Dataset of surface reactions for gwb programs Dataset format: sep22 Surface type: Lang-1 Model type: langmuir Surface potential: n/a Surface capacitance: n/a Thermo dataset: thermo.tdat * * Example dataset for setting up a Langmuir sorption model. * * Follow this format to set up a Langmuir sorption model for a GWB run. * Note that the user sets the number of complexing sites from the command * line with the "exchange_capacity" command. * * * STEP 1: Set a single basis species representing the sorbing site. -end- 1 basis species >L: charge= 0 mole wt.= 0.0000 g 0 elements in species -end- * STEP 2: Set the complexation reaction(s). 2 surface species >L:Ca++ charge= 2 mole wt.= 40.0800 g 2 species in reaction 1.000 >L: 1.000 Ca++ log K a= -2.1000 b= 0.0 >L:Sr++ charge= 2 mole wt.= 87.6200 g 2 species in reaction 1.000 >L: 1.000 Sr++ log K a= -1.3500 b= 0.0 -end- * * IMPORTANT NOTES: * * The Langmuir model in the GWB is similar to the two-layer model, except * that: * (1) there is no specific accounting for electrostatic forces, and * (2) the user sets the number of sorbing sites in the modeling apps using * the "exchange_capacity" command, rather than having the software calculate * this number from the mass and surface area of a sorbing mineral. * * Set a single basis species to represent the sorbing site. The basis * species should be an uncomplexed site of zero charge. * * The surface species are complexes of the basis species with ions in * solution. * * Enter equilibrium constants ("K-ads") for dissociation reactions of * the surface complexes as logarithmic values using log K "a"; you may set * a thermal dependence as the temperature derivative of these values using * "b", or using more terms in a polynomial expansion as described in the * Surface Datasets chapter in the GWB Reference Manual. * * The equilibrium constants here refer to mass action expressions for * the sorption reaction written in terms of species activities, rather * than molalities. In deriving data from the literature, note the * units used and if necessary correct the values according to the * species activity coefficients and extent of complexation.