5. RESTRICTIONS ON THE COMPLEXITY OF THE PROBLEM
Program SOLUPLOT will, when properly employed, produce highly reliable represen- tations of the equilibrium states of a wide variety of chemical systems. In general, the complexing of any ion with a large number of ligands with characteristic atoms oppositely charged with respect to that ion may be readily calculated. Results as accurate as carefully hand-plotted diagrams may be routinely obtained in a fraction of the time required for hand calculations.
The user may wish to consider species of variable composition, such Fe(1-x)S(pyrrhotite). This is generally possible if the input file is suitably constructed. The pyrrhotite solid solution may be represented in this example by a series of "S" cards for the species FeS, Fe11S12, Fe10S11, etc. The resultant diagram will be effectively "contoured" according to relative iron-sulphur composition.
The limitations of this model should be taken into account when attempting more specialised calculations. Specifically, since the program first independently calculates ligand speciation and then calculates main system speciation within each ligand species' area of predominance, no interaction among ligand systems (and non- speciating ions) is considered. Therefore, any attempt to calculate a diagram considering both cations and anions as ligand species or ions will not produce a rigorously correct equilibrium diagram. As an example, a calculation with a main system of copper species and ligand systems of iron species and sulphur species would not produce species forming iron sulphides would not be considered.
Most calculations attempted with this class of model, however, utilise main system cation (or in some cases anion) species reacting with a number of anions (or cations) either as ligand system species or non-speciating ions. In these cases, complexing among ligand species is negligible and all relevant chemical reactions are considered by the program.