The performance of ion exchange resin for ion exchange reaction is manifested in its “ion exchange capacity”, that is, the number of milligram equivalents of ions that can be exchanged per gram of dry resin or per milliliter of wet resin, meq/g (dry) or meq/mL (Wet); When the ion is monovalent, the number of milliequivalents is the number of milligrams (for divalent or multivalent ions, the former is the latter multiplied by the valence of the ion). It also has three expressions: “total exchange capacity”, “working exchange capacity” and “regeneration exchange capacity”.
Generally, the regeneration exchange capacity is 50-90% of the total exchange capacity (generally controlled 70-80%), and the working exchange capacity is 30-90% of the regeneration exchange capacity (for recycled resin). The latter ratio is also called Utilization rate of resin.
In actual use, the exchange capacity of ion exchange resins includes adsorption capacity, but the proportion of the latter varies depending on the resin structure. It is still not possible to calculate separately. In the specific design, it needs to be corrected based on empirical data and rechecked in actual operation.
The measurement of ion resin exchange capacity is generally performed with inorganic ions. These ions are small in size and can diffuse freely into the resin body and react with all the exchange groups inside it. In practical applications, the solution often contains high molecular weight organic substances, which are large in size and difficult to enter the micropores of the resin, so the actual exchange capacity will be lower than the value measured with inorganic ions. This situation is related to the type of resin, the size of the pore structure and the material being processed.