Sorption of Cu by chernozems in southern Russia

The adsorption of Cu2 + by chernozems and parent rocks in Rostov region has been studied under laboratory conditions. It is shown that the adsorption isotherms are described by the Langmuir equation. The Langmuir equation parameters (KL and C∞) have been calculated for all of the studied samples. It is shown that the values of C∞ are in close negative correlation with the values of cation exchange capacity (r = − 0.88 at P = 0.95). A close correlation is revealed between the KL values and the content of clay (r = 0.78), as well as between KL and the content of silt in chernozem haplic and chernozems calcic of different textures (r = 0.80). An even closer correlation exists between these parameters in separate size fractions of chernozems calcic (r = 0.89 for clay and r = 0.91 for the silt fraction). However, no significant correlation exists between the C∞ and KL values and the contents of silt and clay in all samples. Therefore, a conclusion is drawn about the effect of the sample composition, including organic matter, on the adsorption of Cu2 + by the objects studied. Mechanisms for the acidification of equilibrium solutions during the adsorption of Cu2 + by soils and the misbalance between the adsorbed Cu2 + cations and the exchangeable cations displaced into the solution are discussed. XANES and EXAFS analysis indicates a possibility for the formation of chelate Cu2 + complexes with humic acids and the substitution of Al3 + in octahedral positions by Cu2 + during the interactions with clay minerals.