Evaluation of phosphate removal capacity of Fe3O4–ZVINPs from aqueous solution: optimization using response surface analysis

Performance of Nano Zero-Valent Iron Derived from the Decomposition of Siderite in the Removal of Phosphate

Natural siderite was selected as a raw material for preparing nano zero-valent iron (nZVI). The efficiency of the as-synthesized nZVI for PO^3-₄-P removal was investigated, and the effects of the annealing temperature, pH, initial PO^3-₄-P concentration, adsorption temperature and oxygen were investigated. The results indicated that after annealing at 550 °C, nZVI exhibited an average crystal size of 56.3 nm and a surface area of 14.1 m²/g. A decrease in pH and an increase in oxygen availability enhanced the removal efficiency. The adsorption process, which was spontaneous and exothermic according to the thermodynamic analysis, agreed well with the pseudo-second-order kinetic model. Based on the Langmuir equilibrium isotherms, the capacity of nZVI to adsorb phosphorus was determined to be 33.18 mg/L. The optimized conditions for the experimental conditions were defined by an orthogonal experiment as follows: initial P concentration 2 mg/L, initial pH 4, iron dose 2 g/L, adsorption time 60 min. The experimental results suggested that the as-prepared nZVI was a promising adsorbent for the removal of phosphate.