Efficient removal of Cr(VI) contaminant using recoverable silica from volcanic ash as natural adsorbent: Synthesis and activity in the mechanism and kinetic adsorption

Modification of silica purified from the Merapi volcanic ash with magnetic material of Fe3O4 and attachment of cetyl triamine bromide (CTA-Br) on the magnetic cored has been performed to provide recoverable and positive surfaced of natural adsorbent. The magnetic cored was prepared via co-precipitation and CTA-Br attachment was conducted by a facile strategy. Then, the modified adsorbents were characterized by SEM, TEM, XRD, and FTIR instruments and examined for removing anionic Cr(VI) from the water media. The characterization data confirmed that crystals of Fe3O4 coated by SiO2 that has been bound with CTA-Br have been successfully formed. Additionally, increasing CTA-Br loaded gives thicker lamination on Fe3O4@SiO2/CTA-Br, but the CTA-Br loaded with higher than 0.25 mmol, leads to the coating peeled out. It is also demonstrated that Fe3O4@SiO2/CTA-Br prepared with CTA-Br 0.25 mmol is ideal for Cr(VI) anionic removal, regarding to the highest adsorption and very good separation or recovery process. Moreover, the optimal dose of Fe3O4@SiO2/CTA-Br in the Cr(VI) removal was observed at 0.25 g/20 mL under condition of pH 3 for 60 min. The adsorption of Cr(VI) well fits the Langmuir isotherm model with an adsorption capacity of 3.38 mg g(-1) and is in a good agreement with pseudo-second order giving kinetic constant at 0.005 g mg(-1) min(-1). Thus, it is clear that the natural adsorbent material with recoverable properties for more efficient and wider application of removal Cr(VI) contaminant was expected from this study.