Models for Association of Metal Ions with Heterogeneous Envimnmeatal Sorbents. 1 . Complexation of Co(ll) by Leonardiie Humic Acid as a Function of pH and NaC104 Concentration

Authors

John Westall, Oregon State UniversityFollow
John Jones, Oregon State University
Gary Turner, Pacific Northwest National Laboratory
John M. Zachara, Pacific Northwest National LaboratoryFollow

Date of this Version

1995

Citation

Environ. Sci. Technol. 1995, 29, 951-959

Abstract

A discrete log K spectrum model has been developed to represent the binding of protons and Co(II) to leonardite humic acid (LHA) over a wide variation of solution composition: pH 4.5-9.5, [NaC1O₄] 0.01 - 0.1 M, T_Co 200 nM-500 µM. The model is internally selfconsistent over the range indicated without an explicit electrostatic term. The LHA was represented by four acid sites (HL_i = H⁺ + L_i^-) with a fixed pK_a spectrum: pK_a = 4, 6, 8, and 10. From the acid base titration data, total concentrations of these sites and Na⁺ binding constants (L_i^- + Na⁺ = NaL_i) were obtained. From Co₂⁺ binding as a function of pH, constants for the reaction L_i^- + Co₂+ = COL_i⁺ were obtained. Total concentrations of sites and binding constants were similar to those expected from other studies. This discrete log K approach has been selected as the easiest way to parameterize multidimensional data (i.e., data with variations in many solution chemistry parameters) for subsequent application in transport models.