The Usage and Maintenance of Ion Exchange Resins

Proper and rational use of ion exchange resins holds significant importance in extending their lifespan and ensuring stable and reliable resin performance. The use and maintenance of ion exchange resins encompass three aspects:

1. Resin Pretreatment

During the synthesis process of ion exchange resins, the resin surface and voids may contain low molecular weight compounds, inorganic impurities (such as copper, iron, etc.), high molecular weight monomers, and pore-forming agents. Therefore, before putting the resin into operation, these impurities must be removed to prevent resin contamination during usage. It is particularly important to note that in chromate-containing wastewater, chromium compounds act as oxidants. If the resin contains copper or iron, it could catalyze oxidation, accelerating resin deterioration. The pretreatment methods include:

Hot Water Washing:

Newly acquired resins should be thoroughly washed with hot water. For cation resins, hot water at 70-80°C is suitable, while anion resins (especially strong base anion resins) should be washed with 50-60°C hot water. Initially, change the water every 15 minutes during soaking, stirring occasionally. After 4-5 water changes, switch to changing water every 30 minutes, totaling 7-8 water changes. Soak the resin until the washing water is colorless and contains minimal foam.

Acid and Alkali Treatment:

After hot water washing, the resin is loaded into a column and subjected to acid and alkali treatments. For cation resins, pass 1mol/L HCl slowly through the resin bed at a rate of 2-3 times the resin volume. After approximately 2 hours, rinse with water and then pass 1mol/L NaOH through the resin bed at the same rate. After the alkali treatment, rinse until the effluent reaches a pH of around 9, then convert the resin to the H+ form using 1mol/L HCl or 0.5mol/L H2SO4 at 3-4 times the resin volume. Rinse until the effluent’s pH is above 6 before putting the resin into operation.

2. Resin Maintenance

During resin usage, it is essential to prevent contamination from suspended solids, organic compounds, oils, etc., as well as to safeguard against aggressive oxidation from certain wastewaters. Therefore, acidic oxidizing wastewaters should have heavy metal ions removed before entering anion resins to prevent catalytic effects. After each equipment run, discharge the spent water from the exchange column and replace it with tap water or purified water for soaking. Once saturated, the resin should be regenerated promptly, and after regeneration, it should not be left soaking in the regenerant for an extended period but should be rinsed clean.

3. Resin Reactivation

Both cation and anion resins experience a decrease in exchange capacity after several cycles of usage. This capacity decrease is due, on one hand, to incomplete regeneration, resulting in the accumulation of residual ions on the resin; on the other hand, certain substances in wastewater, like H2CrO4 and H2Cr2O7 in chromate-containing wastewater, cause oxidation, leading to the accumulation of Cr3+ ions in the resin. Hence, when a noticeable capacity decline is observed, resin reactivation is necessary.

Anion Resin Reactivation:

The reactivation approach for anion resins depends on the specific wastewater being treated. Successful experiences exist for reactivating anion resins used for chromate-containing wastewater treatment. After normal regeneration, immerse the anion resin in a 2-2.5mol/L H2SO4 solution, and gradually introduce NaHSO3 while stirring gently to reduce Cr6+ on the resin to Cr3+. Soak the resin in this solution for 24 hours, then rinse with clean water. Repeat this process 1-2 times to remove Cr6+ and Cr3+, and finally, transform the resin using NaOH.

Cation Resin Reactivation:

The primary goal of cation resin reactivation is to remove accumulated heavy metal ions, especially those with strong affinities to the resin, such as Fe3+ and Cr3+. In-situ reactivation can be performed. Use a 3.0mol/L HCl solution at a flow rate of 2 times the resin volume to pass through the resin bed. Subsequently, soak the resin in a 2.0-2.5mol/L sulfuric acid solution (1-2 times the resin volume) for a minimum of 8 hours, during which Fe3+, Cr3+, and other heavy metal ions will be removed. After rinsing, the resin is ready for use.

By following these guidelines for ion exchange resin usage and maintenance, you can ensure their optimal performance, prolong their lifespan, and maintain the stability and reliability of your resin-based systems.

Xi’an CHIWATEC Water Treatment Technology is a high-tech enterprise specialized in various water processing devices. Aside from these individual products, which cover a number of types and series, we can also help with related comprehensive engineering projects. Thanks to our hard work and dedication upon our founding, we are now one of the fastest-developing water treatment equipment manufacturers in Western China.

Further reading

C100E ion exchange resin

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