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3.5 Aeration
Aeration for iron helps oxidation of certain substances. Also it can increase the agitation of iron to reduce the possibility of agglomeration and facilitate removal of passive film, which is deposited on the surface of iron, improving the effect of flocculation. However, excessive aeration will also affects contact time resulting in lower removal. Aeration can provide more sufficient oxygen to promote the anode reaction under neutral conditions. On the other hand it can accelerate the electrode reaction with stirring and shaking which decreased concentration polarization. Other than that the electrode performance of the cathode can be improved by adding a catalyst to promote the electrochemical activity of the electrode reaction.
3.6 Iron activation time
The surface of iron should be activated before using it because there is a passivation layer of oxide film on the surface of iron. Studies have shown that K vaule has the stability of the reaction with activating by diluted hydrochloric acid after 20min. Therefore, the appropriate activation time may be 20min.
3.7 Temperature
Temperature increasing can accelerate the reduction reaction. However some equipments for insulation are need to maintain a certain temperature and the acceleration of recation will only be initial so that the recations for industrial application are usually at normal temperature.
3.8 Types of iron
Usually, there are two types of irons used in micro electrolysis: cast iron and steel scrap. Cast iron has better effect for recation because of high carbon content but it has many disadvantages such as low intensity, easy to crush and agglomerate. Although steel scrap has lower carbon ...

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... pH will destruct the flocs produced by the reaction to make the process producing colored Fe2+ less effect. In addtion, many practical operation shows that the reaction will not occur in the neutral or alkaline conditions. Therefore the pH generally should be controlled in acidic conditions.
3.2 Retention time
Retention time is another major factor because the length of it determines how long the redox will be. The longer the retention time is, more thoroughly the redox will be. However, due to the long retention time, the consumption of iron will increase so that the dissolution of Fe2+ will increase significantly and oxidized to Fe3+, resulting in chroma increasing and various problems in subsequent treatment. Therefore, the retention time should be appropriate and it varies from different compositionfor a variety of waste water. The proposed design parameters:
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