Caesium sorption—desorption in clay—humic acid systems

Soaking for 7 d with 0.05 M NaCl resulted in less caesium being sorbed by bentonite and kaolinite, but more by illite, compared to soaking for 2 d prior to addition of Cs. Overall the amount of Cs sorbed by the three clays was in the order bentonite > illite > kaolinite. Addition of humic acid to the clays depressed the sorption of Cs by all three clays, with illite showing the greatest effect. Desorption of added Cs was not totally reversible. The presence of humic acid resulted in an enhanced desorption of Cs from bentonite and to a lesser extent kaolinite. This enhanced desorption in the presence of humic acid was not seen for illite. The order of Cs retention following desorption for both clay and clay/ humic‐acid mixtures was illite > bentonite > kaolinite. A single Kd value could not describe the whole isotherm, but individual values were calculated at different Cs concentrations to cover the range of the isotherm. Kd values for desorption were higher than the corresponding Kd for sorption. For both sorption and desorption, the presence of humic acid resulted in lower Kd values than in its absence.