Aqion
Aqion is a hydrochemistry software tool. It bridges the gap between scientific software
and the calculation/handling of "simple" water-related tasks in daily routine practice. The software aqion is free for private users, education and companies.
Motivation & history
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. 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. The project is active with 1-2 updates per month.
Features
- Validates aqueous solutions
- Calculates physico-chemical parameters: alkalinity, buffer capacities, water hardness, ionic strength
- Calculates aqueous speciation and complexation
- Calculates pH of solutions after addition of chemicals
- Calculates the calcite-carbonate system
- Calculates mineral dissolution, precipitation, and saturation indices
- Calculates mixing of two waters
- Calculates reduction-oxidation reactions
- Plots titration curves
Fields of application
- Water analysis and water quality
- Geochemical modeling
- Education
Limits of application
- only inorganic species
- only equilibrium thermodynamics
- only aqueous solutions with ionic strength ≤ 0.7 mol/L
Basic algorithm & numerical solver
The program aqion belongs to the category LMA approach. In a nutshell: A system of NB independent basis components j, that combines to form NS secondary species i, is represented by a set of mass-action and mass-balance equations:
mass action law: with i = 1... NS
mass balance law: with j = 1... NB
where Ki is the equilibrium constant of formation of the secondary species i, and νi,j represents the stoichiometric coefficient of basis species j in secondary species i. Here, activities ai are symbolized by curly brackets while concentrations ci by rectangular brackets . Both quantities are related by the
activity correction:
with γi as the activity coefficient calculated by the Debye–Hückel equation and/or Davies equation. Inserting Eq. into Eq. yields a nonlinear polynomial function fj for the j-th basis species:
which is the objective function of the Newton–Raphson method.
To solve Eq. aqion adopts the numerical solver from the open-source software PhreeqC.
The equilibrium constants Ki are taken from the thermodynamic database wateq4f.
Examples, test & verification
The software aqion is shipped with a set of example solutions and a tutorial how to attack typical water-related problems. More examples and exercises for testing and re-run can be found in classical textbooks of hydrochemistry.The program was verified by benchmark tests of specific industry standards.