Persulfate (S₂O₈^2–) is being used increasingly for in situ chemical oxidation (ISCO) of organic contaminants in groundwater, despite an incomplete understanding of the mechanism through which it is converted into reactive species. In particular, the decomposition of persulfate by naturally occurring mineral surfaces has not been studied in detail. To gain insight into the reaction rates and mechanism of persulfate decomposition in the subsurface, and to identify possible approaches for improving its efficacy, the decomposition of persulfate was investigated in the presence of pure metal oxides, clays, and representative aquifer solids collected from field sites in the presence and absence of benzene. Under conditions typical of groundwater, Fe(III)- and Mn(IV)-oxides catalytically converted persulfate into sulfate radical (SO₄^•–) and hydroxyl radical (HO^•) over time scales of several weeks at rates that were 2–20 times faster than those observed in metal-free systems. Amorphous ferrihydrite was the most reactive iron mineral with respect to persulfate decomposition, with reaction rates proportional to solid mass and surface area. As a result of radical chain reactions, the rate of persulfate decomposition increased by as much as 100 times when benzene concentrations exceeded 0.1 mM. Due to its relatively slow rate of decomposition in the subsurface, it can be advantageous to inject persulfate into groundwater, allowing it to migrate to zones of low hydraulic conductivity where clays, metal oxides, and contaminants will accelerate its conversion into reactive oxidants.

Potential-pH equilibria and potentiodynamic polarization studies were used to examine the electrochemical behavior of copper in aqueous glycine solutions. Potential-pH diagrams for the copper-water-glycine system were derived at different total copper { Cu T } and glycine { L T } activities. The diagrams show that glycine significantly extended the solubility range of copper. Polarization experiments were conducted in deaerated and aerated aqueous solutions of 10 − 2 M glycine with 10 − 5 M cupric nitrate and 10 − 1 M glycine with 10 − 4 M cupric nitrate at pH values between 9 and 12. The results of these experiments are discussed in terms of the relevant potential-pH diagrams. Good correlations were observed. © 2000 The Electrochemical Society. All rights reserved.