The presence of IRON in groundwater has several origins ; in the form of pyrites ( FeS2 ) , it is usually associated with sedimentary rocks deposited in a reducing environment ( marls, clays ) and metamorphic rocks.

 

It is usually found in strong concentrations in the water of weathered bedrock.

 

The following concentrations in groundwater are reported by ACF :

 

Sedimentary ( Cambodia , 1998 ) : 3-15 mg / l.

Bedrock ( Uganda , 1996 ) : 0,5 - 1,5 mg / l.

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When present in reduced ( ferrous ) form ( Fe2+ or Fe ( II ), iron is oxidised by atmospheric oxygen and precipitates in oxidised ( ferric ) form ( Fe3+ or Fe ( III ), when water is pumped.

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This produces rust stains on the slabs of boreholes or wells, and users may not find the water acceptable, because it stains laundry and has a pronounced taste when consumed directly or in hot drinks.

 

Treatment to remove iron involves aeration of the water in order to oxidise the dissolved Fe2+ to Fe3+, which then precipitates and can be removed by filtration.

 

In-situ analysis is recommended.

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• AEP standard upper limit is 0,2 mg / l.

• WHO recommendation : < 0,3 mg/l.