Iron removal mechanism (contact filtration method)
The iron-removing filter material (Toyolex F) uses ceramics G as a carrier and is coated with iron oxyhydroxide (FeOOH), which has a special crystal structure.
● Iron removal adsorption reaction
The general reaction formula for catalytically removing iron in water is:
2Fe2+＋1/2O2 ＋ 5H2O → 2FeOOH・H2O ＋ 4CO2
The reaction from the viewpoint of iron-removing filter media will be explained in the following figure. As shown in equation (1), when raw water containing Fe2+ touches the surface of FeOOH, Fe2+ ions become H+ ions. Ion exchange.
1. Iron adsorption reaction
In this ion exchange, since the exchange group is finite, the ability to catch Fe2 + should be lost soon, but in reality, the iron removal ability is continuously maintained and the iron removal reaction proceeds continuously. This is because the surface of the filter medium returns to the original FeOOH by the decomposition and oxidation of equations (2) and (3). This is called an autocatalytic reaction.
2. Hydrolysis reaction
3. Air (oxygen) oxidation reaction
Since Toyolex F continuously oxidizes iron by autocatalytic reaction using oxygen in the blown air as an oxidant, iron can be removed without using chemicals such as sodium hypochlorite and PAC. I will. It also has the advantage that it does not capture iron as flocs, resulting in a slower rise in head loss and, as a result, longer filtration duration. From the above, iron removal by the contact filtration method using Toyolex F is the most suitable iron removal method for sites where chemicals cannot be used or where high-concentration iron is contained.
However, when applied to raw water with a pH of 6.8 or less and soluble silica of 40 mg / L or more, it may not function sufficiently and the iron concentration of the treated water may be slightly higher than that of the physical filtration method. Therefore, if microfiltration is required, post-treatment by physical filtration may be required after filtration with Toyolex F.
[Reference] by Yu Takai and Hiroshi Nakanishi, “Iron removal and manganese removal treatment for water”
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