Adsorption of Cu(II) and Zn(II) by estuarine, riverine and terrestrial humic acids

Adsorption constant (Kads) values for Cu(II) and Zn(II) adsorption from an artificial seawater matrix onto suspended humic acids were determined. The humic acids were extracted from estuarine and riverine surface sediments and from surface soils. Solution state 13C nuclear magnetic resonance (NMR) was used to characterize the humic acids. Values of Kads for Cu(II) onto suspended solid humic acids were found to be significantly greater than those for Zn(II), in agreement with the Irving-Williams series, suggesting that the process of metal adsorption by suspended humic acids is similar to the process of metal complexation by specific functional groups of dissolved humic acids. In general, greater Kads values were associated with lignin-rich humic acids as compared to lignin-poor humic acids.