Acid/base, copper binding, and Cu2+/H+ exchange properties of a soil humicacid, an experimental and modeling study

Acid/base, copper binding and proton exchange properties of a soil humic ac id were studied over a range of pHs and ionic strengths. Results indicate t hat multiple classes of copper binding sites exist. A number of model formu lations were used to simulate the data; none were able to reasonably match all aspects of the observed behavior. Model results and analyses suggest th at successful replication of humic behavior over a wide range of conditions requires a model formulation which incorporates electrostatic effects for a variable geometry entity, multiple site classes, and probably both uni an d multi dentate complexation. Additionally site heterogeneity estimates fro m acid/base titration data are not likely to reasonably assess the presence of low concentration, high (metal) affinity sites that can be relevant in the study of trace metal complexation.