ADSORPTIVE REMOVAL OF Pb(II) FROM DILUTE AQUEOUS SOLUTIONS: KINETICS AND EQUILIBRIUM OF THE PROCESS
Abstract
Wastewater from galvanic and metallurgical plants, the mining and engineering industries, and the manufacture of lead-acid batteries, textiles, paints and dyes may contain lead ions at concentrations of 60–120 mg l⁻¹. Adsorption is regarded as one of the most promising and most economically viable methods for the removal of Pb(II) from aqueous media. A priority task is to find effective adsorbents for the removal of Pb(II) from natural and industrial wastewater. The aim of this research is to establish physicochemical regularities of Pb(II) removal from dilute aqueous solutions using a nanosorbent based on silicon and zirconium (IV) dioxides, and to study the kinetics and equilibrium of adsorption, including mathematical modelling of the adsorption kinetics and isotherms. The nanosorbent had a specific surface area 800 m² g⁻¹ and contained 37% of ZrO₂. It was found that under optimal process conditions (adsorbent dosage 1 g l⁻¹, solution pH 10, phase contact time 180 min, temperature 310 K), a Pb(II) removal efficiency of 99.6% can be achieved. Kinetic studies revealed a significant dependence of the adsorption rate on temperature and solution acidity. The process kinetics are the best described by the pseudo-second-order and the Elovich models, suggesting a chemisorption-driven interaction. A mixed-diffusion mass transfer mechanism was identified, with the Dumwald–Wagner model providing the most accurate description of the experimental data. Equilibrium studies demonstrated that the Freundlich, Temkin, and Dubinin–Radushkevich isotherm models show the best agreement with experimental results, with the Temkin model yielding the minimum error. The constants for these models were calculated, and their values confirm the chemisorption nature of adsorption with a certain contribution from ion exchange. The thermodynamic parameters of adsorption indicate the spontaneity of the process (ΔG⁰ads. ≈ −25 kJ mol⁻¹), the endothermic character of adsorption (ΔH⁰ads. = 28.34 kJ mol⁻¹), and increased disorder of the system as a result of adsorption (ΔS⁰ads. = 173.67 ÷ 183.18 J mol⁻¹ K⁻¹). The obtained results may be used in the development of efficient technologies for water purification from toxic lead compounds.