Performance of an optimized Zr-based nanoparticle-embedded PSF blend hollow fiber membrane in treatment of fluoride contaminated water

Enhancing fluoride removal from wastewater using Al/Y amended sludge biochar

This study explored the potential of utilizing aluminum and yttrium amended (Al/Y amended) sewage sludge biochar (Al/Y-CSBC) for efficient fluoride removal from wastewater. The adsorption kinetics of fluoride on bimetallic modified Al/Y-CSBC followed the pseudo-second-order model, while the adsorption isotherm conformed to the Freundlich equation. Remarkably, the material exhibited excellent fluoride removal performance over a wide pH range, achieving a maximum adsorption capacity of 62.44 mg·g-1. Moreover, Al/Y-CSBC demonstrated exceptional reusability, maintaining 95% removal efficiency even after six regeneration cycles. The fluoride adsorption mechanism involved ion exchange, surface complexation, and electrostatic adsorption interactions. The activation and modification processes significantly increased the specific surface area of Al/Y-CSBC, leading to a high isoelectric point (pHpzc = 9.14). The incorporation of aluminum and yttrium metals exhibited a novel approach, enhancing the adsorption capacity for fluoride ions due to their strong affinity. Furthermore, the dispersing effect of biochar played a crucial role in improving defluoridation efficiency by enhancing accessibility to active sites. These findings substantiate the significant potential of Al/Y-CSBC for enhanced fluoride removal from wastewater.

Zirconium/lanthanum-modified chitosan/polyvinyl alcohol composite adsorbent for rapid removal of fluoride

A novel and easily separable adsorbent in the shape of a membrane for the rapid removal of fluoride from water was prepared after testing Zr, La and LaZr to modify a chitosan/polyvinyl alcohol composite adsorbent (CS/PVA-Zr, CS/PVA-La, CS/PVA-LA-Zr). The CS/PVA-La-Zr composite adsorbent can remove a large amount of fluoride within 1 min of contact time, and the adsorption equilibrium can be reached within 15 min. The fluoride adsorption behavior of the CS/PVA-La-Zr composite can be described by pseudo-second-order kinetics and Langmuir isotherms models. The morphology and structure of the adsorbents were characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). The adsorption mechanism was studied using Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS), and which showed that ion exchange occurred mainly with hydroxide and fluoride ions. This study showed that an easily operable, low-cost and environmentally friendly CS/PVA-La-Zr has the potential to remove fluoride effectively from drinking water in a short time.

Dual-function hydrogel composite for post-electroplating cationic and anionic metal removal: A practicality study

Metals produced as by-products of the electroplating process pose threats to both human and environmental health, so it is important that they are removed from electroplating effluents. In this study, a dual-function hydrogel composite, prepared from a pair of cationic and anionic hydrogel composites via a facile method, was tested in batch and in a fluidized-bed column to treat a simulated electroplating effluent. For the batch treatment, both adsorption and desorption reached equilibrium within 30 min, showing the dual-function composite's fast adsorption capacity. Additionally, the removal efficiency was found to be pH-independent, and insignificant effect was found in the co-presence of monovalent ions (up to 10 meq L^-1). Reusability of the dual-function composite was tested for six cycles, where the treated effluent consistently met discharge standards, and the reused adsorbent was confirmed by Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy to be highly stable. The fast settling by gravity of the dual-function composite in batch motivated further studies of the material in a fluidized-bed column. Process variables such as feed flow, airflow, and adsorbent's bed depth were optimized using response surface methodology (RSM). Using an optimal solution, the model predicted a treatable cationic volume of 1045 mL and an anionic volume of 1695 mL; their corresponding experimental values were 1028 and 1680 mL. Therefore, in terms of practicality (fast removal, pH-independence, high stability, and gravity-driven settling), the application of the dual-function composite in a fluidized-bed reactor has shown much promise for the simultaneous removal of post-electroplating cationic and anionic metals.

Role of nano-Fe3O4 particle on improving membrane bioreactor (MBR) performance: Alleviating membrane fouling and microbial mechanism

This study would investigate the effect of nano-Fe3O4 particles on the performance of membrane bioreactor (MBR), including membrane fouling, membrane rejection and microbial community. It can effectively alleviate membrane fouling and improve the effluent quality in MBR by bio-effect rather than nanoparticle adsorption. The lowest membrane fouling resistance was achieved at R4-MBR (sludge and membrane surface with nano-Fe3O4), which decreased by 46.08%. Meanwhile, R3-MBR (sludge with nano-Fe3O4) had the lowest concentration of COD in effluent which was below 20 mg/L in the stable phase of MBR operation. After applying nano-Fe3O4, the content of extracellular polymeric substances (EPS) and soluble microbial products (SMP) were both reduced with a lower molecular weight. From the microbial community analysis, the abundance of Proteobacteria increased from 25.06 to 45.11% at the phylum level in R3-MBR. It contributed to removing organic substances in MBRs. Moreover, the nano-Fe3O4 restricted Bacteroidetes growth, especially in R4-MBR, leading to a more excellent performance of membrane flux. Besides, the applied nano-Fe3O4 promoted the abundance of Quorum Quenching (QQ) microorganism, and declined the percentage of Quorum Sensing (QS) bacteria. Then, a lower content of N-Acyl-l-Homoserine Lactones (AHLs) in containing nano-Fe3O4 sludge. That was also prone to control membrane fouling. Overall, this study indicates the nano-Fe3O4 particle is appropriate for elevating MBR performance, such as membrane fouling and effluent quality, by bio-effect.

A Critical Review on Electric Field-Assisted Membrane Processes: Implications for Fouling Control, Water Recovery, and Future Prospects

Electrofiltration, an electric field-assisted membrane process, has been a research topic of growing popularity due to its ability to improve membrane performance by providing in situ antifouling conditions in a membrane system. The number of reports on electrofiltration have increased exponentially over the past two decades. These reports explored many innovations, such as novel configurations of an electric field, engineered membrane materials, and interesting designs of foulant compositions and membrane modules. Recent electrofiltration literature focused mainly on compiling results without a comprehensive comparative analysis across different works. The main objective of this critical review is to, first, organize, compare and contrast the results across various electrofiltration studies; second, discuss various types of mechanisms that could be incorporated into electrofiltration and their effect on membrane system performance; third, characterize electrofiltration phenomenon; fourth, interpret the effects of various operational conditions on the performance of electrofiltration; fifth, evaluate the state-of-the-art knowledge associated with modeling efforts in electrofiltration; sixth, discuss the energy costs related to the implementation of electrofiltration; and finally, identify the current knowledge gaps that hinder the transition of the lab-scale observations to industry-scale electrofiltration as well as the future prospects of electrofiltration.

Characterizations and fluoride adsorption performance of wattle humus biosorbent

Considering the serious health effects of fluoride contamination, an environment friendly bioadsorbent was derived from wattle humus for fluoride removal by conventional thermal activation process. Analytical characterizations revealed that heterogeneous morphological textured wattle humus enabled remarkable adsorption capacity. XPS analysis substantiated that fluoride had been successfully adsorbed on to the carbonized wattle humus surface through chemisorption. Fluoride adsorption efficiency was systematically rationalized via batch adsorption studies. Experiments were performed at different initial fluoride concentration and scrutinized the impact of contact time (10-120 min), adsorbent dosage (0.5-2.5 g), pH (2.0-9.0), and interfering co-existing ions (SO₄^2-, NO₃^-, Cl^-, and HCO₃^-) on fluoride removal. Even at different adsorbate dosage (2-10 mg/L), 98% fluoride removal efficiency was achieved under pH > 6. The competitive anions do not interfere the wattle humus fluoride adsorption capacity. Moreover, the adsorption isotherms and kinetics studies inferred that monolayer and multilayer adsorption behavior by wattle humus leads to noticeable fluoride adsorption. Adsorbent regeneration test affirms that regenerated adsorbent found higher (>95%) fluoride removal efficiency even at five recycle runs.

Removal of fluoride from industrial wastewater by using different adsorbents: A review

Many industries such as iron and steel metallurgy, copper and zinc smelting, the battery industry, and cement manufacturing industries discharge high concentrations of fluoride-containing wastewater into the environment. Subsequently, the discharge of high fluoride effluent serves as a threat to human life as well as the ecological ability to sustain life. This article analyses the advantages and drawbacks of some fluoride remediation technologies such as precipitation and flocculation, membrane technology, ion exchange technology, and adsorption technology. Among them, adsorption technology is considered the obvious choice and the best applicable technology. As such, several adsorbents with high fluoride adsorption capacity such as modified alumina, metal oxides, biomass, carbon-based materials, metal-organic frameworks, and other adsorption materials including their characteristics have been comprehensively summarized. Additionally, different adsorption conditions of the various adsorbents, such as pH, temperature, initial fluoride concentration, and contact time have been discussed in detail. The study found out that the composite synergy between different materials, morphological and structural control, and the strengthening of their functional groups can effectively improve the ability of the adsorbents for removing fluoride. This study has prospected the direction of various adsorbents for removing fluoride in wastewater, which would serve as guiding significance for future research in the field.

Characterization and physicochemical aspects of novel cellulose-based layered double hydroxide nanocomposite for removal of antimony and fluoride from aqueous solution

A series of novel adsorbents composed of cellulose (CL) with Ca/Al layered double hydroxide (CC_xA; where x represent the Ca/Al molar ratio) were prepared for the adsorption of antimony (Sb(V)) and fluoride (F^-) ions from aqueous solutions. The CC_xA was characterized by Fourier-transform infrared spectroscopy (FTIR), Brunauer-Emmett-Teller (BET), elemental analysis (CHNS/O), thermogravimetric analysis (TGA-DTA), zeta potential, X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX) analysis. The effects of varying parameters such as dose, pH, contact time, temperature and initial concentration on the adsorption process were investigated. According to the obtained results, the adsorption processes were described by a pseudo-second-order kinetic model. Langmuir adsorption isotherm model provided the best fit for the experimental data and was used to describe isotherm constants. The maximum adsorption capacity was found to be 77.2 and 63.1 mg/g for Sb(V) and F^-, respectively by CC₃A (experimental conditions: pH 5.5, time 60 min, dose 15 mg/10 mL, temperature 298 K). The CC₃A nanocomposite was able to reduce the Sb(V) and F^- ions concentration in synthetic solution to lower than 6 μg/L and 1.5 mg/L, respectively, which are maximum contaminant levels of these elements in drinking water according to WHO guidelines.

Experimental and modeling studies for adsorbing different species of fluoride using lanthanum-aluminum perovskite

We investigated the adsorption mechanisms for removing fluoride based on experimental and modeling studies. Lanthanum-aluminum perovskite was designed for treating wastewater contaminated by fluoride. A fluorine-species model was developed to calculate the concentrations of different species of fluorine: F^-, HF, HF₂^-. Multiple kinetic models were examined and the pseudo-second order model was found the best to fit the experimental data, implying fast-chemisorption. The thermodynamic data were fitted by the Langmuir model and Freundlich model at different temperatures, indicating heterogeneous adsorption at low temperature and homogeneous adsorption at high temperature. The La₂Al₄O₉ material had less influence from negative ions when adsorbing fluoride. The adsorption mechanisms were further studied using experiments and Density Functional Theory calculations. The adsorption experiments could be attributed to the lattice plane (1 2 1) and La, O, Al sites. More Al sites were required than La sites for the increase of fluoride concentration. By contrast, more La sites than Al sites were needed for increased pH.

Evaluation of the formation and antifouling properties of a novel adsorptive homogeneous mixed matrix membrane with in situ generated Zr-based nanoparticles

In situ generation is a powerful technique used to prepare homogenous adsorptive mixed matrix membranes (MMMs) containing functional nanoparticles, although the mechanism of formation of the membranes is not yet clear and there have been few published evaluations of membrane fouling. We therefore used this method to prepare a novel homogeneous adsorptive Zr-based nanoparticle–polyethersulfone (PES) MMM and systematically studied the mechanism of membrane formation at the atomic level. As the amount of ZrOCl₂·8H₂O in the casting solution increased, the phase inversion kinetics changed from instantaneous demixing due to the thermodynamic enhancement effect to a delayed demixing process caused by viscosity hindrance. The in situ generation of nanoparticles in these MMMs can be divided into three stages: the migration stage, the exfoliation stage and the stable stage. Our findings provide a fundamental understanding of the interface chemistry in the development of in situ generated MMMs. M2 showed a higher adsorption of As(v) than the pure PES membrane and could be reused after regeneration. The removal of As(v) from the M2 filtration system mainly took place via adsorption rather than size exclusion, as confirmed by EDS and experimental data. The presence of humic acid slightly inhibited the removal of As(v) during the filtration process as a result of the barrier effect caused by the formation of a filter cake via humic acid fouling. The filtration of a bovine serum albumin solution showed that the MMM with in situ generated nanoparticles had better antifouling properties than the PES membrane alone in multiple applications as a result of the enhanced hydrophilic surface.

A homogeneous in situ generated Zr-based NPs/PES mixed matrix membrane with enhanced adsorptive and antifouling performance was developed.

Mechanism of simultaneous removal of aluminum and fluoride from aqueous solution by La/Mg/Si-activated carbon

La/Mg/Si-activated carbon derived from palm shell has been a suitable material for removal of aluminum and fluoride from aqueous solution. In the study, the mechanism of simultaneous removal of aluminum and fluoride by La/Mg/Si-activated carbon (La/Mg/Si-AC) was investigated to understand its high efficiency. It was found that the removal of aluminum and fluoride by La/Mg/Si-AC was favored at lower pH compared to the point of zero charge of La/Mg/Si-AC and high temperature. Adsorption capacity of Al(OH)₄^- was about 10 times higher than that of F^- due to the strong binding affinity of Al(OH)₄^- on protonated surface and competition between F^- and OH^- toward charged adsorption site. Kinetics results showed that the aluminum and fluoride adsorption were explained using the pseudo-second-order kinetic model and intra-particle diffusion model. Adsorption process of Al(OH)₄^- and F^- was driven by the potential rate-limiting step involved in mass transport process occurred on the boundary diffusion layer of porous adsorbent surface. Electrostatic interaction between protonated surface of La/Mg/Si-AC and negatively charged ions (i.e., Al(OH)₄^- and F^-) as well as ion-exchange between hydroxide and ionic metal species were important mechanisms in the process of aluminum and fluoride adsorption. Driving forces for adsorption of individual Al(OH)₄^- and F^- were not entirely different. Identifying the dominant mechanism will be helpful in understanding the adsorption process and developing new adsorbent.

Adsorption mechanism for removing different species of fluoride by designing of core-shell boehmite

Many kinds of adsorbents have been developed for removing fluoride from water. However, the unclear actual mechanism of fluoride adsorption greatly restricts the structural design and application of novel adsorbents. Based on the understanding of the interaction between hydroxyl and fluoride, a novel core-shell nanostructure of boehmite was synthesized via an in-situ-induced assembly for removing fluoride. The formed polycrystalline boehmite (γ-AlOOH) nanostructure significantly enhances adsorption performance. The transformation of fluoride forms (including F^-, HF, HF₂^-) is closely related to the solution property. The acidic solution is more favorable, mainly because of the conversion of HF (pyrazine) and HF₂^- (the bifluoride ion) with a strong hydrogen bond effect from fluoride (F^-) with pH < 3.18. The lattice plane of (0 0 2) belongs to the dominant face for removing fluoride in this structure. According to the experimental and theoretical calculation, strong bonding of Al, O and H sites with fluoride species (F^-, HF, HF₂^-) in acidic solution are demonstrated, but not in alkaline solution due to OH^- interference. The possible mechanism of fluoride adsorption on boehmite (AlOOH) structures is proposed. Our findings show a new potential prospect of structural designing for novel fluoride adsorbent.

One-pot synthesis of Cr(III)-incorporated Zr(IV) oxide for fluoride remediation: a lab to field performance evaluation study

A low-cost Cr(III)-incorporated Zr(IV) bimetallic oxide (CZ) was synthesized by simple chemical precipitation method for removal of fluoride from contaminated water. The physicochemical properties of CZ before and after fluoride removal were established with several instrumental techniques such as TEM with elemental mapping, SEM with EDX, XRD, IR, XPS, zeta potential measurement, etc. Batch adsorption technique were carried out to understand the factors affecting fluoride adsorption, such as effects of initial pH, adsorbent dose, co-occurring ions, contact time, and temperature. The maximum adsorption capacity observed at pH between 5 and 7. The fluoride adsorption processes on CZ obeyed the pseudo-second-order rate equations and both Freundlich and DR isotherm models. The maximum adsorption capacity of 90.67 mg g^-1 was obtained. The thermodynamic parameters ΔH⁰ (positive), ΔS⁰ (positive), and ΔG⁰ (negative) indicating the fluoride sorption system was endothermic, spontaneous, and feasible. The CZ also successfully used as fluoride adsorbent for real field contaminated water collected from the Machatora district, Bankura, West Bengal, India. Graphical abstract Schematic representation of CZ synthesis and its application for lab as well as field water purification purpose.

Carboxymethyl konjac glucomannan mechanically reinforcing gellan gum microspheres for uranium removal

Biosorbents have been a promising adsorbent to remove uranium while their poor mechanical properties prevent them from being widely used in practice. In this study, carboxymethyl konjac glucomannan (CMKGM) was incorporated to gellan gum to form a double-network gel micro spheres (CMKGM/GG-Al) for uranium removal with its mechanical strength fairly being reinforced. The compressive strength of the CMKGM/GG-Al microspheres was about 6 times than that of GG-Ca microspheres we prepared before while the adsorption capacity still be at a better value with the fitting maximum adsorption capacity being of 97.94 mg/g. Its uranium adsorption properties were investigated by considering the influence of pH, the adsorbent dosage, temperature, initial uranium concentration, time and coexisting ions. The adsorption mechanism was also investigated according to the SEM, EDX, FT-IR and XPS data analysis. The isotherm equilibrium data which were best fitted with Langmuir model and the kinetics data which were best fitted with pseudo-second-order model. It was inferred that the adsorption process was mainly the ion-exchange and the coordination with hydroxyl groups on the adsorbent surface and the adsorption process was endothermic and spontaneous. The CMKGM/GG-Al microspheres prepared in this study would be more conducive to practical application for uranium removal.

Fluoride uptake by three lanthanum based nanomaterials: Behavior and mechanism dependent upon lanthanum species

Excess fluoride in water can be efficiently removed by lanthanum based material, however, different lanthanum species exhibited distinct fluoride removal capability. In this study, three typical lanthanum based nanoparticles denoted as L1, L2 and L3 in the form of La(OH)₃, La₂O₃·nH₂O and LaCO₃OH respectively were synthesized and well characterized for fluoride removal. They differ in terms of morphology, surface charge, water content, specific surface area and crystallinity. L2 (La₂O₃·nH₂O) exhibited the highest adsorption capacity (~28.9 mg/g) and selectivity towards fluoride, followed by L3 (LaCO₃OH) (~25.1 mg/g) and L1 (La(OH)₃) (~6.03 mg/g). Despite the relatively low capacity for L1, it could be efficiently regenerated by alkaline solution for repeated use. However, both L2 and L3 suffered significant from capacity loss after regeneration. X-ray photoelectron spectroscopy (XPS), nuclear magnetic resonance spectroscopy (NMR) analysis and molecular configuration modelling suggested the distinct mechanism of fluoride adsorption onto the three materials. Fluoride was captured by L1 and L3 via electrostatic attraction and ligand exchange of different bond strength. However, a stronger LaF interaction via chemical adsorption by L2 was observed. This study provided new insights into the role of commonly used La species for fluoride removal.

Fast Capture of Fluoride by Anion-Exchange Zirconium-Graphene Hybrid Adsorbent

Fluoride contamination is a severe problem affecting the safety of drinking water around the world. High-rate adsorbent materials are particularly desirable for potable water defluoridation. Current research on fluoride adsorbent materials is primarily focused on metal-based adsorbents with high capacities. However, they generally suffer from slow adsorption kinetics due to the adsorption mechanism of a sluggish exchange between coordinated hydroxyl groups and fluoride ions. Designing metal-based adsorbents to mimic the rapid ion-exchange behavior of anion-exchange resins is a promising approach to integrate fast adsorption and high capacity for fluoride removal. Herein, a ZrO(OH)_1.33Cl_0.66-reduced graphene oxide (rGO) hybrid adsorbent containing exchangeable chloride ions was synthesized with the assistance of cation-π interactions. Unlike most adsorbents requiring a high surface area, this composite has a negligible surface area (1.45 m² g^-1), but can deliver a fast fluoride capture performance (reaching equilibrium in 5 min) with high adsorption rate constants of 1.05 min^-1 and 0.171 mg g^-1 min^-1, around 10 times faster than the best result reported in the literature. Besides, ZrO(OH)_1.33Cl_0.66-rGO can also demonstrate a high fluoride uptake (44.14 mg g^-1) and high removal efficiency (94.4%) in 35 mg L^-1 fluoride solution, both among the highest performances for fluoride adsorption.

Coagulation removal of fluoride by zirconium tetrachloride: Performance evaluation and mechanism analysis

Fluoride (F^-) pollution is a worldwide issue. Coagulation with aluminum (Al) salts is an efficient and economical method for the removal of F^-. However, due to the strong complexation between Al³⁺ and F^-, the residual F^- and Al after coagulation usually exceed the limits. Zirconium (Zr) coagulants have drawn increasing attention due to their excellent flocculation ability for organic matter. In this work, the performance and mechanism of ZrCl₄ coagulation for F^- removal were investigated with the widely used Al₂(SO₄)₃ as a reference. The optimum pH range is 4.0-6.0 for ZrCl₄ and 8.0-10.0 for Al₂(SO₄)₃. ZrCl₄ was superior to Al₂(SO₄)₃ for F^- removal as the initial F^- concentration was less than 30.0 mg L^-1. Coexisting substances at environmental concentration levels showed negligible effects on F^- removal by ZrCl₄. Besides the better F^- removal, another advantage of ZrCl₄ over Al₂(SO₄)₃ was the much lower residual metal concentration in the pH range of 4.0-11.0. The hydrolysis of Al₂(SO₄)₃ was significantly inhibited due to the formation of Al-F complexes while the hydrolysis of ZrCl₄ was not influenced even under strongly acidic conditions. Therefore, F^- removal by Al₂(SO₄)₃ was mainly achieved by preliminary complexation between Al³⁺ and F^- and subsequent hydrolysis and polymerization of these complexes, while adsorption onto hydrolysates and ion exchange with surface hydroxyl groups were the main ways of F^- removal by ZrCl₄. The work here provides a new method for F^- removal and may shed light on the application of Zr coagulants for other pollutants.

Development of in situ synthesized Y-based nanoparticle/polyethersulfone adsorptive membranes by adjusting the composition of the coagulation bath for enhanced removal of fluoride

The composition of coagulation bath significantly altered the membrane structure, composition and adsorption performance for defluoridation by affecting the phase inversion kinetics.

In situ-generated yttrium-based nanoparticle/polyethersulfone composite adsorptive membranes: Development, characterization, and membrane formation mechanism

In this study, a series of in situ-generated yttrium-based nanoparticle (NP)/polyethersulfone (PES) composite adsorptive membranes were prepared by the phase inversion method for the first time. The Y(NO₃)₃·6H₂O as precursor, uniformly dispersed at the molecular level in casting solution, reacted with OH^- in a coagulation bath and ambient CO₂ during the phase inversion process. The Y(CO₃)_0.5(OH)₂ NPs were formed in situ and distributed homogeneously in a PES matrix, which was confirmed by X-ray photoelectron spectroscopy (XPS) and Energy Dispersive X-Ray Spectroscopy (EDS) results. The compatibility of the nanocomposite membranes was improved by an in situ preparation method. With the increase in content of Y-based NPs in composite membranes, the surface hydrophilicity and water permeability first increased from M1 to M2, and then slightly decreased from M3 to M5, which was mainly related to membrane structure. From M1 to M5, the demixing way changed from instantaneous demixing to delayed demixing process as a result of thermodynamic enhancement and viscosity hindrance in the phase inversion process. A higher demixing rate led to a structure with large finger-like macro-voids, i.e., M1, whereas a lower demixing rate caused the suppression of finger-like macro-voids, i.e., M5. More importantly, the adsorption study indicated that the nanocomposite adsorptive membranes were stable in the treatment of fluoride-containing water, with no leakage of Y-based NPs from membrane matrix to solution. It is expected that the in situ preparation technique could be used to produce next-generation nanocomposite adsorptive membranes with improved comprehensive properties for application in water treatment.

Adsorptive removal of fluoride from water by granular zirconium-aluminum hybrid adsorbent: performance and mechanisms

Granular zirconium-aluminum hybrid adsorbent (GZAHA) was fabricated for efficient defluoridation of groundwater in filter application. GZAHA was formed through the aggregation of massive Zr/Al oxide nanoparticles with an amorphous pattern. This adsorbent has a satisfactory mechanical strength, a specific surface area of 29.55 m²/g, and numerous hydroxyl groups on the surface. F adsorption equilibrium could be achieved within 12 h, and the sorption process followed a pseudo-second-order reaction rate. The maximum adsorption capacity of F estimated from the Langmuir model was 65.07 mg/g at 25 °C, being greater than most of other granular adsorbents. The removal efficiency of F could be maintained in a wide pH range of 5~9. The presence of phosphate posed an adverse effect on F adsorption due to the competition mechanisms. The saturated adsorbents could be regenerated and reused for four times by using sodium hydroxide solution as an eluent, and the adsorption capacity remained around 80%. Besides electrostatic attraction and Al-F complex, surface complexation and anion exchange were also involved in the adsorption process. Continuous adsorption experiments illustrated that 808 bed volumes of F-contaminated water (F = 5 mg/L) were treated successfully by a GZAHA-packed column without second pollution.

Dual-Functional Ultrafiltration Membrane for Simultaneous Removal of Multiple Pollutants with High Performance

Simultaneous removal of multiple pollutants from aqueous solution with less energy consumption is crucial in water purification. Here, a novel concept of dual-functional ultrafiltration (DFUF) membrane is demonstrated by entrapment of nanostructured adsorbents into the finger-like pores of ultrafiltration (UF) membrane rather than in the membrane matrix in previous reports of blend membranes, resulting in an exceptionally high active content and simultaneous removal of multiple pollutants from water due to the dual functions of rejection and adsorption. As a demonstration, hollow porous Zr(OH)_x nanospheres (HPZNs) were immobilized in poly(ether sulfone) (PES) UF membranes through polydopamine coating with a high content of 68.9 wt %. The decontamination capacity of DFUF membranes toward multiple model pollutants (colloidal gold, polyethylene glycol (PEG), Pb(II)) was evaluated against a blend membrane. Compared to the blend membrane, the DFUF membranes showed 2.1-fold increase in the effective treatment volume for the treatment of Pb(II) contaminated water from 100 ppb to below 10 ppb (WHO drinking water standard). Simultaneously, the DFUF membranes effectively removed the colloidal gold and PEG below instrument detection limit, however the blend membrane only achieved 97.6% and 96.8% rejection for colloidal gold and PEG, respectively. Moreover, the DFUF membranes showed negligible leakage of nanoadsorbents during testing; and the membrane can be easily regenerated and reused. This study sheds new light on the design of high performance multifunction membranes for drinking water purification.

Insight into mechanisms of fluoride removal from contaminated groundwater using lanthanum-modified bone waste

The current worldwide issue of fluoride contamination in groundwater has resulted in an increased demand for efficient adsorbents.

A study of the mechanism of fluoride adsorption from aqueous solutions onto Fe-impregnated chitosan

The adsorption of fluoride from aqueous solutions onto an Fe-impregnated chitosan (Fe-CTS) granular adsorbent was studied, and the adsorption capacity was determined to be 1.9736 mg g(-1) at an initial fluoride concentration of 10 mg L(-1). The effects of the initial fluoride concentration, dosage, and temperature were investigated using factorial design and analysis. The results indicated that high initial fluoride concentrations, low dosages, and low temperatures could enhance the fluoride adsorption capacity. In addition, Fe-CTS exhibited high selectivity for fluoride removal in the presence of high levels of several coexisting anions (nitrate, chloride, bicarbonate, and phosphate), except carbonate and sulfate. The adsorption process followed the Langmuir model at low fluoride concentrations and the Freundlich model at high initial fluoride concentrations. The data also fit the pseudo-second-order model. Scanning electron microscopy (SEM), Fourier-transform infrared (FTIR) spectroscopy, and extended X-ray absorption fine-structure (EXAFS) spectroscopy were used to elucidate the adsorption mechanism. The FTIR and EXAFS analyses revealed that Fe was chelated with -NH2 and -OH groups on the CTS, and fluoride adsorption on the Fe-CTS occurred due to ion exchange between chloride and fluoride.

HIGHLIGHTS

a granular Fe-impregnated chitosan (Fe-CTS) adsorbent was synthesized via chelation of Fe ions to -OH and -NH2 groups of CTS. The Fe-CTS granular adsorbent exhibited high performance for the adsorption of fluoride. The mechanism of fluoride adsorption on Fe-CTS was elucidated using EXAFS and FTIR analyses. Fluoride adsorption on Fe-CTS occurred via ion exchange between chloride and fluoride.

A metal–organic framework/α-alumina composite with a novel geometry for enhanced adsorptive separation

Incorporation of MOF UiO-66 into an advanced α-alumina matrix leads to a novel composite concept for enhanced adsorptive separation.

Fabrication and testing of zirconium-based nanoparticle-doped activated carbon fiber for enhanced arsenic removal in water

A Zr-nanoparticle-doped ACF from this study shows a great potential for removal of arsenic from contaminated groundwater.

Core–shell zeolite@Alg–Ca particles for removal of strontium from aqueous solutions

A core–shell zeolite@Alg–Ca adsorbent was synthesized by a simple method of coaxial electrospinning and applied for the removal of Sr(ii) ions from aqueous solution.

Enhanced removal of fluoride by tea waste supported hydrous aluminium oxide nanoparticles: anionic polyacrylamide mediated aluminium assembly and adsorption mechanism

A novel and low-cost biosorbent of tea waste supported hydrous aluminium oxide (Tea–APAM–Al) was prepared with help of anionic polyacrylamide (APAM) for highly efficient defluoridation of drinking water.