Study On Preparation Of Aluminum-doped TiO₂ Modified Bentonite And Removal Of NH₄⁺ And COD_Mn In Micro-Polluted Water

In recent years, with the development of the society, urban process and the process of accelerating industrialization, the water pollution problem worsening, and more drinking water sources water-quality in district change into micro-polluted water. It directly jeopardizes the drinker’s health. The main pollutants in micro-polluted water are ammonia and organic matters. But the conventional water treatment processes can’t remove ammonia and organic matter effectively. Therefore, a new decontaminate technologies functional materials are needed to be developed.This paper use sodium bentonite as raw material, using TiO2 and AICl3 · 6H2O as modifier. Aluminum-doped TiO2 modified bentonite(hereinafter, modified bentonite) were prepared by microwave radiation. The removal effect of modified bentonite process CODmn and NH4-N is took as the indicator to prepare a new type water treatment agen to remove ammonia nitrogen and organic matter(CODMn). And the prepare conditions of modified bentonite is optimized analysis.The surface morphology and internal structure of bentonite and modified bentonite are characterized. The modification mechanism is discussed through comparison and analysis between characterization results. And the removal mechanism is discussed after investigating the effect of various reaction conditions on ammonia nitrogen and organic matter(CODiMn) removal efficiency in micro-polluted water.The experiment results of preparing modified bentonite indicated that the settle properties of modified bentonite is very good at a CODmn concentration of 15mg/L and a NH4-N concentration of 5mg/L in micro-polluted water. And the best prepare condition is: T/S=13 mmol/1Og, Q=260 W, Al=2 mmol/lOg, t=8 min, L/S=9 mL/g, K=40%.The bentonite samples were characterized by X ray energy dispersive spectrometer(EDS), scanning electron microscope(SEM), fourier transform infrared(FT-IR), X-ray diffraction(XRD), N2 adsorption-desorption, differential scanning calorimetry and thermal gravity analysis(DSC-TGA). The results showed that the modifier enter into the interlayer of bentonite and Ti—O—Si bond is formed between the framework of bentonite in the modified bentonite. The interlayer spacing increase from 1.280nm to 1.533nm, the surface area increase from 39.66m2·g-1 to 72.05m2·g-1, the pore volume increase from 0.1034cm3·g-1 to 0.1405cm3·g-1, while the main pore structure of raw bentonite have not changed, and the BJH desorption pore size distribution of bentonite is the most probable distribution, is still category of mesoporous structures, and the thermal stability is evidently improved by the modification.Investigating the effect of various reaction conditions on ammonia nitrogen and organic matter(CODMn) removal efficiency in micro-polluted water, the results showed that the modified bentonite can synchronous remove organic matter and ammonia nitrogen in micro-polluted water, but the ability of removing organic matter is good, and the ability of removing ammonia nitrogen is general. As the PAC dosage and modified bentonite dosage increases, the removal rate increase, and increasing dosage has little obvious effect on the removal rate of NH4-N and CODMn after the removal rater reaching maximum. In mixture liquid, low CODMn concentration benefits the removal of NH4-N, and the initial concentration of NH4-N is high or low will affect the pH value of mixture liquid, which affects the removal rate of NH4-N and CODMn in micro-polluted water. When the pH value is among 5.0-6.0, the pH value has the best removal efficiency of CODMn, and when the pH value is among 6.0～8.0, the pH value has the best removal efficiency of NH4-N. The removal rate of turbidity is significantly before precipitating 30 min, and the removal rate of turbidity becomes balance and the removal rate of CODMn and NH4-N instead have a downward trend with the precipitation time increasing. With the increase of reaction time and stirring speed at a moderate speed, the removal rate of modified bentonite on NH4-N and CODMn increases gradually, after reaching peak, then decreased gradually. And with the increase of reaction temperature, the removal rate of modified bentonite on NH4-N and CODMn decreased gradually. In addition, the removal rate of NH4-N and CODMn is little difference after different adding sequence of modified bentonite and PAC.