## The Input Panel

Program Start

Just after program start, aqion opens with the main input panel for chemical data – as shown in the right image.

There are two possibilities to enter an aqueous solution:

• by typing-in the chemical data (of a water analysis) via the keyboard

• by loading an existing input water via the button Open (left lower button)

In the following we describe the first option.

Input Data

The input window enable you to enter the following parameters (from top to bottom):1

Filename.  The default filename of the empty input panel is “new”. You can change this name before you save the input solution. Example: water_A3 will be saved as file water_A3.sol (in the user directory aqion/INP)23

pH and T [°C].  pH value (default: 7.0) and water temperature (default: 25).

Mol.  This checkbox switches the concentration units from mg/L to mmol/L (and vice versa); it acts for all elements at once. (In addition, you can change the concentration unit for each element separately by click on the blue listbox next to each element.) Fields with molar units are highlighted with yellow color.

Minerals.  This checkbox opens the mineral table to enter:

• the initial amount (in mmol/L) and/or
• the saturation index (SI)

These data are stored together with the element concentrations in one and the same input-water file.

Element Concentrations.  The major elements are arranged in two columns:

• cations (left):    Ca, Mg, Na, K, Al, Mn, total ammonia
• anions (right):   chloride, sulfate, nitrate, phosphate

The blue listbox on the right side of each element selects the concentration unit: g/L, mg/L, µg/L, mol/L, mmol/L or µmol/L.

DIC – Dissolved Inorganic Carbon.  DIC plays a key role in hydrochemistry and natural waters at all. It is a (non-trivial) topic of its own and will be discussed here.

Fe(2) / Fe(3).  Iron forms compounds and species in the +2 (ferrous) and +3 (ferric) oxidation states. You can enter the iron concentrations in two ways:

• either as total iron (Fe_total)
• or as Fe(2) and Fe(3)

Given Fe_total, aqion converts the total concentration into Fe(2) and Fe(3) in accordance with the redox potential.

More Elements.  This checkbox opens a panel with additional elements:

• cations (left):    Si, As, Sr, Cu, Cr, Pb, U
• anions (right):   B, F, Br

Redox Potential.  This checkbox enables the input of the redox potential:

• either as Eh in mV
• or as pe value

Once this option is checked the aqueous system is forced to attain the chosen redox potential or pe value by exchange of O2 (“Open System”).

In most cases, it is not necessary to specify the redox potential explicitly. The calculations are then performed at the state of redox equilibrium (or at 240 mV, i.e. pe value 4, as default). In any case, you’ll find the information about pe or Eh for every reaction step in the output tables.

Comments.  Optionally, comments can be entered in two lines; they are then stored together with the data.

Evaluation Temperature.  The evaluation temperature can be entered when the corresponding checkbox is checked. This optional parameter is used in calculations of calcite saturation only.4 If no evaluation temperature is entered the program uses the water temperature from the input field above.

File

• Reset solution to “pure water” – same as button H2O
• Open/select input water – same as button Open
• Save input water – same as button Save

Run

• Charge balance, physico-chem parameters … – same as button Start
• Reactions, pH calculator, titration curves – same as button Reac
• Mixing of two waters – same as button Mix
• Calcite-carbonate system

Settings

Extras5

• Dosing of chemicals to attain a target pH – shortcut Alt-P
• Prepare solutions (Buffer Maker) – shortcut Alt-B

Info

 Open Opens the standard dialog to select an existing solution (input water) which are stored in directory INP. Alt-O Save Saves the input water (by storing the data file in directory INP). Note: Saving is not required to run the hydrochemical calculations. Alt-V H2O Clears the complete panel. The empty window represents pure water with pH 7 and 25.1 Alt-H Mix Mixing of two waters. Alt-M Reac Opens the reaction panel to add chemicals (acids, bases, salts) and/or to perform titration calculations.6 Alt-R Start Starts the hydrochemical calculations (chemical equilibrium and speciation, charge balance, calcite saturation etc.)6 Alt-S End Closes the program.

Remarks / Footnotes

1. The “empty” template represents the simplest of all aqueous solutions: pure water (H2O) with pH 7 at 25. This is often the starting point for pH calculations of acids, bases and salts with the reaction module (via button Reac).  2

2. All input solutions of aqion have the file extension sol

3. The input solutions can be used in PhreeqC as input files as well (the syntax is the same).

4. For example: The water sample has 20, but we are interested in the calcite saturation parameters at the evaluation temperature 60

5. only for aqion PRO

6. Start vs. Reac – see here  2