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  • 1 Department of Chemistry, Qinghai Normal University, Xining, Qinghai 810008, People’s Republic of China
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The sorption of Co(II) on Na-montmorillonite was conducted under various conditions, i.e., contact time, adsorbent dosage, pH, ionic strength, foreign ions, fulvic acid (FA), humic acid (HA) and temperature. Results of sorption data analysis indicated the sorption of cobalt on Na-montmorillonite was strongly dependent on pH and ionic strength. At low pH, the sorption of Co(II) was dominated by outer-sphere surface complexation and ion exchange with Na+/H+ on Na-montmorillonite, whereas inner-sphere surface complexation was the main sorption mechanism at high pH. The presence of different cations influenced Co(II) sorption, while the presence of different anions had no differentiable influences on Co(II) sorption. The presence of HA and FA decreased the sorption of Co(II) on montmorillonite. The sorption isotherms are simulated well with the Langmuir model. The thermodynamic parameters (ΔH°, ΔS° and ΔG°) calculated from the temperature dependent isotherms indicated that the sorption reaction of Co(II) on montmorillonite was an endothermic and spontaneous process. The sorption test revealed that the low cost material was a suitable material in the preconcentration of Co(II) from large volumes of aqueous solutions.