Why Regenerate Ion Exchange Resins?

Ion exchange resins gradually accumulate contaminants which diminish their ion removal effectiveness from solutions. Regeneration brings back resin capacity while lowering replacement expenses and cutting downtime. The regeneration method uses particular chemicals to reverse the ion exchange reaction based on whether the resin is cationic, anionic, or mixed-bed.

Step 1: Pre-Cleaning and Backwashing

1. Flush the resin bed with uncontaminated water to eliminate suspended solids and debris. The process loosens resin particles and removes trapped contaminants.

2. Inspect for fouling: Look for discoloration or smell to detect organic or biological fouling. Use a 4–8% NaCl solution or specialized resin cleaners to pre-clean resin beds in cases of extreme fouling.

Step 2: Chemical Regeneration Process

For Cation Exchange Resins (e.g., Strong Acid Cation Resins):

1. Acid treatment: Use 5–10% hydrochloric acid (HCl) or sulfuric acid (H₂SO₄) to displace captured cations (e.g., Ca²⁺, Mg²⁺). Circulate the acid solution for 30–60 minutes.

2. Rinse thoroughly with deionized water until the effluent pH reaches 4–5.

For Anion Exchange Resins (e.g., Strong Base Anion Resin):

1. Alkali treatment: Regenerate with 4–8% sodium hydroxide (NaOH) to release anions (e.g., Cl⁻, SO4²⁻). Ensure a contact time of 45–90 minutes.

2. Neutralize and rinse until the pH stabilizes at 7–8.

Calculation of Ion Exchange Resin Regeneration Agent Dosage

The calculation steps are: Determine both the exchange capacity of the resin and the required hydrochloric acid amount for regeneration. For every equivalent (eq) of cations exchanged in the resin, 1 equivalent of H⁺ is usually required for regeneration.

For hydrochloric acid C_HCl (mol/L), the calculation formula is as follows:

Where: V_HCl (L) for the required volume of hydrochloric acid; C (eq/L) for the resin exchange capacity; V (L) is the resin volume of the; C_HCl (mol/L) for the concentration of the hydrochloric acid solution. The term C_HCl represents the concentration of the regeneration agent instead of the hydrochloric acid stock solution (30%). The concentration of the hydrochloric acid regeneration solution is usually 10%~20%, and more commonly 15%.

If you need to calculate the mass of hydrochloric acid, you only need to use the molar mass of hydrochloric acid (~ 36.46 g/mol) and the concentration to convert, as shown in the following formula.

Where: m_HCl (kg) for the mass of the required commercial hydrochloric acid; φ_HCl for the mass fraction of the hydrochloric acid solution, that is, the 15%~20% we mentioned above; ρ_HCl for the density of the hydrochloric acid solution, which can be referred to the table below.

The calculation of the amount of regeneration agent for anion resin follows a similar calculation process. The term C_NaOH represents the concentration of the regeneration agent instead of the liquid caustic soda solution's concentration which stands at either 30% or 50%. The standard concentration range for liquid caustic soda regeneration solution spans from 2% to 6% with most applications falling between 3% and 5%. The table below includes information about the density of the alkali solution ρ_NaOH.