POLYMIN - University of Waterloo

POLYMIN 2005
Background aqueous chemistry
The background (initial) aqueous chemistry data for POLYMIN is contained in the file
bckgrndpoly.min. An example of this file is included at the end of this section.
There is one line for the each of the background component values. The first variable on these
lines is idx(nnn) [I] , the component I.D. number (see the comp.dbm data file or Felmy et al.
1984), the second variable is T(nnn) [R], the total analytical component concentration in
moles/kg, or for the case of an adsorbed component the concentration of the surface sites in eq/l.
The third variable is gx(nnn) [R], the guess for the log of the activity for the component , use
zero if a good initial guess is not known and for H + and e - components use the pH and pe values
respectively. The final variable of these lines is stad(nnn) [R], the reaction stoichiometry for the
adsorbed phase components (i.e. Na-S); for dissolved components, enter zero.
The total component concentrations (T(nnn)) are determined from the chemical analysis of the
solutions of interest. Often the chemistry will have to be modified to be used in MINTRAN or
POLYMIN by MINTEQA2. This would have to be done for one of the following reasons: for a
solution of known pH, the initial proton condition must be determined by fixing the pH to give
the initial value for the total analytical concentration of H + component, for the simulation of
redox reactions, the distribution of the multi-valence elements must be predetermined from the
solution pe (same procedure as fixing the pH) and e- (idx=1) must be included as a component
(T=0.0), and a type 6 reaction, and for ion-exchange reactions the dissolved and adsorbed phases
must both be included as components with the initial surface site concentration of the adsorbed
phase determined from the cation exchange capacity (CEC) and the individual selectivity
coefficients of the ion-exchange reactions (K s ). For ion-exchange reactions, the thermodynamic
data base (file thermo.dbm) must be modified. Finally, chemical analyses are generally not
perfectly charge balanced and it is advised that the initial background chemistry be charge
balanced with a non reactive anion or cation. In summary, run the chemical data through
MINTEQA2 and use the equilibrated results as input into MINTRAN or POLYMIN.
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