Fraction 3. Metals Bound to Fe-Mn Oxides. Increasing the leaching time from 6 to 24 h did not result in higher iron concentrations in leachate 3 (Figure 2), indicating that the extraction of reducible iron oxide phases is complete; as manganese oxides are known to be more easily leached than iron oxides, it is probable that their extraction is also complete. The low levels of Fe and Mn found in the subsequent leachate (fraction 4, Table I) are an additional indication of the completeness of the extraction.