Characteristics of diethylenetriamine-crosslinked cotton stalk/wheat stalk and their biosorption capacities for phosphate

Two polymeric biosorbents were prepared from cotton stalk (CS) and wheat straw (WS) by the epichlorohydrin-diethylenetriamine-trimethylamine method. Amine-crosslinked cotton stalk (AC-CS) and wheat stalk (AC-WS) were used for the adsorption of phosphate, and their physicochemical properties as well as biosorption properties for phosphate were discussed intensively. Results indicated that the contents of holocellulose in CS and WS corresponded to the distinct phosphate adsorption capacities between AC-CS and AC-WS. Zeta potential and Raman spectra analysis illustrated the electrostatic attraction between phosphate ions and biosorbents. The adsorption of phosphate was not strongly pH dependent when the pH was about 4.0-9.0. The Langmuir isotherm provided the better fit and the maximum adsorption capacity (Q_max) was 51.54 mg/g for AC-CS and 60.61 mg/g for AC-WS. The saturated adsorption capacities of AC-CS and AC-WS in column were 49.05 and 41.9 mg/g, which accounted for about 80.3% and 81.4% of these biosorbents’ Q_max. NaCl and HCl solutions demonstrated the excellent regeneration capacities for the biosorbents, and after three times of adsorption-desorption cycles, the column adsorption capacities of these biosorbents were still higher than 92%.