Removal of Iron from Wastewater 

Iron is normally found in spent pickle and etch baths from plating shops, steel mills, foundries, chemical milling, and wire drawing operations.  It is also found in ground water.  Iron in water is normally found in the ferrous state or iron 2.  The ferric state or iron 3 is very insoluble at neutral pH’s.  Both the iron 2, ferrous, and iron 3, ferric,  can be precipitated to low concentrations by pH adjustment, carbonate, phosphate and sulfide precipitation.  Iron 2 can easily be converted to iron 3 by aerating the water allowing the precipitation to take place at a neutral pH.

Iron 2 is a very strong reducing agent in neutral to basic conditions and is often used to reduce copper and  nickel from solution.  Additionally, iron 2 is used after sulfide precipitation to reduce the residual sulfide concentration and provide a co-precipitant to enhance floc formation, improve settling and filtration of the sulfide precipitant. 

Iron 3 is often found as ferric chloride.  It is use also to aids in floculation at neutral pH’s and as filter coagulant in media filtration.  If ferric chloride is used for water treatment it is important to use water treatment grade ferric chloride. Lower grades are often contaminated with copper and nickel and can cause high effluent concentration of these metals. 

The equipment used for iron removal includes: batch treaters for concentrated solutions, continuous precipitation for weak solutions, and aeration followed by media filtration, ion exchange and green sand filtration for dilute solutions. .