SIMULTANEOUS DETERMINATION OF STABILITY-CONSTANTS OF HUMATE COMPLEXESWITH VARIOUS METAL-IONS USING MULTITRACER TECHNIQUE

Stability constants of humic acid complexes of 19 elements, Be, Ca, Sc , V, Cr, Mn, Fe, Co, Zn, Ga, Sr, Y, Ba, Ce, Eu, Gd, Tm, Yb, and Lu, we re determined simultaneously using the multitracer technique. Since th e results were obtained under an identical method, model, and sample, we could compare the stability constants of humate with various metal ions. As a whole, humate complex of ions having more charge and smalle r ionic radii is more stable, showing the 'hard' character of humic ac id as a complexing ligand. Interpretation of the results of stability constants in terms of simple electrostatic model suggests that a biden tate carboxylate site is responsible for the humate formation with mos t of those trace ions. Among these elements studied, it is estimated t hat humate formation has the most substantial influence on the environ mental behavior of rare earth elements as compared with that on the ot her elements' behavior. (C) 1997 Elsevier Science B.V.