Page:4SIGHT manual- a computer program for modelling degradation of underground low level waste concrete vaults (IA 4sightmanualcomp5612snyd).pdf/131

56. Chemical equilibrium.

Given the number density of ions in a computational element, determine if any of the ions should go in to/out of solution. Determine the pH and adjust H and OH, accordingly.

⟨Function declarations 23⟩$+\equiv$
 void chemical_equilibrium (boolean);

57. Minimizing function. This is the function to minimize for the chemical_equilibrium routine. The objective of chemical-equilibrium is to determine how many moles of salt should be leached/precipitated. Therefore, minfunc must adjust for the pore volume. The equation minfunc is minimizing the square of

$\left[C+{\frac {mx}{V}}\right]^{m}\left[C+{\frac {nx}{V}}\right]^{n}-k_{s}p=0$

where $x$ is moles salt, $m$ and $n$ are stoichiometric ratios, and $V$ is the pore solution volume,

 real minfunc(real, int, int, int);
 real minfunc(real x,int i,int j,int k)
 {
   real C, A;
   int m, n;
   m = sol_array[i][j].m
   n = soLarray[i][j].n
   C = cation[i].c[k]-,
   A = anion [j].c[k]-,
   return SQR(potr(C+m*x/(litre[k] * $\Delta X$[k]),m) * pow(A + n * x/(litre[k] * $\Delta X$[k]), n) — sol-array [i][j].ksp);
 }

58. chemical_equilibrium(). Cycle through sol.array and determine if any ions should go in to/out of solution based upon the concentration, the solubility constant, and the presence of solid salt.

#defineTOL  $1.0\cdot 10^{-}06$
void chemical-equilibrium (boolean Change_Porosity)
{
 int i, j, k, n, m, iterations;
 real w_max $\delta$;
 real xa, xb, xc, fa, fb, fc, moles, tmp;
 real dsolid;
 real $\delta$ litre;   /* change in pore volume */
 real old_cOH;
 real charge,temp;
 boolean NEG_FLAG;
 for (k= FIRST_CELL+1; k< NUM.SURFACES; k++) {
   iterations = 0;
   do {
     w_max = 0.0;
    for (j=0; j < num-amons j++) {
      for (i =0; i < num-cations-, i++) {
        if ($\lnot$(i$\equiv$0$\land$j $\equiv$0)) {