Sorbent For Fluoride Removal Research Articles

Iron functionalized silica particles as an ingenious sorbent for removal of fluoride from water

The paucity of safe drinking water remains a global concern. Fluoride is a pollutant prevalent in groundwater that has adverse health effects. To resolve this concern, we devised a silica-based defluoridation sorbent from pumice rock obtained from the Paka volcano in Baringo County, Kenya. The alkaline leaching technique was used to extract silica particles from pumice rock, which were subsequently modified with iron to enhance their affinity for fluoride. To assess its efficacy, selected borehole water samples were used. Scanning electron microscopy, X-ray diffraction, Fourier transform infrared and X-ray fluorescence spectroscopy was used to characterize the sorbent. The extracted silica particles were 96.71% pure and amorphous, whereas the iron-functionalized silica particles contained 93.67% SiO2 and 2.93% Fe2O3. The optimal pH, sorbent dose and contact time for defluoridation of a 20 mg/L initial fluoride solution were 6, 1 g and 45 min, respectively. Defluoridation followed pseudo-second-order kinetics and fitted Freundlich's isotherm. Fluoride levels in borehole water decreased dramatically; Intex 4.57–1.13, Kadokoi 2.46–0.54 and Naudo 5.39–1.2 mg/L, indicating that the silica-based sorbent developed from low-cost, abundant and locally available pumice rock is efficient for defluoridation.

Lignocellulosic Biomass as Sorbent for Fluoride Removal in Drinking Water.

Water supply to millions of people worldwide is of alarmingly poor quality. Supply sources are depleting, whereas demand is increasing. Health problems associated with water consumption exceeding 1.5 mg/L of fluoride are a severe concern for the World Health Organization (WHO). Therefore, it is urgent to research and develop new technologies and innovative materials to achieve partial fluoride reduction in water intended for human consumption. The new alternative technologies must be environmentally friendly and be able to remove fluoride at the lowest possible costs. So, the use of waste from lignocellulosic biomasses provides a promising alternative to commercially inorganic-based adsorbents-published studies present bioadsorbent materials competing with conventional inorganic-based adsorbents satisfactorily. However, it is still necessary to improve the modification methods to enhance the adsorption capacity and selectivity, as well as the reuse cycles of these bioadsorbents.

Taguchi’s experimental design for the optimization of the defluoridation process using a novel biosorbent developed from the clamshell waste

Developing new adsorbents from waste containing chitosan materials for defluoridation is gaining vast interest. In the current research, a new adsorbent is developed from Clamshell waste and experimental investigation is done using Taguchi’s statistical design approach with orthogonal array for process variables optimization to obtain the maximum fluoride reduction. Maximum defluoridation efficiency of 87.49% and 26.31 mg/g of sorption capacity was achieved at optimum variable values of pH 7, adsorbate initial concentration 10 mg/L, mixing period 90 min, Clamshell dose 10 g/L, and a temperature 323 K. The percentage contribution of each process variable applying ANOVA is pH 34.24% > adsorbate initial concentration 21.17% > mixing period 18.14% > Clamshell dose 15.33% > temperature 11.12%. The fluoride removal with Clamshell adsorbent followed the Freundlich isotherm and fitted well with the pseudo-second-order kinetic model. Thermodynamic parameters (ΔH = 15.075 kJ/mol, ΔS = 0.132 kJ/mol. K) reveal the sorption mechanism is spontaneous and endothermic. SEM and EDAX are used to study surface morphology and FTIR to know the functional groups on the adsorbent that participate in fluoride binding. The reusability study indicates that clamshell absorbent can be reused up to 3 regeneration cycles. The practical feasibility of using the Clamshell sorbent for fluoride removal from field water samples was found to be quite effective.

A review on fluoride adsorption using modified bauxite: Surface modification and sorption mechanisms perspectives

Fluoride has been reported as one of the major water pollutants with myriads of health implications when present in water beyond permissible limits (>1.5 mg L−1). While the adsorption technology of treating fluoridated water remains one of the best options, the choice of suitable adsorbent remains a problem. However, shortcomings of some adsorbents such as low adsorption capacity, slow adsorption rate, narrow pH range, and high-cost make them unsustainable. Modification of adsorbents has become the most attractive method for effectively improving the treatment of fluoridated water. The objective of this work was to bring to light the surface modifications and sorption mechanisms of bauxite as a sorbent for fluoride removal. Bauxite is robust with sufficient mechanical strength and naturally abundant making it a suitable candidate over other conventional adsorbents for fluoride removal. Four main types of surface modification of adsorbents were identified; thermal activation, impregnation, functionalization, and chemical grafting. Materials such as surfactants, oxidizing agents, acids, bases, and metals could be used for surface modification. Modified bauxite demonstrated higher adsorption capacity over their unmodified ones due to the significant improvement in their surface area, pore size, pore-volume, and some structural transformations such as ordered and stable interlinked mesopores which facilitated effective chemisorption. This guarantees a stable chemical structure with more active sites and requires a minimum dose to reach equilibrium at a wider pH range (3–11). Finally, the mechanisms of fluoride sorption onto bauxite is a complex process involving intra-particle diffusion, physisorption, and chemisorption processes.

Advance electrochemical oxidation of fipronil contaminated wastewater by graphite anodes and sorbent nano hydroxyapatite

ABSTRACTDegradation of C12H4Cl2F6N4OS phenylpyrazole insecticide (Fipronil) by advance electrochemical oxidation in aqueous water solution was studied. The process efficiency was figured based on the COD, chloride, and fluoride reduction from fipronil. Further, we tried to highlight the importance of nano-hydroxyapatite (n-Hap) as a cost-effective nano sorbent for removal of fluoride from fipronil. From the advance electrochemical oxidation experiment, it was found that the COD removal was 79%, chloride 52%, and fluoride 80%. The intermediate of fipronil compounds was examined by GC-MS. The final results conclude that advance electrochemical oxidation process was effective for removal of fipronil synthetic wastewater.

Fluoride and nitrate adsorption from water by Fe(III)-doped scoria: optimizing using response surface modeling, kinetic and equilibrium study

Abstract The Fe(III)-doped Scoria was prepared to examine its potential use as an efficient sorbent for removal of fluoride and nitrate from water. Structure and morphology of raw scoria (RS) and Fe(III)-doped scoria (FeS) were studied by scanning electron microscopy, X-ray diffraction analysis and Fourier transform infrared spectroscopy. A four-factor central composite design combined with response surface modeling (RSM) was employed for maximizing fluoride and nitrate removal based on 30 different experimental data obtained in a batch system. At optimum condition, the maximum removal of fluoride and nitrate were 78.36% and 81.4%, respectively. The kinetic of fluoride and nitrate adsorption onto RS and FeS were followed the pseudo-first-order with high determination coefficient values (R2 > 0.997). The isotherm data of fluoride was fitted with the Freundlich model, whereas equilibrium data of nitrate are better fitted to the Langmuir isotherm model. The Langmuir maximum adsorption capacities of Fe(III)-doped scoria for fluoride and nitrate were 0.317 and 11.3 mg/g, respectively. In conclusion, Fe(III)-doped scoria is recommended as an economic and efficient sorbent for nitrate and fluoride removal from contaminated water.

A fluoride ion selective Zr(iv)-poly(acrylamide) magnetic composite

A fluoride ion selective magnetic sorbent has been synthesized by the encapsulation of Fe3O4 nanoparticles in a network of Zr(IV) complexed poly(acrylamide) (Zr–PAM). This magnetic sorbent has been found to be efficient for the selective preconcentration of fluoride ions from natural waters. The Zr–PAM/Fe3O4 composite has been characterized using various physico-chemical techniques i.e. energy dispersive X-ray fluorescence (EDXRF), scanning electron microscopy (SEM), Fourier transform infra-red spectroscopy (FTIR) and a vibrating sample magnetometer (VSM). The Zr–PAM/Fe3O4 composite developed in the present work retains the super paramagnetic properties of Fe3O4 nanoparticles, and the results reveal that the sorption is rapid. The composite has a considerably higher fluoride sorption capacity (124.5 mg g−1) compared to other super-paramagnetic fluoride sorbents reported in the literature. Repeated sorption–regeneration cycles seem to suggest reusability of the sorbent for fluoride removal from natural waters, as well as other aqueous solutions having pH in the range 1–9.

Zirconium–Carbon Hybrid Sorbent for Removal of Fluoride from Water: Oxalic Acid Mediated Zr(IV) Assembly and Adsorption Mechanism

When activated carbon (AC) is modified with zirconium(IV) by impregnation or precipitation, the fluoride adsorption capacity is typically improved. There is significant potential to improve these hybrid sorbents by controlling the impregnation conditions, which determine the assembly and dispersion of the Zr phases on carbon surfaces. Here, commercial activated carbon was modified with Zr(IV) together with oxalic acid (OA) used to maximize the zirconium dispersion and enhance fluoride adsorption. Adsorption experiments were carried out at pH 7 and 25 °C with a fluoride concentration of 40 mg L(-1). The OA/Zr ratio was varied to determine the optimal conditions for subsequent fluoride adsorption. The data was analyzed using the Langmuir and Freundlich isotherm models. FTIR, XPS, and the surface charge distribution were performed to elucidate the adsorption mechanism. Potentiometric titrations showed that the modified activated carbon (ZrOx-AC) possesses positive charge at pH lower than 7, and FTIR analysis demonstrated that zirconium ions interact mainly with carboxylic groups on the activated carbon surfaces. Moreover, XPS analysis demonstrated that Zr(IV) interacts with oxalate ions, and the fluoride adsorption mechanism is likely to involve -OH(-) exchange from zirconyl oxalate complexes.

Iron and aluminium based mixed hydroxides: A novel sorbent for fluoride removal from aqueous solutions

In our previous studies, iron and aluminium based mixed hydroxides were prepared in different molar ratios and fluoride removal efficiencies were evaluated. It was found that the Fe/Al sample with 1:1 molar ratio exhibited maximum adsorption capacity for fluoride. In the present work detailed studies were carried out to understand the effect of fluoride concentration on kinetics, adsorbent dose and competing anion concentrations. Characterisation studies on the adsorbent by XRD, TGA, SEM-EDX, TEM and FT-IR analysis before and after fluoride adsorption were carried out to understand the adsorption mechanism. The particles were irregular in shape, <0.5 μm in size, highly porous and showed specific surface area of 268 m 2 g −1. XRD and FT-IR studies revealed significant changes after fluoride adsorption and showed formation of new complexes on adsorbent surface. Applicability of different sorption kinetic models was studied. The surface sites are heterogeneous in nature and followed heterogeneous site binding model. The presence of phosphate, sulphate and arsenate showed adverse effect on fluoride removal efficiency of Fe/Al adsorbent. The efficiency of material towards ground water samples treatment was tested with and without adjusting pH, and the results are discussed.