A module for the MT3DMS solute transport model forsimulating redox processes

摘要

A module for the widely used solute transport model MT3DMS (Zheng & Wang, 1999) ispresented which allows for the simulation of redox processes. Redox reactions are rewritten as hydrogenproducing oxidation half-reactions and hydrogen consuming reduction half-reactions. The model uses theconcept of a "virtual hydrogen pool" which includes all the hydrogen that has been produced so far byoxidation reactions. The model incorporates three reaction mechanisms: instantaneous reactions are used foroxygen reduction, kinetic rate expressions describe the hydrogen producing oxidation reactions and redoxequilibria relate oxidant and reductant concentrations with hydrogen levels in solution. A direct relationexists between hydrogen levels in solution, the occurrence of redox species and the size of the virtualhydrogen pool. Using an iterative scheme based on the Newton-Raphson method, the hydrogen and redoxcomponent concentrations can be derived from the size of the virtual hydrogen pool. For describing thekinetics of the hydrogen producing oxidation half-reactions, the model uses RPN like instructions defined ina data file, which act upon a LIFO based stack and are translated into binary code as the data are read. Thiseasily allows the redefinition of kinetic reaction networks, without the need to alter the simulator code. Themodel has fast calculation times.