Sorption capacity of sod-podzolic soil in relation to nickel ions
The paper presents the results of a study of the adsorption of nickel ions by sod-podzolic soil. The soil is a biological filter that can absorb and hold various substances, preventing them from entering the groundwater. Nickel as a pollutant enters the environment with emissions from metalworking enterprises, with wastewater, as well as with increasing rates of burning oil and oil products. The purpose of the research is to study the adsorption of nickel ions by sod-podzolic heavy loamy soil of Udmurtia and predicting the possibility of its transition from polluted soil to groundwater and plants. The equilibrium concentration of nickel ions in the soil filtrates was determined by the standard method using atomic absorption spectrophotometry with electrothermal atomization using a Shimadzu-AA7000 instrument. The number of absorbed ions was found by the difference between the initial and equilibrium concentrations. The sorption process can be described by the Langmuir model over the entire range of metal concentrations studied. The nature of the Langmuir isotherm obtained indicates that sod-podzolic soil has a strong ability to absorb nickel ions from solutions. The initial part of the sorption curve is converted into a straight line located at a large angle of inclination to the abscissa axis, which indicates intense metal sorption. Intensive absorption of low concentration of nickel ions by the sod-podzolic soil leads to the fact that as the sorption centers of the soil absorbing complex are filled, the number of unfilled sorption positions decreases and, accordingly, the amount of adsorbed substance decreases too. However, a decrease in the degree of sorption does not mean a decrease in the absolute mass of the sorbate. The amount of nickel ions absorbed by the soil also increased at its high concentration, but not with such intensity as at low concentrations, which means that not all active centers of the soil absorbing complex are fully saturated. During the experiment, the pH of the filtrates remained almost unchanged over the entire range of nickel concentrations studied; therefore, the protons did not participate in the sorption process. Thus, under the conditions of our experiment, nickel replaces only cations in the soil absorbing complex. The use of the Langmuir equation in the description of nickel adsorption in sod-podzolic soil makes it possible to predict its migration along the soil profile and landscapes, taking into account the concentration of pollutant.