Humic acids from coals of the North-Bohemian coal field II.: Metal-binding capacity under static conditions

The interactions of metal cations (Al, Ba, Ca, Cd, Co, Cr, Cu, Fe, Mg, Mn, Ni, Ph, Zn) with solid humic acids (HAs) were investigated in a batch arrangement. The sorption of metals on the surface of HAs depends strongly on the pH - sorption decreases with decreasing pH. The metal-binding capacities estimated from the metal-humate binding model range from ca. 0.4 mmol/g (Fe, Ni, Zn) to 1.7 mmol/g, (Pb). Of the examined metal cations, Pb2+ binds most strongly to solid HAs. The order of the metal-humate binding strength is consistent with series found in the literature and is based on the stability constants of metal-humate complexes. In comparison with coal-derived HAs, soil HAs from chemozem (and also low molecular weight HAs) exhibited markedly higher metal-binding capacities, whereas the capacity of oxyhumolite (the raw material fur IIA production) was lower. (C) 2001 Elsevier Science B.V. All rights reserved.