The oxidation of Cu(I) with H2O2 in seawater and in NaCl solutions has been measured as a function of pH (6 to 9), temperature (5 to 45°C), ionic strength (0.5 to 6 m) and composition. The seawater rate constants, K (M-1 s-1), for the oxidation d[Cu(I)]/dt = -k[Cu(I)][H2O2] have been fitted to the equation log k = 11.55 - 2250/T - 3.71I 1 2 + 2.06I with a σ = 0.04. The energy of activation was 43.1 ± 1.0 kJ mol-1. At a constant ionic strength (I = 1, 3, and 6 m) in NaCl-NaClO4 mixtures, the Cl- dependence has been attributed to the oxidation of various forms of Cu(I) in the solution. At a fixed Cl- concentration, the addition of Mg2+ causes the rate to decrease, and the addition of HCO-3 causes the rate to increase. The increase due to HCO-3 may be due to the formation of CuHCO03 which has a faster rate of oxidation than CuCl0. The decrease caused by Mg2+ may be due to the slow exchange of MgEDTA or MgCO3 with Cu2+, which may cause the overall oxidation rates of Cu(I) to be slower due to back reactions of Cu(II) with H2O2. Empirical equations for the rate of oxidation of Cu(I) with H2O2 in natural waters are given. The H2O2 results are compared with the kinetics of Cu(I) oxidation with O2 in natural waters. At the levels of O2 (200 μM) and H2O2 (0.1 μM) in surface sea waters, the oxygen oxidation is 130 times faster than peroxide oxidation. In rainwaters, however, the concentration of hydrogen peroxide (100 μM) is great enough so that H2O2 is the dominant oxidant for Cu(I).
ASJC Scopus subject areas
- Geochemistry and Petrology