Synthesis and properties of zeolite/hydrated iron oxide composite from coal fly ash as efficient adsorbent to simultaneously retain cationic and anionic pollutants from water

A novel zeolite/Fe2O3 composite material, which was composed of synthetic zeolite and amorphous hydrated iron oxide, was produced by using coal fly ash as raw material. The obtained new material was shown to be unique to simultaneously retain cationic and anionic pollutants from water. Though synthetic zeolite showed a great increase in specific surface area, cation exchange capacity and phosphate immobilization capacity when compared with coal fly ash, synthesis of the composite material resulted in further great enhancement. The specific surface area, cation exchange capacity and phosphate immobilization capacity of the composite material reached 161.5 m2/g, 154.3 cmol/kg and 18.2 mg/g, respectively. For synthetic zeolite and coal fly ash, they are 28.7 and 1.1 m2/g, 137.6 and <3 cmol/kg, 6.0 and 1.6 mg/g, respectively. Synthesis of the composite material yielded rather cleaner effluent than the production of zeolite. The new composite material showed a neutral pH value of 6.60, differing from zeolite with an undesirable strong alkalinity. Phosphorus immobilized by the composite existed predominantly as Fe+Al bound−P and hydrated iron oxide contributed mainly to the phosphate removal. The removal of phosphate increased with decreasing pH while that of ammonium showed an opposite behavior. It was found that neutral pH condition could favor the uptake of both ammonium and phosphate.