Desorption of Exchangeable Cations at Adsorption of Lead Ions by Chernozem in the Presence of Attendant Anions

Abstract

The effect of Cl^–, Ac‾ and NO₃‾ anions on the adsorption of Pb cations by an ordinary chernozem and desorption of exchangeable cations in the soil-solution system has been assessed under model laboratory conditions. It has been shown that the attendant anions affect the shape of the adsorption isotherms, which are described by the Langmuir equation. The greatest influence on the affinity constant of Pb with soil has anion Ac‾. It has been found that the uptake of the Pb cations by chernozem from solutions of different salts is accompanied by the displacement of the exchangeable cations to the solution in the following order: Ca²⁺ > Mg²⁺ > Na⁺ > K⁺. The sum of the displaced exchangeable cations in most cases exceeds the amount of the adsorbed metal cations. The content of Pb cations desorbed by the ammonium acetate buffer solution (pH 4.8) makes up 6-39% of the total Pb adsorbed cations. According to the effect of the anions on the displacing capacity of cations for Pb the following series are formed: Cl¯ > Ac‾ > NO₃¯.