Maximum Fluoride Adsorption Capacity Research Articles

Studying the effects of Aspergillus niger (MF431834) dead biomass on water defluoridation in batch and bed column: Adsorption kinetics, characterization, genotoxicity studies

Fluoride pollution in water caused by biological and anthropogenic activities has been recorded as a significant global issue, posing severe risks to the ecosystem. The present study focuses on the isolated fungus Aspergillus niger (MF431834)-dead biomass served as novel adsorbents for defluorination. The dead fungal mycelium of A. niger was used to study the biosorption of fluoride from an aqueous medium while varying the pH, fluoride concentrations, bio-sorbent concentrations, temperatures, contact periods, and coexisting ions. After the batch experimentation, the maximum fluoride adsorption capacity of 93.85 % was achieved by 0.2 g dosage, a 50-min equilibrium time was predicted as a contact time, considerable fluoride adsorption was observed at 15 mg/L of initial fluoride concentration, the maximum fluoride adsorption of 92 % was achieved by pH 2.0, and NaOH was the best desorption agent. The biosorption of fluoride ion well pseudo-second-order (R20.99) compared to pseudo-first-order and the biosorption equilibrium data were more suited by the Langmuir isotherm than the Freund isotherm model. Thermodynamic parameters such as ΔG°, ΔS°, and ΔH° the biosorption of fluoride ions by endothermic nature. Energy Dispersive Spectroscopy (SEM-EDX) and Fourier transform infrared (FTIR) spectroscopy examine the biosorption of fluoride by fungal bio-sorbent. Fluoride removal was also significantly attained in the column study with bio-sorbent. The findings demonstrated that A. cepa subjected to untreated polluted fluoride water exhibited chromosome abnormalities, including disorganized, disturbed metaphase, chromosomal displacement in anaphase, aberrant telophase, spindle disturbances, and binucleate cells. The highest chromosomal aberrations and mitotic inhibition were found in roots exposed to contaminated fluoride water. The novelty of this research can be used as a biomarker to identify the genotoxic effects of fluoride water contamination on biota. Hence, the native fungus A. niger exhibits as an effective adsorbent for fluoride elimination, being valuable in the theory and practical management of environmental pollution.

High capacity aluminium substituted hydroxyapatite incorporated granular wood charcoal (Al-HApC) for fluoride removal from aqueous medium: Batch and column study

In this study, aluminium substituted hydroxyapatite (Al-HAp) was synthesized in-situ on granular commercial wood charcoal at room temperature for fluoride removal from groundwater. Granular size (0.5–3.0 mm) of the carbon particles was selected considering the practical application of the final adsorbent in a packed-bed column filter. The adsorbent was characterized thoroughly. The Al-HAp phase was precipitated inside the pore channel as well as on the surface of highly porous wood charcoal matrix. The adsorbent had surface area of 442 m2/g and pHzpc value was 5. The maximum fluoride adsorption capacity at 303 K was achieved as 105 mg/g which is the highest for any granular adsorbent reported till date for adsorption of fluoride. Batch studies were used to deduce the effective role of pH, temperature and ion selectivity on adsorption efficiency. The reusability of the media was tested upto five cycles after consecutive regeneration with 1 M NaOH. Using the developed media, continuous column run experiments were conducted at different operating conditions, viz., bed volume, flow rate and feed concentration. The maximum number of bed volume was obtained as 1415 for a 30 cm bed height with flow rate 10 L/day and feed concentration of 3 mg/L. A fundamental mass transport model based on pore-diffusion was used to simulate breakthrough behavior in fixed-bed column runs with the synthetic and real contaminated groundwater. The relevant model parameters, namely, fixed bed mass transfer coefficient (kfb), effective pore diffusivity (Dp) and the coefficient of axial dispersion (Ez) were estimated.

Investigation on water defluoridation via batch and continuous mode using Ce–Al bimetallic oxide: Adsorption dynamics, electrochemical and LCA analysis

With variable atomic ratios, Ce–Al bimetallic oxides were fabricated using the sol-gel combustion method and utilized for efficient fluoride removal. The synthesized bimetallic oxides were extensively studied using advanced characterization techniques, including TGA, XRD, FTIR, BET surface area analysis, EDX-assisted FESEM, XPS and impedance analysis. These techniques facilitate the interpretation of the chemical and physical properties of the synthesized material. The Ce–Al (1:1) bimetallic oxide was selected as an adsorbent for the defluoridation. The Ce–Al (1:1) oxide demonstrates a moderately high surface area of 108.67 m2/g. The sorption behaviour of fluoride on Ce–Al (1:1) was thoroughly investigated using batch and column modes. The maximum fluoride removal efficiency (99.4%) was achieved at a temperature of 45 °C and pH of 7.0 using an adsorbent dose of 0.18 g/L for 35 min. Pseudo-second-order kinetic model appropriately describes the sorption process. Freundlich's adsorption isotherm was more pertinent in representing fluoride adsorption behaviour. The maximum fluoride adsorption capacity is 146.73 mg/g at 45 °C. Thermodynamics study indicates fluoride adsorption on Ce–Al (1:1) bimetallic oxide is spontaneous and feasible. The adsorption mechanism was interpreted through XPS spectra, indicating that the physisorption process is mainly responsible for fluoride adsorption. An in-depth investigation of the adsorption dynamics was carried out using mass transfer models and found that the external diffusion process limits the overall adsorption rate. An electrochemical investigation was performed to understand the effect of fluoride adsorption on the electrochemical behaviour of bimetallic oxide. The fixed-bed column adsorption study suggested that the lower flow rate and increased bed height favourably impacted the overall defluoridation process, and column adsorption results were suitably interpreted through both the Adam–Bohart model and Yoon–Nelson dynamics model. The sustainable aspect of the defluoridation process was elucidated in terms of carbon footprint measurement using life cycle assessment analysis. The carbon footprint of the entire treatment process was calculated as 0.094 tons/year.

Bio-adsorbent hydroxyapatite for drinking water defluoridation: column performance modelling studies.

Waste marble powder (WMP) is a rich source of calcium and magnesium salts having an affinity for fluoride ions and therefore serves as a good defluoridation agent. Hydroxyapatite was synthesized from WMP generated by the marble processing industry to make an adsorbent for drinking water defluoridation. The synthesized marble hydroxyapatite (MA-Hap LR) powder was further formed into 2-3mm pellets by extrusion spheronization technique using a polyvinyl alcohol binder. Continuous column defluoridation studies were conducted to obtain optimized column parameters such as input fluoride concentration, column inflow rates, optimum pellet size, and adsorbent bed parameters to obtain maximum fluoride adsorption capacity. The best breakthrough column performance was a maximum adsorption capacity of 1.21mg/g, treating 10mg/L fluoride concentration. The optimized column flow rate was at 1 LPH using an adsorbent bed height of 25cm, which processed 28.5-bed volumes at an adsorbent exhaustion rate of 7.4g/L. The column breakthrough performance data were fit into various kinetic models (Thomas model and Yoon-Nelson model) to describe adsorption kinetics and obtain correlation coefficients. Thomas's model fitted well with a high correlation coefficient value. Modelling studies indicate MA-Hap as a promising adsorbent for drinking water treatment, and optimum column design parameters were identified for scale-up for real applications.

Regeneration Analysis of Bone Char Used in Water Defluoridation: Chemical Desorption Route, Surface Chemistry Analysis and Modeling

High concentrations of fluoride (F−) in drinking water represent a public health threat, and consequently, effective and sustainable methods are required to improve the water quality, mainly in developing and low-income countries. This study focused on the thermodynamics of fluoride adsorption on bone char regenerated with NaOH for water defluoridation. A detailed analysis of the number of fluoride adsorption/desorption cycles, their impact on the performance and surface chemistry of bone char using different NaOH concentrations, and modeling of the adsorption mechanism using statistical physics theory was carried out. The results showed that 0.075 mol/L NaOH was effective in recuperating the defluoridation properties of bone char with a regeneration efficiency higher than 90% during five adsorption/desorption cycles. Bone char regeneration efficiency decreased up to 64% after ten adsorption/desorption cycles with a maximum fluoride adsorption capacity of 0.18 mmol/g. NaOH restored the bone char surface properties for ligand exchange of the fluoride anions via the hydroxyapatite functionalities contained in this adsorbent. It was calculated that around 0.25–0.46 mmol/g hydroxyapatite ligand exchange sites of regenerated bone char samples could be involved in the fluoride adsorption, which was also expected to be a mono-ligand mechanism. The reduction in defluoridation properties of bone char during the regeneration cycles was attributed to the decrease in the ligand exchange capacity as well as the deactivation and blocking of some functional groups of hydroxyapatite, which limited their participation in consecutive adsorption processes. This study contributes to the optimization of the recycling and reuse of bone char for fluoride removal from water to reduce the operating defluoridation costs, thus enhancing the application of this technology in low-income areas where fluorinated water represents a threat to public health.

Facile synthesis and characterization of multi-walled carbon nanotubes decorated with hydroxyapatite from cattle horns for adsorptive removal of fluoride

Developing a new adsorbent for fluoride removal from cattle horn waste materials by a facile chemical method has shown great potential for fluoride removal. This paper reports the synthesis of multi-walled carbon nanotubes decorated with hydroxyapatite from cattle horns (MWCNT-CH) using a facile chemical method. Characterization studies using standard techniques showed that the composite is mesoporous with a rough morphology and contained MWCNTs uniformly encapsulated by the hydroxyapatite forming a crystalline MWCNT-CH composite. Optimization of fluoride adsorption by the as-synthesized composite using Response Surface Methodology (RSM) showed that a maximum fluoride removal efficiency of 80.21% can be attained at initial fluoride concentration = 10 mg/L, pH = 5.25, adsorbent dose = 0.5 g and a contact time of 78 min. ANOVA indicates contribution of the process variables in descending order as pH > contact time > adsorbent dose > initial fluoride concentration. Langmuir isotherm (R2 = 0.9991) best described the process, and the maximum adsorption capacity of fluoride onto the as-synthesized MWCNT-CH composite was 41.7 mg/g. Adsorption kinetics data were best fitted in the pseudo-second-order kinetic model (R2 = 0.9969), indicating chemisorption. The thermodynamic parameter (Δ H = 13.95 J/mol and Δ S = 65.76 J/mol/K) showed that fluoride adsorption onto the MWCNT-CH composite was a spontaneous, endothermic, and entropy-driving process. Moreover, the adsorption mechanism involves ion exchange, electrostatic interaction, and hydrogen bonding. Fluoride was successfully desorbed (using 0.1 M NaOH) from the composite in four cycles, retaining fluoride removal efficiency in the fourth cycle of 57.3%.

Extraction and preparation of metal organic frameworks from secondary aluminum ash for removal mechanism study of fluoride in wastewater

AlFuMoF was obtained by purifying the secondary aluminum ash and using hydrothermal method and modification treatment. Next, using the β-Cyclodextrin impregnation treatment AlFuMoF, a modified MOF (β-CD@AlFuMoF) was obtained. Both MOFs were subsequently characterized, and their potential for adsorption of fluoride from wastewater was compared. The characterization was performed by SEM, EDS, FTIR, XRD, particle size change and thermogravimetric. The adsorption characteristics of AlFuMoF and β-CD@AlFuMoF under different conditions of pH, contact time as well as initial concentration were evaluated using kinetic and thermodynamic studies and adsorption isotherms. In terms of dynamics, the pseudo second order model fits the experimental data best. According to the Langmuir model, the maximum fluoride adsorption capacity of AlFuMoF and β-CD@AlFuMoF are 22.56 and 39.95 mg g−1, respectively. Thermodynamic studies show that the adsorption of fluoride on AlFuMoF and β-CD@AlFuMoF are spontaneous and mainly controlled by chemical adsorption. According to the findings, β-CD modification of AlFuMoF can be considered as a promising method for removing fluoride from wastewater.

Porous Lanthanum-Zirconium phosphate with superior adsorption capability of fluorine for water treatment

Bimetal oxide is a popular defluorinating material. Hexadecyl trimethyl ammonium bromide (CTAB) as a surfactant successfully synthesizes a novel lanthanum-zirconium phosphate to remove fluorine from groundwater. Lanthanum-zirconium phosphate at a Zr/La molar ratio of 2 exhibited a specific surface area of 455.14 m2/g with a wide pore size, which was achieved by incorporating lanthanum into materials and removing CTAB through calcination. The maximum fluoride adsorption capacity is 109.17 mg/g, which is tenfold that of mesostructured zirconium phosphate. Specifically, analysis revealed that mZrP and LamZrP2-1 were amorphous, which is consistent with HAADF-STEM. The fluoride adsorption fitted well with the pseudo-second-order equation model and Langmuir isotherm mode. LamZrP2-1 had potent anti-interference ability without PO43-. Moreover, LamZrP2-1 was reusable for at least six cycles of adsorption–desorption with little influence. The adsorption mechanism of fluoride was discussed by X-ray photoelectron spectroscopy (XPS), nuclear magnetic resonance spectroscopy (NMR) analysis, and Fourier transform infrared (FTIR) spectroscopy. Fluoride was captured by LamZrP2-1 via charge attraction, ligand exchange of different bond strengths, and ion exchange. Lanthanum-zirconium phosphate is important not only in the research and development of bimetal oxides but also in the treatment of groundwater for fluoride removal.

Fluoride adsorption enhancement of Calcined-Kaolin/Hydroxyapatite composite

The use of waste or natural resources is an interesting approach to preparing adsorbent materials. Most adsorption materials are powder-based, making them impractical for a variety of applications. In this work, the natural kaolin clay and hydroxyapatite synthesized from biogenic waste were studied as defluoridation materials. The point of zero charge (pH PZC ), the fluoride adsorption capability and the adsorption isotherm of calcined kaolin and mixed calcined kaolin/hydroxyapatite in both powdered and moulded forms were investigated. The hardness of the moulded (post-formed) samples was tested before and after in immersion in a fluoride solution. The maximum hardness was 15.8 kilo-pounds for the post-formed calcined kaolin sample. Sample hardness values slightly decreased after immersion in a fluoride solution due to the formation of micro-cracks. Most samples presented high pH PZC values, implying that these materials are suitable for the capture of fluoride anions. The adsorption properties varied with the ratio of calcined kaolin to hydroxyapatite. These properties for post-formed samples were different from those in powdered form. Post-formed samples showed higher fluoride adsorption. The maximum fluoride adsorption capacity and efficiency of the post-formed samples (calcined kaolin) at pH 3 were 1.74 F − mg/g and 87%, respectively. The sorption of fluoride of hydroxyapatite and mixed calcined kaolin/hydroxyapatite powders was found to have the form of the Langmuir isotherm, which indicates a monolayer adsorption on the adsorbent surface. Isotherms of calcined kaolin powder, post-formed calcined kaolin and mixed calcined kaolin/hydroxyapatite samples followed the Freundlich isotherm, which indicates multilayer adsorption on a heterogenous adsorbent surface.

Synthesis of porous hydroxysodalite from aluminosilicate rich clay soils: application towards fluoride and pathogen removal.

This article discussed the potential application of hydrothermally synthesized porous hydroxysodalite material synthesized from aluminosilicate clay material as a multifunctional adsorbent for fluoride and pathogen removal from groundwater. The efficiency of the material towards fluoride removal was evaluated using batch experiments while the efficacy against the E. coli strain was evaluated using well-assay diffusion method. The material showed a maximum fluoride adsorption capacity of 6.01mg/g at initial concentration range of 5 to 100mg/L when 1g/100mL adsorbent dosage was used at initial pH of 6 ± 0.5 after agitation time of 10min. The adsorption kinetics data fitted better to pseudo first order of reaction kinetics indicating the dominance of physiosorption adsorption mechanism while the adsorption isotherm data showed better fit to both Langmuir and Freundlich adsorption isotherm model confirming monolayer and multilayer adsorption. The material was successfully regenerated and reused for up to eight successive regeneration-reuse cycles. However, its efficiency was inhibited by the presence of Cl- and CO32-. The material also proven to have antimicrobial activity against E. coli strain. This study concluded that the porous hydroxysodalite material prepared in this study can be used as a multifunctional adsorbent for fluoride and pathogen removal from groundwater.

Enhanced Fluoride Adsorption on Aluminum-Impregnated Kenaf Biochar: Adsorption Characteristics and Mechanism

In this study, kenaf, a fast-growing plant, was pyrolyzed to biochar, and the biochar was impregnated with aluminum to improve its fluoride adsorption capacity. The Al-impregnated kenaf biochar (Al-KNF-BC) was pyrolyzed at temperatures of 300–700 °C, where the specimen treated at 300 °C (Al-KNF-300) demonstrated the highest fluoride adsorption capacity. The kinetics and equilibrium adsorption of fluoride by Al-KNF-300 followed the pseudo-second-order and Langmuir models, respectively. According to the Langmuir model, the maximum fluoride adsorption capacity of Al-KNF-300 was 13.93 mg/g. The enthalpy and entropy of fluoride adsorption by Al-KNF-300 were 37.80 kJ/mol and 124.1 J/mol K, respectively. Fluoride adsorption by Al-KNF-300 was favorable at pH values as low as 3, and the effect of anion competition followed the order HCO3− > SO42− > NO3− > Cl−. A maximum adsorption efficiency of 99.23% was obtained at an adsorbent concentration of 16.67 g/L, at which point the fluoride concentration decreased from 100 to < 1.5 mg/L (the drinking water standard). Based on these results, Al-KNF-300 can be considered an effective and inexpensive adsorbent for removing fluoride from contaminated water to meet drinking water standards.

Feasibility of fluoride removal using calcined Mactra veneriformis shells: Adsorption mechanism and optimization study using RSM and ANN

In this study, Mactra veneriformis shells (MVS), a seafood by-product with high Ca content, was assessed as an adsorbent for fluoride removal from contaminated water. MVS was calcined at various temperatures (100–900 °C), and MVS calcined at 800 and 900 °C (MVS-800 and MVS-900) had the highest adsorption capacity. The high fluoride adsorption of MVS-800 and MVS-900 originated from the conversion of CaCO3 present in the raw MVS to CaO and Ca(OH)2 by calcination at high temperatures. The kinetic and equilibrium adsorption of fluoride by MVS-800 were accurately described by the pseudo-second-order and Langmuir models, respectively. The maximum fluoride adsorption capacity was 244.61 mg/g, which is comparable to that of other adsorbents reported in the literature. The enthalpy and entropy of adsorption were 7.42 kJ/mol and 56.48 J/mol‧K, respectively, and the Gibbs free energy was negative at all reaction temperatures. The interactive effects of pH, reaction time, dosage, and temperature and the optimal values for fluoride removal by MVS-800 were explored using response surface methodology (RSM) and artificial neural networks (ANN). The RSM results demonstrated that reaction time, dosage, and temperature significantly influenced fluoride removal; however, pH was an insignificant term. The accuracy of the ANN model (R2 = 0.9932) for predicting fluoride removal was higher than that of RSM (R2 = 0.9347). The optimal fluoride removal at a dosage of 3.3 g/L under optimized conditions (pH 5; reaction time 9 h; temperature 35 °C) was predicted to be 98.5% by the ANN model.

Performance and mechanism of lanthanum-modified zeolite as a highly efficient adsorbent for fluoride removal from water

Defluoridation of water is still challenging due to the fluoride pollution of both groundwater and surface water worldwide. In this study, lanthanum-modified zeolite (LMZ) was synthesized from coal fly ash and was investigated for fluoride removal from water by conducting batch and column experiments. Our results indicated that the process of fluoride adsorption was endothermic and the adsorption kinetics on LMZ followed the pseudo-second-order model. A higher temperature increased both the capacity and the rate of adsorption. The maximum fluoride adsorption capacity of LMZ reached 141.5 mg/g with a F/La molar ratio of 4.21, as estimated from the Langmuir model which best fitted the isotherm data. Fluoride adsorption greatly depended on pH, with optimal performance being achieved within ∼5.0–∼7.0. The point of zero charge of LMZ was pH 8.8, at which only bicarbonate ions greatly affected fluoride removal. However, no competing effect was observed at pH 6.3 for all tested anions including chloride, sulphate, nitrate, bicarbonate and acetate. The dominant adsorption mechanism was the ligand exchange of fluoride with hydroxyls on LMZ, as illustrated by the rise in pH due to fluoride adsorption and by the molecular scale spectroscopic FTIR, Raman and XPS studies. Fluoride adsorbed on LMZ was successfully desorbed using NaOH solution, and regenerated LMZ could be reused. The results of column studies showed that LMZ granulated with alginate performed well in treating F−-containing water. In conclusion, LMZ is a promising material for efficient defluoridation from water.

Enhanced stability of hydroxyapatite/sodium alginate nanocomposite for effective fluoride adsorption

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.

Bioremediation: Removal of fluoride and methylene blue from water using eco-friendly bio-adsorbents

Fluoride has either detrimental or beneficial effects based on the concentrations, whereas methylene blue (MB) is a harmful cationic dye found in industrial effluents. Recently, distinct interests have been developed in removing water pollutants using bio adsorbents than synthetic adsorbents. This work reveals the removal of fluoride and MB from water using Moringa Pterygosperma (MP), Phyllanthus Emblica (PE), and Strychnos Potatorum (SP) as adsorbents by the batch adsorption process. The respective maximum fluoride adsorption capacity of MP, PE, and SP was 23 mg/g, 24 mg/g, and 31 mg/g, at 30 min (pH 9). Similarly, maximum MB adsorption capacity of MP, PE, and SP is 2 mg/g, 3 mg/g, and 1 mg/g, respectively. The adsorption of fluoride and MB depends strongly on the surface charges and adsorbent colloidally stability. The fluoride and MB adsorption are monolayer and by chemisorption as confirmed by the Langmuir and pseudo-second-order kinetics, respectively. Moreover the final pH of the MP and SP adsorbent treated solutions, after the adsorption of fluoride and MB was found to be 7 ± 0.5. The presence of other competing ions did not have any influence on the MB adsorption. Furthermore, MP, PE, and SP could be considered as the best adsorbents for water purification owing to their efficiency, cost effectiveness and abundant availability.

Adsorptive removal of fluoride using biochar – A potential application in drinking water treatment

• Elevated fluoride levels in drinking water root cause of dental and skeletal fluorosis. • The Defluoridation capacity using water melon rind biochar(WMRBC was 9.5 mg/g. • Anions such as Cl - , NO 3 – , SO 4 2 , HCO 3 - and CO 3 2- did not affect fluoride adsorption. Fluoride as a geogenic contaminant is commonly encountered in groundwater-based drinking water sources. In the present study Watermelon Rind ( Citrullus lanatus ) Biochar (WMRBC) was investigated for its defluoridation potential. The factors affecting the removal of fluoride, including pH, adsorbent dosage, initial concentration, and contact time were investigated. The experimental data were fitted well by Freundlich isotherm and pseudo-second-order model, the maximum fluoride adsorption capacity being 9.5 mg/g. Thermodynamic parameters indicated that the fluoride adsorption process was a spontaneous exothermic process. The presence of other anions like HCO 3 – , CO 3 2– , Cl − , SO 4 2− , and NO 3 – (100 mg/L) had little effect on the adsorption of fluoride at 50 mg/L. Characterization studies of WMRBC before and after fluoride adsorption by SEM, ATR, EDX and XRD techniques, indicated that the adsorption of fluoride may be by electrostatic attraction through protonated basic functionalities present in WMRBC and by precipitation at the mineral sites. WMRBC could be a viable adsorbent for effective removal of fluoride from drinking water and industrial wastewater.

Defluoridation efficiency assessment of spiny hierarchical-structured calcium hydroxyphosphate particles

In present study, fine calcium hydroxyphosphate (Ca 5 (PO 4 ) 3 (OH), HAP) particles with spiny hierarchical-structured morphology were prepared through a unique phase-transformation process of solid CaSO 4 ·2H 2 O in a controlled double jet precipitation system. The obtained spiny hierarchical-structured-HAP powder was tested on its defluoridation efficiency by using the synthetic solution and real coal mine water samples respectively, and it was confirmed that the spiny nanowhiskers on the surface of the HAP played an indispensible role that made it much better than the commercial HAP particles. The adsorption kinetics and isotherm behavior were also investigated, and the maximum adsorption capacity for fluoride was evaluated as 12.2 mg/g at the neutral pH. All coexisting anions like sulfate, chloride, nitrate, phosphate and carbonate were found to cause about 10–20% decrease in the defluoridation efficiency only when their concentrations were 2–200 factors larger than that of fluoride, and it could be reused for at least 5 cycles of adsorption/elution without decreasing the adsorption efficiency drastically in a batch adsorption mode. The real coal mine water sampled from Ejin Horo Qi, Ordos city, Inner Mongolia, was used for the column adsorption test, and even after 3 cycles of adsorption/elution it still maintained high defluoridation efficiency. The present study provided a promising defluoridation method to remove the excessive fluoride from the real coal mine water efficiently by a cheap and effective way. • A facile novel process to prepare spiny hierarchical-structured HAP particles on large scale were proposed successfully. • Phase transformation of CaSO 4 ·2H 2 O to Ca 5 (PO 4 ) 3 OH is essential to the formation of spiny hierarchical-structure. • Spiny HAP particles had much better defluoridation capability than commercial HAP directly at neutral pH. • Nanowhiskers of HAP was observed by TEM on the surface of the obtained Ca 5 (PO 4 ) 3 OH. • Fluoride in the real coal mine water was efficiently removed by spiny HAP particles.

Removal of fluoride from water using aluminum hydroxide-loaded zeolite synthesized from coal fly ash

The removal of fluoride from wastewater is essential as the excess accumulation of fluoride in environment is harmful to the health of humans. In this study, the defluorination of water by aluminum hydroxide-coated zeolite (AHZ), which was synthesized from coal fly ash, was investigated in batches. The Langmuir maximum adsorption capacity of fluoride by AHZ reached 18.12 mg/g. Aluminum hydroxide was shown to be the major component that adsorbed fluoride. More than 92% removal of fluoride was achieved within 2 h, and the fluoride adsorption kinetics were well fitted to a pseudo-second-order model. The point of zero charge (pHpzc) of the AHZ was determined to be 5.52. Fluoride adsorption by AHZ depended greatly on pH, and maximum performance was obtained at pH 5.5–6.5. The AHZ showed good selectivity for the adsorption of fluoride in the presence of chloride, nitrate, sulfate, bicarbonate, and acetate ions, and the fluoride was nearly exhausted at a sufficiently high dose. The release of OH− due to fluoride adsorption was confirmed. FTIR and XPS studies further illustrated that the adsorption mechanism of fluoride adsorption on AHZ was ligand exchange with hydroxyl groups and the formation of F–Al bonds.

Evaluation of Fluoride Adsorption Mechanism and Capacity of Different Types of Bone Char.

The fluoride adsorption capacity of three types of bone char (BC), including cow BC (CBC), chicken BC (CKBC), and pig BC (PBC), was examined. At the optimum charring conditions (temperature and time), PBC had the highest hydroxyapatite (HAP) content (0.928 g-HAP/g-BC), while CBC had the highest specific surface area (103.11 m2/g-BC). CBC also had the maximum fluoride adsorption capacity (0.788 mg-F/g-HAP), suggesting that fluoride adsorption capacity depends more on the specific surface area of the BC than the HAP content. The adsorption data of CBC, CKBC, and PBC fit well with the pseudo-second-order model and the Langmuir isotherm. The maximum fluoride adsorption capacity of BC reached the maximum value when the solution had a pH of approximately 6.0. Lastly, the highest fluoride desorption occurred when the BCs were soaked in solutions with a pH higher than 11.0.

Room-temperature synthesis of MIL-100(Fe) and its adsorption performance for fluoride removal from water

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 - , NO 3 - and SO 4 2- almost had no negative effects on the adsorption performance of R-MIL-100(Fe). However, the present of CO 3 2- or HCO 3 - 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. • A novel room-temperature synthesis strategy for preparing MIL-100(Fe) was proposed. • The deprotonating agent (aniline) accelerated the formation of MIL-100(Fe) under ambient condition. • Room-temperature synthesis is more energy-saving and environmentally friendly compared to conventional methods. • Fluoride adsorption onto R-MIL-100(Fe) was observed in a wide pH range. • R-MIL-100(Fe) was successfully recycled five cycles with an excellent regeneration ability and recyclability.