Adsorptive removal of lead ions from wastewater using modified diatomite

Abstract

Adsorptive removal techniques offer a promising solution, and this study investigates the synthesis and application of sulfuric acid-modified diatomite for lead ion removal. Modified diatomite synthesized from raw diatomite was chemically modified and the activation parameters (acid concentration (2–10 M), activation time (4–12 h), solid-to-liquid ratio (50–250 g/L), and temperature (50–90 °C)) were optimized to obtain a 77.93 % lead ion removal efficiency under optimal conditions (4 M H₂SO₄, 10 h, 50 g/L, 90 °C). Then, it was characterized using scanning electron microscopy, Fourier transform infrared spectroscopy, Brunauer-Emmett-Teller analysis, and X-ray diffraction. Its structural transformation and surface area increment from 22.39–34.83 m²/g. We evaluated the adsorbent's adsorption efficiency under various experimental conditions, including solution pH (2–10), adsorbent dosage (0.2–1 g/100 mL), contact time (5–75 min), and initial lead ion concentration (10–50 ppm). Adsorption isotherms and kinetics were analyzed using the Langmuir, Freundlich, Sips, and Redlich-Peterson isotherms and pseudo-first-order, pseudo-second-order, and intraparticle diffusion kinetics models. The results demonstrated that modified diatomite effectively removed lead ions from aqueous solutions. Optimal adsorption conditions were determined at pH 7, 0.8 g/100 mL dosage, 45 min contact time, and 10 ppm initial lead ion concentration, yielding a maximum lead removal efficiency of 89.5 %. The adsorption process was well-described by the Langmuir and Sips isotherm models, the best-fit isotherm model, indicating the presence of a monolayer and heterogeneous surface interaction with a maximum adsorption capacity of 25.1 mg/g. Kinetic studies revealed that the intraparticle diffusion kinetics model best fit the kinetic model, suggesting that pore diffusion is the rate-limiting step in the interaction between lead ions and the adsorption site. This study shows that diatomite treated with sulfuric acid has the potential to be a viable and effective adsorbent for the removal of lead ions from wastewater, helping to provide sustainable water treatment solutions.