Lead is a ubiquitous trace metal cation in natural soils. Understanding the interaction of lead with mineral surfaces is important in determining its potential bioavailability. Past research has demonstrated that the bioavailability of trace metals is primarily controlled by adsorption/desorption reactions at the solid-solution interface. Numerous studies have demonstrated that trace metal potential bioavailability decreases with an increase in residence time. Several explanations have been proposed for the residence time effects observed by researchers including diffusion into the defects and fissures of mineral oxides. To test this hypothesis a study was conducted to examine the influence of residence time and stirring speed on the kinetics of Pb²⁺ desorption from goethite. Preliminary adsorption experiments were done in order to select a wide range of experimental conditions that would provide a range in surface loadings while minimizing equilibrium Pb²⁺ in solution. From these data we designed an experiment that incorporates a stirred and non-stirred long-term and short-term study to examine the possibility of a diffusion related residence time effect.