Reasons for ion exchange resin contamination

What are the causes of ion exchange resin contamination? ?

There are several main reasons for resin contamination:

① Organic matter contamination.

Organic matter is a major impurity that contaminates ion exchange resins, especially strong alkaline anion resins. Organic molecules generally have large molecular weights, especially humic acid, which contaminates resins in two main ways. One is the combination of the carboxyl group of organic matter with the active groups of the resin; the other is the adsorption of organic matter on the ion exchange resin through intermolecular forces. Organic matter contamination of the resin reduces its ion exchange capacity.

② Oil contamination.

Oil impurities can clog the micropores of the ion exchange resin, preventing the active groups in these micropores from undergoing ion exchange, thereby reducing the working exchange capacity of the resin. The source of oil is mostly due to careless operation or oil leakage from equipment.

③ Suspended solids contamination.

Suspended particles in water will surround the surface of the ion exchange resin particles, isolating the ion exchange process of the resin and causing resin contamination. This type of contamination is more serious for cation bed resins.

④ Contamination caused by high-valence metal ions.

High-valence metal ions may enter the exchange bed with the bed water due to improper coagulation treatment or equipment corrosion.

Because these high-valence metal ions have a high exchange capacity with the resin, they are firmly adsorbed on the ion exchange resin and are not easily regenerated and "washed away," thus causing the resin to lose its exchange function. This contamination of the exchange resin by high-valence metal ions is referred to as "heavy metal poisoning" in some literature.

⑤ Contamination caused by impure regenerants. If the regenerant is impure and contains many impurities (such as NaCl or iron compounds often found in sodium hydroxide), it will contaminate the resin.

What are the phenomena after ion exchange resin contamination? ?

After ion exchange resin contamination, the following phenomena usually occur:

The color of the resin changes. It usually changes from yellow to dark brown or black.

The exchange capacity of the resin decreases significantly. This is manifested by a significant reduction in the water production of the exchange bed cycle. The effluent water quality deteriorates. This is manifested by a decrease in the effluent pH value, an increase in conductivity, and a significant increase in the amount of "sodium leakage," "hardness leakage," and "silicon leakage" effluent.

The regeneration consumption increases.

The cleaning time is extended, and the amount of cleaning water increases.

How to prevent ion exchange resin from being contaminated? ?

To prevent ion exchange resin from being contaminated, the following aspects should be done:

Do a good pre-treatment job. This is one of the important measures to prevent ion exchange resin from being contaminated. To do a good pre-treatment job, it is very important to correctly select and use coagulants. To remove organic matter from water, aluminum salt coagulant is better than iron salt coagulant. Determine the optimal conditions for coagulation through experiments, operate strictly, and prevent the "back migration" of iron and aluminum ions in the coagulant, causing contamination of the resin, especially the cation exchange resin.

Strictly control the amount of residual chlorine and turbidity in the water entering the cation bed. Prevent the oxidation of the resin by residual chlorine.

Strengthen the management of regenerants. In addition to strictly controlling the quality during procurement, management should also be done during transportation and storage. For example, the transportation pipelines and storage containers of regenerants should use corrosion-resistant materials, and filtration and clarification work should be done before the regenerants enter the bed.

For compressed air that may contact the resin, purification measures should be adopted, requiring no oil and no water, and oil-free compressors should be used as much as possible.