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Effect of pH and fulvic acid on sorption and complexation of cobalt onto bare and FA bound MX-80 bentonite

Summary Bentonite has attracted great interest in nuclear waste management because of its outstanding properties. Herein, the sorption and complexation of cobalt on bare bentonite and fulvic acid (FA) coated bentonite are studied, respectively, under ambient conditions. The experiments are carried out at T = 25 ± 2 °C in 0.01 M KNO3 solutions. Effect of pH, bentonite concentration, fulvic acid and cobalt solution concentration on cobalt sorption to bentonite is also investigated. The results show that cobalt sorption is strongly pH dependent and weakly bentonite content dependent. The presence of fulvic acid enhances Co2+ sorption at low pH values and reduces the sorption of Co2+ at high pH values. Effect of addition sequences of Co2+ and FA to bentonite suspension on cobalt sorption to FA-bentonite colloids is also studied and the results indicate that the sorption of cobalt on FA coated bentonite is dependent on the addition sequences. The mechanism is discussed by the relative strength between both complexes of Co(II) with sorbed and soluble FA and with bentonite.