Pyrolusite potentials

FIGURE 21.25 Potential-pH equilibrium diagram for the manganese-water system at 25 °C. [Considering Mn02 (pyrolusite).] (from Ref. 37). 

The oxidation of Co(II)EDTA to Co(III)EDTA by pyrolusite-coated silica under dynamic flow conditions exhibited breakthrough characteristics (Figure 1) that were consistent with earlier research (Jardine and Taylor, 1995). The oxidation was initially rapid and slowed with continual exposure of Co(II)EDTA to the Mn-oxide. Jardine and Taylor (12) showed that the loss of oxidative potential was not caused by the accumulation of Mn on the surface and postulated that an intermediate Mn(III)-oxide solid phase, Mn203, was formed that impeded the redox reaction. XANES spectroscopy was used to determine the speciation of the solid-phase as a function of reaction time in order to identify the inhibition mechanism. 

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