The oxidation of copper(I) in natural waters

The reduced forms of metals in natural waters can be formed by photochemical, biochemical and geochemical processes. The lifetime of these reduced metals will be determined by the rates of oxidation with O$\sb2$ and H$\sb2$O$\sb2$.In my work, I have concentrated on the kinetics of oxidation of Cu(I) in aqueous solutions. By studying the rate in various media as a function of pH (6 to 9), temperature (5 to 45$\sp\circ$C), and ionic strength (0.1 to 6m), I have examined the effect of ionic interaction on the mechanism of the kinetics of oxidation of Cu(I) in natural waters. A brief description of the results is given below.A. Oxidation of Cu(I) with O$\sb2$ and H$\sb2 O\sb2.$ The oxidation of Cu(I) with O$\sb2$ is not strongly dependent on pH and oxidation with H$\sb2$O$\sb2$ is independent of pH. These results indicate that species such as CuOH$\sp\circ$ are not important reactants. The oxidation of Cu(I) is affected by the strong interactions of Cu$\sp+$ and Cl$\sp-$. The formation of CuCl$\sb2\sp-$ and CuCl$\sb3\sp{2-}$ ion pairs causes the rates to decrease. At a given Cl$\sp-$ concentration, the rates of oxidation in seawater are lower than in NaCl or NaCl-NaClO$\sb4$ mixtures. These differences in seawater are due to a decrease in the rates due to the presence of Mg$\sp{2+}$ and Ca$\sp{2+}$ and an increase in the rates due to the presence of HCO$\sb3\sp-$. The effects of Mg$\sp{2+}$ and HCO$\sb3\sp-$ ions are diminished at higher ionic strengths. The decrease in the rates due to the addition of Mg$\sp{2+}$ and Ca$\sp{2+}$ may be due to a slow exchange of MgL (L--Naturally occurring complexing agent) or MgCO$\sb3$ with Cu$\sp{2+}$ which may cause the overall oxidation rates of Cu(I) to be slower due to back reactions of Cu(I) with H$\sb2$O$\sb2$. The increase in the rates due to addition of HCO$\sb3\sp-$ may be due to the formation of CuHCO$\sb3\sp\circ$ which has a faster rate of oxidation than CuCl$\sp\circ$.The effects of Br$\sp-$ and I$\sp-$ on the rate of oxidation of Cu(I) with O$\sb2$ have been measured. These results show that the rates of oxidation of CuCl, CuBr and CuI ion pairs are the same. I have used this finding to estimate the stability constant for the formation of CuI$\sp\circ$.B. Cu(I) spectral studies. The stoichiometric equilibrium constants, K$\sb3\sp\*$, for the formation of CuX$\sb3\sp{2-}$ from CuX$\sb2\sp-$ + X$\sp-$ where X = Cl$\sp-$ and Br$\sp-$, have been determined from spectral measurements. The measurements were made in NaCl-NaClO$\sb4$ and NaBr-NaClO$\sb4$ solutions from I = 0.5 to 6.0 m at 5, 25 and 45$\sp\circ$C. The measured constants were extrapolated to infinite dilution using the Pitzer equations. The Pitzer parameters $\beta\sp0$, $\beta\sp1$ and C$\sp\phi$ for the interaction of Na$\sp+$ with CuX$\sb2\sp-$ and CuX$\sb3\sp{2-}$ were compared to values for other electrolytes