COAGULANT ferric chloride, hexahydrate, per kg

Coagulant used for treating turbid water.

Crystallised granules/rocks of FeCl₃. Orange-like colour and corrosive to metals, abrasive to the eyes, and of mild toxicity if inhaled. Soluble in water, but may leave a yellowish colour.

Iron (III) chloride hexahydrate

Solid small lumps (balls) of ferric chloride (hexahydrate) which might accumulate to big lumps difficult to use. The product also exists in liquid form, but is not recommended for (air) transport reasons.

Lumps are amber coloured and crystalline with a "slight" odour. They have the following identifiers:

CAS number

• 7705-08-0
• 10025-77-1 (hexahydrate)

Chemical formula FeCl3.6H20

Concentration 60% (40% for the liquid form)

Very hydrophilic: Will even absorb the humidity of the ambient air and start to dissolve completely

Solubility in water: Very soluble in cold / hot water. Hygroscopic.

Stability: Very stable (even when diluted in 1% solution)

Corrosive: Corrosive to metals

Treatment of drinking water

For treating turbid water, a 1 % stock solution (or "mother solution") is used (10 g/litre).

It is made with 10 x (100/60) = 17 g FeCl₃ lumps (60% concentration) for 1 litre of water. The FeCl₃ lumps will dissolve completely.

The stock solution should be kept in an airtight, non-metallic container. It can be kept for a prolonged period, but should be shaken before use to mix the iron which has settled to the bottom.

Certain water analyses should be made beforehand: certainly pH (range of use: 5.0 till 9.0), turbidity, and preferably also conductivity, alkalinity (pH buffer effect) and temperature.

A jar test will have to be performed to determine the dosage needed.

Transparent 1 litre beakers are ideal as the formation and finally the settling of flocs will be very visible. The quantity required for this small volume can then be extrapolated according to the volume of the big sedimentation tank or to the flow of raw water which is pumped into the sedimentation tank or through the Water treatment Unit. Once all flocs have settled (this takes several hours) or when the water has passed the Water Treatment Unit, it still needs to be chlorinated in a separate reservoir.

Attention: Ferric chloride might provoke a slightly yellowish colour to the treated water if sedimentation times are too short and/or if the dosage is not correctly performed. And this might be enhanced once the chlorine is added due to its oxidation effect. Thus a residual iron test is strongly recommended and should preferably be under 0.2 – 0.3 mg/l.

See also:

"Public Health Engineering in Precarious Situations", MSF, 2^nd edition, 2010:

• T.B. 2.14 Coagulants / flocculants
• T.B. 2.15 Jar test for coagulants

for preparation of coagulation solution and their jar test, and

"Public Health Engineering in Precarious Situations", MSF, 2^nd edition, 2010:

• T.B. 2.16 Assisted batch sedimentation
• T.B. 2.17 Filtration methods

for water treatment methods based on coagulants, and

"Public Health Engineering in Precarious Situations", MSF, 2^nd edition, 2010:

• T.B. 2.13 Turbidity measurement
• T.B. 2.22 Monitoring chlorination

for water analysis to be done before and after the coagulant is used.