Iron Salts:

Certain iron compounds such as fericchloride can be used as coagulants and are normally cheaper, produce heavier flocs and operate over a wider pH range than sulphate of alumina. However, they are normally required to be used with lime and are a little more difficult to control. In this context, the following problem should be considered:

(a) Special non-corrosive material may have to be used as liner for the storage containers.

(b) Iron salts tend to form cake in humid conditions.

(c) Iron salts are dirty to handle, causing staining.

(d) Sludge is more difficult to dispose of without giving rise to aesthetic complaints.

(e) Lime must be added, in advance.

(f)  While superior to alum in end results, bigger flocculation chambers may be required.