The separation function of ion exchange resin for mixed ions (including inorganic ions and organic ions) is based on its ion exchange selectivity. In a closed system, the fixed ion (A) of the ion exchange resin exchanges with the ion (B) in the solution, and can reach equilibrium after a certain time.
The selectivity of ion exchange resin is affected by many factors, such as the nature of chemical groups in the ion exchange resin, the degree of crosslinking, the nature and composition of ions in solution, etc. In general, in dilute aqueous solutions at room temperature, the higher the charge of ions, the smaller the radius of hydrated ions (that is, the larger the radius of non hydrated ions), the higher the selectivity of resins. For larger ions, such as complex anions, organic ions, etc., resins tend to exhibit greater ion exchange selectivity due to other non electrostatic interactions (hydrophobic interactions, hydrogen bonding interactions). The selectivity of ion exchange resin will increase with the increase of crosslinking degree.
Different types of ion exchange resins have different ion exchange selectivity.
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