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INTRODUCTION
1D Advective Reaction-Transport Modeling
Reaction-transport modeling simulates advection and chemical reactions as water moves through a one dimensional column. The column is divided into a number of cells, n, which is defined by the user. The cells are numbered 1 through n, and these cells initially contain solutions with identifying numbers 1 through n. A solution composition for each of these integers must have been defined by SOLUTION data blocks (note that data for a range of numbers can be defined simultaneously, for example SOLUTION 1-15) or the SAVE keyword (for example, SAVE solution 1-15). The cells may also contain other reversible or irreversible reactants. For a given cell number, i, if a phase assemblage, exchange assemblage, surface assemblage, gas phase, mixture, reaction, or reaction temperature with identifying number i has been defined, then it is automatically present in cell i during the transport calculation. Thus, the initial conditions and the set of reactants of each cell can be defined individually, which allows the flexibility to simulate a variety of chemical conditions throughout the column.
Advection is simulated by moving the solution in each cell to the next higher numbered cell; SOLUTION 0 must be defined and it is moved into cell 1; the solution from cell 1 is moved to cell 2, and so on, until the solution from cell n-1 is moved to cell n. At this point, the solution in cell n is discarded. All reversible and irreversible reactants except the solution remain in their original cells. After each cell has received its new solution, irreversible reactions are applied within the cell, the solution is equilibrated with the reversible reactants, and the equilibrium compositions of the solution and reversible reactants are saved.
Advective reaction-transport modeling uses the TRANSPORT keyword data block. Usually, one or more simulations precede the TRANSPORT simulation. These preceding simulations often use many of the keywords described in reaction-path modeling to define the initial solutions and reactants of the column and to define the infilling solution (SOLUTION 0).
PhreeqcI--A GUI for the Geochemical Program PHREEQC - 10 OCT 97
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