Visual MINTEQ is a freeware chemical equilibrium model for the calculation of metal speciation, solubility equilibria, sorption etc. for natural waters. It combines state-of-the-art descriptions of sorption and complexation reactions with easy-to-use menus and options for importing and exporting data to/from Excel. Chemical equilibrium modelling has never been easier!
The code, originally built on USEPA’s MINTEQA2 software, is maintained by Jon Petter Gustafsson at KTH, Sweden, since 2000.
Visual MINTEQ will run on most Windows platforms and relies on .NET Framework. For more details, see here.
Version 3 represents a major new release. The interface code has been completely rewritten in VB.NET. The download and installation procedures have changed, and a number of new options has also been introduced. The help file has been updated, and a new user guide is being written; a draft, still not yet complete, is included in the download. Below there is a list of all major changes compared to version 2.6:
Installer and file locations. Version 3 comes with a different installer, which should (in most cases) work more reliably than the old installer. The default location of the downloaded files is in the Program Files folder. When starting the application for the first time, the user will be asked where he/her would like to have the user-editable files located. The default location is in the My Documents folder.
Species tableau. A new table presents the species added to the problem in the form of a tableau, which includes information on the stoichiometry, log K and reaction enthalpy of each species. This tableau is accessible from the component list page.
Option to add a component as an element. A frequently asked question from users has been why it has not been possible to add, for example, arsenate as As(V) (i.e. as arsenic, with a molecular weight as for elemental As) rather than as AsO4-3, which is the standard component for As(V). This is now possible. It means, for example, that you can import As(V) data from Excel when data are given in ug/l As. Previously you had to recalculate such data to a molar unit before Excel import.
More flexibility for predefined adsorption models. On page 2 of the default parameters menu (accessible from Parameters – Various default settings), users can now define their own parameter sets for surface complexation models (SCM:s). This greatly facilitates parameter input when you are working with any other SCM parameter sets than those included in the download package. The parameter sets are saved as a special text file, ‘admodel.txt’, so that the parameter sets can be shared easily between different users.
Different functionality of the adsorption isotherms. The adsorption isotherms remained an underdeveloped part of the 2.xx versions of Visual MINTEQ. It was possible to define many isotherms, but with the important restriction that the dissolved entity of the adsorbate had to be supplied as its free ion activity. Commonly, however, adsorption isotherms are defined using the total dissolved concentration of the adsorbate. From version 3.0, only the linear Kd and Freundlich-type models are included in Visual MINTEQ. For these models it is possible to choose between the free ion activity and the total dissolved concentration as the basis of the calculations.
Saturation indexes for minerals in sweep problems. It is now possible to choose to have the saturation indexes of different minerals listed in the sweep output file.
Visual MINTEQ can simulate the chemical composition in solutions in contact with gases, solid compounds and particle surfaces. To determine whether it is relevant for you, check the following list of what Visual MINTEQ can and cannot do:
Examples of what you can do with Visual MINTEQ
– Calculate the speciation of inorganic ions and complexes in waters
– Evaluate the effect of dissolving or precipitating solid phases on water chemistry
– Investigate the equilibrium speciation of common redox couples
– Simulate the change in chemical composition of a water sample during a titration
– Estimate the binding of ions to (hydr)oxide surfaces and organic matter using state-of-the-art complexation models (SHM or NICA-Donnan for organic complexation, CD-MUSIC, TLM, CCM or DLM for surface complexation).
Examples of problems that are difficult or impossible to solve with Visual MINTEQ
– Problems that require transport calculations. Visual MINTEQ does not contain any transport model. If your aim is to estimate, e.g., the transport rate of heavy metals from a contaminant source to a water body, you will need to find another model. Visual MINTEQ only calculates the chemical composition in one single point.
– Partitioning of organic compounds. Although the partitioning of non-polar organic chemicals can be calculated (in principle) by Visual MINTEQ, there is no database for this type of calculations. Visual MINTEQ was developed mainly for the purpose of calculating equilibria for inorganic ions and trace metals in waters.
– Non-equilibrium processes such as weathering or biological degradation cannot be handled by Visual MINTEQ, since equilibrium is always assumed.
– Problems for environments having high pressure or temperature such as in deep geological formations. Visual MINTEQ has been optimized for use for waters in the temperature range 0-40 deg C and pressures near 1 atm. Again the calculation engine of Visual MINTEQ can, in principle, solve this kind of problems, but the necessary databases have not been assembled. You are therefore advised to use other software for high P-T problems.