Compared to the ethylenediaminetetraacetic dianhydride (EDTAD) which is widely used as a grafting reagent in many chemical modification processes, the SOCl2 activated EDTA grafts only one carboxyl group to the biomass and thus increases the amount of carboxyl group available for metal adsorption. In addition, the conditions of SOCl2 activated EDTA modification are more moderate (2 h at room temperature) than the EDTAD modification (24 h at room temperature or 4 h at 333 K) [22,23].