Adsorption of humic acids and europium-humate colloids onto repository components: Boom clay, bentonite and Fe₂O₃

Batch sorption experiments were carried out to investigate the adsorption of humic acids (HA) and Eu-humate colloids onto repository components: Boom clay, bentonite and Fe₂O₃ as a function of pH. The concentration of humic acids is 150 mg/l and the bulk concentration of Eu is 10^-6 M. Radioactive ¹⁵²Eu was used as a tracer. The adsorption of humic acids onto bentonite and Fe₂O₃ decreased with increasing pH. Humic acids were probably complexed to Al/Fe sites on the adsorbents through COOH and phenolic OH groups. It is difficult to interpret the adsorption of humic acids onto Boom clay because Boom clay itself contains high content of organic matters. The adsorption of Eu-humate colloids onto repository components were performed near neutral pH conditions. Eu was strongly adsorbed by three adsorbents, and pH had little effect on the adsorption in the neutral pH range. The strong complexation of Eu with humic acids did not prevent Eu from being adsorbed. Eu is likely bound to solid surfaces via humic acids. The adsorption of Eu-humate colloids onto mixed adsorbents (Boom clay+bentonite, Boom clay+Fe₂O₃, bentonite+Fe₂O₃, and Boom clay+bentonite+Fe₂O₃) was investigated. Most of Eu-humate colloids was adsorbed by the mixed adsorbents. The desorption of humic acids and Eu from repository components was also examined.