Sorption of europium on a goethite surface: influence of background electrolyte

An experimental and theoretical study of Eu(III) sorption on goethite surface was performed in the presence of different background electrolytes (NaCl, NaNO3, KNO3). Results were described using a simple surface complexation, the double-layer model (DLM), and calculations were performed using either Fiteql3.2 or Jchess codes. The surface acidity constants and sites density were first determined by potentiometric titrations. The influence of electrolyte ions on the value of point of zero charge was studied by both potentiometric and electrokinetic measurements in order to assess their possible retention on goethite. The sorption of Eu(III) was then investigated by the batch method, in the three background electrolytes, as a function of pH. The presence of electrolyte ions was found to decrease the immobilization of Eu on goethite. Sorption results were modelled considering ternary surface complexes (goethite surface/europium/electrolyte ions).