MODELS FOR ASSOCIATION OF METAL-IONS WITH HETEROGENEOUS ENVIRONMENTALSORBENTS .1. COMPLEXATION OF CO(II) BY LEONARDITE HUMIC-ACID AS A FUNCTION OF PH AND NACLO4 CONCENTRATION
Jc. Westall et al., MODELS FOR ASSOCIATION OF METAL-IONS WITH HETEROGENEOUS ENVIRONMENTALSORBENTS .1. COMPLEXATION OF CO(II) BY LEONARDITE HUMIC-ACID AS A FUNCTION OF PH AND NACLO4 CONCENTRATION, Environmental science & technology, 29(4), 1995, pp. 951-959
A discrete log K spectrum model has been developed to represent the bi
nding of protons and Co(II) to leonardite humic acid (LHA) over a wide
variation of solution composition: pH 4.5-9.5, [NaClO4] 0.01-0.1 M, T
-Co 200 nM-500 mu M. The model is internally self-consistent over the
range indicated without an explicit electrostatic term. The LHA was re
presented 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 t
hose expected from other studies. This discrete log K approach has bee
n selected as the easiest way to parameterize multidimensional data (i
.e., data with variations in many solution chemistry parameters) for s
ubsequent application in transport models.