Comparative analysis of mono- and polyelement adsorption of copper, lead, and zinc by an ordinary chernozem from nitrate and acetate solutions

Abstract

Isotherms of mono- and polyelement adsorption of Cu2+, Pb2+, and Zn2+ by an ordinary chernozem were described by the Langmuir equation. The values of the adsorption constant k decreased in the range Cu2+ > Pb2+ ≫ Zn2+ for the monoelement adsorption from nitrate and acetate salt solutions, Cu2+ > Pb2+ > Zn2+ for the polyelement adsorption from nitrate solutions, and Pb2+ > Cu2+ ≫ Zn2+ for the polyelement adsorption from acetate solutions. The maximum adsorption (Cmax, ∞) of individual cations at the polyelement contamination was always lower than at the monoelement contamination because of the mutual competition. At the same time, the values of k for the polyelement adsorption were higher than those for the monoelement adsorption because heavy metals (HMs) interact with most of the specific adsorption centers. It was shown that the ratio between the content of exchangeable cations displaced from the soil exchangeable complex (SEC) into the solution and the content of adsorbed HMs decreased with the increasing concentration of adsorbed HMs. These values could be higher (for Cu2+), equal, or lower than 1 (for Pb2+ and Zn2+). In the former case, this was due to the dissolution of readily soluble salts at low HM concentrations in the SEC. In the latter case, this was related to the adsorption of associated HMs and the formation of new phases localized on the surface of soil particles at high HM concentrations in the SEC.