17:15 〜 18:30
[MZZ47-P02] Redox potential of Fe(II) and Fe(III) concentrations in natural acidic river water
キーワード：酸化還元電位、Fe(II) と Fe(III) 濃度、自然酸性河川
Various elements (e.g., Al, As, Fe, Mn, Zn, Cu, and Ni) are dissolved in acidic river water. However, when Fe is dissolved in acidic river water, it precipitates and Fe(OH)3 or ferrihydrite is formed. Moreover, some metals are sorbed and natural attenuation occurs in acidic river water. Thus, it is important to evaluate the saturation index. The saturation index is used for the determination of the supersaturated, saturated, and unsaturated conditions, under which the minerals of Fe(OH)3 or ferrihydrite are formed. To calculate the saturation index, either the dissolved Fe(II) and Fe(III) concentrations, or the dissolved Fe concentration and Eh value, must be known. Although the electrochemical measurement of oxidation-reduction potential for the determination of the Eh value has provided unreliable results, some studies have reported the usefulness of the electrode oxidation-reduction potential measurement for the determination of Eh values for conditions under a pH of 4 or less and a total dissolved Fe greater than 10–5.5 molality. However, the pH of acidic river water varies with location. Therefore, the purpose of this study was to evaluate the usefulness of measuring the oxidation-reduction potential for the determination of Eh value in acidic river water with pH ranging from 3 to 5.5.
The results indicated that the Eh value calculated on the basis of the concentrations of Fe(II)/Fe(III) agrees with the Eh value calculated from the electrochemical measurements. Thus, the oxidation-reduction potential values electrochemically measured under conditions of pH 5.5 and Fe greater than 10–5.5 molality are useful for the determination of the Eh value. The study suggests that dissolved Fe concentration and Eh value determined by the measurement of oxidation-reduction potential may be important as environmental impact assessment indicators for acidic river water found in geothermal development areas.
The results indicated that the Eh value calculated on the basis of the concentrations of Fe(II)/Fe(III) agrees with the Eh value calculated from the electrochemical measurements. Thus, the oxidation-reduction potential values electrochemically measured under conditions of pH 5.5 and Fe greater than 10–5.5 molality are useful for the determination of the Eh value. The study suggests that dissolved Fe concentration and Eh value determined by the measurement of oxidation-reduction potential may be important as environmental impact assessment indicators for acidic river water found in geothermal development areas.