| It is well known that arsenic is a common contaminant in drinking water and longterm exposure to arsenic can cause various cancers and other serious diseases. World Health Organization has revised the guideline for arsenic in drinking water from50to10μ2g/L, China accepted this standard. Arsenic primarily exists in its common oxidation states, pentavalent arsenic and trivalent arsenic. Compared with As(V), As(III) is more toxic to human and is more volatile in the environment. Therefore, establish a simple and accurate determination of water with different valences of inorganic arsenic analysis methods have important guiding significance for understanding arsenic pollution in water and water pollution prevention and control processing. The first purpose of this paper is to establish a rapid determination of trivalent arsenic and pentavalent arsenic method in water, secondly, to synthesize loaded Mn/TiO2photocatalyst and adsorbent and apply it to the arsenic treatment system. The main content and result of this paper are as follows.1.The arsenite and arsenate concentrations in drinking water were detected through the molybdenum blue method. The detection conditions of arsenite and arsenate level of water sample were optimized. The results showed that complexes reached maximum absorbance at880nm after40minutes in the color temperature range of24to28℃.When the color temperature was above30℃, the reducing reagents became instable and the absorbance of complexes kept on increasing. Increasing the amount of ascorbic acid in the color reagent would compensate the complexes color suppression caused by the superabundant oxidizing reagent. Whereas the reducing reagent had no effect on the complexes color formation.The arsenic concentrations displayed a linear relationship in the range of10-100μg/L, the linear correlation coefficient was0.9977. The detection limit of arsenic was5μg/L, the relative standard deviations were from2.1%to5.9%. The inorganic arsenic concentrations in water samples were detected by this method. The standard addition recoveries of arsenic were from98.2%to104.5%, so the method had high accuracy.2.Mn/TiO2was successfully prepared on foam nickel substrates by sol-gel technique. The adsorption kinetics, adsorption isotherm, and desorption of arsenic on Mn/TiO2were investigated. Furthermore, the effect of pH on arsenic adsorption and the reuse of the Mn/TiO2adsorbent were also studied. It was shown that arsenate and arsenite adsorption equilibria at various pH were established in approximately1.5and2hours, respectively; the maximum adsorption pHs for arsenate and arsenite in solution were4and8, respectively; the saturation adsorption capacities of arsenate and arsenite on Mn/TiO2adsorbent were1.971and1.589mg.g-1at neutral pH, respectively; the removal efficiencies of arsenate and arsenite were still over85%when the adsorbents were reused10times by a basic solution with pH equal to13.5.3.Mn/TiO2catalyst was successfully prepared on foam nickel substrates by sol-gel technique. The factors such as molar ratio of Mn/TiO2, coating cycles of Mn/TiO2, solution pH, and using of the Fresnel lens were investigated on the oxidation rate of As(Ⅲ). It was shown that the optimum molar ratio of Mn/TiO2was1%and then the arsenite was completely oxidized to arsenate after4hours; the optimum coating cycles of Mn/TiO2was two; when the solution pH was9, the oxidation rate of arsenite was fastest and the arsenite was completely oxidized to arsenate after3hours; the oxidation time of arsenite was significantly shorten when the Fresnel lens was used; combined use of photocatalyst and adsorbent, the arsenic was not detected after3.5hours when the volume of solution was20liters and the arsenite concentration was100μg/L. |
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