Removal Of Phosphate Using NZVI Derived From Reducing Natural Limonite And Siderite

With the increasing attention of the human beings to the water eutrophication and environmental quality, seeking high efficiency, low-cost materials and technology of removal of phosphate attracted much attention of researchers both domestic and overseas. New materials-nanometer zero-valent iron is widely used as adsorbent because of its large specific surface area, strong adsorption ability. In this paper, XRD, XRF, TG/DTG and FESEM were utilized to characterize the mineral phase and morphology of limonite and siderite obtained from Tongling city. Zero-valent iron was prepared by thermal treatment of limonite in hydrogen and its performance on removal of phosphate from aqueous solution was investigated by static experiments and flowing column experiments and then the effect of different factors (calcined temperature, initial pH, reaction time, initial concentration, dissolved oxygen, interference ion) on P removal were studied. and reaction kinetics, the study of the adsorption equilibrium. In addition, nanometer zero-valent iron as a dynamic column packing and its performance on removal of phosphate from aqueous solution was investigated by dynamic experiments. Main conclusions are shown as follows:(1)The natural limonite contains goethite(>90wt%)and quartz, the crystal structure of limonite are acicular and sheet with a size of nanoscale, the aggregation looks like bamboo shoot and ball; Heat treatment favor the transformation from goethite into zero-valent iron phase, with nano-structure, porous structure and large surface area.(2) The main component of natural siderite is siderite (FeCO3), which mixed a small amount of quartz, goethite and clay. Under the electron microscope, the physical form of siderite is layered structure, the sheet structure substance is clay and the needles structure substance is goethite, which weathered from siderite.(3)When the calcinations temperature reached 550℃, the natural limonite and siderite could completely transformation into nano zero-valent iron by hydrogen reduction for 3h with the hydrogen flow rate of 200mL/min. According to the analysis of BET and experimental result, it can be concluded that the removal rate of phosphate by nano-iron increase with increasing temperature at the beginning and then decrease with increasing temperature. According to batch experiments, the optimal phosphate removal efficiency was observed for the nano zero-valent iron by hydrogen reduction annealed at 550℃.(4) The performance and mechanism of the nano zero-valent iron on the removal of phosphate with respect to the effects of calcinations temperature, solution pH, dissolved oxygen, initial phosphate concentrations and interfering ions were investigated. The experimental results via the static adsorption show that the removal rate of phosphate by the nano-iron (two kinds of material preparation in this paper) could be reached 95% in the case of weak acid and dissolved oxygen. The effects of reaction time, initial phosphate concentrations, solution pH and dissolved oxygen for the removal rate of phosphate were significant within the experimental concentration ranges observed in phosphate solution except reaction temperature.(5) Through hydrogen reduction by limonite, the preparation of nanometer zero-valent iron as a dynamic column packing to purification simulated containing phosphorus (5 mg/L) wastewater, which could be run more than one year and the removal rate of phosphorus was more than 99.5%, the phosphorus concentration of effluent achieves the II level (0.025 mg/L) of environmental quality.