A study on the metal binding of humic acid by multitracer technique

A method combining radioactive 'multitracer' and dialysis techniques was developed to study the binding of multiple metal ions to humic acid (HA). Technical problems such as the leakage of small-molecule HA segment and the slow diffusion of metal ions through the dialysis membranes were examined. Under the condition of pH = 4.0, I = 0.100 M NaNO3, [Mg-II] = 0 M, or [Mg-II] = 0.500 x 10(-3) M, the interactions between Inogashira humic acid and metal ions (Be-II, Sc-III, Zn-II, Co-II, Mn-II and SO) were investigated by varying the metal concentrations in a wide range. It was found that as the concentrations of the trace metals are significantly smaller than that of HA, there are abundant binding sites available and there are no competition interactions between the trace metal ions of interest. Therefore, the stability constants for multiple metal ions binding onto humic substances can be obtained readily using the present method. The method is useful for quickly determining trace metal binding onto humic substances in environmental chemistry.