High Defluoridation Capacity Research Articles

Reinforced adsorption mechanism of fluorine ions by calcium-depleted hydroxyapatite and application in the raffinate from the vanadium industry

Calcium-deficient hydroxyapatite (Ca-d HAP), an adsorbent of high defluoridation capacity with lattice defect, was prepared from vanadium industrial waste neutralization slag (NS). The adsorption performance was compared to commercially available stoichiometric HAP (S-HAP) under different solution conditions, and Ca-d HAP was superior to S-HAP. The specific surface area of Ca-d HAP was considerable (118.32 m2/g), which was 3.176 times larger than that of S-HAP (37.25 m2/g), and this was the main reason for the strong adsorption performance of Ca-d HAP. Meanwhile, due to the presence of minor impurities, such as Al and Fe, in NS, the doping of Al and Fe reduced the crystallinity after Ca-d HAP synthesis, which provided additional active sites for binding to other ions. In addition, combined with characterization analysis, it was speculated that some Ca ions in Ca-d HAP were replaced by Na ions with stronger ion-exchange properties, enhancing its adsorption performance. The adsorption mechanism of Ca-d HAP on F- ions was further investigated by discussing the surface potential, initial pH, adsorbent dosage, initial fluorine concentration, adsorption thermodynamics, and kinetics. Results showed that the Langmuir isothermal model well predicts the adsorption behavior of Ca-d HAP on F- ions at pH 3.5, with a maximum adsorption capacity of 277.78 mg/g, which is larger than most HAP adsorbents reported in the literature. In addition, the percentage adsorption of Ca-d HAP on F- ions was > 99 % in the raffinate and the NaF solution. In addition, the percentage adsorption of Ca-d HAP on F- ions was > 99 % both in the raffinate and in the NaF solution. The adsorption of F- ions by Ca-d HAP is a heat absorption process, with the ΔG° < 0 at various temperatures, demonstrating the reaction's spontaneity of the reaction. The pseudo-second-order model better described the adsorption kinetics data at 303 to 333 K, and the adsorption was regulated by chemical reactions. Overall, Ca-d HAP with lattice defects has a large ion-exchange rate and specific surface area, which is the key reason for the high adsorption performance of Ca-d HAP. Therefore, this technology provides a prospect for treating acidic wastewater with high fluorine content in the vanadium industry.

Eco-friendly design of functionalized graphene oxide incorporated alginate beads for selective fluoride retention

To defeat the troubles of fluorosis, in this present investigation aimed to fabricate sulfonated graphene oxide (SGO) encapsulated with alginate (Alg) biopolymer which gives easily separable SGO@Alg beads and is employed for efficient fluoride adsorption studies. The influence of initial fluoride ion concentration, SGO@Alg beads dosage, contact time, challenger's anions, temperature and adsorbate pH for the fluoride removal was optimized under batch method. The developed SGO@Alg beads possess highest defluoridation capacity (DC) of 4640 mgF− kg−1 within 30 min than parent materials (SGO) and graphene oxide (GO). The highest DC was attained at pH 6 under batch scale. The developed SGO@Alg beads have selective fluoride adsorption capacity while the co-anion bicarbonate acts as powerful adversary anions during adsorption. Thermal stability, functional groups interactions, surface micro-graphs and binding energy of SGO@Alg beads was studied by TGA, Raman, SEM, mapping, FTIR and XPS analysis. The equilibrium data of fluoride adsorption onto SGO@Alg beads were evaluated by adsorption kinetics, thermodynamic parameters and isotherms in detail. The isotherm of fluoride adsorption was filled by Langmuir model. The rate of the adsorption reaction was fitted by pseudo-second-order and intraparticle diffusion kinetic models. The endothermic, feasibility and spontaneous was verified by thermodynamic studies. The electrostatic interaction makes fast fluoride adsorption process on SGO@Alg beads surface. The repeatable use of SGO@Alg composite beads upto six removal cycles make it as the suitable for pilot scale water treatment studies. In addition, the aptness of SGO@Alg beads was tested with a field sample and field results exhibit that SGO@Alg beads were potentially reduced fluoride concentration below the tolerable level.

Facile hydrothermal fabrication of functionalized multi‐layer graphene oxide encapsulated chitosan beads for enriched fluoride adsorption

AbstractThe present exploration was focused on the fabrication of environmental friendly adsorbent materials using graphene oxide (GO) and chitosan (CS). To modify GO by functionalization with sulphonic acid gives sulfonated GO (SGO), which possess high defluoridation capacity (DC) than GO. To boost the DC, easily separation and make it in an exploitable form of SGO material, SGO was incorporated onto biopolymer CS gives SGO/CS hybrid composite beads and employed for efficient defluoridation of water. The various influencing parameters of adsorption system viz., shaking time, adsorbate pH, initial fluoride concentration, adsorbent dosage, temperature, and interfering anions were optimized to obtain the highest DC. The DC of SGO/CS composite beads were found to be 4950 mg.kg−1 within 30 min for 10 mg/L of preliminary adsorbate solution by 0.1 g dosage. The surface and structural characterization/properties of the prepared SGO/CS composite beads were evaluated by FTIR, TGA, SEM, and XPS investigations. The attained equilibrium data were predicted by isotherms like Fruendlich, Dubinin‐Radushkevich (D‐R), and Langmuir. The acquired equilibrium data of thermodynamic investigations facilitate to predict the nature of fluoride adsorption process onto SGO/CS composite beads. The plausible defluoridation mechanism of SGO/CS composite beads was discussed in detail. The applicability of SGO/CS beads was investigated at field environment with field water sample.

Remediation of fluoride contaminated soil with nano-hydroxyapatite amendment: Response of soil fluoride bioavailability and microbial communities

Nano-hydroxyapatite (NHAP), possessing high defluoridation capacity, has been widely used to remove fluoride (F) from polluted water, but little is known about how it affects the bioavailability and toxicity of soil F towards plants. Here, the impact of NHAP (2% w/w) amendment on immobilization, speciation and accumulation of F was studied in a soil-plant system. The results revealed that the NHAP amendment worked effectively to reduce levels of water-soluble F (37.3%−87.8%) and increase available P (76.6%–147%). X-ray photoelectron spectroscopy analysis indicated that the formation of insoluble CaF2 and the ion exchange of F− with OH− into NHAP might be involved in the mechanism of F immobilization and soil pH elevation. Exposure to NHAP significantly decreased the abundance of Cyanobacteria in tested soils, and Gemmatimonadetes abundance in bulk soil was significantly higher than that in rhizosphere soil at 1,000 mg kg−1 F spiked level. Additionally, NHAP amendment decreased F accumulation in wheat shoots (9.10%–18.7%) and roots (3.88%–22.4%), which could mainly be attributed to the reduction of soil bioavailable F and the supplement of Ca from NHAP. These results suggest that NHAP could be a promising amendment to be applied to acidic soil contaminated with F.

Fluoride sorption from aqueous solution using Al(OH)3-modified hydroxyapatite nanosheet

In this study, Al(OH)3-hydroxyapatite nanosheet (Al(OH)3-nHAP), an adsorbent of high defluoridation capacity, was prepared based on the nano hydroxyapatite (nHAP) with lattice defect (4% calcium deficiency) brought by the addition of EDTA. And the composite was characterized by XRD, TEM-EDS, FT-IR and N2 adsorption method. The effects of adsorbent dosage, pH value, initial fluoride concentration and co-existing ions to the adsorption behaviors were studied, and then kinetics, isotherms, thermodynamics, ion exchange rate, regeneration and dissolution were investigated. The maximum defluoridation capacity of Al(OH)3-nHAP nanosheet were 141.84, 171.88 and 194.2 mg/g at 298, 308 and 318 K in neutral condition with the initial fluoride concentration of 200 mg/L. The high defluoridation capacity was due to the high Al/Ca atomic ratio (1.44). The nHAP with lattice defect might help Al atoms to dope into the nHAP. About 22.14% of Al atoms was doped into the lattice of nHAP and 77.86% was loaded on the surface of nHAP by modifying. Ca9.6(PO4)6(OH)1.2 and 8.5156Al(OH)3-Ca7.5792Al2.4208(PO4)6(OH)4.4208 was proposed as the chemical formula of nHAP and Al(OH)3-nHAP synthesized in this study via calculations. The adsorption performance followed the Pseudo-second-order kinetic model and Freundlich isotherm model, which was a spontaneous and endothermic process. The removal efficiency of regenerated Al(OH)3-nHAP nanosheet always stayed above 81.32% and showed good stability during the four cycles. The concentrations of Al3+, Ca2+ and F− in dissolution experiment were 0.01, 2.11 and 0.56 mg/L, respectively, indicating its safety and stability.

Calcium-loaded hydrophilic hypercrosslinked polymers for extremely high defluoridation capacity via multiple uptake mechanisms

The first metallated hypercrosslinked polymers have been synthesised, characterised and found to have remarkable capacity for uptake of fluoride ions.

Controlled growth of nano-hydroxyapatite on stilbite: Defluoridation performance

In Ethiopia, fluoride-contaminated groundwater used for drinking has become a matter of great concern, particularly in the Rift Valley region, due to its serious health hazard (fluorosis). In this work, we present a systematic study related to the optimization of the synthesis of a composite material having a high defluoridation capacity, consisting of nanohydroxyapatite crystals growth on the external surface of a natural Stilbite zeolite (nHAST) of sizes between 74 and 105 μm. In order to control the growth of significantly small crystals of hydroxyapatite with higher fluoride removal capacity, the most important synthesis parameters, crystallization pH and crystallization time, have been carefully optimized. The obtained materials have been characterized by X-Ray Diffraction, Elemental Analysis, Thermogravimetric Analysis, Infrared Spectroscopy, 31P Nuclear Magnetic Resonance, and Transmission Electron Microscopy; in addition, the defluoridation capacity of the materials has been determined. Interestingly, unlike most adsorbents, nHAST-144h (prepared after 144 h of crystallization) shows significantly high fluoride-removal efficiency in a wide range of pH with maximum F-removal of 86% and minimum of 79% fluoride removal at pH 3 and 10, respectively. Besides, nHAST-144h adsorbent maintains its high defluoridation capacity in the presence of other ions, in particular chloride, sulfate and bicarbonate. In a real situation, nHAST-144h was found to be efficient as well; from real groundwater from the Ethiopian Rift Valley, with a fluoride concentration of 8.2 mg/L and a dose of 10 g/L, nHAST-144h reduced the fluoride concentration down to 1.40 mg/L, below the limit established by World Health Organization (WHO).

In Situ Fabrication of Magnetic Iron Oxide over Nano-hydroxyapatite Gelatin Eco-polymeric Composite for Defluoridation Studies

This research work deals with the defluoridation studies of magnetic iron oxide (Fe3O4) fabricated nano-hydroxyapatite (n-HAp) gelatin (Gel) eco-polymeric composite. The developed hybrid Fe3O4@n-HApGel composite displays a high defluoridation capacity (DC) of 5009 mgF–·kg–1. Batch sorption experiments were performed to find the effect of various influencing parameters such as pH, contact time, competitor co-anions, initial fluoride concentration, and temperature. The structural, surface morphological changes, and elements present in the sorbent were studied using FTIR, XRD, and SEM with EDAX techniques. The equilibrium isotherm study was fitted with Langmuir isotherm model. The thermodynamic parameter values indicate the spontaneous and endothermic nature of fluoride sorption. The proposed mechanism indicates that the enhanced DC of magnetic composite is mainly due to electrostatic adsorption and complexation between fluoride ion and composite in addition to ion-exchange. The regeneration and reusability ...

Enhanced fluoride removal from water by sulfate-doped hydroxyapatite hierarchical hollow microspheres

A novel adsorbent, sulfate-doped hydroxyapatite (HAP) hierarchical hollow microspheres, was prepared and developed for fluoride removal from water. The adsorbent was characterized by using SEM, TEM, XRD, FTIR, XPS and BET analyses, respectively. Batch of adsorption experiments were investigated to study the fluoride removal performance. The sulfate-doped HAP showed enhanced fluoride removal performance with a defluoridation capacity of 28.3mgg−1 with initial fluoride concentration of 100mgL−1 at 25°C under neutral conditions, which was higher than other previously reported HAP-related adsorbents. The adsorption isotherm could be better defined by Freundlich model than Langmuir model. The adsorption kinetic followed the pseudo-second-order model. And the sulfate-doped HAP had a relatively high defluoridation capacity in a wide pH range of 3.0–10.0. The study of adsorption mechanism suggested that the hydroxyl groups and the sulfate groups on the surface were all involved in the fluoride adsorption, and these active sites cooperatively enhanced the fluoride removal.

Synthesis of alginate beads filled with nanohydroxyapatite: An efficient approach for fluoride sorption

ABSTRACTNanohydroxyapatite (n‐HAp) powder is a promising adsorbent material with high defluoridation capacity (DC); however, it causes pressure drop during field applications. To overcome such problems and utilize the advantages of n‐HAp, it is aimed to prepare n‐HAp in a usable bead form with the support of alginate (Alg) biopolymer. n‐HApAlgLa composite beads were synthesized by introducing n‐HAp powder in Alg polymeric gel, and the resulting solution was dropped into La3+ ions for crosslinking. Defluoridation experiments were carried out in batch mode to optimize various influencing parameters like contact time, pH, challenger anions, initial fluoride concentrations, and temperature. The beads were characterized using Fourier transform infrared spectroscopy, X‐ray diffraction, and scanning electron microscopy with energy‐dispersive X‐ray analyzer analysis. The sorption process was explained using diverse isotherms and kinetic models. The values of thermodynamic parameters indicate that the nature of fluoride is spontaneous and endothermic in nature. In field studies, n‐HApAlgLa beads reduce the fluoride concentration below the tolerance limit. The regeneration and reusability studies were proposed to effectively use the sorbent. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41937.

Fluoride removal from water using high-activity aluminum hydroxide prepared by the ultrasonic method

Ultrasonically prepared Al(OH)3 has a high defluoridation capacity and a low residual aluminum concentration in drinking water after defluoridation.

Natural zeolites from Ethiopia for elimination of fluoride from drinking water

Zeolites and fluoride-rich groundwaters are both usually associated to volcanic regions, and hence in this work we study natural zeolites as fluoride-adsorbents in order to develop a cheap and locally-available fluorosis mitigation technology. The defluoridation capacities of eleven samples originally from Ethiopia are studied as raw materials, without any treatment. Results show that one of the samples, containing mainly analcime and mordenite zeolites, has a maximum defluoridation capacity of 0.47mg(F−)/g; interestingly, this adsorbent is able to reduce the fluoride concentration beyond the safe limit established by the World Health Organization of 1.5mg/L. In addition, desorption of fluoride from the adsorbent is easily and quantitatively achieved by subjecting the fluoride-loaded solid to a mild treatment of NaOH 0.001M; such regenerated adsorbent retains 56% of the initial defluoridation capacity. Experiments carried out with real groundwaters show that this sample preserves its high defluoridation capacity in an actual case. Therefore, our study reports a promising cost-effective and locally-available new adsorbent for defluoridation of fluoride-rich groundwaters.

English

Research was carried out at Ngurdoto research station in Tanzania to ascertain the potential development of a water filter made of bauxite, gypsum and magnesite in an attempt to enhance the availability of low-fluoride water. The materials were sourced within Tanzania. The X-Ray fluorescence technique showed that the major components of the materials were: bauxite: Al2O3 (30.33%), SiO2 (15.0%) and Fe2O3 (14.3%); gypsum: CaO (28.09%), SO3 (34.96%), and SiO2 (9.01%); and magnesite: MgO (34.57%) and SiO2(19.3%). The materials were calcined at 350, 400, 450 and 500°C. The activated materials were then mixed in mass ratios of 1:2:3, 1:3:2, 2:1:3, 2:3:1, 3:1:2 and 3:2:1 (bauxite: gypsum: magnesite). One gram of each composite was employed in the batch defluoridation of 1 L of water with fluoride concentration of 12.62 mg/L. The highest defluoridation capacity, 11.89 mg F-/g, was obtained with the 3:2:1 to 500°C composite. The quality of the treated water fell short of WHO standards on sulphates and iron but residual concentrations of Cl-, Al3+, Ca2+, Mg2+, Fe2+ were within the prescribed limits. Sorption behavior followed strongly to Langmuir isotherm, except for the 450°C calcined samples for which the Temkin isotherm behavior was pronounced. Despite the limitations of high residual sulphates and iron, a composite filter of bauxite, gypsum and magnesite was shown to be workable. Key words: Defluoridation, bauxite, gypsum, magnesite, composite, calcine, isotherm.

Defluoridation of water using magnesia/chitosan composite

Magnesia (MgO) is a well-known adsorbent showing extremely high defluoridation capacity (DC). In order to over come the limitations of MgO for field applications, an attempt has been made to modify magnesia with abundant biomaterial chitosan to form magnesia/chitosan (MgOC) composite in a usable form and its merits over conventional magnesia and raw chitosan is established. Removal of fluoride from aqueous solution with MgO and MgOC composite was studied with batch equilibrium experiments. At equilibrium, MgOC composite has a DC of 4440 mg F −/kg while for magnesia it is only 2175 mg F −/kg. The physicochemical properties of the synthesised MgOC composite were analyzed with FTIR and SEM with EDAX studies. The equilibrium data were fitted with isotherm and kinetic models. Thermodynamic parameters viz, Δ G°, Δ H° and Δ S° were calculated to understand the nature of sorption. Field studies were carried out to find the suitability of these sorbents at field conditions.

Optimization of regenerated bone char for fluoride removal in drinking water: a case study in Tanzania

This paper presents findings of a study on optimization and application of the regenerated bone char media for the defluoridation of drinking water in Tanzania where more than 30% of all water sources have fluoride concentrations above the 1.50 mg/I which is recommended by the World Heath Organization (WHO). In this study, regeneration temperature, regeneration duration, contact time, regenerated bone char dosage and particle size were investigated. Results indicate that the highest fluoride removal and adsorption capacity were 70.64% and 0.75 mg-F/g-bc, respectively, for a sample with bone char material that was regenerated at 500 degrees C. In this study the optimum burning duration was found to be 120 min, which resulted in residual fluoride that varied from a maximum value of 17.43 mg/I for a 2 min contact time to a minimum value of 8.53 mg/I for a contact time of 180 min. This study further indicated that the smallest size of regenerated bone char media (0.5-1.0 mm diameter) had the highest defluoridation capacity, with residual fluoride which varied from 17.82 mg/I at 2 min contact time to 11.26 mg/I at 120 min contact time. In terms of dosage of the regenerated bone char media it was established that the optimum dosage was 25g of bone char media with a grain size of 0.50-1.0 mm. This had a fluoride removal capacity of 0.55 mg-F/g-BC. Column filter experiments indicated that regenerated bone media is capable of removing fluoride from dinking water to meet both WHO and Tanzania recommended values.

Water defluoridation using Malawi’s locally sourced gypsum

Free fluoride levels above the WHO guideline maximum value of 1.5 mg/l have been reported in several parts of Malawi. Dental fluorosis has also been observed in the same areas such that search for local defluoridation techniques has become important in the country. The present research intended to determine the potential of using Malawi gypsum in defluoridation, identify the best pre-treatment of the gypsum and optimum conditions under which effective water defluoridation with the gypsum may be obtained. Laboratory experiments were carried out to explore defluoridation of drinking water using locally sourced gypsum and gypsum calcined at high temperatures. A 400 °C calcined phase of gypsum gave the highest defluoridation capacity of 67.80% compared to raw (uncalcined) gypsum, 200, 300 and 500 °C calcined phases. Powder X-ray diffraction (PXRD) pattern of the 400 °C phase revealed existence of less crystalline CaSO 4 that was thought to be responsible for such relatively high defluoridation capacity. The dependence of the fluoride removal by the 400 °C calcined phase on other drinking water quality parameters was assessed by simple correlation analysis. Reaction kinetics and mechanisms of fluoride removal by the materials were also investigated. It was found that ion exchange was the dominant mechanism through which fluoride was removed from water by the materials.