Oxidation Filtration

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There are two kinds of filter media which can be used in beds or cartridges to oxidize ferrous iron, manganese and sulfide ion/hydrogen sulfide in water. (See the Iron Water and Sulfur Water discussions in Section II.) One is a zeolite called “manganese greensand,” either natural or synthetic, loaded up or exchanged with Mn++ ion and then oxidized (regenerated) with chlorine or potassium permanganate (KMnO4). The Mn++ on the zeolite becomes MnO2, called manganese dioxide, which is a good oxidizing agent. When water containing Fe++ or Mn++ or S-2 flows through a bed of this manganese greensand in MnO2 form, they are readily oxidized to Fe+++ or MnO2 or S, respectively, which are all particles for a fine-filter to remove. At the same time, the MnO2 on the zeolite is reduced back to its original Mn++ ionic form, which must then be reoxidized (regenerated) back to MnO2 again in a new cycle. (Careful-don’t be confused by the fact that we’re using manganese to remove manganese and iron and hydrogen sulfide. The M++ in the water is oxidized to MnO2 and removed by filtration later. The MnO2 on the zeolite gets reduced to Mn++ in the process, but that Mn++ is supposed to stay attached and be recycled back to MnO2.) When manganese greensand is used to oxidize Mn++ ion or Fe++ ion or S-2 ion in water, the reactions are:

Zeolite – MnO2 + Mn++ (dissolved) => Zeolite – Mn++ + MnO2
Zeolite – MnO2 + Fe++ (dissolved) => Zeolite – Mn++ + Fe+++ [=>Fe(OH)3]
Zeolite – MnO2 + S-2 (dissolved) => Zeolite – Mn++ + S

All three end-products-the MnO2, Fe(OH)3, and S-are filterable particles. Also do not be confused because one of the possible regenerant chemicals is another form of manganese, potassium perrnanganate. It’s just a coincidence that three different forms of manganese can be involved in this technology.