Ultrapure water process: resurrection of ion exchange resin

Abstract: During the ion exchange process, the resin exchange capacity decreases or the exchange performance is lost due to various reasons, which will cause the abnormal operation of the exchange system or reduce the quality of the system effluent. At this time, the resin must be replaced or recycled. There are several main factors that cause the resin exchange performance to be reduced. According to different factors, corresponding methods are adopted to treat it to restore the exchange activity. In ion exchange processes, various factors can lead to a decline in resin exchange capacity or a complete loss of exchange performance. This results in abnormal system operation and compromised effluent quality. When this occurs, resin replacement or regeneration becomes necessary.

This paper explores the key factors that contribute to diminished ion exchange performance and discusses corresponding treatment methods tailored to each cause.

1. Deterioration of Resin

Resin deterioration refers to the irreversible loss of exchange activity due to factors like breakage, permanent oxidative expansion, or depletion of the active functional groups during usage. This deactivation necessitates replacing the resin with new material to restore normal system function. Improper use and operational controls can accelerate resin degradation.

2. Resin Pollution (Poisoning)

Resin pollution, also known as poisoning,  can manifest in three main ways:

a) Inorganic Pollution:

This occurs when salts containing Cu, Fe, Mn, Ca, Mg, or Al hydrolyze in an alkaline environment, forming hydroxide precipitates that block resin pores. Similarly, high silicon content in water can lead to silica gel formation, hindering exchange performance. Additionally, heavy metal ions can oxidize and alter resin structure, reducing its exchange capacity.

b) Organic Matter Pollution:

This primarily affects anion exchange resins. Organic matter in water often contains linear molecules with negatively charged groups, such as humic and fulvic acids produced by organic decomposition. These negatively charged groups electrostatically bind to the positively charged functional groups of the anion resin, hindering exchange sites. These linear molecules can even form entangled structures within the resin pores, significantly reducing exchange capacity. In severe cases, the exchange reaction might cease entirely.  Regular cleaning methods often prove ineffective in removing this type of contamination. This phenomenon is known as the "bottleneck effect."

c) Microbial Contamination:

During storage or extended periods without regeneration, resins can adsorb algae and microorganisms from the water. These microorganisms thrive on nutrients like nitrates and amines present in the resin, leading to rapid propagation. Besides compromising water quality, they can also damage the resin structure, reducing or eliminating its exchange capacity.

Mitigating Resin Pollution:

To minimize resin pollution and poisoning, proper pre-treatment of raw water before entering the exchange column is crucial.