Batch adsorption and desorption equilibrium experiments were used to evaluate lithium sorption on crushed tuff in contact with ground water. The laboratory studies were conducted in support of saturated zone characterization field tests to be performed near Yucca Mountain, Nevada. These studies included equilibrium experiments conducted at 38° C (expected subsurface temperature) for a 1- to 2,000-mg/l range of initial lithium solution concentrations. Data from the equilibrium experiments were used in the evaluation of Linear, Langmuir, Freundlich, and Modified Freundlich isotherm expressions.

Comparisons of adsorption and desorption isotherms showed that lithium adsorption was reversible for solution concentrations up to 150 mg/l. This conclusion was based on F-test comparisons of predicted adsorption and desorption data from Langmuir isotherms.

Lithium sorption was best represented by the nonlinear isotherms where the Langmuir gave the best fit followed by the Modified Freundlich and Freundlich. When these isotherms were used in a one-dimensional, column adsorption transport code, differences occurred in the predicted breakthrough curves. The transport results showed differences of as much as a factor of five in the time of arrival of lithium for the various isotherms depending on the influent concentration chosen. The differences in the simulation breakthrough curves indicate the importance of isotherm selection. Statistical discrimination and column experiments are suggested as better evaluations of isotherms that are to be incorporated into field-scale transport simulations.