Colloidal particles in natural porous media can be mobilized in situ through traveling chromatographic fronts. This process is often modeled by a single population of particles whose release and deposition is described by a first-order kinetic process with fixed rate constants. We present a new, more realistic approach considering the physicochemical coupling between the corresponding rates and the (changing) chemical composition of the pore water. Neglecting particle deposition, analytical solutions are presented for various relevant situations. In the absence of dispersion the effluent curves are given by simple exponential functions; while in the presence of dispersion, more complicated relations are obtained. Particle deposition influences the release and transport of particles, and analytical and numerical solutions are discussed for this situation as well. In most practical situations, particle release is a strongly nonexponential process, which can be modeled by assuming multiple particle populations, whose properties are described with the corresponding probability distribution. Such a model can be used to rationalize the experimentally observed nonexponential decay. ¿ 2001 American Geophysical Union