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Solubilty On Ferric Oxide at pH 3

  • 1.  Solubilty On Ferric Oxide at pH 3

    Posted 25 days ago
    Is it soluble at that PH?

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    Catalina Zurano

    GlaxoSmithKline
    Buenos Aires
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  • 2.  RE: Solubilty On Ferric Oxide at pH 3

    SENIOR MEMBER
    Posted 25 days ago
    Catalina, can you specify a bit of the background of your question? You do not mention the kind of iron oxide. There are three different kinds. Wustite(FeO) brownish, Hematite Fe2O3 reddish and Magnetite (Fe3O4) black. Wustite is typically formed during post weld heat treatment of steel in a furnace where the atmosphere contains surplus if oxygen and also during atmospheric corrosion. Hematite is typically formed in steam service where the steal delivers the required oxygen for further oxidation. Hematite cannot stick on iron directly. There is always a very thin layer of Magnetite directly on the steel surface below the Hematite layer. Magnetite is instantaneously formed in steam service above 200°C. All these oxide forms can be found in steam boilers.
    The stability if these oxides depend on pH values. This is the reason why it should be aimed at a pH of 9.5 at 20°C normed conditions in boilers where there is a minimum of solubility of magmetite in water. Higher and lower pH values lead to higher solubility.
    This answers your question. Yes, iron oxides are soluble at pH3, probably also iron itself.
    Acid cleaning is typically used for cleaning of boilers. Citric acid, or diluted fluoric acid is used for this purpose. I am not sure about the pH value of the solution recircled for cleaning. If the background of your question is cleaning you should contact a company specialized in chemical cleaning. Solubility and pH may also depend on used temperature and acid.

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    Reinhard Michel
    Bochum
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