Cadmium adsorption on aluminum oxide in the presence of polyacrylic acid

Adsorption of metals from aqueous solution onto oxide and other surfaces is known to affect trace metal transport in many natural and engineered syste ms. It is therefore important to understand whether dissolved metal inputs will be easily bound to particles or will be strongly complexed in solution and transported with the water phase. The effect of poly(acrylic acid) (PA A), representing a model compound for natural organic matter, on the adsorp tion of Cd(ll) onto gamma -Al2O3 was determined using batch adsorption expe riments over a pH range from 4 to 10. Initially, interactions among the ind ividual components were evaluated. Cadmium adsorption onto alumina showed a typical S-shaped metal adsorption curve. PAA adsorption onto gamma -Al2O3 decreased with increase in pH. The-affinity of PAA for Cd2+ increased stron gly with pH. In ternary systems, the presence of PAA resulted in an enhance ment of Cd(II) adsorption below pH 6, apparently due to ternary surface com plex formation. Above pH 6, a decrease in cadmium adsorption onto gamma -Al 2O3 was observed resulting from an increase in the concentration of soluble Cd-PAA complexes. Overall, results indicate that the presence of natural o rganic matter could have a significant impact on the distribution and mobil ity of cadmium in the environment. Simple surface complexation modeling was insufficient to describe behavior in the ternary systems due to the comple xity of the PAA polymer.