Influence of Boom Clay Organic Matter on the adsorption of Eu3+ by Illite

Batch sorption isotherm experiments were designed to evaluate the influence of organic material on the sorption of Eu3+ (1×10-8 – 5×10-7 M) on Silver Hill illite under conditions representative for the Boom Clay. Eu sorption isotherms were measured in SBCW background electrolyte (pH8.3) in the presence of 40ppm dissolved organic matter with different molecular weight distributions. The Eu distribution in all ternary systems, measured after centrifugation and after ultrafiltration, followed a linear sorption relation. The presence of dissolved organic matter in solution after centrifugation decreased the Eu distribution coefficients by an order of magnitude because of complexation reactions between Eu and organic matter. After ultrafiltration, the amount of dissolved organic matter and Eu concentration decreased relative to the size distributions of the different organic matter batches which resulted in increased distribution coefficients. Eu sorption onto illite could be described using the 2 SPNE SC/CE surface complexation model. Eu complexation constants to natural organic matter were fitted from solubility experiments above EuOHCO3 using Humic-Ion Binding model VI. Application of the additivity rule for the ternary systems clearly indicated that the two separate models were able to explain the measured solid-liquid distributions, both after centrifugation and after ultrafiltration.