PEST-ORCHESTRA, a tool for optimizing advanced ion-binding model parameters: derivation of NICA-Donnan model parameters for humic substances reactivity
Janot, N., J.P. Pinheiro, W.G. Botero, J.C.L. Meeussen and J.E. Groenenberg submitted to Environmental Chemistry 19-2-2016
The paper describes the coupling of the chemical speciation software ORCHESTRA with the parameter estimation software PEST. This combination enables the computation of optimized model parameters from experimental data for the ion binding models implemented in ORCHESTRA. For testing this flexible tool the NICA-Donnan model parameters for proton-, Cd- and Zn-binding to Laurentian fulvic acid were optimized. The extensive description of the method implementation and the provided examples facilitate the use of this tool by students and researchers. Three procedures were compared to derive the proton binding parameters, differing in the way they constrain the model parameters and in the implementation of the electrostatic Donnan model. Although the different procedures resulted in significant different sets of model parameters, the experimental data fit obtained was of similar quality. The choice of the relation of the Donnan volume with ionic strength appears to have a strong influence on the derived set of optimal model parameters, especially on the value of the protonation constants. The physico-chemical plausibility of the results is discussed in detail. Coherent sets of NICA-Donnan parameters were derived for Cd and Zn binding to Laurentian fulvic acid.
A copy is available upon request from bertjan.groenenberg (at) wur.nl or bert-jan.groenenberg (at) univ-lorraine.fr