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

Causative mechanisms limiting the removal efficiency of short-chain per- and polyfluoroalkyl substances (PFAS) by activated carbon

Short-chain per and polyfluoroalkyl substances (PFAS) have been found to be relatively high in water treatment systems compared to long-chain PFAS because of the unsatisfactory adsorption efficiency of short-chain PFAS. Knowledge about why short-chain PFAS are less removed by porous carbon is very limited. The study focused on providing causal mechanisms that link the low adsorption of short-chain PFAS and proposing an improved method for removing both short- and long-chain PFAS. The long-chain PFAS with higher hydrophobicity diffused more quickly than the short-chain PFAS due to stronger partitioning driving forces. In the initial adsorption stage, therefore, pores of activated carbon were blocked by long-chain PFAS, which makes it difficult for the short-chain PFAS to enter the internal pores. Although several short-chain PFAS diffuse into the pores, the relatively more hydrophilic short-chain congeners cannot be fully adsorbed on activated carbon due to limited positively charged sites. Moreover, compared to larger particle sizes, smaller activated carbon particles have shorter pore channels near the surface, reducing the risk of pore-blocking and ensuring the pores remain accessible for more efficient adsorption. Additionally, these smaller particles offer a greater external surface area and more functional groups, which enhance the adsorption capacity. It indicates that the smaller particle size of activated carbon would have a positive effect on the short-chain PFAS removal.

Bibliometric analysis and systematic review of fluoride-containing wastewater treatment: Development, hotspots and future perspectives

Water pollution with fluoride can cause dental fluorosis, skeletal deformities, and other diseases, posing serious harm to human health. To understand the development status, research hotspots, and frontier trends in fluoride-containing wastewater (FCW) treatment, this study employed bibliometric methods to visually analyze 2840 publications related to FCW treatment from the Web of Science Core Collection (WOSCC) database. The "bibliometrix" package in R language, VOSviewer, and CiteSpace visualization software were utilized for the analysis. The results revealed a fluctuating upward trend in the annual number of publications, indicating ongoing deepening and development of research in this field. India and China exhibited the strongest research capacity, forming a cooperation network centered around these two countries. High-impact journals such as Desalination and Water Treatment, Journal of Hazardous Materials, and Chemical Engineering Journal frequently publish research related to FCW treatment. Keyword co-occurrence and burst analysis revealed that the current research hotspots in FCW treatment primarily focus on treatment methods (ion exchange, chemical coagulation/precipitation, adsorption, electrochemical, membrane separation, and fluidized bed crystallization), adsorption mechanism, and adsorbent design and optimization. Future research will likely focus on developing efficient treatment technologies and adsorption materials for FCW, as well as the recovery of fluoride resources from FCW, highlighting a dual approach to environmental sustainability and resource management. By employing bibliometrics, this study outlines the development status of FCW treatment and predicts the field's future trends, providing insights for understanding the development trajectory of this field.

Innovative reuse of mineral waste for treatment of a contaminated soil by fluorine: synthesis of hydroxyapatite (HAP) and chemical performance assessments

This research aimed to introduce a novel method for the valorization of mineral waste, focusing on the development of hydroxyapatite (HAP) as an effective and economical adsorbent for immobilizing fluoride ions (F-) in soil. Hydroxyapatites were produced through the reaction between potassium dihydrogen phosphate (KH2PO4) and calcium-abundant limestone soil (CLS). X-ray diffraction analyses revealed that the primary phases in HAPCLS were brushite (CaHPO5·2H2O) and hydroxyapatite (Ca10(PO4)6(OH)2). The FTIR spectra exhibited characteristics akin to natural HAP, including the presence of orthophosphate groups (PO43-), hydroxyl groups (OH-), and both A/B types of carbonates in the apatite structure. The morphology of the synthesized HAP, as observed through SEM-EDS, was consistent with that of phosphocalcic hydroxyapatite crystals. The EDS results indicated a Ca/P atomic ratio of 1.7 for HAPCLS, aligning closely with the typical hydroxyapatite stoichiometry (Ca/P = 1.67). The application of HAP to reduce fluoride (F-) levels in soil proved to be successful; introducing 1% of various HAP formulations reduced the fluoride concentration from 51.4 mg/kg in untreated soil to levels below the IWSI limit (10 mg/kg), achieving a reduction to 8.1 mg/kg for HAPCLS. The sequential extraction of fluoride demonstrated that after soil treatment, fluoride was predominantly removed from the residual fraction (Fraction 4) and was effectively sequestered by the hydroxyapatites (Ca10(PO4)6(OH)2) through anionic exchange with hydroxide ions (OH-), resulting in the formation of stable and insoluble fluorapatite (Ca10(PO4)6F2).

Investigating the effectiveness of rice husk-derived low-cost activated carbon in removing environmental pollutants: a study of its characterization

The chemically activated biochar was produced through the pyrolysis of rice husk. Thermal gravimetric and elemental analysis were conducted to characterize the raw rice husk. The activated biochar product underwent evaluation through SEM, BET and, FT-IR analysis. This cost-effective activated carbon was utilized as an adsorbent for the elimination of environmental pollutants. At a temperature of 25 °C, the activated biochar product exhibited an impressive maximum CO2 adsorption capacity of 152 mg/g. This exceptional performance can be attributed to its notable surface area and porosity, measuring at 2,298 m2/g and 0.812 cm3/g, respectively. This product was also utilized to remove methyl red (MR) dye from an aqueous solution. The optimal parameters for the removal of MR were determined as follows: a pH of 6.0, a temperature of 25 °C, an initial MR concentration of 50 mg/L, and an adsorbent dosage of 0.4 g/L. At a duration of 140 min, the system attained its maximum equilibrium adsorption capacity, reaching a value of 62.06 mg/g. Furthermore, the calculated maximum MR removal efficiency stood at an impressive 99.31%. The thermodynamic studies demonstrated that the MR removal process was spontaneous, exothermic, and increased randomness. Kinetic studies suggested that the pseudo-second-order model can fit well.

Preparation of chitosan mesoporous membrane/halloysite composite for efficiently selective adsorption of Al(III) from rare earth ions solution through constructing pore structure on substrate

The removal of impurity Al(III) from rare earth ion solution by selective adsorption method was one of the challenging tasks. Herein, calcination and acid dissolution treatment were used to construct the pore structure for the halloysite substrate (Hal-650-H) and provide conditions for the formation of the chitosan mesoporous membrane to prepare composite (Hal-H-2CS). The selective adsorption properties and mechanism of the Hal-H-2CS for Al(III) in the rare earth ion solution were studied. The results showed that the formation of mesoporous structures for chitosan provided abundant sites for the adsorption of Al(III). Hal-H-2CS showed remarkable selective adsorption properties for Al(III) in a wide pH range and the binary mixtures with high content of Al(III) or La(III). The maximum adsorption capacity of Al(III) was 106 mg/g, while the adsorption capacity of La(III) was only 1.41 mg/g at pH 4.0. In addition, the Hal-H-2CS exhibited excellent regeneration and structural stability. The remarkable selective properties of Hal-H-2CS was achieved by the synergistic effect between chitosan mesoporous membrane and Hal-650-H, the main adsorption sites were the OH, NH2, CONH2 of chitosan and the oxygen sites of the Hal-650-H. This work provides a new strategy for the design and preparation of outstanding selective adsorbent for Al(III).

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.

Isotherm and kinetic investigations of sawdust-based biochar modified by ammonia to remove methylene blue from water

Chemical industry effluent may pose significant environmental risks to both human health and the economy if it is not properly managed. As a result, scientists and decision-makers are paying increasing attention to developing a sustainable, low-cost wastewater treatment technique. This work aims to investigate the adsorption of Methylene Blue (MB) dye present in water using biochar derived from sawdust modified by boiling in an ammonia solution (SDBA). The properties of SDBA were characterized by BET, SEM, XRD, BJH, FT-IR, DTA, EDX and TGA analyses. The presence of -OH and -NH groups in SDBA was confirmed by FTIR, which proved that the NH4OH treatment of biochar successfully added nitrogen groups on its surface. The influence of pH (2 to 12), MB dye initial concentration (20 to 120 mg/L), adsorbent dosage (0.5 to 4.0 g/L) and contact time (0 to 180 min) on the adsorption process has been investigated. The adsorption of MB dye is more favorable at basic pH, with optimum adsorption at pH 8. Using a starting concentration of 20 mg/L of MB dye and a 4.0 g/L SDBA dose, the maximum percent clearance of MB dye was 99.94%. Experimental results were fitted to the Freundlich (FIM), Tempkin (TIM) and Langmuir (LIM) isotherm models (IMs). The FIM fitted the equilibrium data well, with a 643.74 mg/g Qm. Various error function models were used to test the data obtained from IMs. According to Error Function results, experimental data showed that it fits better for LIM and FIM. Kinetic studies indicated that the MB dye adsorption procedure followed pseudo-second-order (PSOM) kinetics based on film diffusion (FDM), pseudo-first-order (PFOM) and intra-particle diffusion models (IPDM). MB dye sorption on the SDBA involved electrostatic interaction, surface participation, hydrogen bond and π-π interactions. The adsorption mechanism of MB dye by SDBA was proposed as physical adsorption via the electrostatic attraction process. SDBA is an effective adsorbent in removing MB dye from water. Six adsorption-desorption cycles of the MB dye were run through the regeneration of SDBA with only a minimal amount of adsorption capacity loss, demonstrating the reusability of manufactured SDBA.

In-situ modified biosynthetic crystals with lanthanum for fluoride removal based on microbially induced calcium precipitation: Characterization, kinetics, and mechanism

In this research, in-situ modified biosynthetic crystals with lanthanum (BC-La) were synthesized based on anaerobic microbially induced calcium precipitation (MICP) and investigated its capacity for groundwater defluoridation under various operational conditions. The kinetic and thermodynamic models were simulated to explore the effect of the material on the removal of fluoride ion (F^-) under various parameters (pH, initial concentration of F^-, and temperature). BC-La had the maximum F^- adsorption capacity of 10.92 mg g^-1 and 96.66% removal efficiency. The pseudo-second-order kinetic model and Langmuir isotherm model were the best kinetic and isotherm models for F^- removal from BC-La, which indicated that F^- were mainly spontaneously removed through chemisorption and adsorption processes. The specific surface area was 54.26 m² g^-1 and the average pore size was 9.0670 nm. BC-La mainly contained LaCO₃OH, LaPO₄, CaCO₃, Ca₅ (PO₄)₃OH, and F^- was mainly removed through ion exchange with the material surface. Moreover, OH^-, PO₄^3-, and CO₃^2- significantly influenced the F^- removal. This work suggested a novel method for in-situ modification of anaerobic biosynthetic crystals, which improved the defluoridation effect of traditional biosynthetic crystals, increased the stability of the BC-La and allowed to remove F^- from groundwater consistently.

Effective removal of fluoride ions from aqueous solution by marine microalgae as natural biosorbent

In this study, the phytoremediation technology from marine source Dunaliella salina was chosen to eliminate fluoride ions from aqueous solution by Adsorption isotherm, Kinetics and RSM optimization methods. Marine microalgae were collected, identified and mass cultured then its physical characteristics, functional groups and surface microstructure was examined by FT-IR, NMR, XRD and SEM analysis also the same was performed on post treated bioadsorbent. Fluoride removal was optimized by different conditions through response surface methodology and kinetics modelling also performed. Several active functional groups were noticed in IR spectra and NMR of pre and post treated microalgal biosorbent. Many micropores, crystalline structure, voids were observed in pre-treated and lesser in post treated bioadsorbent, removal process was optimized by temperature, pH, dose and time and its showed high influence of removal process. The fluoride removal process was optimized by response surface methodology, Langmuir Isotherm, Freundlich Isotherm, Temkin isotherm, Pseudo I order, Pseudo II order and Intra particle diffusion and revealed that the F ions removal mechanism clearly. Microalgae are novel, low-cost and effective bio based innovative methods which are sustainable for the bioremediation of fluoride from water bodies and industrial wastewaters.

Removal of fluoride using platanus acerifoli leaves biochar - an efficient and low-cost application in wastewater treatment

The fluoride with high-concentration in industrial wastewater will cause great harm to the environment and calcium-modified biochar is an effective adsorbent for the removal of fluoride. Biochar composites were prepared from mature and dried dead leaves and eggshell to remove fluoride from the aqueous solution. The effects of raw material ratio, pH, contact time, adsorbent dosage, temperature, initial concentration of fluoride, and the coexisting ions on the removal efficiency of fluoride were explored. The biochar composites before and after fluoride removal were characterized by the SEM, FTIR, XRD, and XPS, which showed CaF₂ precipitation was formed during the adsorption. The kinetics and isotherm study showed that chemical adsorption was the primary step for the fluoride adsorption of the biochar composites. The removal efficiency of fluoride can reach 98.53% when the amount of adsorbent was 1.6 g/L and the fluoride concentration was 500 mg/L. The BET-specific surface area of platanus acerifoli leaves biochar was 410.14 m²/g, which was suitable for the adsorption carrier. The adsorption capacity of the biochar composite materials was as high as 308 mg/g. The platanus acerifoli leaves-eggshell biochar composite with large pore size and high removal efficiency may be used as an efficient and low-cost adsorbent for treating high-concentration fluoride-containing wastewater.

A comprehensive review on the coagulant recovery and reuse from drinking water treatment sludge

The main treatment unit in conventional systems for surface water is coagulation-flocculation (CF) process, which consumes huge quantities of coagulant, and produces large volume of sludge. The produced sludge is known as one of the components of water treatment sludge (WTS), which is considered as a global issue and hot topic require careful attention from the plant operators and sludge managers to be managed sustainably with applying an ecofriendly method. Among the suggested technologies, recovery and reuse of coagulants from WTS show the potential to decrease the waste disposal and chemicals usage for drinking water treatment significantly. So, this comprehensive review provides a useful insight into environmental and health problems of WTS, reports the sources, physicochemical properties of sludge, describes different sludge management methods by more focus on coagulant recovery (CR), which significantly point out the different aspects of WTS recovery and reuse, and eventually, economic evaluation of the CR process was also discussed. The results of this review confirm that coagulants can be recovered from WTS by different methods and also will be reused for multiple times in the removal of pollutants from water and wastewater. Moreover, the recovered coagulants can be used as building and construction materials, constructed wetlands substrate and other aims.

Conversions of Cement bypass waste to Nano-hydroxyapatite exploited in water purification.. [DOI: 10.21203/rs.3.rs-1871491/v1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

The goal of this study is to convert cement bypass dust into a usable product called hydroxyapatite. Four hydroxyapatites’ samples (Kiln-HA1- Kiln-HA4) were successfully prepared in nano-scale (14.8–25.7 nm). The specific surface areas of all of the samples examined were high: Kiln-HA3 (161.5 m2/g) > Kiln-HA1 (130.2 m2/g) > Kiln-HA2 (81.9 m2/g) > Kiln-HA4 (54.1 m2/g).Tested nano- hydroxyapatite successfully removed Fe3+ and Mn2+ as pollutants from water with efficiencies of up to 95% for both Fe and Mn ions. The maximum adsorption capacities (qmax) of nano hydroxyapatite varied from 147 to 175 mg.g− 1 for adsorbed Fe (III), while were wide ranged from 204 to 344 mg.g− 1 for adsorbed Mn (II).Hydroxyapatite-selectivity for removing Mn and Fe ions in mixed solutions was as follows: Fe3+> Cu2+>Mn2+. In multiple cycles, the investigated materials were able to remove Fe and Mn ions without regeneration. The overall cost of producing 100 grams of hydroxyapatite from cement bypass waste is less than other calcium source which was 184 EGP/100g (9.32 €/100g).

Effective defluoridation of water using nanosized UiO-66-NH2 encapsulated within macroreticular polystyrene anion exchanger

Environmental concerns associated with the efficient defluoridation of contaminated water remain a substantial challenge. In this work, a new nanocomposite, UiO-66-NH₂@PS⁺, was successfully fabricated via in situ precipitation of a water-stable metal-organic framework (UiO-66-NH₂) inside a commercial polystyrene anion exchanger PS⁺. The as-formed nanocomposite UiO-66-NH₂@PS⁺ was characterized using various morphological methods, which demonstrated that nanosized UiO-66-NH₂ was homogenously dispersed within the inner pores of PS⁺. Batch adsorption experiments indicated that UiO-66-NH₂@PS⁺ exhibited outstanding adsorption performance for fluoride over a broad pH range of 3.0-8.0. The saturated adsorption capacity of fluoride at 298 K was 27.5 and 32.8 mg/g for pH 6.5 and 4.5 with the adsorbent dosage of 0.5 g/L and initial concentration of 5-80 mg/L. Moreover, the utilization rate of active adsorption sites of UiO-66-NH₂ was greatly improved after encapsulation. The XPS study indicated that the integrated effects of specific inner-sphere coordination and ligand exchange between fluoride and UiO-66-NH₂ might be the dominant adsorption mechanism. Fixed-bed tests indicated that the UiO-66-NH₂@PS⁺ column could successively produce clean water with bed volumes of 350 and 70 ([F^-] <1.5 mg/L) from simulated fluoride-pollution water at pH 4.5 and 8.0, with a liquid velocity of 20 mL/h, and an empty bed contact time (EBCT) of 15 min, which was higher than that of the other materials. In addition, the exhausted UiO-66-NH₂@PS⁺ was regenerated and reused for 5 times through complete regeneration, highlighting the potential feasibility of defluorination in practical applications.

Stabilization of fluorine-contaminated soil in aluminum smelting site with biochar loaded iron-lanthanide and aluminum-lanthanide bimetallic materials

Trivalent metals-modified-biochar (BC) has been widely used for the removal of fluorine (F) in water, but little is known about its effects on the stability and mobility of F-contaminated soil. Two types of modified-BC materials (BC-loaded iron-lanthanide (BC/Fe-La) and BC-loaded aluminum-lanthanide (BC/Al-La)) were synthesized and used for the remediation of F-contaminated soil. The forms of BC/La_xFe_3x(OH)_y in BC/Fe-La and BC/La_xAl_3x(OH)_y in BC/Al-La were identified by spectroscopy, X-ray dispersion, thermogravimetric, and pore diameter/volume analyses. Following application (4-12%, w/w) to F-contaminated soil for 30 d, water soluble fluoride (WSF) decreased significantly. The modified-BC with a 1:1:1 molar ratio (BC: Al³⁺ or Fe³⁺: La³⁺) were more effective than those at 1:0.5:0.5. The BC/Al-La were the most effective to stabilize F. In particular, the highest decrease in WSF (by 91.75%) was obtained with the application of 12% BC/Al-La-2, while 8% BC/Al-La-2% and 12% BC/Al-La-1 reduced the WSF by 87.58% and 90.17%, respectively; all values obtained were lower than the national standard of China (< 1.5 mg/L). In addition, the sequential extraction results showed that modified-BC promoted the transformation of the other chemical speciation to the Fe/Mn-F.

Efficient Coagulation Removal of Fluoride Using Lanthanum Salts: Distribution and Chemical Behavior of Fluorine

Abstract: La-loaded absorbents have been widely reported for fluoride removal due to the strong affinity of La³⁺ towards fluoride ion. Herein, chemical removal of fluoride from flue gas scrubbing wastewater using lanthanum salt is investigated. The retaining free F⁻ concentration, phase composition and morphology of filtration residues, and the distribution of fluorine have been investigated using ion-selective electrode, analytical balance, scanning electron microscopy, and X-ray diffractor. The results show that at La/F molar ratio ≥1:3.05, the majority of fluorine exists as LaF_x^3−x complexes, leading to the failure of fluoride removal. At 1:3.20 ≤ La/F molar ratio ≤1:3.10, the formation of LaF₃ is facilitated. However, co-existing LaF_x^3−x tends to absorb on the surface of LaF₃ particles, leading to the formation of colloidal solution with large numbers of LaF₃·LaF_x^3−x suspended solids. At an optimized La/F molar ratio of 1:3.10, a fluoride removal of 97.86% is obtained with retaining fluorine concentration of 6.42 mg L⁻¹. Considering the existing of positively charged LaF_x^3−x and LaF₃·LaF_x^3−x, coagulation removal of fluoride is proposed and investigated using lanthanum salts and negatively charged SiO₂·nH₂O colloidal particles, which is in-situ provided via Na₂SiO₃ hydrolysis at pH near 5.5. At a La/F molar ratio of 1:3.00 and Na₂SiO₃ dose of 0.50 g L⁻¹, a fluoride removal of 99.25% is obtained with retaining fluorine concentration of 2.24 mg L⁻¹. When Na₂SiO₃ dose increases to 1.00 g L⁻¹, the retaining fluorine concentration could be further reduced to 0.80 mg L⁻¹.

U(VI) adsorption by green and facilely modified Ficus microcarpa aerial roots: Behavior and mechanism investigation

Uranium (U)-containing wastewater poses serious pressure to human health and environmental safety. The treatment of U-bearing wastewater using green and facilely fabricated materials is considered a promising alternative. Herein, the raw and modified aerial roots of Ficus microcarpa (RARF and MARF, respectively) were prepared and applied to the treatment of synthesized U-containing wastewater. The results showed that the adsorption process was spontaneous and chemically controlled, which was in good accordance with the pseudo-second-order kinetic and the Redlich-Peterson isotherm adsorption model. The adsorption mechanisms were proposed to be the complexation between U(VI) and oxygen/phosphorus-containing functional groups on MARF.

Goethite/montmorillonite adsorption coupled with electrocoagulation for improving fluoride removal from aqueous solutions

A new material GMS is produced as electrodes in the electrocoagulation (EC) process for F− removing from aqueous environments. The removal rate reaches 99.47% through the EC/GMS. Adsorption and co-precipitation are the main F− removal pathways.

Enhanced recovery of phosphate as a value-added product from wastewater by using lanthanum modified carbon-fiber

The aim of this study is to present the potential of activated carbon fiber (CF) impregnated with lanthanum (La) as a novel adsorbent (La-CF) of phosphate-phosphorus (P) and to assess the value-added due to P-recovery from wastewater using La-CF. The CF were loaded with La and the loaded CF was then calcined at 500 °C. The La-CF adsorbent was used in a series of batch experiments to characterize the adsorption of P at pH of 6-10 and P concentrations of 1-200 mg/L. Physical-chemical properties such as surface morphology, surface charge, surface area, and surface chemistry were determined for the La-CF. The La-CF exhibited adsorption capacity of 196.5 mg/g, fast sorption kinetics and high selectivity for P removal from aqueous solution. La-CF removed 97.3% of P from wastewater and achieved P-level to below 2 mg/L. It was repetitively reused over 10 times in successive cycles to remove P from wastewater. The value-added by recovery of P from wastewater was calculated at around 0.12 US$/L, demonstrating economic benefits of La-CF. In conclusion, the successful removal, recycling, and recovery value-added of P using La-CF adsorbent displayed good potential for developing the technology for treatment of wastewaters to recover valuable compounds such as phosphorus.

Sulfur-anchored palm shell waste-based activated carbon for ultrahigh sorption of Hg(II) for in-situ groundwater treatment

This study utilized a facile and scalable one-pot wet impregnation method for Hg(II) adsorption to prepare sulfur-anchored palm shell waste activated carbon powder (PSAC-S). The experimental results revealed that the sulfur precursors promote the surface charge on the PSAC and enhance Hg(II) removal via the Na₂S > Na₂S₂O₄ > CH₃CSNH₂ sequence. PSAC-S prepared using Na₂S had significant Hg(II) sorption efficiencies, achieving a maximum sorption capacity of 136 mg g^-1 from the Freundlich model. Compared to PSAC, PSAC-S had an enhancement in Hg(II) sorption behavior for heterogeneous interactions with sulfur. PSAC-S also demonstrated high Hg(II) sorption capacities over a wide range of solution pH, while ionic strength had an insignificant impact on Hg(II) removal efficiencies. Through various spectroscopic analyses, we identified the mechanisms of Hg(II) removal by PSAC-S as electrostatic interactions, Hg-Cl complexation, and precipitation as HgSO₄. Moreover, PSAC-S unveiled high adsorption affinity and Hg(II) stability in actual groundwater (even in µg L^-1 level). These overall results show the potentials of PSAC-S as an alternative, easily scalable material for in-situ Hg(II) remediation.

Recently Developed Adsorbing Materials for Fluoride Removal from Water and Fluoride Analytical Determination Techniques: A Review

In recent years, there has been an increase in public perception of the detrimental side-effects of fluoride to human health due to its effects on teeth and bones. Today, there is a plethora of techniques available for the removal of fluoride from drinking water. Among them, adsorption is a very prospective method because of its handy operation, cost efficiency, and high selectivity. Along with efforts to assist fluoride removal from drinking waters, extensive attention has been also paid to the accurate measurement of fluoride in water. Currently, the analytical methods that are used for fluoride determination can be classified into chromatographic methods (e.g., ionic chromatography), electrochemical methods (e.g., voltammetry, potentiometry, and polarography), spectroscopic methods (e.g., molecular absorption spectrometry), microfluidic analysis (e.g., flow injection analysis and sequential injection analysis), titration, and sensors. In this review article, we discuss the available techniques and the ongoing effort for achieving enhanced fluoride removal by applying novel adsorbents such as carbon-based materials (i.e., activated carbon, graphene oxide, and carbon nanotubes) and nanostructured materials, combining metals and their oxides or hydroxides as well as natural materials. Emphasis has been given to the use of lanthanum (La) in the modification of materials, both activated carbon and hybrid materials (i.e., La/Mg/Si-AC, La/MA, LaFeO3 NPs), and in the use of MgO nanostructures, which are found to exhibit an adsorption capacity of up to 29,131 mg g−1. The existing analytical methodologies and the current trends in analytical chemistry for fluoride determination in drinking water are also discussed.

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.

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.

Facile modification of graphene oxide and its application for the aqueous uranyl ion sequestration: Insights on the mechanism

Graphene oxide (GO) has been proved with favorable affinity to U(VI), while some drawbacks such as poor dispersity and low adsorption performance limit its application. Herein, cetyltrimethylammonium bromide (CTAB) modified graphene oxide (MGO) composites were successfully fabricated, characterized and compared with graphene oxide (GO) in the sequestration of U(VI) in aqueous solutions. The results showed that maximum adsorption rate of MGO (99.21%) was obviously higher than that of GO (66.51%) under the same initial condition. Simultaneous introduction of C-H and NO coupled with the enhanced dispersity of GO after modification were mainly responsible for the updated performance verified with multiple characterization techniques. Based on the results of kinetics and isotherms investigations, the experimental data were best described by Pseudo-first-order kinetic model and Redlich-Peterson isotherm model. The results of ΔH, ΔS and ΔG show that adsorptive behaviors of uranyl ion on MGO are endothermic and spontaneous. The study provides a feasible alternative to the chemical modification of GO and enhancing the performance towards uranyl ion removal from solution.