Interactions between Humic Acids and Actinides: Recent Advances

Recent advances on the experimental and computational studies of interactions between humic acids (HAs) and actinides are briefly reviewed. It appears that HAs are able to form coordination complexes with actinide cations (An(n+)) mainly via their carboxylate groups, and as a consequence, influence the migration of An(n+). In geomedia, many factors may affect the interactions between HA and An(n+), including pH, ionic strength, mineral surfaces, among which the effect of pH is the most significant. In general, at low pH, HA may enhance the adsorption of An(n+) on the surface of minerals, while when pH is around or larger than 7, HA plays an opposite role. In addition, HAs may reduce high valent oxidative actinide cations, and the reductivity originates from their quinoid and phenol groups. In those HAs with high presence of reduced sulfur, HAs may become more redox sensitive due to the participation of S in the redox reactions. The paper is concluded with an outlook.