Effective Methods for Treating Resin Silicon Contamination

Ion exchange resins are widely used in industrial applications, but they can encounter various challenges, including silicon contamination. In this article, we will address common problems associated with ion exchange resins and provide effective methods for treating resin silicon contamination.

1. Resin Pre-Treatment

In industrial ion exchange resin products, there is often a presence of organic oligomers and inorganic impurities. These impurities can gradually dissolve and release during initial use, affecting water quality or product quality. Therefore, it is essential to pre-treat new resin before use. Here’s how:

  • Rinse the resin layer with clean water in the exchange vessel until the effluent is clear, odorless, and free of fine resin particles. The expansion rate should be 50-70%.
  • Pass a 4-5% HCl solution, approximately twice the resin volume, through the resin layer at a flow rate of 2 m/h. After complete penetration, let it soak for 4-8 hours. Then, rinse with clean water until the effluent is neutral, with a flow rate of 10-20 m/h.
  • Use a 2-5% NaOH solution, about twice the resin volume, following the same method used for HCl. Rinse with clean water until the effluent is neutral.

Repeating the acid and alkali treatments 2-3 times can enhance the effectiveness of resin pre-treatment. After pre-treatment, it is advisable to increase the regenerant dosage during the initial run to ensure complete resin regeneration.

2. Treating Resin Silicon Contamination

Silicon compound contamination occurs in strong alkaline anion exchange units, especially in systems where strong and weak anion resins are used together. This contamination often leads to a decrease in silicon removal efficiency.

The primary cause of this pollution is incomplete regeneration or failure to regenerate the resin promptly after it becomes exhausted. To address this issue, immerse the resin in a dilute, warm alkaline solution with a concentration of 2% and a temperature of approximately 40 degrees Celsius. For severe contamination, cyclic cleaning with a heated 4% sodium hydroxide solution can be effective.

3. Dealing with Organic Substance Contamination

Styrene-based strong alkaline anion exchange resins are susceptible to organic substance contamination, resulting in symptoms such as darker resin color, reduced exchange capacity, increased effluent conductivity, decreased effluent pH, elevated silica content, and increased cleaning water usage.

To prevent organic substance contamination, it’s crucial to remove organic substances from the water during pre-treatment. Additionally, using anti-pollution resins like large-pore weak alkaline anion resins or acrylic-based anion resins can be highly effective.

A commonly used recovery method is the alkaline salt method. This involves using a mixture of 10% NaCl and 4-6% NaOH in a volume equal to three bed volumes. Pass this mixture through the resin layer at a slow flow rate. After the second bed volume has passed, let the resin soak for 8 hours or overnight, then pass the third bed volume of the mixed solution. Heating the solution to 40-50 degrees Celsius and adding about 1% sodium phosphate or sodium nitrate can enhance the effectiveness.

If the alkaline salt method proves ineffective, consider using sodium hypochlorite (NaClO) solution for cleaning. In this case, pass at least one bed volume of 10% NaCl solution through the resin to fully deactivate it. Use a 1% effective chlorine content NaClO solution in an amount equal to three resin bed volumes. Soak the resin in the solution for 4 hours without heating. Ensure thorough rinsing to remove any residual NaClO, including wastewater disposal.

4. Treating Resin Iron Contamination

Iron contamination in cation resins primarily comes from iron ions in the raw water, especially when iron salts are used as coagulants. In anion resins, iron contamination mainly results from regeneration solutions. Iron-contaminated resins exhibit darker color, reduced exchange capacity, and accelerated degradation of anion resins.

The removal method for iron compounds typically involves immersing the resin in a high-concentration hydrochloric acid (10-15%) with added inhibitors for 5-12 hours or longer. Alternatively, complexing agents such as citric acid, ethylenediaminetetraacetic acid (EDTA), or aminotriacetic acid can be used for treatment.

5. Addressing Suspension Particle Blockage

Suspension particles in raw water can block the pores within the resin layer, increasing hydraulic resistance and covering the resin particles’ surfaces, thus reducing the working exchange capacity. To prevent blockage, enhance raw water pre-treatment to reduce suspension particle content. To remove particles within the resin layer, consider increasing backwash frequency and duration or using compressed air scouring methods.

6. Calcium Sulfate Precipitation

When regenerating calcium-type cation resins with sulfuric acid, improper operation can lead to the precipitation of calcium sulfate within the resin layer. This makes post-regeneration cleaning difficult, results in hardness in the effluent, and reduces resin exchange capacity.

To prevent calcium sulfate precipitation, reduce the sulfuric acid concentration during regeneration and increase the regeneration solution flow rate. Alternatively, adopt a stepwise regeneration method, gradually increasing the concentration while decreasing the flow rate. If calcium sulfate precipitation is detected, immerse the resin in a 10% hydrochloric acid solution for 1-2 days or consider using hydrochloric acid for regeneration multiple times.

7. Resin Storage and Transportation

  • For long-term resin storage or when resin needs to be stored within out-of-service equipment, strong resins should be converted to the salt form, while weak resins can be converted to the corresponding hydrogen form or free amine form to maintain resin performance stability. Keep resins submerged in clean water. If equipment needs to be drained, ensure it is sealed to prevent resin moisture loss.
  • Ion exchange resins contain a certain amount of equilibrium water. During storage and transportation, it’s essential to keep them moist to prevent dehydration. Store resins indoors or under cover at temperatures ranging from 5 to 40 degrees Celsius. Avoid direct exposure to sunlight and keep them away from heating devices such as boilers and heaters to prevent dehydration.
  • If resin dehydration is observed, do not immerse dry resin directly in water, as it may rapidly swell and break upon contact with water. Gradually add 10% saline water to the resin based on the degree of dehydration. Allow it to soak for several hours, then gradually dilute with clean water.
  • In environments where the temperature drops to or below freezing, take precautions to prevent resin cracking due to internal water freezing. Implement insulation measures or store the resin in different concentrations of saline water according to temperature conditions. If resin freezing is detected, allow it to thaw naturally without applying mechanical force.
  • Resin that has been out of use for an extended period and left inside exchange vessels can become irreversibly contaminated by microorganisms such as algae and bacteria. Before stopping operation, thoroughly backwash the resin to remove accumulated suspended matter. Periodically rinse and replace water or thoroughly backwash before implementing the following measures:
    • For anion resins: Pass a mixture of 10% NaCl and 2% NaOH, three times the resin volume, through the resin layer in two stages. Allow it to stand for several hours each time, then drain. If necessary, rinse with 0.2% hydrogen peroxide solution, about twice the resin volume, before reusing the resin bed.
    • For cation resins: Fill the exchange vessel and piping with a 0.5% formaldehyde solution and maintain this concentration during the period of non-use. Alternatively, immerse the resin in brine and rinse with 0.2% hydrogen peroxide or 0.5% formaldehyde solution before equipment reactivation.

Conclusion

These methods can help ensure the effective treatment of common issues related to ion exchange resins, including silicon contamination, organic substance pollution, iron contamination, suspension particle blockage, calcium sulfate precipitation, and storage and transportation considerations. By following these guidelines, you can maintain the performance and longevity of your ion exchange resin 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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