| Arsenic is similar to heavy metal pollutant. In the industrial wastewater, As is one of the most common heavy metal pollutants together with Pb, Cu, Zn and Cd, which are the most harmful pollutants to the environment. Arsenic pollutants in environment were generated in metallurgy industry, pharmacy industry and the early production of herbicide. Owing to characters of high toxicity, nonbiodegradable and easy to accumulating in living organisms, arsenic had harmful effects on human physiology and biological systems in natural environment. Usually, arsenite was pre-oxidated and then removed by ferric trichloride by action of adsorption and precipitation in industry treatment. This method was applied widely because of its low cost, good removal ratio, and simple operation process.Considering the perfect removal ratio of arsenite in yangzonghai lake arsenic treatment using ferric trichloride without preoxidation, influence of impact factors, such as pH value, Fe/As ratio and interfering ions, on arsenite removal ratio was studied in this paper. The results may provid the scientific evidence to treatment of asenite removed by ferric trichloride without preoxidation in industry. Meanwhile, the applicable environmental condition using ferric trichloride removing arsenite in natural water was suggested.(1) Since the pH value is the most influential factor in environment for removing arsenic, the effect of pH value on arsenite removal ratio by ferric trichloride was studied. Along the increasing pH from 4 to 10, the removal ratio increased then decreased. And the removal ratio reached the maximum value at pH=7. Therefore, pH value of 7 was the best for adsorbing arsenite. When pH value was close to 7 and Fe/As ratio was 10,20 and 30, the removal ratio was 45.04%,72.43%, and 82.88%, respectively.(2) By fixing pH value as 7, the influence of Fe/As ratio on the removal ratio of arsenite was studied. The results indicated that increasing Fe/As ratio was helpful to removal ratio of arsenite using ferric trichloride without preoxidation. When Fe/As ratio was 30, the removal ratio was up to 82.88%.(3) Oxygen acid radical anion has a competitive and suppressive effect on removal ratio of arsenite using ferric trichloride without preoxidation. When concentration of oxygen acid radical anion was rising, the removal ratio was reduced. And the bigger ionic charge was, the higher influence was. The order of the competitive effect was PO43->SO42->HCO3-.When pH<7, bicarbonate ion tended to buffer pH to a higher value then had a light enhanced effect on the removal ratio of arsenite.(4) Metal cation has a synergistic and enhancing effect on removal ratio of arsenite using ferric trichloride without preoxidation. When concentration of metal cation was rising.the removal ratio was increased. And the hydroxide complex of metal cation was bigger, the influence was higher. Ions of Ca2+ had a stronger enhancing effect than Mg2+.(5) Changing pH value just only influenced the degree of flocculation of sediment. Along the increasing pH from 4 to 10, a lot of iron hydroxide flocs was generated. And when floes were precipitated, arsenite was adsorbed by trapping and adsorption.(6) Binding energy of Fe should be in the vicinity of 712.82 when Fe combined with As. Binding energy of Fe increased when Fe adsorbed Oxygen acid radical anion which replaced AsO2-. The sequence of binding energy of Fe, when Oxygen acid radical anion combined with Fe, was PO43>SO42->HCO3-. By combining with metal cation through form of M-Fe-As, binding energy of Fe increased. And the form of Ca-Fe-As was more stable than the form of Mg-Fe-As. |
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