Basic Types Of Ion Exchange Resins

(1) Strong acidic cationic resin

This type of resin contains a large number of strongly acidic groups, such as sulfonic acid SO3H, which can easily dissociate H+in solution, thus exhibiting strong acidity. After resin dissociation, the negatively charged groups contained in the body, such as SO3-, can adsorb other cations in the bound solution. These two reactions cause the H+in the resin to exchange with the cations in the solution. Strong acidic resins have strong dissociation ability and can undergo ion exchange in both acidic and alkaline solutions.

After a period of use, the resin needs to undergo regeneration treatment, which involves using chemicals to reverse the ion exchange reaction and restore the functional groups of the resin to their original state for reuse. The cationic resin mentioned above is regenerated using strong acids. At this time, the resin releases the adsorbed cations, which then combine with H+to restore its original composition.

(2) Weakly acidic cationic resin

This type of resin contains weakly acidic groups, such as carboxyl COOH, which can dissociate H+in water and become acidic. The remaining negatively charged groups after resin dissociation, such as R-COO - (where R is a hydrocarbon group), can adsorb and bind with other cations in the solution, resulting in cation exchange. This type of resin has weak acidity and dissociation ability, making it difficult to dissociate and exchange ions at low pH. It can only function in alkaline, neutral, or slightly acidic solutions (such as pH 5-14). This type of resin is also regenerated using acid (which is easier to regenerate than strongly acidic resins).

(3) Strong alkaline anion resin

This type of resin contains strong alkaline groups, such as quaternary amine - NR3OH (R is a hydrocarbon group), which can dissociate OH - in water and exhibit strong alkalinity. The positively charged groups of this resin can adsorb and bind with anions in the solution, resulting in anion exchange.

This resin has strong dissociation and can function normally at different pH levels. It is regenerated using strong bases such as NaOH.

(4) Weakly alkaline anion resin

This type of resin contains weak alkaline groups, such as primary amino (also known as primary amino) - NH2, secondary amino (secondary amino) - NHR, or tertiary amino (tertiary amino) - NR2, which can dissociate OH - in water and exhibit weak alkalinity. The positively charged groups of this resin can adsorb and bind with anions in the solution, resulting in anion exchange. In most cases, this resin adsorbs the entire other acid molecules in the solution. It can only work under neutral or acidic conditions (such as pH 1-9). It can be regenerated using Na2CO3 and NH4OH.

(5) The Transformation of Ionic Resins

The above are the four basic types of resins. In practical use, these resins are often transformed into other ion forms for operation to meet various needs. For example, strong acidic cationic resins are often converted into sodium type resins for reuse by reacting with NaCl. During work, sodium type resin releases Na+and exchanges and adsorbs cations such as Ca2+and Mg2+in the solution to remove these ions. No H+is released during the reaction, which can avoid the decrease in solution pH and the resulting side effects (such as sucrose conversion and equipment corrosion). After operating in a sodium form, this resin can be regenerated with salt water (without the need for strong acids). For example, anion resin can be converted into a chlorine type for reuse, releasing Cl - during operation and adsorbing and exchanging other anions. Its regeneration only requires a solution of salt water. Chlorine type resins can also be converted to hydrogen carbonate type (HCO3-) for operation. After being transformed into sodium and chlorine types, strong acidic and strong alkaline resins no longer possess strong acidity and alkalinity, but they still have other typical properties of these resins, such as strong dissociation and wide working pH range.