Introductory example for reactive mass transport

The following example shows the result of a column experiment with an 8 m long column filled with a cation exchanger. First of all, the column was 

Chloride behaves like an ideal tracer and is only affected by dispersion. Calcium is still not in solution even after a single exchange of all water within the column (shift = 40) as it is exchanged for Na and K. When all sodium has been removed from the exchanger, Ca can only be exchanged for K that leads to a peak in the K-concentration. Only after the water of the column has been exchanged about 2.5 times, the concentration of calcium increases at the outlet. 

In the next example the PHREEQC job is presented that simulates the experiment. To adjust the model to the data observed, the exchange capacity (X under EXCHANGE, here 0.0015 mol per kg water), the selectivity coefficients in the data set WATEQ4F.dat and the chosen dispersivity (TRANSPORT, dispersivity, here 0.1 m) are decisive besides the spatial discretisation (number of cells, here 40). If one sets the dispersivity to a very small value (e.g. T10 6) in the input file Exchange and rerun the job, one will see that no numerical dispersion occurs showing that numerical stability criteria are maintained properly. 

TITLE column experiment with exchangers PRINT 

It is important to notice that a SOLUTION has to be given by default for all 40 cells of the column, at the beginning of the job (SOLUTION 1-40). When additionally kinetics and equilibrium reactions have to be taken into account, the same is true for the keywords KINETICS and EQUILIBRIUMPHASES. Writing 

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