Aqion

Aqion is a

First. Most of the hydrochemical software is designed for experts and scientists. In order to flatten the steep learning curve aqion provides an introduction to fundamental water-related topics in form of a "chemical pocket calculator".

Second. The program mediates between two terminological concepts: The calculations are performed in the "scientific realm" of thermodynamics (activities, speciation, log K values, ionic strength, etc.). Then, the output is translated into the "language" of common use: molar and mass concentrations, alkalinity, buffer capacities, water hardness, conductivity and others.

History. Version 1.0 was released in January 2012 (after a half-year test run in 2011). The project is active with 1-2 updates per month.

Features

• Validates aqueous solutions (charge balance error, parameter adjustment)
• Calculates physico-chemical parameters:
  water hardness, ionic strength
• Calculates aqueous speciation and complexation
• Calculates
  bases, salts
  )
• Calculates the calcite-carbonate system (closed/open CO₂ system,
  Langelier Saturation Index
  )
• Calculates mineral
  dissolution, precipitation
  , and saturation indices
• Calculates mixing of two waters
• Calculates reduction-oxidation (redox) reactions
• Plots titration curves

Fields of application

• Water analysis and water quality
• Geochemical modeling (in simplest form)
• Education

Limits of application

• only inorganic species (no organic chemistry)
• only equilibrium thermodynamics (no chemical kinetics)
• only aqueous solutions with ionic strength ≤ 0.7 mol/L^[2] (no brines)

Basic algorithm & numerical solver

There are two fundamental approaches in hydrochemistry:

with γ_i as the activity coefficient calculated by the Debye–Hückel equation and/or Davies equation. Inserting Eq.(1) into Eq.(2) yields a nonlinear polynomial function f_j for the j-th basis species:

(4)       ${\displaystyle f_{j}(c_{1},c_{2},...,c_{N_{B}})\,=\,[j]_{TOT}-[j]-\sum _{i=1}^{N_{S}}{\frac {\nu _{i,j}}{\gamma _{i}}}\,K_{i}\,\prod _{k=1}^{N_{B}}\{k\}^{\nu _{i,k}}\,=\,0}$

which is the objective function of the

To solve Eq.(4) aqion adopts the numerical solver from the open-source software PhreeqC.^[1][4] The

Examples, test & verification

The software aqion is shipped with a set of example solutions (input waters) and a tutorial how to attack typical water-related problems (online-manual with about 40 examples). More examples and exercises for testing and re-run can be found in classical textbooks of hydrochemistry.^[6][7][8]

The program was verified by benchmark tests of specific industry standards.^[9]

Screenshots

• 
  Input panel for chemical elements
• 
  Output of pH calculator (example)
• 
  Calculated parameters of the calcite carbonate system
• 
  titration curves (example: addition of NaOH to a given input water)

References