Compared with the adsorption capacity of 0.06–0.15 mmol/g for
goethite atpH5 [21,22], 0.041 mmol/g for aluminum hydrous oxide
at pH 7 [21], and 0.024 mmol/g for kaolinite at pH 5 [18], the SAz-
1 montmorillonite exhibits a much higher adsorption capacity of
1.0 mmol/g for CIP at similar pH environments. The high adsorption
amount and cation exchange phenomenon indicate that the
CIP molecules were not only adsorbed on the external surfaces but
also into the interlayer of montmorillonite. A relatively low adsorption
capacity of 0.18 mmol/g was previously reported for another
montmorillonite material (STx-1) atpH6.5 [19]. The differencemay
be due to the employment of amuch lower initial CIP concentration
of 33 mg/L and a lower montmorillonite content (∼68%) in the sorbent
material in that particular study. However, as cation exchange
is the major mechanism of CIP uptake by montmorillonite, using a
lower initial CIP loading to assess the solute adsorption capacity
due to cation exchange would provide much lower values