2. Experimental
2.1. Materials
2.1.1. Resins
The properties of Purolite S950 (Purolite International Co., Ltd.) are listed in Table 1. Purolite S950 is a macroporous polystyrenebased chelating resin with an aminophosphonate functional group (see Fig. 1). The resin was received in sodium (Na+) form. Prior to use, the resin was converted to the hydrogen