Study On Prearation And Phosphorus Adsorption Capacity Of Modified Diatomite

Phosphorus is one of critical nutrients for biological and chemical processes innatural water bodies. The excess of phosphate has been recognized as the main factorfor eutrophication. With the advantage of large specific surface area, good chemicalstability and low-cost, diatomite has been regarded a new type of adsorbent used inwater adsorption treatment. The modification experiment, in order to improvephosphate adsorption capacity of diatomite, is useful for eutrophication control.With FeCl₃as the modification agent, the modified diatomite was prepared in thealkaline solution and the synthesized conditions were optimized using theorthogonality experiments. The morphology, chemical component and structure of themodified diatomite were characterized using scanning electron microscope （SEM）,X-ray diffraction （XRD）, fourier transform infrared ray （FTIR） and N₂gasadsorption/desorption measurements. The adsorption properties of the modifieddiatomite for phosphate were examined using static adsorption methods. The effects ofdifferent controlling parameters such as pH of the solution, temperature, contact time,initial phosphate concentration and coexisting ions on the adsorption capacity of themodified diatomite were analyzed. The adsorption/desorption properties of themodified diatomite adsorbents were studied. Quantitative analysis for adsorption wasconducted to investigate the kinetics, adsorption isotherm and thermodynamics.The best modification method, making natural diatomite soaked in NaOH of2mol/L concentration and FeCl₃of 20% concentration for 3h, was established inexperiment. XRD and FTIR measurements reveal that FeOOH was blended todiatomite. In addition, SEM and N₂gas adsorption/desorption measurementsdemonstrate that the specific surface area of diatomite was increased obviously.The static adsorption results indicate that the modified diatomite possesses anexcellent adsorption property of phosphate. The phosphate uptake decreases with theincrease of pH in the studied range of pH. The adsorption process is favored in higherphosphorus concentration. Coexisting ions have no obvious effects on adsorption. The adsorption isotherm fits better to the Langmuir isotherm model. The adsorptionkinetics accords with the pseudo-second-order kinetics model. Thermodynamicparameters,ΔH⁰is less than 0,ΔG⁰is lower than 0, andΔS⁰is greater than 0, show thatthe adsorption of phosphate by the modified diatomite is spontaneous and exothermicprocesses. Analysis of the adsorption/desorption experimental results indicates that themodified diatomite can be reused.