Synthesis of Fe2O3-coated and HCl-treated bauxite ore waste for the adsorption of arsenic (III) from aqueous solution: Isotherm and kinetic models

Ciprofloxacin Removal via Acid-Modified Red Mud: Optimizing the Process, Analyzing the Adsorption Features, and Exploring the Underlying Mechanism

In this study, RM (red mud) was acidified with sulfuric acid, and the acidified ARM (acidified red mud) was utilized as an innovative adsorption material for treating antibiotic-containing wastewater. The adsorption conditions, kinetics, isotherms, thermodynamics, and mechanism of ARM for CIP (ciprofloxacin) were investigated. The characterization of the ARM involved techniques such as scanning electron microscopy (SEM), transmission electron microscopy (TEM), Brunauer-Emmett-Teller (BET), X-ray diffraction (XRD), X-ray fluorescence (XRF), thermogravimetric analysis (TGA), and NH3-TPD analysis. Adsorption studies employed a response surface methodology (RSM) for the experimental design. The results showed that ARM can absorb CIP effectively. The RSM optimal experiment indicated that the most significant model terms influencing adsorption capacity were solution pH, CIP initial concentration, and ARM dosage, under which the predicted maximum adsorption capacity achieved 7.30 mg/g. The adsorption kinetics adhered to a pseudo-second-order model, while equilibrium data fitted the Langmuir-Freundlich isotherm, yielding maximum capacity values of 7.35 mg/g. The adsorption process occurred spontaneously and absorbed heat, evidenced by ΔGθ values between -83.05 and -91.50 kJ/mol, ΔSθ at 281.6 J/mol/K, and ΔHθ at 0.86 kJ/mol. Analysis using attenuated total reflection Fourier-transform infrared spectroscopy (ATR-FTIR) indicated a complex reaction between the Al-O in the ARM and the ester group -COO in CIP. The C=O bond in CIP was likely to undergo a slight electrostatic interaction or be bound to the internal spherical surface of the ARM. The findings indicate that ARM is a promising and efficient adsorbent for CIP removal from wastewater.

Enhanced arsenic removal using lateritic bauxite modified by heating and blending

The use of bauxite to remove arsenic from wastewater has been confirmed to be effective, but its removal efficiency in literature is not up to 90%, hence the need to devise a more effective method to remove arsenic from wastewater. In this study, a novel material was prepared by thermally modifying and blending yellow and red lateritic bauxite to form thermally modified and blended yellow and red lateritic bauxite (TYB + TRB). The adsorption isotherm, morphology and chemical composition of the novel material were determined by the Langmuir and Freundlich models, Scanning Electron Microscopy (SEM) and X-ray Fluorescence (XRF), respectively. Application of the novel material in arsenic removal resulted in >97% removal efficiency within 60 min. The arsenic adsorption by TYB + TRB conformed to the Freundlich model. The SEM image depicted a compacted earth material after use of the TYB + TRB to remove arsenic from the wastewater. The XRF results also showed a drastic reduction in the chemical composition of the novel bauxite except Ti, thus suggesting the occurrence of multiple mechanisms during the arsenic removal. This study demonstrated the potential of TYB + TRB to be developed and used as the most suitable material for wastewater treatment.

Facile auto-combustion synthesis of calcium aluminate nanoparticles for efficient removal of Ni(II) and As(III) ions from wastewater

We herein report the synthesis of monoclinic calcium aluminate (CaAl₂O₄) nanoparticles via a facile auto-combustion method followed by calcination. We performed the auto-combustion method using aluminium nitrate and calcium nitrate as oxidants and different fuels as reductants such as urea, glycine, and a mixture of urea and glycine, with various fuel-to-oxidant equivalence ratios (Φc). Then, the combusted samples were calcined at different temperatures; 600 and 800 °C. The products were characterized by means of X-ray diffraction, Fourier transform infrared spectroscopy, thermo-gravimetric analysis, field-emission scanning electron microscope, and high-resolution transmission electron microscope. CaAl₂O₄ nanoparticles with an average crystallite size of 40.4, 38.8, and 33.7 nm were obtained after calcination at 800 °C using the aforementioned fuels, respectively. TEM images revealed that CaAl₂O₄ nanoparticles tend to form partially sintered aggregates owing to the high thermal treatment temperature, so they have non-uniform shapes. The produced CaAl₂O₄ nanoparticles exhibited good absorptivity toward Ni(II) and As(III) ions form aqueous media. The maximum sorption capacities (q_m) of CaAl₂O₄ for the removal of Ni(II) and As(III) were found to be 58.73 and 43.9 mg.g^-1, at pH 7 and 5, respectively. The equilibrium isotherms and adsorption kinetics studies revealed that the adsorption data fitted well Freundlich isotherm and pseudo-second-order models, respectively. Besides, the adsorption of Ni(II) and As(III) ions on CaAl₂O₄ nanoparticles is physisorption. Overall, the obtained results indicated that calcium aluminate nano-adsorbent is a good candidate for the removal of Ni(II) and As(III) ions from wastewater, due to its high efficiency, stability, and re-usability.

Synergistic modification of bentonite by acid activation and hydroxyl iron pillaring for enhanced dye adsorption capacity

Despite the fact of natural abundance, low cost and environmental friendliness, the far-from-sufficient adsorption capacity of natural bentonite (BT) has limited such a promising application to remove dye pollutants. In this paper, we proposed a facile modification strategy to enhance adsorption performance of bentonite utilizing synergistic acid activation and hydroxyl iron pillaring, by which the adsorbent (abbreviated as S-Fe-BT) exhibited the highest adsorption capacity (246.06 mg/g) and a high rapid adsorption rate for a typical organic dye, Rhodamine B (RhB). This could be ascribed to the increased interlayer spacing, the increased specific surface area, and the optimized OH/Fe ratio after the synthetic modification of the pristine BT. The adsorption behavior of RhB onto S-Fe-BT was well described by the pseudo-second-order kinetic model, indicating a chemical-adsorption-controlled process. Furthermore, its adsorption isotherm matched well with the Langmuir model due to a monolayer adsorption process. This paper opens a promising direction to remove the dye pollution using low cost bentonite adsorbents treated by such a convenient modification strategy.

Increased As Adsorption on Maghemite-Containing Red Mud Prepared by the Alkali Fusion-Leaching Method

This study investigates the use of red muds as adsorbents for As (V) removal. Red mud is a waste that contains a large amount of iron oxides and hydroxides, which are excellent adsorbents of arsenic, especially those possessing magnetic properties and a large specific surface area. The purpose of the experiments was to study the possibility of obtaining an effective adsorbent by the direct extraction of alumina from bauxite using the caustic alkali fusion method and to compare the arsenic removal effectiveness and other properties of these red muds with industrial samples. Red muds were described using methods such as X-ray diffraction spectrometry (XRD), X-ray fluorescence spectrometry (XRF), SEM, vibrating sample magnetometry (VSM), and the Brunauer–Emmett–Teller (BET) method. The main iron-containing phase of the red muds obtained by fusing bauxite with caustic alkali is maghemite, which has a large specific surface area. The specific surface area of the obtained samples varied in the range of 6.1–54.9 m2/g. Arsenic adsorption experiments were carried out using five different types of red muds: industrial Bayer, industrial sintering, and red mud obtained through bauxite alkali fusion at 300, 500, and 700 °C. The red muds obtained by fusing bauxite with caustic alkali at 300 and 500 °C had the highest effectiveness removing arsenic; their As(V) uptake capacity was over 30 mg/g.

Clean application of magnetic biomaterial for the removal of As (III) from water

Magnetite-coated pine cone biomass was successfully synthesized, characterized, and its interaction with As (III) in water evaluated in order to apply it as an efficient adsorbent. Transmission electron microscope, scanning electron microscope, and imaging studies revealed that spherical magnetite particles were evenly distributed over the pine cone surface. Adsorption studies showed that the optimum pH of As (III) adsorption was 8 and that Fe (III) leaching was negligible at this pH. The optimum Fe₃O₄:pine cone ratio for As (III) removal was 2.0 g Fe₃O₄:1.5 g pine cone with adsorption capacity of 13.86 mg/g. The pseudo-second-order model best fitted the kinetic data with activation energy of adsorption was calculated to be 23.78 kJ/mol. The Langmuir isotherm described the equilibrium data best while the values of Dubinin-Radushkevich mean free energy suggests anion-exchange process. Increasing ionic strength slightly increased As (III) capacity of MNP-PCP from 13.86 to 17.82 mg/g at optimum solution pH of 8, but As (III) adsorption reduced by [Formula: see text]anions and humic acid due to competition. Adsorption mechanism was confirmed with evidence from FTIR, XPS, pH_PZC, and [Formula: see text] replacement by As (III) adsorption onto the [Formula: see text]-loaded composite.