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.