Cation Resin Loading

Before loading the resin, put some demineralized or exit-anion quality water into the bottom of the unit. The cation resin can then be loaded into the column.

When loading the cation resin, it is critical to make sure that the top of the cation resin is positioned correctly in relation to the central system. Once loaded, cation resin should be given an extended backwash so that the bed is graded to its full expanded and settled volume. If there is no inert spacer resin, you must allow for the volume change between different ionic forms. The central collection system should be slightly buried into the surface of the cation resin when it is in its exhausted form.

Cross contamination must be minimized in all polishing mixed beds, however it is not completely avoidable when intermediate spacer resins are not used. The effect of getting caustic onto cation resin is much less of an operating problem then contacting anion resin with hydrochloric or sulfuric acid during regeneration.

Rinse the cation bed to drain before loading the next resin in order to remove leachables left from the manufacturing process.

Inert Spacer Resin Loading

If using Purolite™ IP3 or Purolite IP7 inert spacer resin, it must be loaded into the column next. One should ensure that the inert resin covers and surrounds the central collection system by at least 50 mm (2 inches) on all sides. For example, a 100 mm (3.9 inches) wide center system would require a 200 mm (7.9 inches) depth of intermediate inert spacer. The inert resin can be changed manually from the top of the vessel. Loading inert resin should be carried out with a layer of water 600 mm (23.6 inches) above the cation resin so that disturbance of the bed is kept to a minimum.

Anion Resin Loading

Before loading the anion component, check that the central collection sight glass will clearly show the position of the interface between the cation and inert/spacer resins. Mark the interface position on the site glass for future reference. 

Loading of the anion resin should be carried out with a layer of water 600 mm (23.6 inches) above the cation (inert) resin to keep disturbance of the bed to a minimum. The anion should be loaded in the same manner as described for the cation resin. The anion resin bed can then be backwashed and expanded to its graded form through the central collection system. If this is not practical, it may not be prudent to carry out a full bed backwash to grade the anion component before the initial regeneration as this can give rise to clumping.

If you are changing the generic resin type or the grading of the products, you may have to adjust the backwash rate to achieve optimum expansion and operation. Your Ecolab technical sales team is available for guidance.

After the backwash of the anion, check the top of the bed and remove any debris that may be on the surface of the bed. Also check the interface position on the sight glass.

Remember the cation resin, if supplied in exhausted sodium form, will swell when regenerated.

As with the resin loading, all water used during the commissioning of the beds must be either treated water or water of a quality from the preceding cation-anion units. Use of raw water can result in magnesium hydroxide precipitation when it comes in contact with caustic or OH^- form anion resin.

The normal acid and caustic regeneration procedure can now be performed. If supplied in the exhausted form, then a double or triple regeneration is recommended. This does not mean going through the whole regeneration cycle two or three times. Instead, double or triple the amount of chemical applied. This may involve refilling the chemical measure.

Once regeneration and individual rinses are complete, the unit can move forward to the next stage of the regeneration cycle. This is normally a drain-down, followed by air mixing, bed settle, refill and final rinse.

During drain-down, make sure the water level drains to just above the resin bed, and that during air mixing, that the mixing is vigorous. There is always a risk of clumping with new mixed bed resins, and the air mix stage can be extended to ensure good mixing.

During the final rinse stage, extend the rinse to drain. New resins release organic leachables when first used, particularly if they have been held in stock for some time. Depending on the application, treated water quality specifications, storage time, it may take a while to achieve desired water quality. When monitoring water quality during this extended rinse, look at the conductivity and silica levels that may be achieved quickly. TOC release should be monitored as well if it is important to your final use, as for high-purity applications.

In order to maintain high quality water and performance, mixed beds should never be run to exhaustion. They are normally taken off line early, either based on the amount of time the resin has been in operation, or based on the volume of water treated. The water quality to service should not be allowed to be less than a resistivity of 200,000 ohms specific resistance (Conductivity 5 micromhos/cm).

Problems experienced on new resins in mixed bed units are often due to the following:

• Poor separation due to incorrect backwash rate
• Incorrect positioning of interface at central collection system
• Incorrect drain-down position
• Inadequate air mixing
• Clumping

In the event of clumping within the bed, additional regenerant chemicals can be used to overcome the problem during subsequent regenerations. Alternatively, if the clumping is very bad, declumping chemicals and a procedure for its application can be obtained from Purolite.

Resin Types / Ionic Form

Remember that regardless of the resin manufacturer, when ordering replacement mixed bed resins, resins supplied in the exhausted form (cation in the sodium form and anion in the chloride or sulfate forms) are more easily commissioned as they are less prone to clumping. Cation resins in the H⁺ (hydrogen) form can be loaded with chloride or sulfate form anion resins successfully, but OH^- (hydroxide) form anion resins are more prone to clumping when new.