Cr(VI) adsorption from aqueous solution and its reactions behavior on the surfaces of granular Fe–Mn binary oxides

Abstract

A granular Fe–Mn binary oxide (GFMO) was prepared for Cr(VI) removal and characterized by its Brunauer–Emmett–Teller surface area, scanning electron microscopy, X‐ray photoelectron spectroscopy, X‐ray diffraction, and Fourier transform infrared spectroscopy. Scanning electron microscopy images of the GFMO showed it had a rough surface and heterogeneous porous structure. The Brunauer–Emmett–Teller surface area was 57.64 m2/g. X‐ray photoelectron spectra showed that manganese and iron existed mainly in the +IV and + III oxidation states, respectively. Adsorption of Cr(VI) by the GFMO was investigated. Kinetic data showed that the Cr(VI) adsorption onto the GFMO followed a pseudo‐second‐order model, indicating that the adsorption process was chemisorption. Equilibrium data were analyzed by both the Freundlich and Langmuir models, and the Langmuir isotherm model fitted better with the maximum adsorption capacity of 16.79 mg/g at 318 K. The Cr(VI) adsorption on GFMO was endothermic and nonspontaneous in nature. It was also strongly pH dependent, with higher Cr(VI) removal efficiency occurring under acidic conditions and a sharp decrease in adsorption as the pH increased. Coexisting anions competed with Cr(VI) for adsorption on the GFMO in the order silicate > sulfate > nitrate. Cr(VI) adsorption on the GFMO mainly occurred via anion exchange, surface complexation, and electrostatic attraction. Novelty or Significance: Combined adsorbent with iron oxides and manganese oxides was usually synthesized for heavy metal removal and showed an excellent adsorption capacity. However, the Fe–Mn binary oxide adsorbent mentioned above were mostly exhibited in particles, limiting its engineering application due to the dispersion state in aqueous solutions. Therefore, novel granular Fe–Mn oxide adsorbents, with good stability and high adsorption capacity, are highly desired. A novel granular Fe–Mn oxide (GFMO) adsorbent with the polyvinyl alcohol (PVA) as the adhesive was synthesized to investigate its adsorption behaviors for Cr(VI) for further used as filler in most water treatment equipment. © 2018 American Institute of Chemical Engineers Environ Prog, 38: S176–S184, 2019

Non‐competitive and competitive adsorption of Zn(II), Cu(II), and Cd(II) by a granular Fe‐Mn binary oxide in aqueous solution

“…As shown in Figure 6, the FTIR spectrum obtained from the GFMO before adsorption exhibited a broad peak at 3411 cm −1 and a sharp peak at 1618 cm −1 , assigned to the stretching and bending vibration of hydroxyl groups of water molecules, respectively 42 . The peaks at 1111 and 1132 cm −1 are attributed to the bending vibration of hydroxyl groups of Fe‐OH, and the peak at 1384 cm −1 corresponds to the vibration of Fe‐O‐Mn groups 13 …”

“…42 The peaks at 1111 and 1132 cm −1 are attributed to the bending vibration of hydroxyl groups of Fe-OH, and the peak at 1384 cm −1 corresponds to the vibration of Fe-O-Mn groups. 13 After Zn(II), Cu(II), and Cd(II) adsorption, the peak at 1618 cm −1 underwent a slight red shift, while the peaks at 1132 and 1111 cm −1…”

“…The GFMO synthesis procedure has been previously reported in the literature. 13 In a typical synthesis, FeSO 4 Á7H 2 O and KMnO 4 were coprecipitated by the addition of a 5% PVA (wt/vol) solution (pH 8.0) with mechanical stirring for 1 h. The resulting brown solid was separated and shaped into spheres that were dried to obtain the GFMO. (5,10,20,30,60,120,240, 480, 600, 960, and 1440 min) were passed through 0.45 μm polycarbonate membranes.…”

“…As such, series of Fe–Mn oxide adsorbents with different Fe/Mn molar ratios (from 1:1 to 9:1) in granular states using polyvinyl alcohol (PVA) as the conjunction were synthesized to investigate Cr(VI) adsorption capacity. It demonstrated that the granular Fe–Mn oxide (GFMO) with Fe/Mn molar ratio of 5:1 showed a good hydraulic load resistance and was most effective for Cr(VI) removal 13 . Therefore, the performance of GFMO for Cd(II), Cu(II), and Zn(II) non‐competitive and competitive adsorption was investigated in this study.…”

Synthesis, Optical Characterization, and Adsorption of Novel Hexavalent Chromium and Total Chromium Sorbent: A Fabrication of Mulberry Stem Biochar/Mn-Fe Binary Oxide Composite via Response Surface Methodology

“…Besides (Aryal et al, 2011;Granados-Correa and Bulbulian, 2012), Fe-Mn mixed metal oxide nanocomposites also showed good regeneration and stability activity for Cr(VI) removal (Wang and Fu, 2013). The granular Fe-Mn binary oxide (GFMO) was prepared and the adsorption capacity of GFMO for Cr(VI) was 16.79 mg/g (Du et al, 2019). Fe-Mn bimetal oxide (IMBO) nanospheres were synthesized by template-free method and the adsorption capacity of IMBO towards Cr(VI) was 105.96 mg/g (Wen et al, 2017).…”