| Manganese is widespread in nature, and a common element in drinking water. In recent years, the phenomenon of excessive amounts of manganese in drinking water gradually caused extensive concern of countries. Long-term consumption of manganese excessive amounts of water can make body produce chronic poisoning. At the same time, the residual manganese deposit in the procedure of distribution water, affect the pipeline capacity, increase energy consumption of water supply, and influence disinfection effect. When hydraulic pressure or water quality change, manganese deposit in the network are likely to occur secondary release. Dissolved oxygen and residual chlorine in water pipe network are main inorganic oxidants which oxidizes Mn(Ⅱ). The dynamics process of the oxidizing Mn(Ⅱ) is the important factors which can reveal the reaction mechanism of Mn(Ⅱ) in drinking water distribution system.This article mainly simulated the behavior of manganese oxidition in the drinking water distribution system by using beaker experiment, and researched on the chemical kinetics reaction process of manganese in laboratory water, which is oxidized by the two main oxidants in actual distribution system: dissolved oxygen and residual chlorine. At the same time, the impact on the rate of manganese oxidation reaction by the common metal ion(Fe3+ and Al3+) was studied, and influence of the p H and alkalinity was analyed. The main content of the research and the results are as follows:(1) Beaker test was applied to study the oxidation kinetics of manganese which was oxidized by oxygen in hommogeneous solution and the influence of different water quality. The results showed that the divalent manganese was hardly oxidized to the particle state of MnO2 by oxygen in the pH range(6.5~8.5) of drinking water. The oxidation rate of manganese by oxidized oxygen was always slow and almost negigible by changing pH and the content of Fe3+ and Al3+.(2)The sudy of the oxidation kinetics between residual chlorine and manganese showed that the rate of manganese oxidation was slow in a relatively single solution; while the oxidation rate was fast in actual running water, and along with the higher concentration of residual chlorine, the reaction rate was faster. The linear correlation coefficient was 0.95 which was a strong correlation between the reaction rate with residual chlorine concentration.The oxidation rate accelerated when the solution contained commen metal ions(Fe3+ and Al3+), and the linear correlation coefficient respectively was 0.72 and 0.93 between the oxidation rate and the concentration of Fe3+ and Al3+. Fe3+ and Al3+ had a promopting effect on the oxidation between residual chlorine and manganese. The mechanism was that theredox reaction of residual chlorine and manganese was interface reaction, and the interface of reaction was provided when Fe3+ and Al3+ hydrolyzed, corprecipating with manganese dioxide. At the same time, FeOOH had a catalytic role in the reaction which was the hydrolysate of Fe3+.In the solution with Fe3+ or Al3+, the concentration of residual chlorine as the oxidant had a great influence on the reaction rate. The linear correlation coefficient in the resolution of the reaction rate and residual chlorine was 0.94 and 0.99 at the concentration of 0.1mg/L which were a strong correlation, respectively.In the range of pH 6.5~8.5, the rate of oxidation had little difference, so the change of pH had less effect on the reaction. The influence of alkalinity(25~100mg/l) of the reaction was weak because of little change in the concentration of manganese. |
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