Cation Transport in Packed Bed Reactor of Soil

A model of cation transport through a reactor of soil has been utilized which includes the processes of convection, dispersion, and cation exchange. Results from the model by finite differences show that it describes the breakthrough curves very well for a variety of flow rates and feed concentrations. A criterion for convergence of the numerical solution has been presented. For the homovalent system K+ - NH₄+ maintained at constant ionic strength and pH the exchange process is symmetric, i.e., the exchange coefficients are equal. These coefficients show a linear correlation with velocity, which probably arises from a diffusion limited transfer normal to the particle surface. Quadratic correlation between dispersion coefficient and velocity reflects a rather complex relationship between concentration gradients and fluid flow. Cation exchange capacity of the soil increases with ionic strength. This behavior is characteristic of colloids of the metallic oxides and hydroxides, which exhibit constant surface potential rather than constant surface charge. The soil is known to contain aluminum and iron hydroxides.