Anion vs. Cation Ion Exchange Resins
Ion exchange resins are made up of a highly porous, polymeric material that is acid, base and water insoluble. The tiny beads that make up these resins are derived from hydrocarbon and are about ½ millimeter in diameter.
There are two main types of resins used for ion exchange: anion and cation. Within these two types, there are four main classifications of ion exchange resins:
- Strong Base Anion
- Weak Base Anion
- Strong Acid Cation
- Weak Acid Cation
Anion vs. Cation
Anion resins and cation resins are the two most common resins used in the ion exchange process. The difference between anion and cation resins is that one is positively charged (anion) and the other is negatively charged (cation).
Negatively charged ions are attracted to positively charged anion resins vs. cation resins, which attract positive ions with their negative charge. There are a number of physical and chemical properties to take into consideration when selecting an anion vs. cation resin, and which will help to determine the best resin for your needs, such as:
- The size of the resin beads.
- The amount of water the resin can hold.
- The amount of ions the resin can filter out before needing to be regenerated.
- The rate at which the ion exchange resin allows water to flow through it.
- The type and amount of contaminants in the source water.
- The desired quality of the final effluent water.
Anion vs. Cation Dealkalization
Strong base anion resins may be used for demineralization or dealkalization, while weak base anion resins work best for removing acids and organics from water. Anion dealkalizers are primarily used to remove alkalinity from boiler feedwater with a low-to-moderate amount of total dissolved solids (TDS). Anion dealkalizers may also be used to remove carbonate, bicarbonate, sulfates and nitrates from feedwater.
Strong acid cation resins can be used for dealkalization (most commonly in hydrogen form) or for split stream dealkalization. However, both methods of dealkalization require the use of hazardous acids to regenerate resin beds, as well as the use of a degassifier to remove carbon-dioxide created during the treatment process.
Weak acid cation resins can also be used for demineralization and dealkalization. In most water treatment cases, weak acid cation resins are used to remove divalent ions associated with alkalinity. Weak acid cation resins work best when water has a hardness and alkalinity ratio of 1:1 or higher.
Contact WaterProfessionals® for help in designing and manufacturing a custom ion exchange system for your business!