Copper Adsorption by Chernozem Soils and Parent Rocks in Southern Russia

Laboratory data in Cu2+ adsorption by chernozems and parent rocks in Rostov region show that adsorption isotherms can be approximated by the Langmuir equation, whose parameters (K-l and C-infinity) were calculated for all of the samples. The values of C-infinity show a strong negative correlation with the values of cationexchange capacity (CEC) (r = -0.88 at P = 0.95), and K-l is correlated with the content of physical clay (particles < 0.01 mm) (r = 0.78) and with clay (particles < 0.001 mm) content in ordinary chernozem and southern chernozems of various particle size distribution (r = 0.80). Even stronger correlations were detected between these parameters in southern chernozems (r = 0.89 for the physical clay (PC) and r = 0.91 for the silt). However, none of the samples displays a significant correlation of C-infinity and K-l with the contents of physical clay and silt. This led us to conclude that the composition of the samples, for example, their organic matter, can affect Cu2+ adsorption by the soils and parent rocks. Acidification mechanisms of the equilibrium solutions during the Cu2+ adsorption by soils are discussed, as also are the reasons for the absence of balance between Cu2+ adsorbed by soils and exchangeable cations transferred into solution. Analysis of the fine structures of the XANES and EXAFS spectra suggests that Cu2+ can form coordinated chelate complex compounds with humic acids (HA) of soils and can substitute Al3+ at octahedral sites when interacting with clay minerals in soils.