I am going to use iron (ii) and (iii) solutions in my experiment and need to prevent the formation of iron hydroxide. As the precipitation might occur at high ph and the target ph for my experiment is 5, I want to know if there are any other methods (chemical) to prevent the formation of iron hydroxides?
Regards and thanks.
One idea would be to work in a less oxidizing environment if we start with a Fe (II) solution. It may also be interesting to try to create a Fe (II) / Fe (III) stoichiometric gap.
Dear Mohammad,
A lot depends on the concentration of iron ions in the solution. Greenish Fe(OH)2 begins to precipitate at pH=7.5 (from 0.01M solutions), and rust-colored Fe(OH)3 begins to precipitate at pH=2 (from 0.01M solutions). So if you have Fe2+ ions in solution, there is a high probability that no hydroxide will precipitate. If there are Fe3+ cations, the pH of the solution should be controlled and kept at a low level, e.g. by adding small amounts of a strong acid (e.g. H2SO4).
Dear Mohammad,
My opinion is that if there is a slightly oxidizing environment in the solution, precipitation will occur, only the kinetics and mineralogical character of the product will change. If I remember correctly, ferrihydrite has a field of stability just around pH 5. At very low pH values below 2, the minerals of the jarosite group will precipitate and at pH values 2-4, with the addition of SO4-2, schwertmannite is stable. The safest way to prevent the precipitation of Fe oxyhydroxides will be to precipitate oxyhydroxides. Otherwise, it would be necessary to buffer the redox potential or chelate Fe 3+.
I would be interested in the stoichiometric gap as stated by @Mwanat Henock-Michel. Of course, transient FeII / FeIII compounds exist.
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