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!
Visual MINTEQ will run on most Windows platforms and relies on .NET Framework. For more details, see here.