A chemically based model for metal partitioning to organic matter

The overall goal of this doctoral dissertation is to develop and test a chemically based model for metal speciation and partitioning to organic matter in natural systems using the Windermere Humic Aqueous Model (WHAM) framework. To better understand the distribution of sites on organic matter, the proton binding distribution of model humic and fulvic acid molecules is studied. The work summarizes an approach to define proton binding constants of organic matter. The proton binding constants of various model humic and fulvic acid structures are compared to WHAM VI proton constants and sample datasets. A comparison of model results to experimental observations suggests that model humic and fulvic structures can be used to represent the proton binding distributions of natural organic matter.;Irving-Rossotti Linear Free Energy Relationships (IR-LFERs) for nitrogen donor atoms are developed to define equilibrium metal-ligand binding constants for monodentate and bidentate ligands. The Irving-Rossotti slopes for 8 metals; Mn2+, Fe+2, Co2+, Ni2+ , Cu2+, Zn2+, Cd2+, Ag +1 are calculated. The development of these new LFERs is important because the metal binding constants to any ligand for which the proton binding constant is known will be estimated. Furthermore, the theory provides insight into how metals bind to NOM and can be used in conjunction with existing equilibrium speciation models as WHAM VI.;Finally, Irving-Rossotti equilibrium constants for monodentate and bidentate ligands containing oxygen donor atoms are used in the WHAM VI model and compared to the default WHAM VI constants. Further comparisons are made using various datasets for Ca2+, Cu2+ and Cd2+ binding to humic acid individually as well as in competition. The results of this research demonstrated that, the Irving-Rossotti LFER model, which has not been calibrated to metal-DOM data, other than that the proton binding spectrum of WHAM VI, and therefore has no metal fitting constants, produced results for metal-DOC binding that are comparable to the calibrated WHAM VI model.