MIXING CELL MODELS FOR NONLINEAR EQUILIBRIUM SINGLE SPECIES ADSORPTION AND TRANSPORT

A simple improved mixing cell model is shown to be more accurate than the standard mixing cell model when used to solve solute transport pro blems with a nonlinear adsorption isotherm included. The solution obta ined from the improved model is found to agree closely with that calcu lated using a Crank-Nicolson scheme, and an exact analytical solution for solute transport subject to a nonlinear solute adsorption isotherm . Application of the improved mixing cell model was demonstrated by ap plication to experimental data from a laboratory Ca-K exchange experim ent in which a solution containing Ca was passed through a column fill ed with K-saturated soil. The model was used in conjunction with the e xperimentally determined nonlinear adsorption isotherm to predict the experimental breakthrough data. The data and the predictions agreed re asonably well, indicating that the equilibrium assumption is reasonabl e. However, it is suggested that an appropriate isotherm is necessary to describe well the concentration history curve.