Greensand Iron Removal Filters will remove, Iron, Manganese, and Sulfur. Greensand is the name commonly applied to a sandy rock or sediment containing a high percentage of the mineral glauconite. Typically it is an Efficient and economical media for the reduction of dissolved iron, hydrogen sulfide and manganese compounds we see these units used on well water supplies. Greensand Iron Removal Filters can be a single tank, Duplex, and even Triplex depending on requirements. Greensand Iron Removal Filters can be either Fiberglass, Steel, or Stainless Steel

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.

Greensand filters principle :

Iron removal filters can be based on different filtration media, depending on the iron and manganese concentration, the oxygen level, CO2 content, and hardness of the water. Greensand Filers offers a long material life. it's Regenerated with either chlorine or potassium permanganate solutions and Requires periodic backwashing.

Filtration media choice are:
- Sand + MnO2 for high iron concentrations
- Calcite for acidic waters
- Birm
- Greensand

industrial water filtration for oxidizing use chlorine and/or potassium permanganate, a strong oxidizer. Because the oxidation reaction required to convert the soluble material into solid particles, followed by successful filtration must be accomplished in 1-2 minutes of filter residence time, the water chemistry must be conducive to rapid reaction kinetics.

Oxidation chemicals can be used for highly contaminated waters :
- Ozone
- Chlorine
- Chlorine dioxide
These chemicals also have a biocide effect but might interact with other component.

for small commercial or residential systems air is injected in order to oxidize the iron. The oxidized iron will then precipitate on a sand filter. Manganese dioxide (MnO2) layer in the sand bed will catalyze the oxidation of residual iron. Backwash will be done by water and by air

Iron removal

Iron removal by physical-chemical way consists in iron oxidation by air followed by sand filtration, but other techniques exist as well:

  1. Oxidation + sand filtration (physical chemical way) : For water with pH > 7, low redox potential, low iron content (< 3mg/L)
  2. Oxidation + sand filtration + MnO2 filter : For higher iron content and/or manganese
  3. Oxidation + green sand : More efficient than sand filtration but required KMnO4 regeneration
  4. Oxidation + Limestone contactor : For acidic water with low redox potential, the limestone contactor increases aggressive water pH by binding CO2
  5. Ion exchange : 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 water containing iron, chlorine fed at a concentration of 1.0 to 1.2 times the iron should be adequate to oxidize the iron and “regenerate” the manganese greensand. Since excess chlorine is not deleterious to greensand filtration, it is possible to feed enough to provide adequate free chlorine residual in the filtered water sufficient for introducing into the clearwell and pumping to service.

Manganese removal

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

For water containing manganese and iron pretreatment is similar feed chlorine followed by potassium permanganate upstream of the greensand filters. Start with a chlorine dose calculated as 1.0 times the iron and 2.0 times the manganese concentration and introduce a small feed of permanganate. Collect minimum one-liter samples in a glass container (a one-liter Erlenmeyer flask is ideal) just upstream of the greensand filters and observe the color in good light. Chlorine alone should cause a yellowish tinge. When a pink tinge is first observed, the permanganate dose should be about right. If the color is distinctly pink, the potassium feed is too high.

Hydrogen sulfide pretreatment is similar to that for manganese. Start with a chlorine dose about 2.0 times the hydrogen sulfide and adjust permanganate to achieve the same color.