Adsorption of copper by ordinary and southern chernozems from solutions of different salts

The aim of this work was to study the effect of the attendant anions and particle-size distribution on the adsorption of copper by chernozems of Rostov region (Russia). The samples of soil in the natural cationic form were treated with solutions of copper nitrates, acetates, chlorides, and sulfates at a soil: solution ratio of 1:10. The concentrations of the initial copper solutions varied in the range from 0.05 to 1 mM/L. The suspensions were shaken for 1 h, left to settle for a further 24 h and then filtered. The metal concentrations in the filtrates were determined by atomic absorption spectrometry. The concentrations of the adsorbed copper cations were calculated from the difference between the metal concentrations in the initial and equilibrium solutions. The effect of the attendant anions Cl−, SO42 −, Ac−, and NO3− and particle size distribution on the adsorption of copper by chernozems of the Rostov region has been studied under laboratory conditions. The shape of the adsorption isotherms varies depending on the attendant anion and is described by the Henry, Freundlich, and Langmuir equations. The adsorption of copper by the soil is accompanied by the acidification of equilibrium solutions (рНeq): 0.53 ≤ ΔрНeq ≤ 2.06, which depends on the attendant anion. The highest value of ΔpHeq corresponds to the adsorption of Cu2 + from the copper sulfate solution and its lowest value, from the copper chloride solution. The effect of the attendant anions decreases in the series: Cu(Ac)2 > CuCl2 > Cu(NO3)2 > > CuSO4. In the southern chernozems, a close correlation is observed between the maximum copper adsorption and the content of clay and silt (R = 0.99). No correlation is found between the values of adsorption constants and particle size distribution, which is related to the changes in the chemistry and mineralogy of the soils studied.