Dissolution and Precipitation
The mineral table – as shown in the right screenshot – is part of aqion’s main input panel. It opens/closes when the upper checkbox Minerals is checked/unchecked. Once the mineral table is open you can enter the following parameters:
- the amount of mineral in mmol/L (as an initial value for mineral dissolution)
- the saturation index (SI)
In order to enter these values, please double-click on the row of the corresponding mineral.
The right screenshot shows an example where gypsum is added to pure water (with an initial amount of 20 mmol/L).
Typical applications are:
The complete table of all solid phases used in aqion is presented here (about 100 minerals).
Alphabetical Sorting. You can sort the mineral phases by one click on the gray table header:
- click on Mineral – sorting by the name of the mineral
- click on Formula – sorting by the chemical formula of the mineral
Only those minerals that are selected by the left checkbox in the table will enter the equilibrium calculations. In this way, the user is able to enable or disable minerals from the aqueous system.
From the entire ensemble of available minerals only a small subset is preselected as default (this subset is marked by ‘x’ in the tables here). The preselected minerals are characterized by a relatively fast dissolution and/or precipitation kinetics. Among them are calcite, gypsum, hydroxides and other amorphous phases.
Configuration. Once the user selects/unselects minerals in the table, this configuration remains valid for all subsequent calculations until program exit. Any new program start resets the mineral list to its default configuration.
In addition, the user has the possibility to define and save its own mineral configuration which replaces the default (and keeps valid after program exit). For this purpose you should use the Settings in the upper menu bar, which opens the config panel.
Activating the checkbox of a mineral is a necessary but not sufficient condition for its precipitation. The mineral will only precipitate if the solution is supersaturated (SI > 0), otherwise nothing will happen.
The amount of the precipitated phase in mmol/L is determined by thermodynamics. In equilibrium calculations, the precipitation stops when exact saturation is achieved (SI = 0).
Three conditions should be fulfilled for the dissolution of a given mineral:
- incorporation of the mineral into the equilibrium calculations (by activating the checkbox in the above table)
- a non-zero initial amount of the mineral in mmol/L
- the solution should be undersaturated with respect to the mineral phase (SI < 0)
The dissolution stops when either saturation is achieved (SI = 0) or when the initial inventory is exhausted.
In some cases we are interested in the composition and pH of a water after a definite amount of mineral is dissolved. To answer this question we refer to the so-called forced mineral dissolution.