Journal of soil science vol:43 issue:4 pages:669-677
The use of a new method for characterizing humic acids based on the measurement of the cobaltihexammine cation exchange capacity (CEC) vs. pH is examined. The method was first verified on a macroporous weak-acid cation exchange resin: charge vs. pH curves and pK values from cobaltihexammine adsorption identify with results from discontinuous acid-base titrations at high ionic strength (5 m). Similar agreement was obtained for humic acids from a Podzol soil: the cobaltihexammine-CEC identifies with the macromolecular charge (from continuous acid-base titrations) at ionic strength of 3 and 5 m, but slightly underestimates (5%) the humic acid charge at 1 m ionic strength. The cobaltihexammine method is suitable for determining the potentially available charge in the pH range 2 to 12 and the intrinsic pK values of humic acids.