Overview

Running the Resin Sample Trial

Preparing the Column for Testing

Once the column is loaded, the resin should be backwashed with demineralized water in an up-flow direction for 10–15 minutes to classify the bed fully.

During backwash, the resin bed will expand, and the larger particles will fall towards the bottom of the bed while the smaller beads will be located near the surface.

Following this process and depending on the particle size range of the resin, the height of the resin will increase. This resin height or bed volume (BV) must be noted and be used for all test calculations in the future.

Drain the column to leave a maximum of 1 cm of water above the bed. Discard the initial run-off.

Service Operation

Once a trial run begins, the resin should continue to operate to exhaustion or desired endpoint. The experiment should not be stopped mid-cycle, as most ion exchange reactions are reversible, and if the solution is stopped, it tries to reach an equilibrium. When this happens, the ions come back off the resin into solution. This can cause premature resin exhaustion and false results.

In tests with normal conditions, the bed must remain covered with solution. Never drain the column and introduce air into the bed. Air bubbles are difficult to remove and will result in poor test performance. Three consecutive cycles producing consistent results should be obtained before changing any operating conditions.

Sampling

Begin feeding the solution into the column. Adjust the opening of the bottom valve on your column set-up to control the total flow through the resin.

It is important to routinely sample the resin effluent during service runs to monitor performance. Frequent analysis of the target analyte will also reveal critical information about column loading. Additional testing may be for alkalinity, leakage, pH or other attributes as desired.

Regeneration of Resin Bed
The simplest, most common regeneration method is co-flow (often referred to as co-current), where the regenerant passes down through the resin in the same direction as the service flow. In co-flow regeneration, the first stage of every regeneration cycle is to backwash the bed to relieve compaction and remove suspended matter.

Solutions (or water) above trace solids levels should be filtered before entering the test column. The regeneration solution is passed through the resin at a slow rate to allow adequate contact time. This is followed by a slow displacement rinse and then a final fast rinse. In laboratory work, demineralized water is preferred for regenerant dilution and the rinsing stages. This will make capacity calculations easier and ensure there is no ionic loading of the resin.

A more efficient and thorough regeneration can be achieved using counter-flow regeneration (often referred to as counter-current or reverse flow). Counter-flow regeneration will produce lower leakage from the bed and better regenerant efficiency. The regenerant passes in the opposite direction to the service flow. Counter-flow regeneration is somewhat difficult to set up in a laboratory, and parameters such as bed depth are more critical.

Additionally, it is vital to prevent the bed from fluidizing when the regenerant is passed in an up-flow direction. Place cotton or glass wool on top of the resin to fill the freeboard space to prevent fluidization. This will stabilize the column and prevent beads from rising. Guidance from a Purolite technical expert is recommended.

Suggested regeneration parameters:

Regenerant Flow Rate: 2-6 BV/h (2 BV/h typical)
Regenerant Contact Time: 15-60 minutes (> 30 minutes preferred)
Slow Rinse: Normally same flow rate and time as the regenerant.
Fast Rinse: Same flow rate as the service flow, typically 30 minutes.

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