Colloidal iron is a very fine solid particulate material (typically between 0.1 and 0.001 microns in diameter) which, when suspended in water, can neither be settled nor be filtered.

Fortunately, these particles can be removed by utilising a Purolite^® Macroporous Strong Base Anion resin. The Purolite^® resins typically selected for this application are:

A501P
Tanex

Metal hydrides, metal oxides, and colloidal matters are removed by both these Purolite^® resins when in the chloride form. The operating capacity (or loading factor) is determined by on-site testing with pilot scale units. 

Purolite^® A501P is regenerated with Sodium Chloride solution. The colloidal iron being removed from the resin by the brine squeeze effect of the NaCl.