title: Influence of addition order and contact time on thorium(IV) retention by hematite in the presence of humic acids.
abstract: The influence of addition order and contact time in the system hematite (alpha-Fe2O3)-humic acid (HA)-thorium(IV) (Th(IV)) was studied in batch experiments. Th(IV) is considered here as a chemical analogue of other actinides (IV). The sorption isotherms were acquired varying pH in the range 2-10 and HA concentration in the range 1-100 mg/L. As already observed by numerous authors, Th(IV) retention was hindered when HA and hematite were equilibrated beforehand during 24 h. As it has been observed in a previous study, this effect was drastic when the ratio between humic and surface (iron oxide) sites exceeds a critical value. However, when HA was added after a 24-h equilibration of the hematite-Th(IV) system, Th(IV) was barely desorbed from the iron oxide surface. Furthermore, no drastic effect of the ratio between humic and surface sites could be evidenced, as the increase of HA concentration only results in a slight monotonic decrease in Th(IV) retention. Increasing contact time between components of the systems only indicated slight Th(IV) retention variation. This was interpreted as a consequence of slow kinetic controls of both the Th(IV)-HA complexation and HA-hematite sorption.
authors.affiliation: CEA, CE Saclay, DPC/SECR, Laboratoire de Speciation des Radionucléides et des Molecules, F-91191 Gif sur Yvette CEDEX, France. pascal.reiller@cea.fr
authors.forename: Pascal
authors.initials: P
authors.lastname: Reiller
authors.forename: Florence
authors.initials: F
authors.lastname: Casanova
authors.forename: Valérie
authors.initials: V
authors.lastname: Moulin
mesh_terms: D000327:Adsorption; D003102:Colloids; D005290:Ferric Compounds / Q000737:chemistry*; D006812:Humic Substances; D007700:Kinetics; D012990:Soil Pollutants, Radioactive / Q000032:analysis*; D013910:Thorium / Q000737:chemistry*
chemical_list: D003102:Colloids; D005290:Ferric Compounds; D006812:Humic Substances; D012990:Soil Pollutants, Radioactive; C000499:ferric oxide; D013910:Thorium