Adsorptive removal of Cr(VI) from aqueous solution using sulfuric acid-treated diatomite

Abstract

In this study, diatomite underwent acid treatment and was examined for its capability to adsorb chromium (VI) (Cr (VI)) from water. The diatomite was treated with sulfuric acid (H₂SO₄) in varying concentrations (2–10 M) over different activation times (4–12 h), solid-to-liquid ratios (50–250 g/L), and activation temperatures (60–90). Optimal Cr (VI) removal was achieved with a 4 M H₂SO₄ concentration, an activation time of 10 h, a solid-to-liquid ratio of 50 g/L, and an activation temperature of 90 °C. Both raw diatomite and acid-treated diatomite (TDE) were characterized using scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FTIR), Brunauer, Emmett, and Teller (BET), and X-ray diffractometer (XRD). BET analysis showed an increase in surface area from 22.39 m²/g to 34.83 m²/g after treatment. The maximum Cr(VI) removal efficiency of 86.7 % was achieved at pH 2, 0.3 g/100 mL adsorbent dosage, 60 min contact time, and 10 ppm initial Cr(VI) concentration, according to the optimization of adsorption studies that were carried out across varying pH (2−10), adsorbent dosage (0.1–0.5 g/100 mL), contact time (15–75 min), and initial Cr(VI) concentration (10–30 ppm). The Freundlich and Sips isotherm models provided the best description of the adsorption process, revealing heterogeneous surface interactions and a maximum adsorption capacity of 16.395 mg/g. Chemisorption was confirmed as the major mechanism by kinetic analysis, which showed that the pseudo-second-order model fit the data the best. Thermodynamic studies validated the process as spontaneous and endothermic. These findings show that diatomite treated with sulfuric acid is a very efficient adsorbent for removing Cr(VI) from tainted water.