Effect of environmental conditions on the adsorption of Co on vermiculite

In this work,adsorption of radionuclide Co(Ⅱ) from aqueous solution onto vermiculite was investigated by using batch technique under various environmental conditions such as contact time,pH,solid content and humic acid(HA).The results indicated that the adsorption of Co(Ⅱ) onto vermiculite was very fast and the adsorption equilibrium can be obtained in a short time.Thus,the adsorption kinetic was well fitted by pseudo-second-order model.The results also indicated that the adsorption of Co(Ⅱ) onto vermiculite was strongly dependent on pH.At low pH value,the adsorption of Co(Ⅱ) was dominated by outer-sphere surface complexation and ion exchange with Na+/H+ on vermiculite surfaces,whereas inner-sphere surface complexation was the main adsorption mechanism at high pH value.Addition of HA increases Co(Ⅱ) adsorption at pH conditions below the adsorption edge observed in HA-free suspensions and diminishes Co(Ⅱ) adsorption at pH above the HA-free adsorption edge.The results are important for assessing the potential of practical application of vermiculite in Co(Ⅱ) and related radionuclide pollution management.