Sorption behavior of plutonium(IV) onto soils in the presence of humic acid

Abstract

Influence of humic acid on the sorption of 238Pu onto geologic media using a coastal sand, which does not sorb humic acid, and an ando soil, which sorbs humic acid very well, was examined with respect to molecular sizes of humic acid. Apparent sorption affinity of 238Pu for the coastal sand decreased with increasing humic acid concentration. As to the ando soil, the sorption affinity of 238Pu became largest in the presence of several mg/dm3 of humic acid. The humic acid fraction smaller than 100,000 daltons relates to the complexation with 238Pu and the sorption onto the soils, particularly the humic acid fraction of 30,000-100,000 daltons was dominant. Most 238Pu formed humic compounds even in a low humic acid concentration region; resulting plutonium humates are considered to control the apparent sorption affinity of ~38Pu. It is concluded from above results that a specific molecular size of humic acid controls the complexation ability and the apparent sorption affinity of 238Pu.