Copper adsorption on humic acid coated gibbsite: comparison with single sorbent systems

Copper adsorption processes on aluminium oxides may significantly control the mobility and transport of copper ions in soils and surface waters. The binding of protons and copper to humic acid (HA) and to gibbsite as single sorbent systems was investigated and the results then used to test the validity of the Linear Additivity Model (LAM) for describing copper binding to gibbsite/HA systems. More copper was adsorbed in the gibbsite/HA/Cu(2+) ternary system, at pH 4 and 6 and ionic strength 0.1 M, than in the corresponding binary systems. Although copper adsorption on gibbsite at pH 4 is rather small, the enhancement in sorption was noteworthy, and can be attributed to the formation of ternary complexes and changes in the electrostatic potentials at the mineral surface or at the HA as a result of their mutual interaction. The LAM predicted satisfactorily the experimental results at pH 6, whereas it underestimated the copper binding at pH 4.