The sorption of Co(II) on Na-attapulgite as a function of contact time, solid content, pH, ionic strength, foreign ions, fulvic
acid (FA) and temperature under ambient conditions was studied. The kinetic of Co(II) sorption on Na-attapulgite was described
well by pseudo-second-order model. The sorption of Co(II) on Na-attapulgite was strongly dependent on pH and ionic strength.
The sorption of Co(II) was mainly dominated by outer-sphere surface complexation and/or ion exchange at low pH, whereas inner-sphere
surface complexation or surface precipitation was the main sorption mechanism at high pH values. The presence of FA did not
affect Co(II) sorption obviously at pH <7, and a negative effect was observed at pH >7. The Langmuir and Freundlich models
were used to simulate the sorption data at different temperatures, and the results indicated that the Langmuir model simulated
the data better than the Freundlich isotherm model. The thermodynamic parameters (∆G°, ∆S°,∆H°) calculated from the temperature-dependent sorption isotherms indicated that the sorption of Co(II) on Na-attapulgite was
an endothermic and spontaneous process. The results suggest that the attapulgite sample is a suitable material in the preconcentration
and solidification of radiocobalt from large volumes of aqueous solutions.