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How Do Ion Exchange Resins Work?

• Structure

  Ion exchange resins are composed of three parts: the insoluble three-dimensional space network polymer skeleton, the ion functional group connected to the skeleton, and the exchangeable ion pore with opposite charges on the functional group.

  Polymer skeleton: It is composed of cross-linked polymers, such as cross-linked polystyrene, polyacrylic acid, etc.

  Ion exchange group: It is connected to the polymer skeleton and has ionic functional groups with exchangeable ions, such as -SO₃Na, -COOH, -N(CH₃)₃Cl, etc., or polar non-ionic functional groups, such as -N(CH₃)₂, -N(CH₃)H, etc.

  Pore: It is the pore in the polymer structure (gel pore) and the pore (capillary pore) between the polymer structures that exist in both dry and wet ion exchange resins.

• Working Principle

The principle of ion exchange resin is the process that ion exchange resin removes the salt in the solution.

Cation exchange resin principle: The metal cations (Na⁺, Ca²⁺, K⁺, Mg²⁺, Fe³⁺, etc.) contained in the aqueous solution perform ion exchange with the H+ (generated from acid groups such as sulfonic acid group (-SO₃H), carboxyl group (-COOH) or phenol group (-C₆H₄OH)) on the cation exchange resin, so that the cations in the solution are transferred to the resin, and the H+ on the resin is exchanged to the water.

Anion exchange resin principle: The anions (Cl^-, HCO^3-, etc.) in the aqueous solution are exchanged with the OH^- (generated from contain basic groups such as quaternary amino groups [-N(CH₃)₃OH], or amine groups (-NH₂)) on the anion exchange resin, the anions in the water are transferred to the resin, and the OH^- on the resin is exchanged to the water.

Taking sodium chloride (NaCl) to represent inorganic salts in water, the working principle of ion exchange resin is as follows:

Cation exchange resin: R—H + Na⁺ —— R—Na + H⁺

Anion exchange resin: R—OH + Cl^- —— R—Cl + OH^-

The general reaction formula of cation and anion exchange resin can be written as:

RH + ROH + NaCl——RNa + RCL + H₂O

It can be seen from equation that the NaCl in the water has been replaced by the H⁺ and OH^- on the resin, and the reaction product is only H₂O, so the effect of removing salt in the water has been achieved.

Applications

The main uses of ion exchange resins are very extensive, mainly distributed in the following industries:

• Wastewater Treatment

  The demand for ion exchange resin in the wastewater treatment industry is large, accounting for about 90% of its production. At present, the largest amount of ion exchange resin is used in the treatment of pure water in thermal power stations, followed by atomic energy, semiconductor materials, and the electronics industry.

• Food Industry

  Ion exchange resins can be used in industrial equipment such as sugar, chicken essence, special wine, and biological products. For example, the production of fructose syrup is to extract starch from corn, then undergo hydrolysis to produce fructose and glucose, and then undergo ion exchange treatment to convert it into fructose syrup. The use of ion exchange resins in the food industry ranks after sewage treatment.

• Pharmaceutical Industry

  Ion exchange resins in the pharmaceutical industry play an important role in the development of new antibacterial drugs and the improvement of the quality of original antibacterial drugs. The successful development and design of streptomycin is an outstanding example. In recent years, research has also been done on the extraction of Chinese herbal medicines.

• Generative Chemistry and Crude Oil Chemical Industry

  In organic chemistry, acids and bases are often used as metal catalysts for esterification, hydrolysis, transesterification, hydration and other reactions. The above reaction can also be carried out by using ion exchange resin instead of strong oxidizing agent and alkali, and has more advantages. These advantages include that the resin can be used continuously, the product is easily separated, the tubular reactor will not be corroded, the environment will not be polluted, and the reaction is easy to control.

• Conservation of Ecosystem

  Ion exchange resins have been used in many ecological and environmental protection issues of great concern. At present, many solutions or non-solutions contain toxic positive ions or non-positive ions, which can be recycled with resins, such as removing metal cations in electroplating process wastewater.

• Hydrometallurgy and Other Industries

Ion exchange resin can be used to separate, extract and purify uranium from depleted uranium ore and obtain rare earth elements and precious metals.