Chitosan modified zeolite as a versatile adsorbent for the removal of different pollutants from water

With the goal to develop a coal fly ash-based versatile material toward a broad range of pollutants in water, a zeolite (ZFA) was synthesized from coal fly ash and subsequently modified by chitosan. The chitosan modified zeolite (CMZFA) was examined for its capability to sequester cationic (ammonium), anionic (phosphate) and organic (humic acid) pollutants from water. The cation exchange capacity in the internal pores was regarded as the retention capability for cationic ammonium. From the difference between the total and external cation exchange capacity, it was estimated to be 0.90 mmol/g (16.2 mg/g). Results showed an improved adsorption of CMZFA for phosphate when compared with ZFA, and a maximum adsorption capacity of 4.05 mg/g was obtained for CMZFA from the Langmuir model. Though ZFA presented little affinity for humic acid, modification by chitosan largely enhanced the adsorption performance with a Langmuir maximum of 31.6 mg/g. The negative charge in the internal pores of zeolite, the oxides of CaO, Al2O3 and Fe2O3 in the non-zeolite fraction, and the monolayer chitosan on the external surface of zeolite were interpreted as the binding bodies for the retention of cationic ammonium, anionic phosphate, and organic humic acid, respectively.