No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Performance of Fe-La-Ce biochar derived from Bidens pilosa L. for adsorbing fluoride in water
... Adsorption of F by BC in soil and aqueous phases involves complex interactions of physical, chemical and electrostatic interactions (Abeysinghe and Baek 2022; Kumar et al. 2023a, b;Li et al. 2023;Sadhu et al. 2021). These mechanisms include surface adsorption, ion exchange, complexation and precipitation, which are influenced by solution chemical reactions, BC properties and environmental conditions, mainly dependent on pH (Table 3). ...
Emerging contaminants (ECs) pose a growing threat to the agricultural ecosystems and human health. Biochar (BC)
may be applied for the remediation of ECs in soils and water. There are some research papers that have been pub
lished about the potentiality of BC for the remediation of ECs in soils and water; however, there have been no critical
and comprehensive review articles published on this topic up to now. Therefore, this review explores the application
of pristine and modified BC for the remediation of various emerging inorganic contaminants (EICs), including vana
dium (V), antimony (Sb), thallium (Tl), mercury (Hg), fluoride (F−), and rare earth elements (REEs) in soils and water.
The review explores the specific mechanisms by which BC removes these EICs from water and soil. The roles of ion
exchange, complexation, electrostatic interactions, and precipitation in the removal of these EICs from water by pris
tine and functionalized BC have been reviewed and discussed. Particular attention is also paid to the interaction
and potential immobilization of those EICs in soils with pristine and functionalized BC, highlighting some applicable
strategies for treating EIC-contaminated soils, particularly paddy soils, aiming to mitigate the associated ecological
and human health risks. Finally, the potential environmental implications and further research on the applications
of pristine and functionalized BC for remediation of EICs in water and soils have been summarized. This article pro
vides a comprehensive overview on the potential applications of different pristine and engineered BCs for the sustain
able remediation of EICs contaminated soils and water
In the present work, pond clay was modified with lanthanum and applied for fluoride uptake from an aqueous environment. The clay soil was treated with a 0.1 M solution of lanthanum oxide and heated at 500 ℃ for 90 min in a muffle furnace. The modified clay was characterized by the following techniques: particle size analysis, zeta potential, Fourier-transform infrared, scanning electron microscopy, transmission electron microscopy, pH at the zero point of charge, X-ray diffraction, Brunauer–Emmett–Teller, and X-ray photoelectron spectroscopy. The adsorption experiments revealed that modified clay soil was very effective in removing fluoride with an adsorption capacity of 1.96 mg/g. The fluoride removal was followed well with Langmuir isotherm (R² = 0.999), pseudo-second-order kinetics (R² = 1), and the adsorption was an exothermic process. The performance of lanthanum-modified clay (LMC) in a fixed bed column was evaluated using different models, including the Thomas, Adams–Bohart, Yoon–Nelson, and Clark models. A regeneration study was compared with NaOH and NaHCO3 and successfully performed for four adsorption cycles. A probable mechanism is proposed including ligand exchange, electrostatic attraction, and inner complexation for fluoride adsorption on the LMC. The developed adsorbent was also tested for the treatment of natural groundwater.
Aquatic pollution caused by antibiotics poses a significant threat to human health and the ecosystem. Inspired from “Emmental Cheese” that owns lots of natural pores, we here fabricated a hierarchical cheese-like porous Spirulina residue biochar (KSBC) activated by KHCO3 for efficiently boosting the removal of sulfathiazole (STZ). Through learning form nature that the CO2 produced by bacteria can serve as the natural pore maker (like cheese-making), KHCO3 was thus selected as the gas generating agent in this study. The effect of adding KHCO3 on the surface properties of KSBC was comprehensively investigated. Benefiting from the activation, the KSBC with the mass ratio of 2:1 (2K-SBC) possessed the largest specific surface areas (1100 m² g⁻¹), which was approximately 81 times that of the original (not activated) Spirulina residue biochar (SBC) (13.56 m² g⁻¹). Moreover, 2K-SBC exhibited the maximum adsorption capacity for STZ (218.4 mg g⁻¹), dramatically higher than the SBC (25.78 mg g⁻¹). The adsorption kinetics and adsorption isotherms exhibited that the adsorption behavior of 2K-SBC for STZ was consistent with the pseudo-second-order and Langmuir models. Additionally, the adsorption thermodynamics revealed that the adsorption of STZ on 2K-SBC was spontaneous and exothermic. The pore-filling and electrostatic interaction were considered the main mechanism for the adsorption of STZ on 2K-SBC, whereas the π-π electron donor-acceptor (EDA) interaction and hydrogen bond would also partially contribute to the adsorption process.
Fluoride contamination is the main contributor to environmental pollution, which occurred mainly due to anthropological activity. Owing to their biocompatibility, biomaterials have been widely used as an adsorbent for the removal of toxic ions by adsorption techniques. The hydroxyapatite (HAp) and its composites of sodium alginate (HAp/SA) were synthesized by the co-precipitation method. Batch adsorption experiments were used to find adsorption capacity by varying physical parameters such as the contact time, pH, initial concentration, and co-anions . At pH 7, the maximum fluoride adsorption capacity of HAp, HAp/SA1, and HAp/SA4 was 10 mg/g, 35 mg/g, and 50 mg/g, respectively. The fluoride ion adsorption capacity was increased by 92% compared to the HAp-sodium alginate compound reported so far. The recycling efficiency of HAp/SA4 showed (96%) sustained fluoride removal for five consecutive recycles. The fluoride adsorption follows the monolayer and chemisorption mechanisms, as confirmed by the Langmuir and pseudo second-order kinetics, respectively. The higher electronegative fluoride ions can be exchanged with phosphate, carbonate, and the hydroxyl surface functional groups of adsorbent. Therefore, this result suggests that the HAp/SA composites can be used as an efficient fluoride ion absorbent in water.
This work investigated the adsorption capacity of banana and orange peels, magnetite and their corresponding magnetic composites in the removal of caffeine from synthetic wastewater. The characteristics of the adsorbents were studied using proximal analysis, Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), Brunauer, Emmett and Teller (BET) analysis and X-ray diffraction. Batch adsorption tests were conducted to determine the influence of the adsorbent dose (0.5 and 10.0 g/L), contact time (5 – 180 min) and initial caffeine concentration (10 – 50 mg/L) in the caffeine removal. The fittings of the experimental data to the pseudo first order, pseudo second order, Elovich, and diffusion kinetic models, as well as to the Langmuir, Freundlich and Sips isotherm models were also studied. The use of magnetic peels improved around 1.7 times the adsorption capacity of peels. The effective doses were 3.5 g/L of orange peel, 9.5 g/L of banana peel, 2.5 g/L of orange peel composite, 5.5 g/L of banana peel composite, and 5 g/L of magnetite, achieving caffeine removal efficiencies of 95.5 ± 0.3%, 90.5 ± 0.5%, 93.6 ± 0.2%, 89.2 ± 0.01% and 54.8 ± 0.8%, respectively. The adsorption using the peels, magnetite, and their magnetic composites better fitted the pseudo first order kinetic model and the Langmuir and Sips isotherm models.
In this study, bone chars were obtained from an alien aquatic species “devilfish” bones by pyrolysis of 500–800 °C. Bone chars were evaluated as a sustainable adsorbent of fluoride, and it was found pyrolyzed bone char at 500 °C adsorbed the most amount of fluoride. Thermodynamic parameters of fluoride adsorption on devilfish bone chars were estimated as ΔH° = 7.213 kJ mol−1, ΔG° = 23.61 kJ mol−1, and ΔS° = 103.4 J mol−1 K−1 indicating that adsorption is endothermic, spontaneous, and with a great affinity of fluoride on bone char. The fluoride desorption study showed that fluoride is desorbed from the material of 0.24 to 20.06%, so the adsorption is considered to be partly reversible. The regeneration of the bone char at 400, 500, and 600 °C was studied, and it was noted that its adsorption capacity decreases slightly, so it could be considered appropriate for the use in water treatment technologies. Adsorption of fluorides from drinking well water of a rural community with dental fluorosis problems and high levels of fluoride in water revealed that by increasing the amount of the bone char of 0.05 to 0.8 g, the disposal of fluoride increases from 69.1 to 98.7%. Lastly, it was established that the bone char synthesized from devilfish is a low-cost, viable, sustainable material to remove fluorides from water and represents an environmental management strategy of this alien species.
In this study, novel adsorbent ceria nanoparticles (CeNPs) entrapped in tamarind powder ([email protected]) were efficiently utilized for the simultaneous adsorption of aqueous mercury [Hg(II)] and aqueous lead [Pb(II)]. Surface interactions between the adsorbent and heavy metal ions play an important role in the adsorption process, and the surface morphology can significantly improve the adsorption capacity of the adsorbent. The Langmuir adsorption capacity of [email protected] for Hg(II) and Pb(II) was found to be 200 and 142.85 mg/g, respectively. The surface area of utilized adsorbent was found to be very high, that is, 412 m²/g. The adsorption kinetics of [email protected] for both ions follow pseudo-second-order, and the adsorption process is also thermodynamically feasible. Column study favors multilayer adsorption of the heavy metal ion. The spectral analysis of the adsorbent revealed that hydroxyl, carboxylic, and ester groups, as well as CeNPs, are responsible for Hg(II) and Pb(II) adsorption. The cost-benefit analysis confirms the economic viability of the synthesized [email protected] composite for heavy metal removal. The adsorbent is best suited for Hg(II) adsorption as compared to Pb(II). This is a novel study on the utilization of tamarind leaf powder with CeNPs for heavy metal ion adsorption and its adsorption mechanism, which has not been reported to date.
Water defluoridation properties of a protonated clinoptilolite has been studied and analyzed. This adsorbent has been obtained by a thermochemical treatment with NH4Cl to protonate the zeolite surface and to increase its specific surface area. Results of adsorption kinetics and isotherms showed that the defluoridation properties of this protonated clinoptilolite were better than those reported for raw and modified zeolites with multivalent cations such as aluminum or iron. Defluoridation performance of this protonated clinoptilolite was endothermic and increased at acidic conditions in contrast to other zeolites modified with multivalent cations that should operate at pH 7 to maintain the adsorbent chemical stability. In addition, new models have been also developed to fit the fluoride adsorption on this protonated zeolite. These models were based on a hybridization of artificial neural networks and Langmuir and Pseudo-second order equations. Results showed that these hybrid models satisfactorily fitted the kinetics and isotherms of the fluoride adsorption on protonated clinoptilolite. These new models are promising to correlate and predict the fluoride adsorption with this zeolite or other types of adsorbents.
Challenges remain in developing sustainable (high-efficient and recyclable) phosphate removal systems with lower costs and reduced secondary pollution when lanthanum (La)-based sorbents are applied to control phosphate in the aquatic environment. To address this issue, a phosphate stabilizing compound, namely magnetic lanthanum/iron co-modified attapulgite (M-LaFeAP), was fabricated by incorporating lanthanum into an iron-modified attapulgite (M-FeAP). Batch experiments demonstrated that 88.34% of the phosphate was rapidly sequestered from aqueous solution within the first hour, and the composites reached a maximal sorption capacity of 43.32 mg/g. The pseudo-second-order model was found to better explain the M-LaFeAP adsorption kinetics and the equilibrium data fitted very well with the Langmuir isotherm model. With the initial phosphate concentration ranging from 2 to 100 mg/L, the M-LaFeAP exhibited superior adsorption performance from 2 to 10 of pH values. In addition, M-LaFeAP presented an excellent selectivity for phosphate when co-existing ions often occurring in water bodies were present, in which the solution ionic strength exerted little influence on phosphate sorption behavior. Notably, the recyclable M-LaFeAP possessed a saturated magnetization of 25.83 emu/g and was easily separated under the external magnetic field. After five serial adsorption-desorption cycles, M-LaFeAP still possessed a better sorption performance (35.78 mg/g), which demonstrated its appreciable reusability for phosphate removal. Our findings indicate that the separable and recyclable M-LaFeAP demonstrated high-efficient phosphate removal in a sustainable way, which is promising in phosphate removing and recovering applications.
Fluoride contamination is a severe problem affecting the safety of drinking water around the world. The study focused on the facile synthesis of activated carbon (AC) impregnated with cerium and iron via ultrasonication and performance evaluation of these novel adsorbents using sono-sorption for defluoridation of drinking water. The use of ultrasound demonstrated maximum removal efficiency of 95.4% just after 20 min compared to shaker, where only 87% fluoride was removed after 60 min using AC having Ce/Fe molar ratios of 2:1 (AC/Ce/Fe–1). The key finding which makes our study outstanding is the rapid increase in adsorption rate upon application of ultrasonication while improving the adsorption capacity. The kinetics data obtained was best fitted with the pseudo-second-order model. The maximum adsorption capacity of AC/Ce/Fe–1 was obtained as 52.3 mg/g at room temperature and the synthesized material maintained its relatively high fluoride uptake up to the fourth cycle. The material shows the highest adsorption capacity as compared to the metal-modified AC available in the literature, making it ideal for fluoride removal from drinking water.
Bauxite is a widely available Al-O-rich mineral with great potential for abating fluoride. However, low adsorption capacity, a narrow workable pH range, and a lack of clarity on the best removal mechanism hinder its application. In this work, a highly efficient bauxite nanocomposite ([email protected]) was synthesized via doping and pyrolysis, and its fluoride adsorption in industrial wastewater was examined. Doping Ce/La synergistically improved the fluoride adsorption affinity of the composite (from pHPZC 8.0 ~ 10.0) and enhanced the •OH. The materials were characterized by SEM-EDS, BET, XRD, and TGA while XPS, FTIR, and DFT were used to investigate the mechanism of fluoride sorption. Results show that [email protected] 500 has a positive zeta potential of 26.3–23.1 mV from pH 1~ 10. The Langmuir model was the best fit with a maximum adsorption capacity of 88.13 mg/g and removal efficiency up to 100% in 50 ppm F⁻ solution. The high F⁻ removal was attributed to the enhanced surface affinity and the formation of adequate •OH on the material. Except for carbonate and phosphate ions, other ions exhibited negligible effects and the selective removal of F⁻ in real wastewater was high. The main mechanism of adsorption was the ligand/ion exchange and electrostatic attraction.
Fluoride pollution in groundwater is a serious problem threatening millions of people worldwide. Calcite is considered an ideal adsorbent for defluoridation owing to its widespread presence and low cost. To further enhance its performance, we synthesize a series of phosphate-modified calcites with varying phosphate concentrations. The surface modification led to the formation of a nanosized hydroxyapatite (HAP) coating on the calcite surface. With increasing concentrations of phosphate used for modification, the BET specific surface area of the adsorbents was dramatically enhanced, resulting in a great enhancement of F uptake. At low F concentrations (i.e., <1 mM), surface-modified calcite can achieve up to 25 times higher F removal efficiency than calcite. The ¹⁹F solid-state MAS NMR spectra yielded three distint peaks at δ(¹⁹F) = −86 ppm, −99 ppm, and −122 ppm, representing the formation of carbonate fluorapatite (CFA), fluorapatite (FAP), and coprecipitated F, respectively. This provides strong evidence for the contribution of newly formed HAP to F removal. In contrast, at high F concentrations (e.g., >2 mM), surface modification did not enhance F uptake by calcite. The ¹⁹F solid-state MAS NMR analysis revealed that the predominant deflurodation mechanism is the formation of CaF2 precipitates (δ(¹⁹F) = −108 ppm) for both pristine and modified calcite at high F concentrations. Under this condition, the contribution of the newly formed nanosized HAP to F uptake is insignificant. Taken together, our results demonstrated the potential of surface modification of calcite as a cost-effective technique for defluoridation for most F-rich groudwater.
The decrement of low concentration of fluoride to below standard (< 1 mg/L) is one of the current research hotspots. In this work, reed biochar beads cross-linked with cerium alginate were prepared by the gelation-spheroidization-carbonization method to serve as an efficient fluoride adsorbent. The results of batch adsorption experiments showed that RBM-Ce (dosage of 1 ± 0.01 g/L) could rapidly remove fluoride (concentration of around 10 mg/L) over a wide range of pH 3 - 9, and showed trace leaching amount of Ce ions during adsorption. The maximum adsorption capacity was 34.86 mg/g at normal temperature (20℃), and the most consistent curve was Langmuir model in adsorption isotherms. In adsorption kinetics experiments, RBM-Ce showed a rapid adsorption rate capable of treating fluoride under certain standard within 15 min, and the fit was consistent with the pseudo-second order model. The SEM, EDS and XRD characterization indicated that CeO2 nanoparticles was dispersed and immobilized on the surface of biochar beads. From zeta potential, XPS, FTIR and Raman analyses, the adsorption mechanisms included ion exchange, electrostatic attraction, hydrogen bonding and complexation. All characterization and adsorption experiments pointed to RBM-Ce beads as promising adsorbents for fluoride removal.
Efficient removal of oxytetracycline hydrochloride (OTC) from wastewater is of great significance but extremely challenging. Herein, a novel adsorbent lignin-based multi-metal ferrite biochar (FeNiZn-LBC) was synthesized through pyrolysis with controllable temperature and hydrothermal reaction using lignin of sinocalamus oldhami as raw material. The adsorption property of FeNiZn-LBC for OTC was systematically researched, and the results displayed that adsorption of FeNiZn-LBC to OTC accorded with the Langmuir model and the equilibrium adsorption capacity was 476 mg g⁻¹. Notably, FeNiZn-LBC can be regenerated with 0.100 mol L⁻¹ NaOH. Additionally, we raised rational explanations for the mechanisms of adsorption behavior based on the zeta potential and XPS spectra. The adsorption of FeNiZn-LBC for OTC was mainly controlled by the electrostatic interactions, hydrogen bonds and complexation involving FeNiZn-LBC and OTC, especially the metal-oxide bond (M-O) generated after loaded with multi-metal ferrite played a positive role in the removal of OTC from water. Our work highlighted the potential of FeNiZn-LBC for excellent adsorption of OTC in next generation.
Raw fly ash (RFA) was modified using NaOH and FeCl3 (NaOH/Fe-MFA) to enhance the adsorptive properties for removal of fluoride from water. SEM-EDX, XRD and FTIR, point for zero charge (PZC), specific surface area, and particle size were considered to contrast adsorbent properties of RFA and NaOH/Fe-MFA. The impact of operating variables such that initial solution pH, contact time, adsorbent dosage over fluoride adsorption were evaluated using synthetic water samples. Isotherm and kinetics studies were performed for NaOH/Fe-MFA. Adsorption experiments showed a higher adsorption capacity for NaOH/Fe-MFA over RFA. After 2 h reaction, maximum fluoride removal of 92% was observed with 2 g L⁻¹ of NaOH/Fe-MFA at pH 2. At pH 7, under similar conditions, 34% of removal was observed. Fluoride adsorption from NaOH/Fe-MFA was followed Langmuir isotherm, and monolayer fluoride adsorption on homogeneous NaOH/Fe-MFA was confirmed with a considerably high capacity of 18.6 mg g⁻¹. Chemisorption adsorption was revealed from well-fitted kinetics data with pseudo-second-order model. Dominant mechanism for fluoride adsorption from NaOH/Fe-MFA was identified as iron exchange with surface OH⁻, which bonds to Fe³⁺ ions.
Fluoride (F⁻) is that the foremost toxicant affecting almost 200 million people worldwide. Present work involves defluoridation experiments utilizing magnetic iron oxide nanoparticles (Fe3O4NPs) fabricated on the graphene/alginate nanocomposite hydrogel. The Fe3O4NPs was synthesized via waste flowers (rose) obtained from temples via green route and chemically graphene oxide (GO) was prepared through lead of pencil. Batch trials were conducted to analyze the relation of F⁻ ions with different parameters such as pH, contact period, fluoride concentration and dose. The surface structure of nanoparticles (NPs), functional groups contribution and elements availability in the hydrogel was examined through field emission scanning electron microscope (FESEM), x-ray diffraction (XRD), energy dispersive x-ray analysis (EDX), fourier transform infrared spectroscopy (FTIR) techniques. The developed hybrid Fe3O4/graphene/alginate nanocomposite hydrogel exhibits a maximum defluoridation capacity of 7.51 mg g⁻¹. Maximum removal percentage was attained for 2 and 10 mg L⁻¹F⁻ content as 85.5% to 59% at pH 5 and 120 min. The equilibrium isotherm study was fitted with Freundlich isotherm model. Pseudo-second-order kinetic model (R² = 0.988) was favoured divulged that the insight of F⁻ ions took place through chemisorption processes on GO/Fe/Alginate nanocomposite hydrogel.
Excess fluoride in water poses a threat to ecology and human health, which has attracted global attention. In this study, a series of lanthanum-based metal-organic frameworks (La-MOFs) were synthesized by varying the organic ligands (i.e., terephthalic acid (BDC), trimesic acid (BTC), biphenyl-4,4-dicarboxylic acid (BPDC), 2,5-dihydroxyterephthalic acid (BHTA), and 1,2,4,5-benzenetetracarboxylic acid (PMA)) to control the microscopic structure of the MOFs and subsequently apply them for the removal of fluoride in water. The maximum capture capacities of La-BTC, La-BPDC, La-BHTA, La-PMA, and La-BDC at 298 K are 105.2, 125.9, 145.5, 158.9, and 171.7 mg g-1, respectively. The adsorption capacity is greater than most reported adsorbents. The adsorption isotherms of La-MOFs for fluoride are well fit to the Langmuir isotherm model. In addition, the adsorption kinetics of La-BTC, La-BPDC, La-BHTA, La-PMA, and La-BDC follows the pseudo-second-order kinetic model, and the kinetic rate-limiting step of adsorption is chemical adsorption. Thermodynamics revealed that temperature is favorable for the adsorption of fluoride. Meanwhile, La-BTC, La-BPDC, La-BHTA, La-PMA, and La-BDC are suitable for the removal of fluoride in a relatively wide pH range (4.0-9.0). Simultaneously, from X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR) analysis, electrostatic attraction and ligand exchange are identified as the main action mechanisms for the adsorption of fluoride of La-MOFs. The prepared La-MOFs are used as efficient adsorbents for removal of fluoride in actual water, indicating that they have great potential in removing fluoride in real and complex environmental water. This work provides a new strategy for designing adsorbents with adjustable microstructure and expected function to effectively recover fluorosis in water.
A novel Fe-Al-La composite adsorbent was synthesized via the co-precipitation method for water defluorination. The adsorbent was characterized by XRD, BET, SEM/EDS, and FT-IR. Its adsorption behavior was thoroughly carried out to investigate the fluoride removal performance in synthetic and real groundwater samples. The Langmuir model was found to describe the adsorption isotherm, presenting a maximum adsorption capacity of 28.06 mg g⁻¹ at 298 K and pH = 8.25. The adsorbent material's fluoride removal performance can be associated with the synergistic effect of some properties such as amorphous structure, porosity, and Fe-Al-La interactions in the surface material. The linear driving force model was successfully used for describing the adsorption capacity with a surface diffusion ranging from 3.52 to 5.928 ×10-9 cm² s⁻¹. Results showed that the new composite might be applied to remove fluoride from water aiming at human consumption, achieving the established permissible limit for Water Health Organization (<1.5 mg L⁻¹).
Efficient elimination of fluoride from wastewater is an urgent need for ensuring water safety. In the present study, a stable and reusable nanocomposite ([email protected]) was synthesized by impregnating nanosized cerium oxides (NCO) inside a porous polystyrene anion exchanger (PAE) host for efficient fluoride removal from wastewater. The newly fabricated [email protected] exhibited excellent resistance to acid and alkali environment, allowing it to be utilized in a wide pH range (2–12). Fluoride uptake onto [email protected] was a pH-dependent process, which could reach the maximum capacity at pH 3.0. Compared with its host PAE, [email protected] showed conspicuous adsorption affinity towards fluoride in the coexistence of other competing anions at high concentrations. Adsorption kinetics confirmed its high efficiency for achieving equilibrium within 120 min. Fixed-bed adsorption runs demonstrated that the effective processing capacity of [email protected] for synthetic fluoride-containing wastewater (initial fluoride 2.5 mg/L) was about ∼330 BV (bed volume), while only 22 BV for the host PAE. The exhausted [email protected] could be effectively revived by a simple in-situ desorption method for long-term cycle operation without conspicuous capacity loss. All the results indicated that [email protected] is a reliable and promising adsorbent for water defluoridation.
In this paper, CaAl hydrotalcite or hydroxyapatite decorated invasive plant (Solidago canadensis)-derived biochar were synthesized by co-precipitation and high temperature pyrolysis method. The three composites and bare biochar were characterized by Scanning electron microscopy (SEM), X-ray spectroscopy (EDX), the Fourier transform infrared spectroscopy (FT-IR), X-ray diffractometer (XRD), and X-ray photoelectron spectroscopy (XPS) techniques, and employed to remove Eu(III) from wastewater under a series of environmental conditions. The results indicated that the Eu(III) adsorption on [email protected]@HAP was higher than that on BC, [email protected], and [email protected], and belonged to multi-layer adsorption, which was different from the monolayer adsorption of biochar. The adsorption could be fitted best by Langmuir model and the maximum adsorption capacity of Eu(III) on [email protected]@HAP was up to 714 mg/g at pH∼6. The characterization results suggested that this excellent adsorption of [email protected]@HAP arose from the abundant P-, C-, O-containing functional groups rather than larger specific surface area. The spectra of XPS, FT-IR, and XRD uncovered that the adsorption mechanisms of Eu(III) on [email protected]@HAP involved surface complexation, ion exchange, and precipitation. Moreover, the absorbed Eu(III) was formed into two precipitate induced by P-containing groups and carbonate groups. This research confirmed [email protected]@HAP is a promising material for the removal of Eu(III) in wastewater.
Fluoride removal is an urgent problem in the field of water treatment. In this study, fluoride adsorption was performed using Ca-Modified Mg-Zr Mixed Metal Oxides (CCMZ), which was successfully prepared by a green hydrothermal process followed by high-temperature calcination. CCMZ was prepared using a lamellar MgO and ZrO2 Mixed Metal Oxide (MMO). Then, calcium (Ca, a strong fluorophilic metal) was dispersed over the MMO, to form a 3D spongy structure. The obtained microstructural features significantly enhanced the fluoride migration and diffusion, resulting in an adsorption capacity of 144.05 mg/g. The agglomeration of the products was effectively avoided, so CCMZ showed good selectivity and reusability. Batch adsorption experiments and subsequent sample characterization showed that the fluoride adsorption mechanism of CCMZ involved electrostatic attraction and ion exchange mechanism. Therefore, this manuscript provides a rational design and a simple preparation method for a new class of fluoride adsorbents.
The co-occurrence of arsenic and fluoride in the water environment has led to many health concerns for living beings. Simultaneous removal of such ions is crucial to the safety of water resources, and biochar has been extensively engaged to address this issue. Here four magnetic biochars (mBCs) including pristine magnetic biochar and three aluminum (Al) and/or magnesium (Mg) oxides-anchored magnetic biochar (i.e., Al-mBC, Mg-mBC, and MgAl-mBC) were prepared via a facile pyrolysis method and then comprehensively evaluated as adsorbents for enhanced co-uptake of arsenate (AsV) and fluoride (F⁻) from synthetic water. The mBC shows a high specific surface area of 205 m² g⁻¹, which dropped to 116, 80, and 114 m² g⁻¹ upon the anchoring of Al, Mg, and Mg + Al, respectively. Our results suggest that the adsorption of either AsV or F⁻ is highly pH-dependent, and pH 4–6 is the optimal range for maximum adsorption. The adsorption isotherm data indicate that the MgAl-mBC adsorbent outranks all other mBCs for co-uptake of both AsV and F⁻. The adsorption capacity maxima of MgAl-mBC are 34.45, and 21.59 mg g⁻¹ for AsV and F⁻, respectively (pH = 5, T = 10 °C), also highly outstripping other biochars reported in the literature. The magnetic feature of these mBCs enables us to fast reclaim and regenerate the exhausted adsorbents by an external magnet and dilute NaOH. The Al- and Mg-anchored mBCs are expected to be used as highly efficient adsorbents for environmental remediation of waters contaminated by both AsV and F⁻.
Cadmium (Cd) due to its strong toxicity and high mobility, which poses a considerable threat to soil environment and human health, has aroused widespread concern. Biochar has been used for remediating Cd-contaminated soil recently, however this method has the risk of fixed-Cd re-release. Phytoremediation can make up for its shortcoming. In this study, a pot experiment was carried out, where Bidens pilosa L. (B.pilosa) was as the tested plant and biochars (maize straw biochar and wheat straw biochar with two particle sizes) were as amendments. The mechanism of how biochars promoted B.pilosa Cd accumulation in Cd-contaminated farmland soil was explored. Results showed that the application of 5% wheat straw fine biochar (WF), wheat straw coarse biochar (WC), maize straw fine biochar (MF) and maize straw coarse biochar (MC) increased the total Cd accumulation of B.pilosa to 251.57%, 217.41%, 321.64% and 349.66%, respectively. Biochars amendment significantly promoted B.pilosa growth and increased Cd accumulation by improving soil physical properties, nutrient levels (available nitrogen, available phosphorus (AP), available potassium (AK) and organic matter (OM)) and microbial activity, and changing the nutrients distribution in B.pilosa organs although tissues although DTPA-Cd reduced to some extent. The effect of MF on AP increase was better than MC, while the effect of WF on AK increase was better than WC. Fine-particle was superior to coarse-particle in increasing B.pilosa biomass of aboveground, OM and microbial activity in soil. The changes of N, P and K concentrations in B.pilsosa roots, stems and leaves were closely related to the changes of AN, AP and AK in soil after biochars application. The results indicated that the combination of straw biochars and hyperaccumulators had the synergistic effect. This study can provide data support and meaningful reference values for remediating actual Cd-contaminated soil.
A novel strategy of room-temperature synthesis of MIL-100(Fe) with organic amine as deprotonating agent was proposed. The as-prepared solid product was denoted as R-MIL-100(Fe). The material was systematically characterized via XRD, FT-IR, XPS and SEM. The effects of operation parameters such as initial fluoride concentration, reaction time, initial pH and co-existing anions on the fluoride adsorption performance of the synthesized R-MIL-100(Fe) were studied. The maximum fluoride adsorption capacity of R-MIL-100(Fe) was as high as 23.53 mg/g at 298 K in the fluoride solution. The results indicate that the adsorption process of fluorine on R-MIL-100(Fe) belongs to surface adsorption and intraparticle diffusion. An excellent fluoride adsorption performance of R-MIL-100(Fe) was observed in a wide pH range of 4-10. The co-existing anions including Cl⁻, NO3⁻ and SO4²⁻ almost had no negative effects on the adsorption performance of R-MIL-100(Fe). However, the present of CO3²⁻ or HCO3⁻ brought an obvious reduction of F⁻ adsorption capacity of R-MIL-100(Fe). Thermodynamic study results illustrate that the adsorption process was an exothermic chemisorption. Chemical combination of iron and fluorine was confirmed by FT-IR and XPS. The strong combination brings the excellent F⁻ adsorption performance of MIL-100(Fe). R-MIL-100(Fe) was successfully regenerated and recycled five cycles with an excellent regeneration ability and recyclability.
Phosphate is a primary plant nutrient, serving integral role in environmental stability. Excessive phosphate in water causes eutrophication; hence, phosphate ions need to be harvested from soil nutrient levels and water and used efficiently. Fe-Mg (1:2) layered double hydroxides (LDH) were chemically co-precipitated and widely dispersed on a cheap, commercial Douglas fir biochar (695 m²/g surface area and 0.26 cm³/g pore volume) byproduct from syn gas production. This hybrid multiphase LDH dispersed on biochar (LDHBC) robustly adsorbed (∼5 h equilibrium) phosphate from aqueous solutions in exceptional sorption capacities and no pH dependence between pH 1-11. High Langmuir sorption capacities were found for both LDH (154 to 241 mg/g) and LDH-modified biochar (117 to 1589 mg/g). LDHBC was able to provide excellent sorption performance in the presence of nine competitive anion contaminants (CO3²⁻, AsO4³⁻, SeO4²⁻, NO3⁻, Cr2O7²⁻, Cl⁻, F⁻, SO4²⁻, and MoO4²⁻) and also upon remediating natural eutrophic water samples. Regeneration was demonstrated by stripping with aqueous 1 M NaOH. No dramatic performance drop was observed over 3 sorption-stripping cycles for low concentrations (5 ppm). The adsorbents and phosphate-laden adsorbents were characterized using Elemental analysis, BET, PZC, TGA, DSC, XRD, SEM, TEM, and XPS. The primary sorption mechanism is ion-exchange from low to moderate concentrations (10-500 ppm). Chemisorption and stoichiometric phosphate compound formation were also considered at higher phosphate concentrations (>500 ppm) and at 40 °C. This work advances the state of the art for environmentally friendly phosphate reclamation. These phosphate-laden adsorbents also have potential to be used as a slow-release phosphate fertilizer.
Graphene oxide possesses appreciable defluoridation capacity (DC) of 2451 mgF⁻ kg⁻¹. To enhance the DC and its properties, amine functionalized graphene oxide (AGO) was developed for fluoride removal. In addition, the prepared AGO have the vital defluoridation capacity (DC) of 4001 mgF⁻ kg⁻¹. The sophisticated instrumentations techniques namely SEM, TGA, FTIR, XRD, XPS and Raman analysis were explored for AGO and individual materials. The optimization of the responsible parameters (shaking time, solution pH, AGO dosage, interfering anions, temperature and initial fluoride ion concentration) for fluoride adsorption was employed under batch condition. The influence of adsorption isotherms (Freundlich, Dubinin-Radushkevich (D-R) and Langmuir), kinetics (particle/intraparticle diffusion and pseudo-first/second-order models) and thermodynamic studies (ΔH°, ΔS° and ΔG°) of defluoridation by AGO was investigated. The fluoride removal mechanism of AGO was found to be electrostatic attraction. The reusability and field study of AGO was also scrutinized.
In this study, fluoride removal from polluted potable water using magnetic carbon-based adsorbents derived from agricultural biomass was thoroughly investigated. An experimental matrix is designed considering the interactive effects of independent process variables (pH, adsorbent dose, contact time, and initial fluoride concentration) on the removal efficiency. Isotherms and kinetics studies, as well as anions interactions, were also investigated to understand the adsorption mechanisms further. The model parameters of isotherms and kinetics are estimated using nonlinear differential evolution optimization (DEO). Approaches like adaptive neuro-fuzzy inference system (ANFIS) and response surface methodology (RSM) are implemented to predict the fluoride removal and identify the optimal process values. The optimum removal efficiency of GAC-Fe3O4 (89.34%) was found to be higher than that of PAC-Fe3O4 (85.14%). Kinetics experiments indicated that they follow the intraparticle diffusion model, and adsorption isotherms indicated that they follow Langmuir and Freundlich models. Both PAC-Fe3O4 and GAC-Fe3O4 adsorbents have shown an adsorption capacity of 1.20 and 2.74 mg/g, respectively. The model predictions from ANFIS have a strong correlation with experimental results and superior to RSM predictions. The shape of the contours depicts the nonlinearity of the interactive effects and the mechanisms in the adsorption process.
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.
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.
To reveal the adsorption mechanisms of imazamox, imazapic, and imazethapyr on sediment and batch experiments were carried out in this study. The adsorption kinetics of three imidazolinone herbicides on sediment were accurately described by the pseudo-second-order kinetic model(R²>0.9004). The values of adsorption capacity (Qe.cal) were ranged from 0.0183 to 0.0859 mg/kg for three herbicides. Adsorption equilibrium was reached within 24 h for three herbicides on sediment, and well fitted by the Freundlich model(R²>0.9561). The KF of values for adsorption obtained sediment samples were ranged from 0.2501 to 1.322 L1/n mg1-1/n kg⁻¹for three herbicides. These results indicated that intraparticle diffusion and external mass transport were the main rate controlling steps of the adsorption of herbicides on sediment and that the chemical adsorption was dominant during the adsorption processes. The calculated hysteresis coefficient H were 0.9422,0.7877 and 0.744 for imazmox, imazapic and imazethapyr in raw sediment, respectively, indicating that there is a hysteresis in desorption. The influences of solution pH and sediment organic carbon content on the imidazolinone herbicide adsorption behaviors were also examined. Which shown that the adsorption process for herbicides was highly pH-dependent and adsorption efficiency was closely related to the organic matter content of the sediment, suggesting that electrostatic interactions played crucial roles in the adsorption behavior between sediment and imidazolinone herbicides, and the herbicides were mostly absorbed by the amorphous materials of sediment. These research findings are important for assessing the fate and transport of imidazolinone herbicides in water–sediment systems.
Ni/Al2O3 spherical catalysts were prepared by high shear mixer (HSM)-assisted coprecipitation (CP) and spray drying (SD) method for carbon monoxide (CO) and carbon dioxide (CO2) methanation. The effect of HSM technology on low-temperature methanation performance was studied. Ni/Al2O3 (HSM-CP-SD) catalysts provide excellent performance such as CO conversion of 100% and CH4 selectivity of 90% at 300 °C; the CO2 conversion was 86.2% and CH4 selectivity was 95.3% at 350 °C. Even at 200 °C, the catalyst prepared by HSM still offers a CO conversion of 90% and CH4 selectivity of 82%, whereas the Ni/Al2O3 (CP-SD) has no activity. The high performance was attributed to the small Ni nanoparticles and high dispersion. The Ni/Al2O3 (HSM-CP-SD) catalysts exhibit micro-spherical morphology with a big pore size of 3.46 nm, stronger metal-support interactions, and CO adsorption capacity. The catalyst prepared by HSM shows potential application for CO/CO2 methanation, and HSM technology can optimize other heterogeneous catalytic reactions.
To deal with the drinking water safety caused by fluoride, a novel carboxylated polyacrylonitrile nanofibrous membrane (C-PAN NFM) is designed and fabricated massively for the first time by adopting synchronously biaxial stretching and carboxylation. The C-PAN NFM is composed of the layered stack structure by cross-linked nanofibers. Due to its high specific surface area, excellent hydrophilicity, a large amount of carboxyl and amine groups, C-PAN NFM owns high fluoride adsorption capacity and outstanding selectivity. Both the carboxylation and acid treatment of C-PAN NFM improved the fluoride adsorption capacity remarkably. Specifically, C-PAN NFM shows excellent reusability without secondary pollution. The fluoride adsorption behavior of C-PAN NFM is dominated by chemical adsorption, and the adsorption mechanism is mainly driven by hydrogen bonding and ion exchange. The mass-produced C-PAN NFM is a novel polyacrylonitrile-based porous membrane that shows a great application potential for fluoride removal with good efficiency and recyclability.
In drinking water treatment, sand filters are frequently used to remove turbidity. We enhanced the performance of the sand by a chemical modification using graphite oxide (GO). Repeated coating of sand granules with graphite oxide (GO) followed by low temperature (120 ⁰C) pyrolysis yielded hierarchical core-shell structures. The sand granules can be coated with GO in a single (hereafter S-GO1) or multiple (presently five cycles, hereafter S-GO5) coating steps. The GO coated sand composites were characterized using spectroscopic, microscopic, and conventional techniques. When compared to S-GO1, the GO coatings on S-GO5 show enhanced stability in contact with water. The S-GO5 removes over 70% fluoride around pH 6.30±0.02 according to Hill adsorption model. We also used a simulated water sample to assess the efficacy of sand/GO composites to remove fluoride and turbidity. When S-GO5 is used, the solution turbidity has reduced by 87% (from 0.08 to 0.01 NTU). However, in the presence of S-GO1, the turbidity has increased by + 75% (from 0.08 to 0.14 NTU). The gradual dissolution of adhered GO on S-GO1 enhanced the turbidity of treated water. The S-GO5 can be used to regulate excess fluoride and turbidity in water, simultaneously.
Biosynthetic crystals (BC) were prepared through microbially induced calcium carbonate precipitation (MICP) for fluoride (F⁻) removal from the groundwater. Batch experiments were conducted to evaluate the fluoride adsorption capacity and the impacts of critical factors (organic matter, pH, initial fluoride concentration and BC dosage) on defluorination efficiency of BC. The maximum adsorption amount and defluorination efficiency were recorded as 5.10 mg g⁻¹ and 98.24%, respectively. The adsorption kinetics and isotherms studies showed that pseudo-second-order kinetic model and Freundlich isotherm model were best fitting to the reaction. Adsorption thermodynamic parameters indicated a spontaneous, endothermic and thermodynamically favorable adsorption process. Moreover, the mechanism of F⁻ removal by BC was further analyzed by SEM, XPS, XRD and FTIR. The method can cope with the problem of applying the external organic substances in MICP, and avoid the microbial safety risk in the effluent. As an economically and environmentally friendly adsorbent, BC can be used for F⁻ removal from groundwater.
Invasive plants harm ecosystems and human health due to their strong environmental adaptability, fast reproduction and spreading capabilities. Management of invasive plants, therefore, attracted more and more attention recently. Biochar is a carbon-rich solid substance formed by pyrolyzing organic substances under low or limited oxygen conditions. It has high aromaticity and strong resistance to decomposition and is widely used in agriculture, environment, energy, and other fields. As a special raw material, the high diversity and wide distribution make invasive plants ideal feedstocks for biochar production. Pyrolysis of invasive plants to prepare biochar not only realizes the protection of ecosystemsbut also benefits human health. In addition, compared with traditional biochar, invasive plant-derived biochar (IP-DB) showed significant differences in structure, composition, and adsorption performance. As an economical and easily available adsorbent, IP-DB has been gradually used in environmental remediation and agricultural soil amendment, but there are relatively few reports compared with other types of biochar, and the research is scattered. Therefore, it is necessary to review the potential of invasive plants to prepare biochar and its application value. Here we make a review on current research status of invasive plants, focusing on their potential for biochar productions and applications. Based on these reviews, we proposed possible future development in this research field, which could serve as theoretical basis for further researches.
Adsorption of fluoride from aqueous solutions by aluminum-impregnated biochar derived from food waste (Al-FWB) was studied. The individual and interactive effects of various factors on fluoride adsorption, including pyrolysis temperature and time, and aluminum content, were investigated. The optimum conditions for the synthesis of Al-FWB, predicted through a Box–Behnken-based response surface methodology model, which were as follows: a temperature of 315 °C, time of 0.65 h (39 min), and an aluminum content of 5.89%. Batch experiments were conducted to assess the feasibility of using Al-FWB for fluoride removal, and its mechanism. The Langmuir isotherm model and pseudo-second-order kinetics proved to be the best fit for the equilibrium data, with a maximum adsorption capacity of 123.4 mg/g. Thermodynamic results revealed a spontaneous endothermic reaction for fluoride adsorption. The Al-FWB showed a superior removal efficiency (91.4%) in a wide pH range (5–11) due to its pH buffering capacity during the adsorption process. The influence of co-existing anions on the fluoride adsorption was as follows: PO4³‾ > SO4²‾ > HCO3‾ > NO3‾. Therefore, Al-FWB can be used as an effective adsorbent to remove fluoride from aqueous solutions.
Fluoride contamination in water environment due to natural and artificial activities has been recognized as one of the major problems worldwide. Developing effective and robust technologies for excess fluoride removal from water environment becomes highly important. Among the commonly used treatment technologies applied for fluoride removal, adsorption technique has been explored widely and offers a highly efficient simple and low-cost process for fluoride removal from water. This review reports the recent developments in fluoride removal from water environment by adsorption methods. Studies on fluoride removal from aqueous solutions using various carbon materials are reviewed. It is evident that various adsorbents with high fluoride removal capacity have been developed, however, there is still an urgent need to transfer the removal process to industrial scale. Regeneration studies need to be performed in more extent to recover the adsorbent in field conditions, enhancing the economic feasibility of the process. Based on the review, four technical strategies of adsorption method including nano-surface effect, structural memory effect, anti-competitive adsorption and ionic sieve effect can be proposed. The design of adsorbents through these four strategies can greatly improve the removal efficiency of fluoride in water and provide guidance for the development of new efficient methods for fluoride removal in the future.
Exotic invasive plants endanger the integrity of agricultural and natural systems throughout the world. Thus, the development of cost-effective and economic application of invasive plants is warranted. Here, we characterized fifteen biochars derived from five invasive plants at different temperatures (300, 500, and 700 °C) by determining their yield, ash content, pH, CEC, surface area, elementary composition, functional groups, and mineral composition. We conducted batch adsorption experiments to investigate the adsorption capacity and efficiency for Cd²⁺ and Cu²⁺ in wastewater. Our results suggest that all invasive plants are appropriate for biochar production, temperature and plant species had interacting effects on biochar properties, and the biochars pyrolyzed at 500 and 700 °C exhibited high metal adsorption capacity in neutral (pH = 7) solutions. The adsorption kinetics can be explained adequately by a pseudo-second-order model. BBC500 (Bidens pilosa L. derived biochar at 500 °C) and MBC500 (Mikania micrantha) exhibited higher metal equilibrium adsorption capacities (38.10 and 38.02 mg g⁻¹ for Cd²⁺, 20.01 and 20.10 mg g⁻¹ for Cu²⁺) and buffer abilities to pH than other biochars pyrolyzed at 500 °C. The Langmuir model was a better fit for IBC500 (Ipomoea cairica), MBC500, and LBC500 (Lantana camara L.) compared to the Freundlich model, whereas the opposite was true for BBC500 and PBC500 (Praxelis clematidea). These results suggest that the adsorption of metals by IBC500, MBC500, and LBC500 was mainly monolayer adsorption, while that by BBC500 and PBC500 was mainly chemical adsorption. Our results are important for the utilization and control of invasive plants as well as the decontamination of aqueous pollution.
Phytoremediation, especially phytoextraction, is a good alternative for remediation of soils contaminated with heavy metals. This method requires selection of species for their tolerance, high accumulation levels in harvestable parts, and high biomass production. Bidens pilosa L. has been reported as tolerant to and potentially hyperaccumulator of several heavy metals, including Pb, but with variable results in terms of effectiveness. The aim of this study was to analyse the intra- and interpopulation variability of B. pilosa in response to Pb in individuals from two populations: one historically exposed to Pb and another with no history of exposure. Bidens pilosa L. presented tolerance to Pb pollution in soil, evidenced in a higher survival rate, a better antioxidant response, and an efficient reduction in cell membrane damage mainly due to history of exposure. The period of exposure (30 years) was not long enough to obtain a B. pilosa population that provides seeds for phytoextraction projects, since the average value of total extraction was relatively low. Collecting seeds from a historically exposed population will provide some suitable individuals with Pb accumulation and translocation capabilities, but not a sufficient amount to conduct a large phytoremediation project. The individual accumulator profile of B. pilosa is not related to the physiological behaviour or to the Pb entry into the vascular bundle in root, but to the incorporation of other heavy metals that are micronutrients.
High levels of fluoride, though, naturally occurring (which can reach as high as 2,800 mg F−/L) in the environment can be toxic to various living organisms. Moreover, it can be transported by water and by its confluences and exacerbated by anthropogenic activities making it an environmental and public health concern. World Health Organization has set the standard for drinking water at 1.5 mg F−/L while the average national effluent standard is 15 mg F−/L. Hence, different defluoridation techniques of aqueous solutions were developed in the past years. This study provides an overview of the popular methods in defluoridation (i.e. adsorption, ion-exchangers, precipitation, membrane, electrocoagulation, and electro-dialysis). The mechanisms, critical operational conditions, and research progress are presented. The results further reveal that adsorption, regarded as the primary technique for defluoridation, still needs further development and mostly on its bench-scale and is only proven effective at low initial concentrations. In this study, sorption techniques are also estimated to be 10 to 20 times more expensive in operational costs relative to the other treatments. Furthermore, the majority of the examined literature demonstrated defluoridation at limited initial concentration <100 mg F−/L. In contrast, industrial effluents may reach 250–1,000 mg F−/L (up to ∼10,000 mg F−/L at extreme cases). Inadequate removal of fluoride in water by single treatment also compels researchers to explore hybrid treatments. In addition, due to the lack of wastewater treatment facilities requiring high capital cost, bioremediation, a commonly overlooked alternative, is presented for temporarily alleviating fluoride levels. Finally, challenges such as limited literature for disposal of secondary pollution and cost evaluation along with other potential research perspectives are further discussed.
We evaluated Mytilus coruscus shells (MCS) as an adsorbent for fluoride removal. Its removal efficiency was enhanced by thermal treatment and MCS at 800 °C (MCS-800) increased significantly its fluoride adsorption capacity from 0 to 12.28 mg/g. While raw MCS is mainly composed of calcium carbonate (CaCO3), MCS-800 consisted of 56.9% of CaCO3 and 43.1% of calcium hydroxide (Ca(OH)2). The superior adsorption capacity of MCS-800 compared to untreated MCS can be also explained by its larger specific surface area and less negative charge after the thermal treatment. X-ray photoelectron spectroscopy and X-ray diffraction analysis revealed that the fluoride adsorption of MCS-800 occurred via the formation of calcium fluorite (CaF2). Fluoride adsorption of MCS-800 approached equilibrium within 6 h and this kinetic adsorption was well-described by a pseudo-second-order model. The Langmuir model was suitable for describing the fluoride adsorption of MCS-800 under different initial concentrations. The maximum fluoride adsorption amount of MCS-800 was 82.93 mg/g, which was superior to those of other adsorbents derived from industrial byproducts. The enthalpy change of fluoride adsorption was 78.75 kJ/mol and the negative sign of free energy indicated that this phenomenon was spontaneous. The increase of pH from 3.0 to 11.0 slightly decreased the fluoride adsorption capacity of MCS-800. The adsorption was inhibited in the presence of anions and their impact increased with following trend: chloride < sulfate < carbonate < phosphate. The fluoride adsorption capacities of MCS-800 after washing with deionized water and 0.1 M NaOH were reduced by 31.5% and 57.4%, respectively.
Global expansion of invasive plant species has caused serious ecological and economic problems. Two such invasive species, ragweed and horseweed, were pyrolyzed at temperatures of 350, 450 and 550 ℃ for biochar production (RB350, RB450, RB550 and HB350, HB450, HB550). The biochars produced were used for Cd(Ⅱ) and Pb(Ⅱ) removal in aqueous solutions. The results indicated that the properties of the biochars varied with pyrolysis temperature, which further affected their adsorption performance. The maximum adsorption capacity of RB450 for Cd(Ⅱ) (139 mg·g⁻¹) and Pb(Ⅱ) (358.7 mg·g⁻¹) was much higher than that shown in previous studies. The immobilized Cd(Ⅱ) and Pb(Ⅱ) fraction on RB450, RB550, HB450 and HB550 was mainly attributable to the acid soluble and non-available fractions. These findings suggested that pyrolysis of invasive plants at 450 ℃ could not only be an option to control invasive plants but also could be of benefit in using biochar as excellent adsorbent.
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 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 process 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 Al(OH)4⁻ and F⁻ species, as well as ion exchange between hydroxide and ionic metal species, is important mechanism in the process of aluminum and fluoride adsorption. Driving forces for adsorption of individual Al(OH)4⁻ and F⁻ to the adsorption are not entirely different. Identifying the dominant mechanism will be helpful in understanding the adsorption process and developing new adsorbent.
Biochar is a promising agent for wastewater treatment, soil remediation, and gas storage and separation. This review summarizes recent research development on biochar production and applications with a focus on the application of biochar technology in wastewater treatment. Different technologies for biochar production, with an emphasis on pre-treatment of feedstock and post treatment, are succinctly summarized. Biochar has been extensively used as an adsorbent to remove toxic metals, organic pollutants, and nutrients from wastewater. Compared to pristine biochar, engineered/designer biochar generally has larger surface area, stronger adsorption capacity, or more abundant surface functional groups (SFG), which represents a new type of carbon material with great application prospects in various wastewater treatments. As the first of its kind, this critical review emphasizes the promising prospects of biochar technology in the treatment of various wastewater including industrial wastewater (dye, battery manufacture, and dairy wastewater), municipal wastewater, agricultural wastewater, and stormwater. Future research on engineered/designer biochar production and its field-scale application is discussed. Based on the review, it can be concluded that biochar technology represents a new, cost effective, and environmentally-friendly solution for the treatment of wastewater.
Zirconium dioxide-biochar (ZrO2/BC) with excellent fluoride adsorption properties, was successfully prepared by calcining the zirconium-impregnated byproduct from Camellia oleifera (C. oleifera) seed shell in a one-step method. Compared with C. oleifera seed biochar, the zirconium-impregnated C. oleifera seed shell biochar can effectively adsorb fluoride in water. The adsorption process is consistent with a pseudo second-order kinetic model and the Langmuir adsorption isotherm. Fluoride adsorption was tested in solutions ranging from pH to obtain the best pH value for adsorption. The fluoride adsorption mechanism was better understood by Zeta potential analysis. Thermodynamic studies indicated that the adsorption process was a spontaneous endothermic reaction. Scanning electron microscopy (SEM), Energy-Dispersive Spectroscopy (EDS) and X-ray diffraction (XRD) analyses revealed that the morphology and crystal form of the ZrO2/BC were improved and that fluoride could be effectively absorbed. Fourier-transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS) were used to show how ZrO2 affects the surface of the zirconium-biochar and to show that the fluoride was removed from the water by ion exchange. This work can not only effectively remove fluoride from the water, but also reuse waste C. oleifera seed to reduce environmental pollution.
In this paper, Ce-AlOOH were investigated to develop as an adsorbent for removing fluoride. Oxalic acid was selected as an effectively modified reagent to improve the performance of adsorption. Cerium existed in the form of CeO2 and kept good stability during the adsorption process through XRD, TEM, BET, Raman, and Infrared spectra. The adsorption capacity could be improved with the addition of cerium (62.8 mg/g). Specially, the oxalic acid modification significantly promoted the adsorption capacity to 90 mg/g. There adsorption isotherm and kinetics were estimated independently. These adsorption behaviors were in accordance with the Freundlich model and pseudo-second-order model, indicating that chemisorption was the rate-determining step. the obtained adsorbents all exhibited good recycling performance using oxalic acid as the regeneration reagent. The species of tetravalent cerium was the important adsorption sites. The mechanism was carefully explored by XPS analysis. The fluoride adsorption process can be ascribed to the combined effect of the electrostatic action, surface coordination, and ion exchange between M-OH and F-. Furthermore, modification of oxalic acid exhibited a new easier way to quickly increase M-OH content, which contributed to the dominated adsorption sites.
The removal of F⁻ from aqueous solution using lanthanum and cerium modified mesoporous alumina (La/MA and Ce/MA) was studied, and characteration of the adsorbents by XRD, BET, XRF, FTIR, TEM, XPS and the pHZPC measurements were carried out. The adsorption was investigated in both batch and column adsorption systems. Batch experimental results showed that adsorption capacities of adsorbents were recorded in the following order: La/MA > Ce/MA > mesoporous alumina (MA). Besides, adsorption datas were fitted well by Sips isotherm model and Elovich kinetics model, and the maximum adsorption capacity of La/MA was 26.45 mg·g⁻¹ in Sips model at the dosage of 2.0 g·L⁻¹ and near neutral condition (pH = 6.0 ± 0.1). Moreover, thermodynamic parameters were illustrated that adsorption process of fluoride ion over La/MA was spontaneous and endothermic. In the adsorption process, the interaction between metal and fluoride, the adsorption capacity was increased due to form the bond of M···F (M = La or Ce). Furthermore, the influence of coexisted anions on F⁻ removal was investigated, and it was indicated that removal efficiency was slightly affected by the presence of Cl⁻ and NO3⁻, while SO4²⁻ and CO32– caused a sharp fall in removal efficiency. Column experiments results were indicated that time of break-through of La/MA was twice as much as that of MA.
Fluoride (Fˉ) has been renowned as one of the solemn problems in groundwater which causes severe health effects such dental and skeletal fluorosis in human being. Here we demonstrate, pectin biopolymer based binary metal oxide composite, which has been efficaciously employed as an adsorbent for Fˉ adsorption from water. A factorial design method was utilized to assess the quantitative adsorption of Fˉ ion by synthesized Pectin-Al-Fe (PAF) composite from aqueous solution. Three factors namely adsorbent dose, initial Fˉ concentration, and temperature were explored to study their effect on the adsorption of Fˉ. These experimental factors and their corresponding levels were as follow viz. adsorbent dosage (1 ≤ A ≤ 5.0 g/L), initial fluoride concentration (10 ≤ B ≤ 1000 mg/L), and temperature of solution (298 ≤ C ≤ 313 K). The experimental adsorption capacity values analyzed by adsorption isotherms and kinetic models were 243.9 and 286.90 mg/g, respectively, and the maximum monolayer adsorption capacity was found 333.0 mg/g. Thermodynamic investigations illustrated that the adsorption process was feasible, spontaneous, and exothermic, whereas, the nature of adsorption process was physisorption together with chemisorption. Altogether this study scrutinizes the novel synthesis of PAF biopolymer composite for the adsorption of Fˉ and it also added with factorial design method for the study of quantitative adsorption of Fˉ, which favors the batch adsorption experiment results. However, no literature has been reported yet which used the factorial design experiment and utilization of pectin biopolymer with bimetallic oxide entrapped adsorbent for Fˉ adsorption.
s
Zirconium phosphate (ZrP) has been developed as an efficient adsorbent, since the 1960s, but most research involving ZrP focuses on metal cation (e.g. K⁺/Ca²⁺/Pb²⁺/Cu²⁺) capture. Herein, we synthesized a ZrP nanoflake by simple in-situ precipitation procedures and successfully explored a new application area for it: fluoride scavenging. Completely different from the conventional metal oxides, the resultant ZrP exhibits good chemical stability in acidic or basic environments. More importantly, preferable fluoride uptake can be achieved at high concentrations of competitive anions (SO4²⁻/Cl⁻/NO3⁻) addition, exceeding that of commercial D201, activated Al2O3, manganese sands, etc. Kinetic results further demonstrate its efficiency for approaching equilibrium in 5 min. Furthermore, the actual application proves superior treatment capacities of approximately 1800 kg and 3900 kg for groundwater and acidic wastewater treatment, respectively and the exhausted materials can be readily regenerated using 5% NaOH solution for at least five cycles. XPS and FT-IR investigation reveal that the preferable fluoride adsorption can be ascribed to strong inner-sphere complexation achieved by ZrF bonds. All the results demonstrate that the representative ZrP nanoflake is an efficient and rapid fluoride-removing candidate for cleaning water.