Investigation of manganese greensand activation by various oxidants

Manganese greensands are used routinely in industry for Mn(II) and Fe(II) removal from drinking water and groundwater, however little is understood about the effect of changing the activation conditions on removal performance. This study directly compared the change in removal performance for Mn(II) and Fe(II) across five commercially available greensands when using bleach or potassium permanganate as the oxidant for greensand activation. The performance of these medias when no activation process was employed was also compared. The results indicated that enhanced performance was achieved when higher concentrations of oxidant were used. Activating the medias with potassium permanganate was found to achieve slightly higher removal performance for both Mn(II) and Fe(II), although bleach was found to limit the effect of reductive dissolution when treating Fe(II) solutions. A notable observation was that activation of the medias induced a discrete removal mechanism that involved a negatively charge surface species. This species was thought to exist as a higher oxidation state than Mn(IV), analogous to a Mn(VII) species. XPS spectra indicated that activation influenced the greensands' surface structure, and supported the change in surface Mn oxidation state, however the surface speciation was inconclusive as to an exact structure. This study used fixed bed columns to examine the various activation conditions, as well as XPS to observe any changes in Mn oxidation state.