PREDOM: Predominance Area Diagrams
How it works
PREDOM uses a point to point technique, which is slow, and has a plot
resolution that depends on the interval between points. The advantage is that
log(Tot.Conc.) can be the variable in an axis.
- The concentration area to be studied is divided with 50 steps in each axis,
giving a grid of 2601 chemical compositions to solve. Larger grids
(smaller steps) may be selected by the user.
- For every point in the grid, the mass-balance equations are solved
(if the Tot. Conc. is given for at least one component) by calling the
HALTAFALL algorithm, and then the species
distribution is determined.
- If no solid is present, the predominant soluble species is the one with a
highest fraction of the main component.
For example, for Fe2(OH)24+, the
fraction is 2[Fe2(OH)24+]/[Fe]TOT
while for Fe(OH)2+, the fraction is
[Fe(OH)2+]/[Fe]TOT. Therefore, the first
complex will dominate over the second only if [Fe2(OH)24+]
> ½[Fe(OH)2+].
- If at least one solid is formed by the main component, the predominating species
in the diagram will be the solid with the largest fraction of the main component.
In this case the predominant species in the plot is the solid, even in the case
where the solid's concentration (mol/L) is smaller than the predominating aqueous
species.