Reactive transport is modeled by the sequentially coupled code MCOTAC that couples one-dimensional advective, dispersive, and diffusive transport with chemical equilibrium complexation and precipitation/ dissolution reactions in a porous medium. Transport, described by a random walk of multispecies particles, and chemical equilibrium calculations are solved separately, coupled only by an exchange term. The modular-structured code was applied to incongruent dissolution of hydrated silicate gels, to movement of multiple solid front systems, and to an artificial, numerically difficult heterogeneous redox problem. These applications show promising features with respect to applicability to relevant problems and possibilities of extensions.