Iron and manganese are unaesthetic parameters present mostly in groundwater, causing
unwanted precipitation and color.
Iron removal is based on the precipitation of dissolved iron (Fe2+) into its oxidized
form (Fe3+), as Fe(OH)3 or Fe2O3.
Iron removal by physical-chemical way consists in iron oxidation by air followed
by sand filtration,
but other techniques exist as well:
Oxidation + sand filtration
(physical chemical way)
For water with pH > 7, low redox potential, low iron content (< 3mg/L)
Oxidation + sand filtration + MnO2 filter
For higher iron content and/or manganese
Oxidation + green sand
More efficient than sand filtration but required KMnO4 regeneration
Oxidation + Limestone contactor
For acidic water with low redox potential, the limestone contactor increases aggressive
water pH by binding CO2
Recommended for continuous process with low iron content. Not pH dependent
Oxidation can be carried out by various chemicals like chlorine, ozone but is mostly
done by compressed air.
Complex bound iron and manganese, e.g. complex bound with humic acids, can be very
difficult to remove. In this case oxidation with ozone can be a solution.
For manganese removal only, Manganese dioxide (MnO2) is used as an adsorbent according
to the following reaction:
Mn + MnO2 (s) --> 2 MnO (s)
Manganese oxides are then adsorbed on MnO2 grains. When all MnO2 has been consumed,
it can be regenerated by sodium hypochlorite.
Manganese removal by physical-chemical way (aeration and sand filtration) can also
be used but manganese oxidation kinetics are too slow at pH< 9.