The effect of ionic interaction on the rates of oxidation in natural waters

Abstract

The effect of ionic interactions on the kinetics of disproportionation of HO 2, and the oxidation of Fe(II) and Cu(I) has been examined. The interactions of O 2 with Mg 2+ and Ca 2+ ions in seawater increases the lifetime by 3–5 times compared to water. The effect of OH − on the oxidation of Fe(II) in water and seawater shows a second degree dependence from 5 to 45°C. The effect of salinity on the oxidation of Fe(II) was found to be independent of temperature, while the effect of temperature was found to be independent of salinity. The energy of activation for the overall rate constant was found to be 7 ± 0.5 kcal mol −1. The effect of pH, temperature, salinity and ionic composition on the oxidation of Cu(I) has also been examined. In NaCl solutions from 0.5 to 6 M, the log k for the oxidation was a linear function of pH (6–8) with a slope of 0.2 ± 0.05. The reaction was strongly dependent on the Cl − concentration with variation of t 1 2 from 0.3 to 340 min from 0.5 to 6 M Cl −. The rates of oxidation of Cu + and CuCl 0 responsible for these effects are dependent upon ionic strength. The energy of activation for the reaction was 8.5–9.9 kcal mol −1 from 0.5 to 6 M. Studies of the oxidation in various NaX salts (X = I −, Br − and Cl −) give rates in the order Cl − > Br − > I − as expected, due to complex formation of Cu + with X −.