The influence of humic substances on the interaction between mineral surfaces and europium

The influence of humic substances on the interaction between europium and selected mineral surfaces has been investigated at neutral pH (6-7). The minerals included were γ-alumina, in the form of boemite, kaolinite, in its sodium form, and goethite. It appeared that in all cases the presence of humic substances in solution significantly reduced the sorption of europium to the mineral surfaces. The investigations comprise the ternary mineral (S) - humic substances (HS) - europium (Eu) system and three different starting conditions, i.e. the reaction systems HA-Eu + S, HA-S + Eu and Eu-S + HA, respectively, were studied. It turned out that the amount of europium bound to each mineral surfaces at equilibrium is independent of the starting conditions, i.e. identical equilibrium situations are reached. However, the equilibrium situation apparently is reached somewhat more slowly in the case of boemite compared to kaolinite and goethite. (orig.)