Green synthesis of a novel hybrid sorbent of zeolite/lanthanum hydroxide and its application in the removal and recovery of phosphate from water.

The traditional process of zeolite synthesis from coal fly ash produces large amount of waste alkaline solution, besides zeolite product. A novel hybrid sorbent, which was composed of zeolite and lanthanum hydroxide (La-ZFA), was produced by using soluble lanthanum chloride to react with waste alkaline solution after the traditional process. This study investigated the capability of phosphate removal by La-ZFA. The sorbent has a high phosphate removal capacity, with a sorption maximum of 71.94 mg/g, according to the Langmuir model. The removal of phosphate by La-ZFA performs well at a wide pH range, reaching>95% from pH 2.5 to pH 10.5 when initial P concentration<100 mg/L. Release of OH(-) during the interaction of phosphate with La-ZFA was observed. The formation of the monoclinic LaPO4 phase was identified by XRD analysis. The uptake of phosphate by La-ZFA was explained on the basis of the adsorption mechanism of the ligand exchange process. The sorbed phosphate could be recovered by hydrothermal treatment in 3M NaOH at 250°C, with a simultaneous regeneration of La-ZFA. Repeated sorption-desorption tests indicated that regenerated La-ZFA could be reused for phosphate removal. Therefore, synthesis of La-ZFA could impart additional function of phosphate removal to original zeolite, with the effective utilization of waste alkaline solution.