Fig. 9

Summary of recovered Fe(III) and Mn after resuspension of Mn/Fe mixed-phase solids in HCl. Theoretical extraction results based on a 1 Fe: 1 Mn (dashed lines) or 2 Fe: 1 Mn (dotted lines) reaction stoichiometry are provided for reference. Data cluster more closely around the 1:1 reaction line, indicating that Fe(II) may be reacting with Mn(IV) to produce Mn(III), which remains in the solid phase. A majority of data points cluster above the 1:1 line, due to the presence of ~ 0.6 mM Mn already existing in solution at the onset of acid addition, as a result of the initial reaction between pyrolusite and Fe(II) (see Fig. 2). Reactions were performed in 60 mL HEPES buffer with 60 mg MnO₂