Mass-Transfer Rates in Ion Exchangers

The rates of ion-exchange reactions are limited by the rates of diffusion of the counterions in the external solution and in the pores of the resin particles. Equilibrium can be assumed to exist at any point inside each particle. With favorable 

The exact shape of the breakthrough curve and the value of tb are hard to predict. Therefore, the design of large units is usually based on experience or tests with a small column. If the particle size and liquid velocity are kept constant, and care is taken to ensure uniform distribution of the feed, the LUB should not change in going to a larger column. 

Water containing 7.0 meq/L of Ca2+ and 0.86 meq/L of Na+ will flow at the rate of 13 L/s through a fixed bed of gel resin with a cation capacity of 2.9 eq/kg of wetted resin. The cylindrical bed is 2.6 m in diameter and 3.0 m long. The resin beads have a density of 1.34 kg/L and are packed with a bed porosity of 0.38. Estimate the ideal breakthrough time for the ion exchanger. 

---

The change in effluent solution concentration with time is determined from the uranium concentration at the bottom of the bed at 5.4 ft, the equilibrium relation between bed and solution concentrations (Fig. 5.11), and mass transfer rates in ion exchange. Curve C of Fig. 5.12 is an estimate of how the effluent concentration from the first bed would change with time in cyclic operation. 

---