Ultrapure Water Process: Revitalizing Ion Exchange Resins

Resin Reactivation

During ion exchange, a decrease in resin exchange capacity or loss of exchange performance due to various reasons can cause abnormal operation of the exchange system or a decline in the quality of the effluent. In this case, the resin must be replaced or regenerated. Several factors can cause a decrease in resin exchange performance, and appropriate methods should be used to treat each factor and restore its exchange activity.

I. Resin Deterioration

Resin deterioration mainly occurs during use due to factors such as resin breakage, irreversible oxidation and swelling, or loss of active groups in the ion exchange resin, resulting in partial or permanent deactivation. For resin deactivation caused by deterioration, generally only replacing the resin can restore normal system operation. Improper use or operation control can accelerate resin deterioration.

II. Resin Contamination

Resin contamination, also known as resin poisoning, can be categorized into three types:

1. Inorganic Contamination: Inorganic contamination primarily results from the hydrolysis of salts such as Cu, Fe, Mn, Ca, Mg, and Al in alkaline environments, forming hydroxide flocculent precipitates. High silica content in the water can also lead to silica gel formation. These substances clog resin pores, affecting their function. The presence of heavy metal ions can further oxidize the resin, altering its structure and reducing its exchange capacity.

2. Organic Contamination: Organic contamination of resins generally refers to anion exchange resins. Organic matter in the water mainly consists of negatively charged linear molecules such as humic acid and fulvic acid produced from the decomposition of decaying plants and animals. These negatively charged groups recombine with the positively charged fixed groups of the anion exchange resin, causing them to adhere tightly to the exchange sites. These linear molecules typically carry multiple negatively charged groups that can recombine with various exchange sites on the resin, forming a tangled substance that wraps around the resin's pore structure. This not only damages the resin's functional groups but also clogs the resin channels, reducing its exchange capacity and, in severe cases, preventing ion exchange reactions from occurring. It is difficult to remove this substance from the resin channels using conventional cleaning methods; this phenomenon is called the "bottleneck effect." Furthermore, the degradation products of strongly acidic cation exchange resins—diethylbenzene—and the colloidal substances with negatively charged groups formed by the mechanical breakage of cation exchange resins can also contaminate anion exchange resins.

III. Microbial Contamination

When resin is stored or not regenerated for an extended period, it adsorbs algae and microorganisms from the water. These microorganisms rapidly multiply using nitrates, amines, and other substances within the resin as nutrients. Microorganisms not only contaminate the water but can also damage the resin structure, reducing or eliminating its exchange capacity. Therefore, to reduce resin contamination and poisoning, the raw water should undergo certain pretreatment before entering the exchange column.

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