Investigation of adsorption equilibrium in the system of ammonium ions and a calcined sorbent from ash and slag waste of thermal power plants

A calcined sorbent from ash and slag waste of thermal power plants was used for water purification from ammonium ions. Experiments were carried out under static conditions at a temperature of 25±2 °С. The concentration of ammonium ions in the solution was measured by the spectrophotometric method according to the established graduation characteristic tested for convergence and correctness. The sorption process was studied at a sorbent dose of 1.0 g per 50 cm3 of the model solution taking the specific pore volume of the sorbent into account. For a solution with an ammonium ion content of 20 mg/dm3, the following modifications were carried out: the frequency of magnetic stirrer rotation was varied from 50 to 500 rpm; the pH of the solution – from 4 to 9; and the time to equilibrium – from 10 to 210 min. The time to equilibrium was 180 min. The effect of initial concentration of ammonium ions (2.0; 5.0; 20; 50 and 100 mg/dm3) in the solution on the adsorption process was studied under optimal sorption parameters. The adsorption equilibrium in the “ammonium ions–calcined sorbent” system was studied for the initial concentration of ammonium ions from 5 to 300 mg/dm3. Experimental data were processed using Langmuir and Freundlich adsorption isotherms. The maximum value of adsorption comprised 1.1251 mg/g. The experimental data were found to agree with the Langmuir theory. To describe the adsorption kinetics, the parameters of pseudo-first and pseudo-second order equations were determined. The highest convergence between the experimental and calculated data was achieved by the pseudo-first order model.