Water treatment technology - ion exchange principle

Technical principle:

Ion exchange resin is a kind of polymer material with ion exchange function. In solution, it can exchange its own ions with ions of the same number in solution. According to the different properties of the exchange groups, ion exchange resins can be divided into two types: cation exchange resins and anion exchange resins.

Most of the cation exchange resins contain acid groups such as sulfonic acid group (-SO3H), carboxyl group (-COOH) or phenol group (-C6H4OH), and the hydrogen ions in them can be exchanged with metal ions or other cations in the solution. For example, high polymers of styrene and divinylbenzene are subjected to sulfonation treatment to obtain strong acidic cation exchange resins, whose structural formula can be simply expressed as R — SO3H, where R represents the resin matrix, and the exchange principle is

2R — SO 3 H ＋ Ca 2+  ( R — SO 3 ) 2 Ca ＋ 2H +

This is also the principle of hard water softening.

Anion exchange resins contain basic groups such as quaternary amine groups [-N (CH3) 3OH], amine groups (-NH2) or imine groups (-NR'H). They can generate OH- ions in water and can exchange with various anions. The exchange principle is

R - N (CH3) 3OH + Cl-  R - N (CH3) 3Cl + OH-

Since the ion exchange effect is reversible, the used ion exchange resin is generally washed with an appropriate concentration of inorganic acid or alkali, and can be restored to its original state and reused. This process is called regeneration. The cation exchange resin can be rinsed with dilute hydrochloric acid, dilute sulfuric acid and other solutions; the anion exchange resin can be treated with sodium hydroxide and other solutions for regeneration.

Technical Features:

• It can produce ultrapure water, and the water quality is better;

• The pretreatment requirements are simple, the process is mature, the effluent water quality is stable, and the initial investment in equipment is low;

•Because the principle of water production is similar to replacing ions in water with acid and alkali, the operating cost is lower in the application area with low salt content in raw water.

Application fields:

•Electronics industry: preparation of ultrapure water and cleaning water for integrated circuits in the semiconductor industry;

• Electric power industry: preparation of high-pressure boiler feed water;

•Pharmaceutical industry: preparation of medical purified water;

•Chemical industry: desalination and purification of solutions;

• Experimental analysis: preparation of ultrapure water for analysis.