid. In general, in the presence of humic acid (2 mg/L), the sorption increased at lower pH (<5) while it decreased in the pH range 6.5-8 and above pH 8, the sorption was found to increase again. As curium forms strong complex with humic acid, its presence results in the enhancement of curium sorption at lower pH. At higher pH the humic acid present in the solution competes with the surface sites for curium thus decreasing the sorption. The decrease in the Cm sorption in presence of humic acid was found to be less when humic acid was added after the addition of curium. Linear additive model qualitatively reproduced the profile of the Cm(III) sorption by silica in presence of humic acid at least in the lower pH region, however it failed to yield quantitative agreement with the experimental results. The results of the present study evidenced the incorporation of Cm into the silica matrix.
authors.affiliation: Radiochemistry Division, Bhabha Atomic Research Centre, Mumbai 400 085, India.
authors.forename: Aishwarya Soumitra
authors.initials: AS
authors.lastname: Kar
authors.forename: Sumit
authors.initials: S
authors.lastname: Kumar
authors.forename: B S
authors.initials: BS
authors.lastname: Tomar
authors.forename: V K
authors.initials: VK
authors.lastname: Manchanda
mesh_terms: D000327:Adsorption; D000465:Algorithms; D002245:Carbon Dioxide / Q000737:chemistry; D002614:Chelating Agents / Q000737:chemistry*; D003102:Colloids / Q000737:chemistry; D003476:Curium / Q000302:isolation & purification*; D006812:Humic Substances; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D015233:Models, Statistical; D012822:Silicon Dioxide / Q000737:chemistry*
chemical_list: D002614:Chelating Agents; D003102:Colloids; D006812:Humic Substances; D002245:Carbon Dioxide; D012822:Silicon Dioxide; D003476:Curium