Competitive adsorption of Cu(II)-EDTA and Cd(II)-EDTA onto TiO2

Cu(II), EDTA, Cu(II)-EDTA, Cd(II)-EDTA, and Cu(II)/Cd(II) and Cu(II)-EDTA/C d(II)-EDTA competitive adsorption onto TiO2 has been studied with variation of pH and concentration. For Cu(II) and EDTA, typical cationic and anionic types of adsorption are noted, respectively. Ligand-type adsorption is fou nd for Cu(II)-EDTA and Cd(II)-EDTA under both single and competitive condit ions, Surface complexation modeling considered inner-sphere complexation an d the diffuse layer model employing MINTEQA2; surface complexes used includ e Ti-(OH2)O-Cu+, Ti-(OH)EDTAH(2)(-2), Ti-(OH)EDTA-Cu-2, and Ti-(OH)EDTA-Cd- 2. Experimental and model predictions suggest no competitive adsorption bet ween Cu(II) and Cd(II) at 5 x 10(-5) M. On the other hand, adsorption data and model predictions indicate that Cd(II)-EDTA adsorption is favored over that of Cu(II)-EDTA with some competition for adsorption sites. Cd(II)EDTA adsorption was only slightly affected by the presence of Cu(II)-EDTA; howev er, Cu(II)-EDTA adsorption was strongly influenced by the presence of Cd(II )-EDTA, especially as the molar ratio of Cd(II)-EDTA/Cu(II)-EDTA increased. A modified surface complexation constant for Cd(II)-EDTA is required to ex plain the competitive data, suggesting surface site heterogeneity. (C) 1999 Academic Press.