Measurement of Changing Ferrous Iron Concentration Using Redox Potential

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  • 酸化還元電位を用いたFe<SUP>2+</SUP>イオン濃度の時間変化測定法

Abstract

A method of determining the oxygenation rates of Fe(II) to Fe(III) was developed in relation to the mechanism of phosphate release from sediments because it is related to the redox reaction of Fe(II)-Fe(III). <BR>The method uses observed redox potential (Ehobs) to determine Fe(II) concentration in high pH region, because it is too low to be determined by spectrophotometry. <BR>The redox potential is based on the redox reaction Fe3++e-_??_Fe2+ and expressed by Eh=Eh0-0.059 log([Fe2+]/[Fe3+])(25°C). On condition that produced ferric hydroxide is in solution equilibrium, the change of Fe2+ concentration with time was expressed as log([Fe2+]t=t/[Fe2+] t=0)={(Ehobs)t=0-(Ehobs)t=t}/0.059(25°C). Here, the solution equilibrium of Fe3+ and OH- was found to be in an apparent equilibrium [Fe3+][OH-]2.68=10-35.8. <BR>The redox potential in the test solutions was found to be also affected with the redox equilibrium between NO2- and NO3-, formed from the absorbed NO2 gas. Therefore, it is necessary to use the initial part of the observed redox potential changes to determine the oxygenation rates of Fe(II).

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