XAFS CHARACTERIZATION OF COPPER IN MODEL AQUEOUS SYSTEMS OF HUMIC-ACID AND ILLITE

Adsorption of heavy metals at mineral surfaces and complexation with r eactive organic-matter functional groups are important processes regul ating the solubility and fate of soil contaminants. To determine the n ature of Cu(II) bonding in complex clay-organic systems, XAFS analyses were conducted on aqueous suspensions containing Cu(II) in various fo rms: (i) complexed with soil humic acid (HA) at various HA:Cu ratios, (ii) bound to illite, or (iii) bound in a mixture of illite and HA. Sp ectral features for Cu bound to HA did not depend significantly on the HA:Cu ratio, and average first-shell Cu-O bond lengths were consisten tly shorter than for the Cu-illite systems. In the mixed clay-organic suspension, Cu bonding was more characteristic to that of Cu bound wit h HA.