Water

METHODS
OF IRON REMOVAL
FROM DOMESTIC
WATER SUPPLIES

S mall amounts of iron are quite common in water because of the
presence of iron in the soil and rock formations through which the water
passes in reaching its point of use. When the iron exceeds as little as 0.3 ppm,
it becomes objectionable because of its tendency to discolor plumbing fixtures, beverages, laundry, glasses anddishware and it should be removed
from the water.
iron is present in a water supply in many different forms and may or
may not be apparent to the eye. The ferrous or dissolved form of iron is not
visible while the ferric or oxidized form of iron becomes apparent through
precipitation. In order to condition the water correctly for iron removal, the
type of iron must first be identified. Then theequipment or combination of
units which will cope with the particular problem can be selected
Some of the forms in which iron can be present are:
F e r r o u s b i c a r b o n a t e F e ( H C 03 ) 2
Ferric Hydroxide Fe(OH)3
Organic iron
Corrosion products usually Fe 3 0 4
F e r r o u s B i c a r b o n a t e - this is iron that is dissolved in an oxygen-free water
supply. It is not visible tothe eye in a freshly drawn sample because the water
appears clear. But on standing in contact with air, the ferrous ion will become
oxidized to the ferric state and start to precipitate as a reddish brown floc. It
can then be seen and if allowed to remain in the supply will cause discolored
water as indicated above.
F e r r i c H y d r o x i d e - This can best be considered as theprecipitate which
appears when the ferrous ion is oxidized by the presence of oxygen in the
water. This reaction causes a lowering of the pH by converting the bicarbonates in the water to carbonic acid which dissociates to carbon dioxide and
water.
Organic Iron - Iron may be combined or complexed with organic matter in a
non-ionized form so that it is difficult to remove. The iron does not oxidizecompletely but is apparent in a finely colored suspension which does not settle. In some surface waters containing organic matter, the complex iron compounds are immediately apparent in the highly colored composition of the
sample when taken.
Iron
iron.
lines
give

Organisms - Crenothrix and other organisms thrive in water containing
Growths are formed which become attached to the inside ofthe pipe
and accumulate there. Reactions take place which may cause odors and
color to the water.

Corrosion Products - Corrosive water of low pH and high dissolved oxygen
content, flowing through iron piping, will dissolve some of the metal and thus
add iron to the water. The iron pickup will then become apparent at the point
of use.
2

I ron can also be present as ferrous sulphate,ferrous carbonate, and
other forms; but our discussion will be only of those iron compounds described above.
Ferrous Bicarbonate: Visual examination of the water sample and chemical
analysis are the guides as to the kind of iron in the water and the type of treatment necessary. For example, let us assume a well water analysis shows the
following:
Well Water A
Total hardness, grains per gallonas CaC0 3
pH
Iron, as (Fe)
Turbidity
Color
Taste or Odor
C o m m e n t - water clear when drawn at pump outlet

5 (85.5 ppm as
C a C 03 )
6.4
8.0 ppm
50 APHA units
10 APHA units
Irony

This analysis shows a water of moderate hardness, but objectionable
iron content of 8.0 ppm. The pH is below the neutral point of 7.0. While the
water was clear when drawn, by the time it reachedthe laboratory some oxygen was picked up while drawing it, and from the air space in the sample
bottle. This caused oxidation of some or all of the iron as shown by the 50 units
of turbidity now present.

This is typical of what will happen when ferrous bicarbonate becomes
oxidized to ferric hydroxide.
2 Fe(HC03 ) 2 + l / 2 02 + H2 0
2 Fe (OH)3 + 4 C O2
ferrous bicarbonate + o x y g e n +...