The HPx reactive transport models: Summary of recent developments and applications

The HPx reactive transport codes are developed to couple flow and transport processes in variable-saturated porous media with a variety of low-temperature geochemical processes. It consists of the HYDRUS models for flow and transport models (HYDRUS-1D 4.16 and HYDRUS2/3 2.02) with the generic thermodynamic and kinetic model PHREEQC-2.17. As such, HPx, no available for one (HP1) and two dimensional flow and transport problems, expands significantly the capabilities of the individual codes. Recent developments and applications are: Gas diffusion. One important application of this is to simulate CO2 sequestration in soil. HPx gives a large flexibility in defining different kinetic networks with rate coefficients depending on temperature, water content or any other variable. Extension to two-dimensional flow problems Inverse optimization of geochemical parameters. An example is given in which exchange parameters are fitted on data from a water adsorption experiment Feedback between change in geochemical variables and transport properties. As an example, leaching of material and the progression of pH and porosity fronts are discussed. Benchmarking of several of these new developments with other reactive transport codes.