Significance of FeZr-modified natural zeolite networks on fluoride removal

Structural modification of aluminum oxides for removing fluoride in water: crystal forms and metal ion doping

In this paper, the effect of different crystal forms of Al₂O₃ on fluoride removal was studied. All crystal forms of Al₂O₃ were based on the same boehmite precursor and were obtained using a hydrothermal and calcination method. γ-Al₂O₃ had higher fluoride removal performance (52.15 mg/g) compared with θ-Al₂O₃ and α-Al₂O₃. Density functional theory (DFT) calculations confirmed that fluoride removal was greatest for γ-Al₂O₃, followed by θ-Al₂O₃ and α-Al₂O₃, and γ-Al₂O₃ possessed the strongest fluoride binding energy (-3.93 eV). The typical adsorption behaviour was consistent with the Langmuir model and pseudo-second-order model, indicating chemical and monolayer adsorption. Different metal ions were used to modify γ-Al₂O₃, and lanthanum had the best effect. Lanthanum oxide was shown to play an important role in fluoride removal. The best La/Al doping ratio was 20 At%. The adsorption process of the composite was also consistent with chemical and monolayer adsorption. When the La/Al doping rate was 20%, the adsorption capacity reached 94.64 mg/g. Compared with γ-Al₂O₃ (1.39 × 10^-7 m/s), the adsorption rate of 20La-Al₂O₃ was 3.93 × 10^-7 m/s according to the mass transfer model. Furthermore, DFT was used to provide insight into the adsorption mechanism, which was mainly driven by electrostatic attraction and ion exchange.

An Experimental Study of Fluoride Removal from Wastewater by Mn-Ti Modified Zeolite

The emerging interest in fluoride-removal from wastewater has attracted attention to zeolite since it has been considered as a natural adsorbent. However, the fluoride-removal efficiency of natural zeolite is generally low. As part of the effort to improve the zeolite adsorption efficiency, we have produced and tested the Mn-Ti modified zeolite. In the current work, the material preparation is discussed, and prepared materials were characterized by X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS), scanning electron microscopy, and Fourier transform infrared (FTIR) spectra. Both static and dynamic experiments were conducted to examine the effects of independent variables. In the static adsorption section, sensitivity analysis experiments were conducted for independent variables, such as adsorbent dosage, pH, temperature, and competitive ions. The maximum adsorption capacity is 2.175 mg/g, which was obtained at PH = 7, temperature = 25 °C, and initial fluoride concentration = 10 mg/L. For adsorption kinetics, both Lagergren and Pseudo-second order models predict the experiments very well, which probably demonstrates that the current process is a combination of physical sorption and chemisorption. For adsorption isotherms, the Freundlich model performs better than the Langmuir model since it is usually applied to illustrate adsorption on inhomogeneous surfaces. In the dynamic adsorption section, sensitivity analysis experiments were also conducted for independent variables, such as adsorbent thickness, flow velocity, initial fluoride concentration, and PH. Additionally, the adsorption mechanism is also discussed. The main reason is the hydrated metal fluoride precipitate formation. As we know, the current work provides the first quantified comparison of the natural zeolite and the Mn-Ti modified zeolite regarding fluoride-removal efficiency.

Competitive adsorption of pollutants from anodizing wastewaters to promote water reuse

Anodizing wastewater contains principally phosphate (PO₄^3-) anions according to previous studies, but with the purpose to promote water reuse in this type of industry, a complete characterization of wastewater was made to remove other anions and cations also present in significant concentration. Particularly, the adsorption of sodium (Na⁺), potassium (K⁺), fluoride (F^-), sulfate (SO₄^2-) and phosphate (PO₄^3-) was studied using different sorbents such as: coconut shell activated carbon, bone char, bituminous coal activated carbon, natural zeolite, silica, anionic and cationic exchange resins, a coated manganese-calcium zeolite, coconut shell activated carbon containing iron and iron hydroxide. All sorbents were characterized using FT-IR spectroscopy, potentiometric titration, nitrogen adsorption isotherms at 77 K, X-ray diffraction and SEM/EDX analysis to study the adsorption mechanism. The adsorption studies were performed in batch systems under constant agitation using both standard solutions of each ion and real anodizing wastewater. Results showed that, in general, the adsorption of all anions and cations is higher when mono-component standard solutions were used, since in the anodizing wastewater all species are competing for the active sites of the adsorbent. Na⁺ present in anodizing wastewater was efficiently adsorbed on coated manganese-calcium zeolite (20.55 mg/g) and natural zeolite (18.55 mg/g); while K⁺ was poorly adsorbed on all sorbents (less than 0.20 mg/g). Anions such as F^-, SO₄^2- and PO₄^3-, were better adsorbed on the anionic resin (0.17, 45.38 and 2.92 mg/g, respectively), the iron hydroxide (0.14, 7.96 and 2.87 mg/g, respectively) and the bone char (0.34, 8.71 and 0.27 mg/g, respectively). All these results suggest that adsorption is a promising tertiary treatment method to achieve water reuse in the anodizing industry.

Enhanced fluoride adsorption from aqueous solution by zirconium (IV)-impregnated magnetic chitosan graphene oxide

In this study, zirconium (IV)-impregnated magnetic chitosan graphene oxide (Zr-MCGO) was synthesized for removing fluoride from aqueous solution in batch mode. Characterization approaches (pH_pzc, FTIR, SEM, XRD, VSM, Raman, BET, and XPS) proved the successful incorporation of Zr into the adsorbent. Zr-MCGO exhibited a relatively favorable and stable capacity of defluoridation at lower pH with a wide range of pH from 4.0 to 8.0, while there was slightly negative effect of ionic strength on adsorption. In addition, Elovich kinetic model and Koble-Corrigan isotherm model could describe the uptake of fluoride well. The adsorption capacity was 8.84 mg/g at 313 K and Zr-MCGO was easily separated from mixtures using external magnet. Based on the experiments and XPS, electrostatic force, ligand exchange, and Lewis acid-base interaction might be potential adsorption mechanisms. Pseudo-second-order model was more compatible with the desorption process by 0.01 mol/L NaHCO₃ solution. Therefore, Zr-MCGO was a promising candidate for defluoridation on wastewater pollution remediation.

Defluoridationof drinking water by metal impregnated multi-layer green graphene fabricated from trees pruning waste

A novel adsorbent with excellent adsorptive properties for fluoride was prepared through a green and cheap synthesis route. Populus caspica pruning wastes, a cheap agri-waste material, were reduced to multi-layer green graphene (MLG) and then post-modified to aluminum/iron modified multi-layer green graphene (AMLG and IMLG). Batch experiments revealed the effect of pH (3-11), contact time (0.5-12 h), and initial fluoride concentration (5-40 mg/L). The conversion of raw material to MLG increased the specific surface area about 120 times (from 4 to 475 m²/g). Furthermore, a significant improvement in zero points of charge (pHzpc) was attained for IMLG (7.1) and AMLG (8) compared with pristine MLG (4.3). Fluoride showed superior affinity to AMLG and IMLG compared with MLG. Fluoride removal increased gradually by pH from 3 to 8 and then decreased sharply up to pH 11. The study of process dynamics demonstrated the monolayer fluoride adsorption onto AMLG and IMLG controlled by the chemisorptions. The highest predicted adsorption capacities based on the Langmuir model were 31.52, 47.01, and 53.76 mg/g for MLG, IMLG, and AMLG, respectively. Considering economic and technical feasibility presents AMLG and IMLG as a promising candidate against water contamination by elevated fluoride. Graphical abstract.

The adsorption of fluoride from aqueous solutions by Fe, Mn, and Fe/Mn modified natural clinoptilolite and optimization using response surface methodology

Natural clinoptilolite was modified using iron, manganese, or iron-manganese for adsorption of fluoride from aqueous solutions. Natural and modified clinoptilolite samples were characterized by X-ray fluorescence spectrometry, scanning electron microscope, X-ray diffraction, and Brunauer-Emmett-Teller. For all modified clinoptilolite samples, the time required to reach equilibrium was determined as 5 hr. The effects of adsorbent dose, pH, and initial fluoride concentration for fluoride adsorption were determined using the Box-Behnken Design. Maximum fluoride removal efficiency was 80.23% at the solution pH of 11, iron-modified clinoptilolite amount of 1.08 g/50 ml and at the initial fluoride concentration of 2 mg/L. Fluoride adsorption on iron-modified clinoptilolite showed good compatibility with the Freundlich isotherm and the pseudo-second-order kinetic model. The adsorption capacity of iron-modified clinoptilolite was found to be 1.72 mg/g for the initial fluoride concentration of 50 mg/L. This study has shown that BBD is an effective and dependable method in determining the optimum conditions for fluoride adsorption. PRACTITIONER POINTS: Response surface methodology is effective in determining the optimum conditions for fluoride adsorption using modified clinoptilolite. Fluoride adsorption on iron-modified clinoptilolite is well described Freundlich isotherm and follows pseudo-second-order kinetic model. Fluoride removal percentage not only depends on the adsorbent dose, but also depends on the initial fluoride concentrations. Regeneration process using acid solution is not very effective for desorption of iron-modified zeolite. The natural clinoptilolite is an effective and economical adsorbent for adsorption of fluoride.

Development of adsorbent from Mentha plant ash and its application in fluoride adsorption from aqueous solution: a mechanism, isotherm, thermodynamic, and kinetics studies

In the present study, Mentha plant ash was modified by Na and Al for the synthesis of adsorbent and applied for the removal of Fluoride from an aqueous solution. Mixture of acid washed Mentha plant ash (MPA) and NaOH (in the ratio 1:1.3) thermally treated at 600°C in a muffle furnace then treated with aqueous solution of sodium aluminate. The characterization of sodium aluminum modified ash (Na-Al-MA) powder was done such as SEM (Scanning Electron Microscopy), Particle Size Analysis (PSA), Fourier transformed spectroscopy (FTIR), Zeta Potential, XRD (X-ray Diffraction) analysis, and Brunauer-Emmett-Teller (BET) analysis. The removal of fluoride from an aqueous solution carried out with Na-Al-MA by batch adsorption process. The Na-Al-MA was found to be very effective as adsorbent. The maximum removal of fluoride was achieved ̴ 86% at neutral pH and at room temperature. It was investigated that Langmuir adsorption isotherm and pseudo-second-order kinetic was best fitted for fluoride adsorption. The fluoride adsorption on Na-Al-MA was an exothermic process. A possible mechanism including electrostatic attraction, hydrogen bonding, and metal-fluoride interaction for fluoride adsorption on Na-Al-MA have described in this study. Novelty statement: Utilization of Mentha plant ash for the development of adsorbent and its application in adsorptive removal of fluoride from aqueous solution is the novelty of this work. Adsorbent preparation may be the better way of waste biomass management.

Synthesis and Surface Modification of Small Pore Size Zeolite W for Improving Removal Efficiency of Anionic Contaminants from Water

The presence of regulated inorganic contaminants in water such as AsO₄^3- and PO₄^3- anions, is becoming a relevant environmental research topic. The harm that these anions cause to human health and the ecosystem have been reported in several works. The adsorption processes using low-cost materials, such as zeolites, have proven to be an option to removal hazardous contaminants from water. The coal fly ash, a waste from thermoelectrical plants, offers a raw pollutant material to synthesis an effective adsorbent (Zeolite W). In this research was studied the removal of arsenic and phosphates anions from water, applying a functionalized by iron and zirconium Zeolite W, which was modified using a fast and efficient process through microwave-assisted method (1 min at 150°C). The obtained Zeolite W did not show significant changes in its structure and morphology. The maximum adsorption capacity (Qm expressed in mg g^-1) was found to be 42.31 (Iron-zirconium-zeolite) and 27.82 (Iron-zeolite) for AsO₄^3-, while it reached 50.89 for PO₄^3- using Zirconium-zeolite. Results showed that functionalized zeolites are efficient adsorbents for hazardous anionic species; therefore, it could be useful for aqueous effluents remediation.

The performance and mechanism of simultaneous removal of fluoride, calcium, and nitrate by calcium precipitating strain Acinetobacter sp. H12

A calcium precipitating and denitrifying bacterium H12 was used to investigate the F^- removal performance and mechanism. The results showed that the strain H12 reduced 85.24% (0.036 mg·L^-1·h^-1) of F^-, 62.43% (0.94 mg·L^-1·h^-1) of Ca²⁺, and approximately 100% of NO₃^- over 120 h in continuous determination experiments. The response surface methodology analysis demonstrated that the maximum removal efficiency of F^- was 88.98% (0.062 mg·L^-1·h^-1) within 72 h under the following conditions: the initial Ca²⁺ concentration of 250.00 mg·L^-1, pH of 7.50, and the initial C₄H₄Na₂O₄·6H₂O concentration of 800.00 mg·L^-1. The scanning electron microscopy images, the X-ray photoelectron spectroscopy, and X-ray diffraction results suggested the following removal mechanism of F^-: (1) the bacteria, as the nucleation site, were encapsulated by bioprecipitation to form biological crystal seeds; (2) Biological crystal seeds adsorbed F^- to form Ca₅(PO₄)₃F and CaF₂; (3) Under the induction of bacteria, calcium, fluoride and phosphate coprecipitated to form Ca₅(PO₄)₃F and CaF₂. In addition, the gas chromatography data indicated that F^- had little or no effect on the gas composition during denitrification, and the fluorescence spectroscopy analysis also proved that the extracellular polymeric substance (protein) is the site of bioprecipitation nucleation.

Green synthesis of a novel water-stable Sn(ii)-TMA metal–organic framework (MOF): an efficient adsorbent for fluoride in aqueous medium in a wide pH range

An Sn(ii)-TMA MOF displaying positive zeta potential over a broad pH range (3–10) for selective fluoride adsorption from aqueous medium.

Fluorine removal and calcium fluoride recovery from rare-earth smelting wastewater using fluidized bed crystallization process

As a regulated pollutant, fluorine compounds affect the health of millions of people all over the world. Their removal using a fluidized bed reactor (FBR) through crystallization process is a new method. Instead of chemical precipitation, which produces large amounts of sludge-containing wastewater hard to recover and treat. In this work, FBR was applied to a typical rare-earth smelting wastewater containing fluorine. Influence of different seed materials, seed size, and seed amounts on the fluorine removal and calcium fluoride recovery in the FBR were studied. When silica sand was used as the seed crystal and the amounts reached 30g, the concentration of fluorine in the actual wastewater decreased to 8.2 mg L^-1 or lower. The removal efficiency of fluorine and recovery ratio of calcium fluoride were obtained as 93.79% and 89.45%, respectively. The particle size of recovered calcium fluoride was about 1.5mm. The results show that FBR with silica sand as seed crystal is a feasible and economical method for removing fluorine and recovering calcium fluoride from rare-earth industrial wastewater.

Characterization and adsorption mechanism of ZrO2 mesoporous fibers for health-hazardous fluoride removal

One-dimension ZrO₂ mesoporous fibers were successfully synthesized by utilizing the electrospinning device combining with the soft-template method. The morphology and composite of the fibers were characterized by XRD, SEM, TEM, FT-IR, TGA/DSC and XPS, and the pore structure and surface area were calculated according the BET measured results. The fluoride adsorption performance of the fibers was investigated and the adsorption capacity was upto 297.70 mg g^-1. Moreover, the equilibrium concentration could be reached to 1.41 mg L^-1 with the initial of 30 mg L^-1, and the removal rate could be reached to 95.3%. The adsorption data were well fitted with the Freundlich isotherm model and pseudo-second-order kinetic model. The fibers had a good reusability and long-term utilization for fluoride adsorption. All the results suggested that the as-prepared ZrO₂ mesoporous fibers with high surface area could be an excellent adsorbent for the wastewater defluoridation treatment.