DOWEX Ion Exchange Resins WATER CONDITIONING MANUAL

Ion Exchange Cleaning Procedures
10 ION EXCHANGE CLEANING PROCEDURES
10.1.1 Removal of Iron and Manganese from Cation Resins
Iron has a complex chemistry and may be present as inorganic precipitates (oxides/hydroxides), as
cationic species, or as organometallic complexes. In water-treatment applications, iron is generally
converted to the less-soluble Fe (III) form within the resin bed. Manganese also may be present as
inorganic precipitates. Three possible cleaning procedures are described:
Air brushing: This is used in condensate polishing and other water-treatment applications such as makeup
demineralization to remove insoluble, particulate iron (crud).
1. Exhaust the resin.
2. Air-brush the bed and then backwash for 30 min.
3. Regenerate the resin as normal.
If the particulates are large, backwashing may not be effective in removing them. In this case, the solids
can be driven down to the bottom of the bed and removed through the screen/drain using the following
procedure:
1. Air-brush the bed for 30 s at a rate of approximately four volumes air per min per volume resin and
then drain the bed for 30 s, adding more water at the top.
2. Repeat step 1 about 10–20 times.
3. Regenerate the resin as normal.
If soluble iron is also present, air-brushing should be followed by acid treatment.
HCl treatment: This is used to remove crud and soluble contaminants. If possible, the acid injection in
step 2 and the displacement step 4 should be made upflow into the resin bed to move the bed and
increase contacting. If only downflow injection is possible, a normal backwash should be made first to
loosen the bed prior to the treatment.
1. Exhaust the resin and backwash.
2. Pass two bed volumes of 10% HCl solution with a contact time of 30 min.
3. Leave to soak for 2–4 h.
4. Displace with two to three bed volumes of water.
5. Rinse out with three to five bed volumes of deionized water fast rinse (downflow).
Note: HCl is very corrosive and can cause severe burns on contact. Avoid inhalation of the fumes and
provide adequate ventilation when handling the acid. Refer to the manufacturer’s safety information. The
acid can also cause problems with materials of construction, so ensure that the acid is compatible with
the plant equipment before use.
Reference Document: Tech Facts 177-01852
Reducing agent treatment: This treatment uses a reducing agent (sodium dithionite, Na2S2O4) to
convert Fe(III) to the more soluble Fe(II). It is used in water softening and other applications, where acid
can damage the materials of construction. If possible, steps 2, 4, and 6 should be made upflow into the
resin bed to increase contact. If only downflow injection is possible, a normal backwash should be made
first to loosen the bed prior to the treatment. Do not use air-brushing to agitate the resin bed because this
will impair the reducing agent performance.
1. Exhaust the resin and backwash.
2. Pass one bed volume of 5% Na2S2O4 solution with a contact time of 30 min.
3. Leave to soak for 2 h.
4. Pass one bed volume of 5% Na2S2O4 solution with a contact time of 30 min.
5. Leave to soak for up to 24 h if possible.
6. Displace with two to three bed volumes of water.
7. Rinse out with three to five bed volumes of deionized water fast rinse.
8. Double regenerate the resin (same NaCl concentration, double time).
DOWEX Ion Exchange Resins 57 Water Conditioning Manual