IRON REMOVAL METHOD FROM GROUND WATER

 

IRON REMOVAL METHOD FROM GROUND WATER

Iron is one of the most abundant metals of the Earth's crust. It occurs naturally in water in soluble form as the ferrous iron (bivalent iron in dissolved form Fe²⁺ or Fe(OH)⁺) or complexed form like the ferric iron (trivalent iron: Fe³⁺ met in the precipity Fe(OH)₃). The occurrence of iron in water can also have an industrial origin ; mining, iron and steel industry, metals corrosion, etc.
In general, iron does not present a danger to human health or the environment, but it brings unpleasantness of an aesthetic and organoleptic nature. Indeed, iron gives a rust colour to the water, which can stain linen, sanitary facilities or even food industry products. Iron also gives a metallic taste to water, making it unpleasant for consumption. It can also be at the origin of corrosion in drains sewers, due to the development of microorganisms, the ferrobacteries.
In aerated water, the redox potential of the water is such as it allows an oxidation of the ferrous iron in ferric iron which precipitates then in iron hydroxide, Fe(OH)₃, thus allowing a natural removal of dissolved iron.
However ground waters are naturally anaerobic: so iron remains in solution and therefore it is important to remove it for a water use.

The elimination of the ferrous iron, by physical-chemical way, is obtained by raising the water redox potential by oxidation thanks to oxygen of the air and this by simple ventilation. In the case of acid water, the treatment could be supplemented by a correction of the pH. Thus, the ferrous iron is oxidized in ferric iron, which precipitates in iron hydroxide, Fe(OH)₃. The precipitate is then separated from water by filtration on sand or decantation. The stage of precipitation by chemical oxidation can also be carried out with the stronger oxidants such as the chlorine dioxide (ClO₂), ozone (O₃) or the potassium permanganate (KMnO₄).
This elimination can be carried out by cascade or spraying open-air systems (for an acceptable maximum content of Fe²⁺ of 7mg.L^-1) known as gravitating systems. Those systems require a significant place on the ground, but, in addition to an easy and a cheap exploitation cost, they also make possible aggressive CO₂ and hydrogen sulfide (H₂S) removal. There are also pressure systems, which in addition to their compactness, make possible to treat water whose Fe²⁺ concentrations between 7 and 10mg.L^-1.

Iron removal system schema

Iron is often found in water in complexed forms. In order to be eliminated, iron complexed requests a coagulation stage, which comes in between oxidation and filtration.

SUMMERY:

TYPE –I :Different units of the treatment plant for iron are :

1. Aeration Tank , b) Rotary type air blower with aeration grid complete with nozzles, c) Dosing tank with potassium permanganate (KMnO₄) solution , d) Pump ,e) Activated Carbon Filter

TYPE –II :
Different units of the treatment plant for iron are :

1. Pump ,b) Online Air Injector , c) Online auto doser for dosing of potassium permanganate (KMnO₄) solution , d) Online Air Mixer, e) Activated Carbon Filter

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