Fast and efficient phosphate removal on lanthanum-chitosan composite synthesized by controlling the amount of cross-linking agent

In the present study, non-crosslinked lanthanum-chitosan (La-CTS-0X) and crosslinked lanthanum-chitosan (La-CTS-1X/2X) composites were prepared as new complex biosorbents for effective phosphate removal from wastewater. Batch adsorption experiments were investigated by varying the influencing parameters, viz., pH, initial concentration of phosphate ions, contact time, temperature and co-existing anions. Experimental data were well fitted to the Langmuir isotherm model (R2 = 0.9998) as well as the pseudo-second-order model (R2 = 1.000), indicating that the phosphate adsorption process was homogeneous, mono-layered and chemisorption dominated. Besides, the maximum phosphate adsorption capacity for La-CTS-0X/1X/2X was 47.28, 57.84 and 31.01 mg g−1 at pH 6, respectively. Thermodynamic parameters including ΔH° (−43.7 kJ mol−1), ΔS° (−132 J mol−1 K−1) and ΔG° (−4.60 kJ mol−1) revealed that the essence of adsorption was spontaneous and exothermic. The regenerated materials could be repeatedly used for three cycles without obvious degradation of performance. Characterization of the adsorbent using FTIR, SEM, EDS and XPS techniques suggested that the possible adsorption mechanisms were electrostatic attraction as well as ligand exchange. More importantly, the La-CTS-1X had rapid removal rate for phosphate within 10 min and the remained P concentration met the permissible limit by the U.S. Environmental Protection Agency (EPA).