Magnetization of Bauxite Residue to Enhance the Removal Efficiency Towards Heavy Metals

Bauxite residues are a mass of industrial wastes derived from aluminum metallurgy. This work provided a simple pyrolysis method to magnetize the bauxite residue to serve as a magnetic adsorbent towards heavy metals removal. The X-ray diffraction patterns and Mossbauer spectrum results confirmed the partial reduction of iron species with an obvious enhancement in magnetization. The magnetized bauxite residue exhibited excellent removal efficiencies for Cu²⁺, Cd²⁺ and Pb²⁺ with maximum adsorption capacities of 219.0 mg g^-1, 275.4 mg g^-1, and 100.4 mg g^-1, which could be quickly separated through a magnet. The adsorption equilibrium data were fitted to the Langmuir isotherm model, while the adsorption kinetics followed a pseudo-first-order model. According to the characterization results, chemical precipitation and sorption was the major mechanism for the removal of Cu²⁺, Pb²⁺, and Cd²⁺. Thus, the magnetized bauxite residue exhibited promising applications for heavy metals removal in wastewater.

Magnetic adsorbent developed with alkali-thermal pretreated biogas slurry solids for the removal of heavy metals: optimization, kinetic, and equilibrium study

Discharge of effluents containing heavy metal without adequate treatment causes contamination of water resources and creates environmental and health issues. Adsorption could be applied to remediate heavy metals from wastewater effectively. In this study, a low-cost adsorbent was prepared by magnetic modification of pretreated biogas slurry solids (BSS) to remove heavy metals such as Cu²⁺, Cd²⁺, and Pb²⁺. The temperature (423 K) and time (1.5 h) of pretreatment, the BSS to KOH ratio (1:10 w/v), and the ratio of magnetic iron nanoparticle (MIN) to pretreated BSS (PSS) (1:2 w/w) were optimized for the preparation of adsorbent. The magnetically modified pretreated biogas slurry solid (MMPSS) adsorbent was characterized by BET isotherm, FTIR, XRD, FESEM, VSM, and EDX analysis. MMPSS attained equilibrium at 60 min and showed an adsorption capacity of 26.84 mg/g, 24.79 mg/g, and 23.86 mg/g with removal percentages 89.46%, 82.63%, and 79.54% for Cu²⁺, Cd²⁺, and Pb²⁺, respectively, at 310 K and pH 6 with an initial concentration of 150 mg/L. The adsorption process followed a pseudo second-order model with an R² value above 0.9 for all metals with a well-approaching equilibrium pattern. The good fit of experimental data by the Langmuir isotherm model implied monolayer adsorption. The metal ions adsorbed onto MMPSS were able to desorb effectively in the presence of HCl and retained 83.01%, 84.66%, and 81.83% of the initial adsorption capacity for Cu²⁺, Cd²⁺, and Pb²⁺ respectively after 5 consecutive cycles.

Removal of metal ions using a new magnetic chitosan nano-bio-adsorbent; A powerful approach in water treatment

In this study, a magnetic chitosan/Al₂O₃/Fe₃O₄ (M-Cs) nanocomposite was developed by ethylenediaminetetraacetic acid (EDTA) functionalization to enhance its adsorption behavior for the removal of Cd(II), Cu(II) and Zn(II) metal ions from aqueous solution. The results revealed that the EDTA functionalization of M-Cs increased its adsorption capacity ~9.1, ~5.6 and ~14.3 times toward Cu, Cd and Zn ions. The maximum adsorption capacity followed the order of Cd(II) > Cu(II) > Zn(II) and the maximum adsorption efficiency was achieved at pH of 5.3 with the removal percentage of 99.98, 93.69 and 83.81 %, respectively, for the removal of Cu, Cd and Zn ions. The metal ions adsorption kinetic obeyed pseudo-second-order equation and the Langmuir isothermal was found the most fitted model for their adsorption isothermal experimental data. In addition, the thermodynamic study illustrated that the adsorption process was exothermic and spontaneous in nature.

Fe3O4@PDA@PANI core-shell nanocomposites as a new adsorbent for simultaneous preconcentration of Tartrazine and Sunset Yellow by ultrasonic-assisted dispersive micro solid-phase extraction

In this research, novel magnetic Fe₃O₄@PDA@PANI core-shell nanoparticles were designed and fabricated as an efficient adsorbent in the service of ultrasound-assisted dispersive micro-solid phase extraction for simultaneous preconcentration of Sunset Yellow (SY) and Tartrazine (Tar) before UV-Vis spectrophotometric detection. This adsorbent was fully characterized by Fourier Transform Infrared (FT-IR) spectroscopy, Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), and Energy Dispersive X-ray (EDX) analysis. To overcome the spectral overlapping of SY and Tar dyes, the derivative spectrophotometric method was successfully used for the simultaneous detection of dyes in their binary solutions. The operating parameters affecting preconcentration efficiency and spectrophotometric determination were optimized. Under optimal conditions, the limit of detections (LOD) was obtained 0.2 and 0.5 ng mL^-1 for SY and Tar, respectively. The adsorption capacity and reusability of core-shell nanoparticles were significant. The satisfactory results of analysis of a few real samples indicate that the method is very favored in the analysis of various complex matrices.

Highly efficient porous magnetic polydopamine/copper phosphate with three-dimensional hierarchical nanoflower morphology as a selective platform for recombinant proteins separation

The separation and purification of recombinant pharmaceutical proteins is a fundamental and challenging step in the biotechnology industry. Hierarchical nanostructures with unique features and high stability can be used as efficient adsorbents. In this study, hierarchical magnetic polydopamine-copper phosphate nanoflowers (Cu-PDA MNFs) were synthesized as high-performance magnetic adsorbents in a simple and low-cost method based on green chemistry. The prepared hybrid Cu-PDA MNFs revealed great performance for separating pure recombinant human growth hormone (rhGH) and the rhGH acquired from recombinant Pichia pastoris yeast fermentation. The analysis confirmed that Cu-PDA MNFs exhibited a high adsorption capacity of 257.4 mg rhGH g^-1 Cu-PDA MNFs and a fast adsorption rate for approaching the adsorption equilibrium within less than 30 min with a recovery efficiency of 74% of rhGH from the real sample. In addition, recycling tests demonstrated the stability and recyclability of Cu-PDA MNFs for at least six cycles with almost constant adsorption capacity and no toxicity. Based on these results, Cu-PDA MNFs could be considered as a promising candidate for separation and purification of rhGH. This work presents a new approach to using organic-inorganic nanoflowers as the hierarchical nanostructure for purification of pharmaceutical proteins with high performance.

A novel synthesis of sulfurized magnetic biochar for aqueous Hg(II) capture as a potential method for environmental remediation in water

Due to public health threats resulting from mercury (Hg) and its distribution in the food chain, global restrictions have been placed on Hg use and emissions. Biochar is a porous, carbonaceous adsorbent typically derived from waste biomass or organic matter, making it an eco-friendly material for aqueous mercury (Hg(II)) control. Functionalization of biochar can improve performance in pollution control applications. In this work, carbonization, magnetization, and sulfurization of biochar were combined into a single heating step to prepare sulfurized magnetic biochar (SMBC) for Hg(II) removal from water. Results indicate that SMBC prepared at 600 °C adsorbed 8.93 mg/g Hg(II), more than materials prepared at 400, 500, 700, 800, and 900 °C. Additionally, Hg(II) adsorption onto SMBC was 53.0% and 11.5% greater than onto magnetic biochar (MBC) and biochar (BC), respectively. Hg(II) adsorption is shown to be favorable in acidic conditions (pH 3.5-5), thermodynamically spontaneous, and endothermic. Adsorption results fit the pseudo-second-order (R² = 0.990 and the sum of squared error (SSE) = 5.382) and external mass transfer (R² = 0.971 and SSE = 9.422) models. The partitioning coefficients were 4.964 mg/g/μM in freshwater, 0.176 mg/g/μM in estuary water, and 0.275 mg/g/μM in seawater, highlighting the importance of salinity in environmental remediation applications. In summary, SMBC can be readily prepared with minimal processing steps. The product is a robust adsorbent for Hg(II), and it can potentially be applied to remediate contaminated water/sediment/soil in the future.

Facile preparation of taurine modified magnetic chitosan nanocomposites as biodegradable adsorbents toward methylene blue

A novel magnetic Fe₃O₄@chitosan@taurine adsorbent (MCT) was prepared by surface modification of magnetic chitosan nano-composites with taurine-glutaraldehyde solution. The adsorbents were characterized by FTIR, SEM, TEM, XRD, TGA and VSM techniques, respectively. According to the FTIR spectrum of MCT, the characteristic peaks of the SO₃^-group on MCT were observed to have a shift after adsorption of the cationic dye, which indicates that there may be electrostatic attraction between the MCT and the cationic dye. Moreover, the saturation magnetization of MCT was found to be 20.797 emu g^-1, suggesting that MCT has sufficient magnetic response to meet the need of magnetic separation. The adsorption properties of cationic dyes by MCT were further investigated by using methylene blue (MB) as a representative. The adsorption behaviour of MB by MCT was well described by the pseudo-second order kinetic model and the Langmuir isotherm model, respectively. The maximum adsorption capacity of MB calculated from the Langmuir model fitting was 204.1 mg g^-1 at pH 5 and 384.6 mg g^-1 at pH 9, respectively, and the adsorption equilibrium could be reached within 10 min. Besides, the negative values of ΔG° and ΔH° suggested that the adsorption process was spontaneous and exothermic, and the good reusability indicated that MCT could act as a recyclable adsorbent for dye adsorption. All of these results illustrate that MCT has great potential for practical application in removal of cationic dyes from aqueous solutions.

Thiol-methyl-modified magnetic microspheres for effective cadmium (II) removal from polluted water

For effective removal of cadmium (II) (Cd(II)) from polluted water, a magnetic adsorbent of Fe₃O₄@SiO₂ core-shell microspheres modified with methyl-protected thiol groups (Fe₃O₄@SiO₂-SH-Protected) was synthesized and characterized by scanning electron, transmission electron, energy dispersive X-ray spectroscopy, Fourier transform infrared spectroscopies, as well as X-ray diffraction, Raman spectroscopy, and magnetic measurements. Characterization results showed that thiol groups on the surface of Fe₃O₄@SiO₂ material were protected to avoid disulfide formation. Batch adsorption experiments were conducted by varying the contact time, initial pH, solid-liquid ratio, temperature, Cd(II) concentrations, and interfering cations. Fe₃O₄@SiO₂-SH-Protected material exhibited much higher adsorption capacity than Unprotected forms and other adsorbents due to methyl group protection. The maximum adsorption capacity calculated from the Langmuir fitting was 27.5 mg·g^-1 (pH 7, 25 °C), and the adsorption kinetics followed a pseudo-second-order model, and adsorption mainly dominated by film diffusion processes. Thermodynamic parameters indicated that the adsorption process was a spontaneous, endothermic, and positive entropic process. Cd(II)-loaded on the adsorbent was easily desorbed with 0.1 M HCl and the adsorbent stable in 0.1 M HCl for long times, showing good reusability and stability.

Efficient removal of acetochlor pesticide from water using magnetic activated carbon: Adsorption performance, mechanism, and regeneration exploration

In this study, MnFe₂O₄ supported activated carbon magnetic adsorbent (MnFe₂O₄@AC) was successfully prepared by a simple one-pot solvothermal method and used for the adsorption and removal of acetochlor from aqueous media. Results showed that MnFe₂O₄@AC with a MnFe₂O₄/AC mass ratio of 1:2 was characterized by good magnetism and high acetochlor adsorption capacity over a wide ranging pH, ionic strength, and humic acid concentration in an aqueous solution. Acetochlor was adsorbed on MnFe₂O₄@AC mainly by hydrogen bonding, π-π interactions, and pore-filling via film, intraparticle, and pore diffusion steps. Adsorption reaction generally approached an equilibrium after 10 h, with the adsorption capacity being ca. 226 mg g^-1 for 0.2 g L^-1 adsorbent at 25 °C. Adsorbate (acetochlor) degradation and adsorbent regeneration were simultaneously achieved through heat-activated peroxymonosulfate (PMS) oxidation catalyzed by MnFe₂O₄ on the AC surface with >90% degradation efficiency at ≥9.6 mM PMS concentration at 70 °C within 12 h. However, the adsorption capacity of the regenerated adsorbent decreased by 50% of its original capacity. This needs to be addressed in future studies. MnFe₂O₄@AC adsorbent has the advantages of high adsorption capacity, good magnetism, and catalyzation, which are promising for adsorption, separation, and degradation for the effective removal and treatment of acetochlor as well as other organic contaminants in different types of waters.

As(V) adsorption by a novel core-shell magnetic nanoparticles prepared with Iron-containing water treatment residuals

A novel core-shell magnetic nanoparticle was synthesized through heterogeneous nucleation technique and utilized to remove As(V) from water. Both the magnetic core and the coating material, amorphous FeOOH shell, were prepared with iron-containing water treatment residuals (WTRs), also called iron sludge. The bare magnetic nanoparticles (MNPs) and coated magnetic nanoparticles (c-MNPs) were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), Brunauer-Emmett -Teller analysis (BET), vibrating sample magnetometer (VSM) and Fourier transform infrared spectroscopy (FTIR). The c-MNPs, mainly consisting of maghemite (γ-Fe₂O₃) as the magnetic core and amorphous FeOOH as the coating material, could be easily separated from water through a hand-held magnet, the saturation magnetization of which is 36.4 emu/g. Freundlich adsorption isotherm model could better described the As(V) adsorption behavior of c-MNPs than Langmuir model, and kinetic data could be described well by the pseudo-second order model. The maximum As(V) adsorption capacity of c-MNPs (26.05 mg/g) was more than twice that of MNPs (12.74 mg/g). At 25 °C, 0.2 g/L of the c-MNPs could reduce the As(V) from 400 μg/L to below the maximum contaminant level (MCL) of 10 μg/L over a broad pH ranging from 4 to 8. The c-MNPs still exhibited effective adsorption in the presence of co-existing anions including nitrate, chloride, carbonate, and sulfate, whereas, silicate and phosphate had a negative influence on the As(V) adsorption. Throughout five consecutive cycles, the adsorbents could still maintain high As(V) adsorption capacity.

Efficient removal of various coexisting organic pollutants in water based on β-cyclodextrin polymer modified flower-like Fe3O4 particles

HYPOTHESIS

The construction of porous β-cyclodextrin polymer (β-CDP) modified flower-like Fe₃O₄ particles (CDP@Fe₃O₄) is expected to remove various organic pollutants from water, based on the larger specific surface area of flower-like Fe₃O₄ particles and the active sites provided by β-CDP. With the help of various noncovalent interactions, the removal ability of CDP@Fe₃O₄ for various water-soluble and water-insoluble organic pollutants were systematically studied.

EXPERIMENTS

CDP@Fe₃O₄ were successfully synthesized and applied for the simultaneous removal of various organic pollutants with different electrical properties, structure and hydrophobicity. Adsorption efficiency, adsorption process, adsorption mechanism and the reusability of CDP@Fe₃O₄ for single pollutant and mixed pollutants were comprehensively investigated.

FINDINGS

CDP@Fe₃O₄ exhibited excellent adsorption capabilities for various pollutants. Importantly, when these pollutants were coexisting, CDP@Fe₃O₄ still maintained a comparable removal ability for various pollutants. Efficient removal of organic pollutants was attributed to varieties of noncovalent interactions between organic pollutants and CDP@Fe₃O₄, including hydrophobic interactions, hydrogen bonds, π-π and electrostatic interactions. These results revealed that the excellent adsorption ability and convenient regeneration make CDP@Fe₃O₄ being a potential candidate in various complex organic wastewater purification.

Adsorption mechanism of rhein-coated Fe3O4 as magnetic adsorbent based on low-field NMR

In the present study, a magnetic adsorbent, rhein-coated magnetic Fe₃O₄ nanoparticle (RMNP), for Pb²⁺ and Mg²⁺ had been developed, and adsorption mechanism was studied via low-field NMR. RMNP was characterized by TEM, FTIR, and XRD. RMNP could adsorb and remove Pb²⁺ and Mg²⁺ from water and was successfully applied to remove Pb²⁺ and Mg²⁺ from wastewater, with satisfactory recovery rates and high adsorption capacities. The calculated maximum adsorption capacity for Mg²⁺ and Pb²⁺ was approximately 69.3 and 64.9 mg g^-1 of RMNP, respectively, which was better than some results reported. Low-field NMR results showed that Pb²⁺ or Mg²⁺ enhanced the T₂ relaxation time of RMNP, which suggested that RMNP selectively coordinated with Pb²⁺ or Mg²⁺ and led to the aggregation of RMNP, furthermore removal of Pb²⁺ or Mg²⁺ from water. The standard curves for △T₂-cation concentration exhibited good line correlation. The linear ranges were from 4.2 × 10^-6 to 2.0 × 10^-4 mol L^-1 for Pb²⁺ and from 5.0 × 10^-6 mol L^-1 to 1.0 × 10^-4 mol L^-1 for Mg²⁺, respectively. The limits of detection were 1.4 × 10^-6 mol L^-1 for Pb²⁺ and 2.1 × 10^-6 mol L^-1 for Mg²⁺, respectively. In short, low-field NMR could clearly display the interaction between RMNP and Pb²⁺ or Mg²⁺, even be used to detect Pb²⁺ or Mg²⁺ in suitable condition. Besides, this method could be expanded to study the interaction between other magnetic adsorbents and analytes.

La(OH)3-modified magnetic sodium carboxymethyl cellulose for sequential removal of pollutants: adsorption of phosphate and subsequent photocatalytical reduction of Cr(VI)

In this study, La(OH)₃-modified magnetic sodium carboxymethyl cellulose (La-MC) was prepared as adsorbents for phosphate, which exhibited excellent adsorption performance up to 62.98 mg P/g and magnetic property for easy recovery. The recovered adsorbents after phosphate sorption were subsequently used for photocatalytic reduction of Cr(VI) and possessed good photocatalytic activity. This work provided an excellent reference for developing a new way of extending life cycle of adsorbents by combining phosphate adsorption with photocatalysis for sequential removal of pollutants from water in the future.

Removal of aflatoxin B1 from contaminated peanut oils using magnetic attapulgite

The efficient magnetic adsorbent (Fe₃O₄@ATP) was prepared by precipitation through the dispersion of Fe₃O₄ nanoparticles on the natural attapulgite (ATP) and then tested as an adsorbent for aflatoxin B₁ (AFB₁) removal from contaminated oils. The adsorbent characterization results revealed that the Fe₃O₄ were incorporated into the ATP, affording the Fe₃O₄@ATP composite. This magnetic composite displayed a good ability to eliminate AFB₁ from contaminated oils with a removal efficiency of 86.82% using a 0.3% dosage. The Fe₃O₄@ATP possessed paramagnetic character with a saturation magnetization of 50.86 emu/g, enabling its easy separation from the medium using an external magnet. The adsorption process followed the pseudo-second-order model and fitted the Freundlich isotherm well. Moreover, the thermodynamic studies showed that AFB₁ adsorption onto Fe₃O₄@ATP was exothermic and spontaneous. The novelty of this study lies in the fabrication of magnetic composite adsorbents for AFB₁ elimination from oils.

Fabrication and characterization of magnetically responsive Fe3O4@TiO2 core-shell adsorbent for enhanced thallium removal

Thallium (Tl) contamination in natural waters can pose a severe risk to human health. In this study, a magnetically responsive Fe₃O₄@TiO₂ core-shell adsorbent was developed for the effective removal of thallium(I) from water. The isoelectric point of the adsorbent surface was decreased from 6.0 to 4.8 due to the loading of nano-sized TiO₂, leading to an enhanced electrostatic interaction between the adsorbent and Tl(I) ions in a wider pH range. The Fe₃O₄@TiO₂ magnetic adsorbent exhibited a threefold higher BET specific surface area compared to pristine Fe₃O₄ particles. The kinetics study showed that approximately 82% of the maximum Tl(I) loading amount could be achieved within 30 min at the initial Tl(I) concentration of 8 mg/L and adsorbent dosage of 0.1 g/L. The adsorption of Tl(I) was significantly increased with increasing solution pH. The experimental data was better fitted by the Langmuir and Temkin isotherms than the Freundlich isotherm and the maximum adsorption capacity of the magnetic adsorbent was 101.5 mg/g at pH 7.0. The interference of co-existing cations in the Tl(I) adsorption followed the subsequence: Cu²⁺ > Mg²⁺ > Ca²⁺ > Na⁺. The hydroxyl groups bonded on titanium atoms might play a key role in the uptake of Tl(I) ions. During the adsorption, the Tl(I) ions can be effectively adsorbed on the adsorbent surface via the formation of Ti-O-Tl linkages. Graphical Abstract.

Adsorption of Sr(II) ions and salicylic acid onto magnetic magnesium-zinc ferrites: isotherms and kinetic studies

Magnetic magnesium-zinc spinel ferrite Mg_1 - xZn_xFe₂O₄ (where x = 0.4, 0.6, and 0.8) was investigated as adsorbent for the efficient removal of Sr(II) ions and salicylic acid (SA) contaminants from aqueous medium. The characterization of ferrites was carried out using XRD, VSM, BET, SEM, and EDS. The surface charge of magnetic adsorbents was measured by the drift method. The determination of SA and Sr(II) ion concentrations in the solution phase was carried out by UFLC and complexometry, respectively. It was shown that varying of the Zn(II) content affected the adsorption capacities of magnesium-zinc ferrites. The increasing of zinc content from x(Zn²⁺) = 0.4 to x(Zn²⁺) = 0.6 increased the adsorption of Sr(II) ions from 50 to 65 mg/g, and then it was decreased to 36 mg/g for the sample with x(Zn) = 0.8. The Mg_0.4Zn_0.6Fe₂O₄ sample demonstrated the maximum adsorption capacity of 74 mg/g. The adsorption isotherm for Sr(II) was fitted by the Dubinin-Radushkevich, Langmuir, Freundlich, and Sips models. The adsorption kinetics of Sr(II) was analyzed by PFO, PSO, and Elovich models. The adsorption kinetics of SA was also investigated. It was demonstrated that the Mg_0.2Zn_0.8Fe₂O₄ sample exhibited 90% removal of salicylic acid from the water solutions. The results demonstrated that magnetic Mg-Zn ferrites with spinel structure are good sorbents for the removal of SA and Sr(II) ions from aqueous solution.

Performance and mechanism of polypeptidylated hemoglobin (Hb)/iron oxide magnetic composites for enhanced dye removal

Composites of polypeptidylated hemoglobin supported on different iron oxide weights (0.5:1 and 1:1) were developed and demonstrated to function as efficient adsorbents for Eriochrome black-T dye removal. The synthesis of these adsorbents were performed through N-carboxyanhydride (NCA) polymerization at low temperature (4 °C) and near-neutral pH for 24 h followed by chemical co-precipitation. The synthesized adsorbents were found to exhibit BET surface area (54-87 m²/g), pore volume (0.30-0.35 cm³/g), average pore diameter (160-218 Å) and average pore width (136-171 Å). The developed adsorbents were tested in a batch dye adsorption system. Adsorption was found to follow pseudo-second order kinetics and the Langmuir adsorption capacities were 123, 204 and 217 mg/g for Fe₃O₄, 0.5:1 and 1:1 adsorbent samples, respectively. Chemical regeneration was successfully carried out using methanol and the reusability of the adsorbents were demonstrated with a decrease in adsorption capacities from ∼49 to ∼33 mg/g after the fourth reuse.

A simple magnetic solid-phase extraction method based on magnetite/graphene oxide nanocomposite for pre-concentration and determination of melamine by high-performance liquid chromatography

In this study, a clean and simple magnetic solid-phase extraction (MSPE) procedure using magnetite/graphene oxide nanocomposite as an adsorbent was developed for melamine separation and preconcentration from water and dairy products. After synthesis and characterization of the adsorbent, adsorption isotherms and kinetic studies of the adsorption were carried out. The analyte quantification was performed by reversed phase high-performance liquid chromatography after elution of the preconcentrated analytes from the adsorbent surface. Several factors affecting the extraction/preconcentration procedure such as pH, adsorbent amount, extraction time, sample volume, type, and volume of eluent were investigated. The optimizing of some important parameters was assessed by employing a response surface method. The constructed calibration curve in the optimized conditions is linear in the working range of 0.10-100 μg L^-1 with a correlation coefficient of 0.9999. The detection limit, limit of quantification, and enrichment factor are 0.03 μg L^-1, 0.10 μg L^-1, and 500, respectively. The melamine relative recoveries from different real samples are between 97.20 and 103.10% with relative standard deviations of 1.07-4.98%.

Preparation of microwave-activated magnetic bio-char adsorbent and study on removal of elemental mercury from flue gas

In this study, novel activated magnetic bio-char adsorbents were proposed to remove the element mercury (Hg⁰) from flue gas. Microwave activation and Mn-Fe mixed oxides impregnation assisted by ultrasound treatment were applied on the modification of renewable cotton straw chars. The influence of different preparation methods, loading value of Mn-Fe, molar ratio of Mn/Fe, calcining temperature, reaction temperature and individual flue gas ingredients (O₂, NO, SO₂ and H₂O) on removal of Hg⁰ was investigated in a fixed bed system. The characterization results reveal that microwave activation is advantageous for the development of the pore structure, and ultrasound treatment can optimize the dispersion of Mn and Fe active ingredients. MnFe4%(3/10)/CSWU700 adsorbent exhibits the optimal Hg⁰ removing performance. O₂, NO, low concentration of SO₂ (<600 ppm) and low concentration of H₂O (<2%) are found to be favourable for the capture of Hg⁰, while high concentrations of SO₂ and H₂O inhibit the removal of Hg⁰. Chemical adsorption acts a pivotal part in the process of Hg⁰ removal. Mn and Fe active ingredients are consumed in large quantities during the Hg⁰ capture. In addition, chemisorbed oxygen (O_β) also plays an indispensable in the oxidation process of Hg⁰. Furthermore, the magnetic adsorbent MnFe4%(3/10)/CSWU700 presents a good regeneration performance and adsorption capacity.

Carbothermal preparation of magnetic-responsible ferrihydrite based on Fe-rich precipitates for immobilization of arsenate and antimonate: Batch and spectroscopic studies

The present study provides the starch-mediated carbothermal preparation of magnetic-responsible ferrihydrite (MFHP) based on Fe-rich precipitates which is recovered by mine drainage for immobilization of arsenate and antimonate in water. Fe K-edge X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) represented partial transformation from ferrihydrite to magnetite in MFHP due to the carbothermal reduction process, resulting in an effective saturation magnetism (= 19.2 emu/g). As and Sb K-edge EXAFS revealed that arsenate ion combines onto the surface of MFHP as inner-sphere binuclear bidentate surface complex, and antimonate forms inner-sphere mononuclear bidentate complex. In addition, the leachability by toxicity characteristic leaching procedure (TCLP) implies the environmental friendly preparation method for preparing magnetic-responsible adsorbents using mining waste.

Study on adsorption properties and mechanism of thallium onto titanium‑iron magnetic adsorbent

Thallium (Tl) contamination caused by the industrial wastewater leakage has become a serious environmental problem due to thallium's high toxicity. In this study, a novel titanium‑iron magnetic nano-sized adsorbent was synthesized and applied for the effective removal of thallium(I). The physicochemical properties of the adsorbent were investigated by a series of techniques such as scanning electron microscope (SEM), X-ray powder diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). About 83% of equilibrium adsorption capacity could be accomplished within the initial 30 min. The adsorption of Tl(I) was found to be highly dependent on solution pH. The maximum adsorption capacity of Tl(I) was 111.3 mg/g at pH 7.0. The presence of such co-existing cations as Na⁺, Mg²⁺, Ca²⁺ and Cu²⁺ could have a certain influence on the uptake of Tl(I). The adsorption mechanism was proposed as a surface complexation process of Tl(I) ions by binding to deprotonated sites of hydroxyl groups on the adsorbent surface. The prepared magnetic adsorbent would be suitable for effectively treating thallium-containing water due to its promising adsorption ability towards Tl(I) and ease in operation.

Preparation of magnetic hydrogel microspheres of lignin derivate for application in water

A low-cost and well-separated approach is introduced for adsorption pollutants in water. Chemical modified lignin is prepared with diethylenetriamine to enhance the reaction activities, then used to prepare lignin derivate magnetic hydrogel microspheres (LDMHMs) via blending with Fe₃O₄. The LDMHMs are successful prepared by the determination of FT-IR data, and the morphology shown from SEM imagine indicates the LDMHMs are in nanosized. The prepared LDMHMs are used as adsorbents for organic dyes, such as methylene blue (MB), methyl orange (MO) and malachite green (MG), the plateaus data are 43 mg/g, 39 mg/g and 155 mg/g, respectively. For inorganic pollutions, such as Pb²⁺, Hg²⁺ and Ni²⁺, the plateaus data are 33 mg/g, 55 mg/g and 23 mg/g, respectively. The adsorption data of unmodified lignin are 2.6 mg/g (Pb²⁺), 3.3 mg/g (Hg²⁺), 2.1 mg/g (Ni²⁺), 8 mg/g (MB), 10 mg/g (MG) and 2 mg/g (MO) in the same condition. The adsorbents are recycled by magnetic separation, regenerating from acid condition and reused for multiple cycles. The regeneration ratios are all above 90%, indicating a highly reusability and further reducing the cost of the treatment.

Thermal conversion of pineapple crown leaf waste to magnetized activated carbon for dye removal

Pineapple crown leaf was successfully converted to the magnetized activated carbon (MAC) as an attractive solution to overcome separation problems. The activated carbon (AC) was produced by an innovative method combining KOH activation and microwave heating while the magnetization process was prepared by a co-precipitation method. In this sense, the activation stage was studied at different impregnation ratio. The resulted magnetic adsorbent was further tested its feasibility for methyl violet dye removal. The result shows that MAC consists of both micropores and mesopores with more oxygen-containing functional groups, indicating it can be used to remove dye from contaminated water. The increase of impregnation ratio led to an increase in the MAC porosity and a decrease in the magnetic property. The adsorption behavior of methyl violet dye onto MAC was well described by the Redlich-Peterson isotherm model.

Experimental and theoretical investigations of Cs+ adsorption on crown ethers modified magnetic adsorbent

Carboxyl Fe₃O₄ nanoparticles (Fe₃O₄@R-COOH) modified with 18-Crown-6 ether functional groups have been prepared via an amidation reaction and used as bifunctional adsorbent for Cs⁺. The adsorbent has a superparamagnetic property, allowing an easy recycling, and a high capacity of Cs⁺ adsorption on the crown ether. The adsorption isotherms and kinetic behaviors agree well with the Langmuir and the pseudo-second-order models. The material exhibits a high selectivity for Cs⁺ in the solution with co-existing cations (NH₄⁺, Rb⁺, K⁺, Na⁺ and Li⁺). A theoretical calculation according to density functional theory (DFT) is used to estimate the structure of Cs⁺ adsorption on crown ether, demonstrating an exothermic process and showing a good agreement with the experimental observations. The adsorption behavior is affected not only by the size of macrocyclic crown ethers, but also by the chelating symmetry and the binding energy. The newly developed adsorbent has a potential application for removing cesium out of wastewater and salt lakes.

Synthesis of novel sepiolite-iron oxide-manganese dioxide nanocomposite and application for lead(II) removal from aqueous solutions

In this study, the sepiolite-iron oxide-manganese dioxide (Sep-Fe₃O₄-MnO₂) nanocomposite was synthesized and applied as a magnetically separable adsorbent for removal of Pb(II) ions from water in a batch system. The effects of initial Pb(II) concentration, adsorbent dosage, contact time, pH value, and temperature were investigated to optimize the conditions for maximum adsorption. The equilibrium adsorption data were analyzed with the Langmuir, Freundlich, and Temkin models. The adsorption process closely agreed with the Langmuir adsorption isotherm, and the monolayer saturation adsorption value was achieved as 131.58 mg g^-1. The adsorption kinetics follow the pseudo-second-order (PSO) model that illustrated the rate controlling step might be chemisorption. Thermodynamic investigations for the removal process were conducted by determining the values of ∆G°, ∆H°, and ∆S°. The adsorption behavior of Pb(II) on the Sep-Fe₃O₄-MnO₂ was a spontaneous and endothermic process. Several consecutive adsorption-desorption cycles confirmed that the proposed Sep-Fe₃O₄-MnO₂ nanocomposite could be reused after successive lead removal. Furthermore, the practical application of the adsorbent was successfully realized by the treatment of real Pb-contaminated water samples.