What is Manganese Greensand and its working explained …
(Iron Removal Media)
Another media that converts soluble forms of iron and manganese to insoluble forms that can then be filtered is manganese greensand.
Manganese greensand has been used for several decades and is formed from processed glauconite sand. The glauconite is synthetically coated with a thin layer of manganese dioxide, which gives the dark sand a definite green color and thus its name
The combination of a strong oxidant and manganese greensand filtration media for iron removal is commonly referred to as the “Manganese Greensand Process.” Either potassium permanganate or chlorine can be used to effectively regenerate manganese greensand filters. However, if chlorine is used alone, it may be necessary to periodically regenerate the manganese greensand using potassium permanganate by a batch process in order to maintain the optimum effectiveness of the media.
Prechlorination is often recommended if iron levels are significantly greater than 1 mg/L in order to reduce the need for the more expensive potassium permanganate. Manganese greensand is somewhat smaller than typical filter sand, with an effective size of 0.30-0.35 mm and a specific gravity of about 2.4
The density of greensand at 38 Kg/ft³ considerably lower than pyrolusite, but greater than Birm.
A vigorous backwash by air scouring is recommended. Backwash rates typically are in the range of 25-30 m³/m² and should be preceded by an air scour of the media to attain at least 30% bed expansion. A gravel support bed with a gravel retaining screen is recommended over the underdrain system.
The continuous regeneration of greensand using a strong oxidant has two purposes: (1) it reactivates the manganese dioxide on the greensand and (2) it oxidizes Fe(II) and As(III). This allows the newly formed As(V) and any residual As(V) to adsorb to the ferric hydroxide particles, which then are captured in the filter bed. Potassium permanganate should be fed in the piping far enough ahead of the filter to allow mixing and contact for several seconds before entering the filter.
For more information or to buy manganese greensand contact us: info@starkefiltermedia.com
