The sorption properties of BAU-A activated carbon with respect to nickel ions have been studied. The studies were carried out at room temperature on a model solution in the pH range of 5-8. It is shown that the adsorption isotherms of nickel ions by activated carbon BAU-A at different solution pH can be described with equal accuracy by two classical equations: Freundlich and Langmuir. The absence of a correlation between the parameters of the Freundlich equation and the change in the pH of the solution was found, which indicates the empirical nature of the description of the experimental data by this equation. The parameters of the Langmuir equation naturally change with a change in the pH of the solution. With an increase in the pH of the solution, the adsorption capacity of BAU-A with respect to nickel ions decreases, while the adsorption equilibrium constant, on the contrary, increases. Estimation of the free energy of adsorption according to the Dubinin-Radushkevich equation showed that it does not exceed 1 kJ/mol, which excludes the ion-exchange interaction of nickel ions with BAU-A. Comparison of the parameters of the Langmuir equation for the sorption of nickel ions with similar data for copper(II) ions shows that the adsorption capacity of BAU-A for nickel ions is approximately an order of magnitude higher than for copper(II) ions. This makes it possible to recommend this sorbent for the selective extraction of nickel and copper ions from mixed solutions.
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