[Phosphorus Removal Performance and Mechanism of Modified Zeolite Using Alum Sludge Acidified Extraction Liquid]

To improve the capacity for phosphorus removal and to reduce the cost of treatment, alum sludge from a water supply plant was obtained to prepare modified zeolite coated with layered double hydroxide (LDHs), which was synthesized using an acidified extraction liquid. The surface characteristics and chemical composition of raw zeolites, Al-Zn modified zeolites, and alum sludge modified zeolites were determined, and the isothermal adsorption and adsorption kinetics were analyzed. The performance and mechanism of phosphorus removal by the alum sludge modified zeolites were evaluated. The results showed that the optimum conditions for acidification extraction were 60 min treatment time, 150 r·min^-1, and pH 1.0, which achieved 77 mg aluminum extraction rate per gram of alum sludge. Compared to raw zeolites, the maximum saturated adsorption capacity and the desorption performance of the zeolites were significantly increased by this modification. In addition, the theoretical maximum adsorption capacity of alum sludge modified zeolites was increased from 30.24 mg·kg^-1 to 170.40 mg·kg^-1. The modification changed the main mode of phosphate adsorption by zeolite from physical adsorption to chemical adsorption. Alum sludge modification could improve the efficiency of phosphate adsorption and the regeneration capacity of zeolite, which could reduce the risk of water eutrophication caused by high phosphate concentrations, and could achieve the purpose of waste control by waste.