Date of this Version
Environ. Sci. Technol. 1995, 29, 951-959
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, TCo 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 (HLi = H+ + Li-) with a fixed pKa spectrum: pKa = 4, 6, 8, and 10. From the acid base titration data, total concentrations of these sites and Na+ binding constants (Li- + Na+ = NaLi) were obtained. From Co2+ binding as a function of pH, constants for the reaction Li- + Co2+ = COLi+ 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.