Ion Exchange Resin Swelling Rate Related to Crosslinking Degree, Active Groups and Solution Concentration

Installation & Precautions

When viewing the specification data of ion exchange resin, you may encounter some nouns that are not easy to understand. We explain these nouns and hope it can really help you.

  • Resin factory type. Easily transformed ions that ion exchange resin carries itself, such as Na+ and Cl-.
  • Mass total exchange capacity. The total amount of all exchangeable ions in the ion exchange resin per unit mass.
  • Volume total exchange capacity. the total amount of all exchangeable ions in the ion exchange resin per unit volume.
  • Particle size. It refers to the diameter of the beads, usually the particle size of spherical beads is expressed by the diameter, and the particle size of cubic beads is expressed by the side length. The more uniform the particle size, the better the overall performance of the resin. The particle size affects the exchange rate, exchange capacity, pressure loss and the height of the resin layer unfolding during backwashing. The particle size range is generally between 0.315 and 1.25 mm, which is beneficial to improve the use of the resin in water treatment equipment.
  • Water content. The crosslinking degree of the reactive resin and the size of the void. A large water content of resin means that it has a large porosity and a low crosslinking degree.
    Moisture content (W) = (mass of wet resin - mass of dry resin) / mass of wet resin × 100%
  • The difference between true density and bulk density
    True density
    . It refers to the true density of the resin after full swelling in water. True density (ρZ) = wet resin mass / true volume of wet resin (ρZ = 1.04–1.03 g/mL)
    Bulk density. It refers to the bulk density of resin after full swelling in water. Bulk density (ρS) = mass of wet resin / volume of wet resin (ρS = 0.60–0.85 g/mL)
  • Sphericity after attrition. The lower the breakage rate of the ball, the higher the strength of the resin.
  • Transformation swelling rate (swelling property). Ion exchange resin contains a large number of hydrophilic groups, which absorb water and swell after contact with water. When the ions in the resin change, the strong acid cation exchange resin changes from Na+ to H- and the strong base anion exchange resin changes from Cl- to OH-, both swell due to the increase in ion diameter, thus increasing the volume of the resin. Factors affecting the transformation swelling rate of ion exchange resins are as follows.
    • Crosslinking degree. High crosslinking degree resins have lower "swelling" ability.
    • Active groups. The easier the active groups are to ionize, the greater the swelling rate of the resin.
    • Solution concentration. The greater the concentration of electrolyte in the solution, the lower the difference in osmotic pressure between the solution inside and outside the resin, and the smaller the swelling of the resin.