Initial Fluoride Concentration Research Articles

Characterizations and fluoride adsorption performance of wattle humus biosorbent.

Considering the serious health effects of fluoride contamination, an environment friendly bioadsorbent was derived from wattle humus for fluoride removal by conventional thermal activation process. Analytical characterizations revealed that heterogeneous morphological textured wattle humus enabled remarkable adsorption capacity. XPS analysis substantiated that fluoride had been successfully adsorbed on to the carbonized wattle humus surface through chemisorption. Fluoride adsorption efficiency was systematically rationalized via batch adsorption studies. Experiments were performed at different initial fluoride concentration and scrutinized the impact of contact time (10-120 min), adsorbent dosage (0.5-2.5 g), pH (2.0-9.0), and interfering co-existing ions (SO42-, NO3-, Cl-, and HCO3-) on fluoride removal. Even at different adsorbate dosage (2-10 mg/L), 98% fluoride removal efficiency was achieved under pH > 6. The competitive anions do not interfere the wattle humus fluoride adsorption capacity. Moreover, the adsorption isotherms and kinetics studies inferred that monolayer and multilayer adsorption behavior by wattle humus leads to noticeable fluoride adsorption. Adsorbent regeneration test affirms that regenerated adsorbent found higher (>95%) fluoride removal efficiency even at five recycle runs.

Removal of fluoride from groundwater using MnO2 bentonite-smectite rich clay soils composite

A clay based composite adsorbent for fluoride was fabricated by blending the locally available smectite rich clay and MnO2 coated bentonite clay. The efficiency of the material towards fluoride adsorption was evaluated using fixed-bed column experiments. The results from column experiments showed that increasing parameters such as bed height and initial fluoride concentration increases the adsorption capacity whereas increasing flow rate decreases the column adsorption capacity. The paramount adsorption capacity of obtained at breakthrough point 0.6 mg/g when flow rate of 0.65 mL/min, bed height 2.5 cm and adsorbate concentration of 3.75 mg/L were used. The prepared composite was successfully regenerated using 0.01 M Na2CO3 and reused for up to 2 cycles. Thomas breakthrough model confirmed that fluoride adsorption by the prepared composite involves chemical interaction and transfer of ions into the internal layers of the adsorbent particles. The obtained results showed that MnO2 bentonite-smectite rich clay composite has potential for use in groundwater defluoridation.

Evaluation of bentonite clay in modified and unmodified forms to remove fluoride from water.

The feasibility of fluoride adsorption from aqueous solutions using naturally available bentonite clay in both modified and unmodified forms is investigated in this report. Scanning electron microscopy (SEM), energy dispersive X-ray (EDX), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy analysis was applied to describe the structure and nature of modified and unmodified bentonite clay. The physicochemical characteristics of the adsorbent were also investigated for moisture content, pH, apparent density, specific surface area, cation exchange capacity and its point-of-zero charge. SEM images reveal particles are dispersed homogeneously and are irregular in shape. XRD and EDX analyses reveal that the bentonite is composed of seven materials: calcite, silica, alumina, hematite, bornite and green cinnabar, and chloride which are considered as impurities. Raw bentonite clays have shown very low fluoride removal efficiency (47.19%). Modification of the clay surface with HCl and aluminum oxide, on the other hand, increased fluoride removal efficiency to 79.77% and 94.38%, respectively. At 5 mg/L initial fluoride concentration, 10 cm bed depth packed dose of adsorbent, and 180 min breakthrough time, a 2.88 mg/g of fluoride removal capacity was observed. As a result, aluminum oxide modified bentonite clay was chosen for further investigation and the results are not presented here.

Facile synthesis, characterization and application of heterogeneous Al@Si materials for adsorptive mitigation of fluoride: Optimization and cost analysis

The present study reports on the investigation on the facile synthesis of Al-Si based low cost heterogeneous adsorbent from the naturally available laterite soil and clay. The soil-clay mixture was blended at a ratio of 3:1, which was thermochemically activated and was applied for fluoride separation from synthetic groundwater. The developed material was validated through some characterization techniques, such as SEM-EDX, FTIR, XRD and BET surface area measurement. Optimization on various operating parameters such as contact time (0.5–10 h), pH (4.5–9.5), adsorbent dose (10–60gL−1), stirring speed (20–120 rpm) and initial fluoride concentration (2–15 mgL−1), for fluoride separation were performed in batch operation, which was further optimized with Central Composite Design approach of Response Surface Methodology in Design-Expert software where Analysis of Variance suggested the validity and success of the model with its high R2 value (>0.97). Experimental validation with RSM software prediction delivered the optimum parameter values. At pH 6.5, initial fluoride concentration of 10 mgL−1, adsorbent dose of 60 gL−1, contact time of 10 h and stirred speed of 120 rpm, the activated adsorbent material showed > 96% fluoride removal efficiency. Extensive kinetic, isotherm and thermodynamic studies were formulated and validated with experimental data. Pseudo 2nd order model and Langmuir isotherm model were the best fits for kinetics and for adsorption equilibrium. It was found that the adsorbent could be used up to 3 cycles of operations and regeneration while retaining up to 86% rejection efficiency to fluoride. For the treatment of fluoride rejects for safe disposal, concrete blocks of 20 MPa compressive strength were developed where the adsorbed fluoride was stabilized and fixed. After TCLP test, fluoride concentration of 0.16 mgL−1 was obtained in the extraction fluid which was well below the permissible limit. Fluoride free drinking water at low cost (0.17 $/m3) confirms high sustainability to the complete process.

Recycling electro-coagulated sludge from textile wastewater treatment plants as an adsorbent for the adsorptions of fluoride in an aqueous solution

This research investigated the high content of iron-based materials from recycled electro-coagulated (EC) sludge for the adsorptive removal of fluoride, and the properties of the material were characterized. The thermal activation of EC sludge in which the unwanted impurity was removed by beneficiation and thermally activated at 500 °C, and was used for fluoride removal. Basic operating parameters (mixing time, adsorbent dosage, adsorbate concentration, solution pH, and temperature) were examined to evaluate the optimum de-fluoridation capacity (DC). The functional groups, the crystalline structure, and surface morphology of thermally treated and raw EC sludge were analyzed using FTIR, XRD, and SEM, respectively, and demonstrates that thermally activated EC sludge contains significant content of magnetite and hematite. The optimum DC was recorded as 5.12 mg of F−/gm with experimental conditions: mixing time = 20 min, adsorbent dosage = 0.3 gm/100 ml, initial fluoride concentration = 1 mg/L, and pH = 5 at the temperature of 353 K. The Langmuir isotherm model was fitted, and the capacity is calculated as 6.43 mg/g. The adsorption process follows the Pseudo-Second-order kinetic models. It can be concluded that the prepared adsorbents have excellent fluoride removal capacity, and EC sludge can be used as an alternative adsorbent for de-fluoridation.

Process Performance Combining Natural Coagulant Moringa oleifera Lam and Ultrafiltration for Groundwater Defluoridation

The reduction of the excess fluoride present in groundwater and surface water is of paramount importance to the public supply, given that its excess can trigger various harmful effects on human health, such as dental and skeletal fluorosis. In this context, the objective of the present investigation was to evaluate the defluoridation of groundwater using coagulation/flocculation/sedimentation (C/F/S) process using the natural coagulant Moringa oleifera Lam (MO) followed by ultrafiltration membrane process. C/F/S tests were carried out in a Jar test apparatus with different concentrations of the coagulant and subsequent ultrafiltration in a membrane module. The tests used different initial fluoride concentrations, coagulant dosages, and water samples (distilled, ground, and surface water). Fluoride removal was most effective using 5 ppm of fluoride initial concentration and 5 g/L of MO coagulant dosage; however, an increase in turbidity was observed. The ultrafiltration step was used to improve water quality parameters, and at a pressure of 2 bar, it was obtained 97% of turbidity and color removal and 83% of fluoride removal. Thus, the results obtained applying the combined process of C/F/S followed by ultrafiltration can be considered a promising alternative to defluoridation of groundwater intended for public supply.

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.

Design and fabrication of sulfonic acid functionalized graphene oxide for enriched fluoride adsorption

In this research paper, sulfonic acid functionalized graphene oxide namely sulfonated GO (SGO) was utilized as an adsorbent material for defluoridation from water environment. Fluoride adsorption experimentations were employed under batch scale to optimize the diverse influencing factors such as contact time (10–60 min), SGO dosage (0.025 to 0.25 g), initial fluoride concentrations (2–14 mg/L), temperature (303, 313 and 323 K) and adsorbate pH (3−11). The defluoridation capacity (DC) of SGO was identified to be 4260 mgF− kg−1 for 10 mg/L of initial fluoride solution using 0.1 g SGO dosage. The contact time and adsorbate pH for enhanced defluoridation was noted at 40 min and pH 6 respectively. The sophisticated instrumental methods like TEM, FTIR, XPS, SEM, and TGA were performed to evaluate the physiochemical properties of adsorbent material. The experimentally obtained equilibrium data of SGO were applied to three adsorption isotherm models viz., Langmuir, Dubinin-Radushkevich (D-R) and Freundlich isotherms. In kinetic models, the obtained equilibrium data follows intraparticle diffusion and pseudo-second-order models for fluoride adsorption by SGO. Thermodynamic investigation shows that the defluoridation process of SGO was spontaneous and endothermic in nature. Regeneration studies of SGO material was carried out and its results exhibit that SGO was regenerable one. Moreover, field sample taken from fluoride endemic village was also investigated using synthesized SGO material.

Enhanced biosorption of fluoride by extracted nanocellulose/polyvinyl alcohol composite in batch and fixed-bed system: ANN analysis and numerical modeling.

The present investigation attempted to examine the defluoridation feasibility onto the extracted nanocellulose/PVA polymer composites. Nanocellulose were derived from sugarcane bagasse and blended with PVA (polyvinyl alcohol) polymer matrix. The defluoridation potential of nanocellulose/PVA was observed to be significantly dependent on the various operational factors including pH, time interval, etc. the Temkin isotherm (R2 = 0.989) as well as the Langmuir isotherm equation (R2 = 0.982) could well fit with the investigational data. Following the Langmuir isotherm, the maximum monolayer adsorption capacity for fluoride elimination at 25°C was obtained as 11.363 mg g-1. The nature of rate-limiting steps involved in defluoridation process might be effectively predicted by pseudo-second-order kinetics. Values of thermodynamic state properties achieved as of the thermodynamic analysis showed that the defluoridation process was spontaneous, exothermic, and feasible. The diffusion and mass transfer study were estimated by following the Boyd's model. Average effective diffusion coefficient (De) at various initial fluoride concentrations (4-10 mg L-1) was obtained as 15.3343×10-7 m2s-1 and the estimated magnitude of the mass-transfer coefficient (Kf) was 0.0346×10-9 m s-1 (temperature = 298 K, C0= 6 mgL-1). An ANN (artificial neural network) model applied to optimize and simulate the defluoridation procedure. Furthermore, continuous flow column reactor was conducted to investigate the practical applicability of composites in the defluoridation process. The Yoon-Nelson and the Thomas model exhibited excellent conformity with the breakthrough curves. Nanocellulose/PVA satisfactorily eliminated fluoride from its aqueous solution and can be considered as a suitable bio-sorbent for defluoridation.

Pilot-scale valorization of hazardous aluminum dross into γ-Al2O3 nanoadsorbent for efficient removal of fluoride

In this study, secondary aluminum dross as an alumina-rich resource was valorized into the gamma-aluminum oxide ( γ -Al 2 O 3 ) via a pilot-scale extraction system. The pilot-scale process was designed for a total γ -Al 2 O 3 production of ∼ 5 kg/day. The extraction process included leaching, precipitation, hydroxide separation, aluminum hydroxide re-precipitation, drying and high-temperature dihydroxylation The obtained γ -Al 2 O 3 was then characterized using XRD, XRF, BET, and FESEM. The XRD analysis disclosed the emergence of the gamma-crystalline phase with a crystallite size of 19.6 nm. The XRF revealed a purity of more than 99 wt%. The BET surface area, pore volume, and mean pore size were ∼ 170 m 2 /g, 0.45 cm 3 /g, and 17.4 nm, respectively. The FESEM and TEM indicated that the as-synthesized γ -Al 2 O 3 was in the form of agglomerates, consisting of <20 nm particles. The γ -Al 2 O 3 was then used to adsorb aqueous fluoride with two different concentrations of 10 and 20 ppm. The adsorption results revealed that the amount of fluoride adsorbed by γ -Al 2 O 3 was 16.5 mg/g when adsorbent dosage, initial fluoride concentration, pH, and equilibrium time were 1 g/l, 20 ppm, 4, and 1 h, respectively. The maximum monolayer adsorption was obtained 35.6 mg/g by Langmuir model. Investigating the influence of the adsorbent dosage indicated that the adsorbent dosage of 4 g/l resulted in 98% fluoride removal. It was found that fluoride adsorption occurred through chemisorption, and carbonate and phosphate anions had the most interference with fluoride adsorption. The regeneration experiments showed that the regenerated γ -Al 2 O 3 can exhibit good fluoride adsorption performance, even after 8 times regeneration. • Aluminum dross was valorized into high purity γ -Al 2 O 3 by a pilot-scale setup. • γ -Al 2 O 3 capacity production of extraction setup was about 5 kg/day. • The obtained γ -Al 2 O 3 could remove 98% of fluoride from aqueous solution after 1 h. • The maximum monolayer adsorption was obtained 35.6 mg/g by Langmuir model. • γ -Al 2 O 3 exhibits 75% of its initial adsorption capacity after 8 times regeneration.

Bivalve shells (Corbula trigona) as a new adsorbent for the defluoridation of groundwater by adsorption-precipitation

Defluoridation of groundwater was performed in a batch reactor using bivalve shell powder (BSP) as adsorbent. The physicochemical characteristics of BSP, studied by Fourier Transform Infrared, X-ray Diffraction and Inductively Coupled Plasma-Optical Emission Spectrometry after dissolution, have shown that BSP was mainly composed of crystalline CaCO3 (∼97.8%). The effects of pH, initial fluoride concentration, adsorbent dose and contact time on the adsorption capacity of BSP were investigated. For an initial fluoride concentration of 2.2 mg/L and with 16 g/L of BSP, after 8 hours of treatment, 27.3% were eliminated at pH 7.5 versus 68% at pH 3, highlighting the efficiency of the adsorption process. The difference in adsorption capacity as a function of pH was correlated to the pHpzc of the BSP, which was equal to 8.2. Thus, at pH below pHpzc, electrostatic attraction between the fluoride anions and the positively charged adsorbent could justify the adsorption mechanism. Fittings of experimental data have evidenced that the adsorption kinetics were of pseudo-second order whereas the adsorption isotherms were of Langmuir type. The chemical precipitation of calcium fluoride was also revealed to occur upon release of Ca2+ from partial dissolution of CaCO3 in acidic conditions.

Adsorption Behavior of Polyhydroxy‐Iron‐Modified Coal‐Bearing Kaolin for Fluoride Removal

AbstractAccording to previous research on polyhydroxy‐iron‐modified coal‐bearing kaolin for the removal of anionic dyes, we first performed a ball milling treatment and then modified the kaolin samples with polyhydroxy‐iron to prepare a high‐surface‐area adsorbent. This process not only increased the surface area up to 100 m2 g−1 while successfully avoiding high‐temperature calcination and acid treatment but also significantly increased the fluoride adsorption performance in terms of the removal rate, which reached 90 %. Compared with the removal rate of raw kaolin (11 %), that of polyhydroxy‐iron‐modified coal‐bearing kaolin (without ball milling) was ∼44 %. Various adsorption conditions that affect the adsorption capacity of the adsorbent were investigated, including the adsorption time, initial solution pH and initial fluoride concentration. The effect of the initial pH showed a wide (pH=6–8) application range. The adsorption kinetics of fluoride fit well with the pseudosecond‐order kinetic model, and the equilibrium data can be well described by the Freundlich adsorption model.

Hydrothermally treated aluminosilicate clay (HTAC) for remediation of fluoride and pathogens from water: Adsorbent characterization and adsorption modelling

Presence of fluoride and pathogen in drinking water is an issue of concern due to their health effects and as such much effort is being directed towards finding sustainable material for use in water treatment. Adsorption based water treatment techniques are often considered as the most effective and easy to use in rural set up. However, most of the adsorbents are not multifunction and are only effective towards fluoride. In this study aluminosilicate activated clay was hydrothermally treated and applied for fluoride and pathogen removal from water. Fourier transform infrared (FTIR), Brunauer-Emmett-Teller method (BET), X-ray diffraction spectroscopy (XRD) and Scanning electron microscopy-energy dispersion spectroscopy (SEM-EDS) techniques were employed to characterize hydrothermally treated aluminosilicate clay (HTAC). Batch defluoridation experiments were used to evaluate the fluoride removal efficiency while well diffusion assay method was used to evaluate the antimicrobial efficiency. The BET results showed increase in surface area from 17.19 m2/g to 33.56 m2/g after treatment. Batch defluoridation showed maximum adsorption capacity of 1.75 mg/g with 53% fluoride removal from initial fluoride concentration of 6 mg/L using 0.8 g/40 mL dosage at initial pH 5.8 and contact time of 5 min at room temperature. The adsorption kinetics data showed a better fit to pseudo-second order model while the adsorption isotherm data showed correlation coefficient and chi-square values of 0.98 and 0.01, respectively indicating a better fit to both Langmuir and Freundlich adsorption isotherms. The regeneration studies showed that the material can be reused for up to six times using 0.1 M KCl as regenerant. Antimicrobial studies showed that HTAC has potency against Escherichia coli (E. coli) strains. The study showed that synthesized HTAC has strong potential for application in fluoride and pathogen removal.

Assessment of fluoride removal in a batch electrocoagulation process: A case study in the Mount Meru Enclave.

The presence of excessive amounts of fluoride than prescribed standards has been reported in various sources of domestic water supply around the slopes of Mount Meru and other parts in Tanzania. Efforts to remove the excessive fluoride have been carried out using various technologies. In this study, electrocoagulation experiments were carried out to assess its efficiency on fluoride removal. The fluoride concentration tested ranged from 1.37 to 48 mg/L in both synthetic and natural waters. The voltage applied in the electrocoagulation (EC) process ranged from 0 to 50 V while maintaining pH values of 4 to 9. The representative experimental results for the Ngarenanyuki river water with initial fluoride concentration of 29.5 mg/L accomplished a removal efficiency of 90% at an optimal electrolysis time of 30 min, an applied voltage of 30 V and an optimal pH of 6. The method showed efficient fluoride removal in water to allowable limits by World Health Organization (WHO) and Tanzania Bureau of Standards (TBS) (1.5 mg/L). Despite the voltage applied (30 V), the pH at neutrality remained unchanged thus making the process more efficient. At this voltage (30 V) the process has been reported previously also to have the capability of disinfecting the water and hence rendering such water safe for use.

Efficient Fluoride Removal from Aqueous Solution Using Zirconium-Based Composite Nanofiber Membranes.

Herein, composite nanofiber membranes (CNMs) derived from UiO-66 and UiO-66-NH2 Zr-metal-organic frameworks (MOFs) were successfully prepared, and they exhibited high performance in adsorptive fluoride removal from aqueous media. The resultant CNMs were confirmed using different techniques, such as X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), and Brunauer–Emmett–Teller (BET) in addition to Fourier-transform infrared spectroscopy (FTIR). The parameters that govern the fluoride adsorption were evaluated, including adsorbent dose, contact time, and pH value, in addition to initial concentration. The crystalline structures of CNMs exhibited high hydrothermal stability and remained intact after fluoride adsorption. It could also be observed that the adsorbent dose has a significant effect on fluoride removal at high alkaline values. The results show that UiO-66-NH2 CNM exhibited high fluoride removal due to electrostatic interactions that strongly existed between F− and metal sites in MOF in addition to hydrogen bonds formed with MOF amino groups. The fluoride removal efficiency reached 95% under optimal conditions of 20 mg L−1, pH of 8, and 40% adsorbent dose at 60 min. The results revealed that UiO-66-NH2 CNM possesses a high maximum adsorption capacity (95 mg L−1) over UiO-66 CNM (75 mg L−1), which exhibited better fitting with the pseudo-second-order model. Moreover, when the initial fluoride concentration increased from 20 to 100 mg/L, fluoride adsorption decreased by 57% (UiO-66 CNM) and 30% (UiO-66-NH2 CNM) after 60 min. After three cycles, CNM revealed the regeneration ability, demonstrating that UiO-66-NH2 CNMs are auspicious adsorbents for fluoride from an aqueous medium.

Process modeling, characterization, optimization, and mechanisms of fluoride adsorption using magnetic agro-based adsorbent

In this study, fluoride removal from polluted potable water using magnetic carbon-based adsorbents derived from agricultural biomass was thoroughly investigated. An experimental matrix is designed considering the interactive effects of independent process variables (pH, adsorbent dose, contact time, and initial fluoride concentration) on the removal efficiency. Isotherms and kinetics studies, as well as anions interactions, were also investigated to understand the adsorption mechanisms further. The model parameters of isotherms and kinetics are estimated using nonlinear differential evolution optimization (DEO). Approaches like adaptive neuro-fuzzy inference system (ANFIS) and response surface methodology (RSM) are implemented to predict the fluoride removal and identify the optimal process values. The optimum removal efficiency of GAC-Fe3O4 (89.34%) was found to be higher than that of PAC-Fe3O4 (85.14%). Kinetics experiments indicated that they follow the intraparticle diffusion model, and adsorption isotherms indicated that they follow Langmuir and Freundlich models. Both PAC-Fe3O4 and GAC-Fe3O4 adsorbents have shown an adsorption capacity of 1.20 and 2.74 mg/g, respectively. The model predictions from ANFIS have a strong correlation with experimental results and superior to RSM predictions. The shape of the contours depicts the nonlinearity of the interactive effects and the mechanisms in the adsorption process.

Chemical precipitation at extreme fluoride concentration and potential recovery of CaF2 particles by fluidized-bed homogenous crystallization process

Excessive and industrial advances have increased fluoride quantity in the effluents. However, the environmental carrying capacity for fluoride is relatively slim immediately affecting both aquatic and terrestrial animals while its transport can further contaminate the water source. To protect the public and the environment, different environmental agencies globally set their respective effluent standard restricting F- concentration to 15 mg/L as the median value. However, various processes from previous investigations have mostly been limited in treating 100–1000 mg F-/L with secondary pollution commonly overlooked. Re-assessing the available defluoridation technologies, chemical precipitation has still been the most feasible among the technologies, especially extremely high fluoride concentrations. In this study, fluoride removal through chemical precipitation was investigated using conventional precipitation and fluidized-bed homogeneous crystallization. Parameters such as a wide range of initial concentrations from 100 to10,000 mg/L and pH 2.0–11.0 under conventional precipitation were varied and analyzed. To reduce high water content sludge, a 550-mL cylindrical glass was modified to simulate a fluidized-bed reactor to investigate homogenous crystallization varying influent concentration, bed-support size, and fluid flow. Results showed that chemical precipitation could effectively remove fluoride even at very high fluoride concentrations ranging from 1,000 to 10,000 mg/L. Alternatively in the fluidized-bed granulation process, an initial very low flow without recirculation flow was required to initiate particle formation. The predominant size of the recovered particle was < 0.2 mm which was relatively heavy atypically not reaching the upper region of the reactor. Under the observed optimum condition with an initial fluoride concentration of 450 mg/L, both total removal and crystallization ratio could reach ∼ 98% efficiency lowering fluoride concentration to < 15.0 mg F-/L within 7 days.

OPTIMISATION AND MODELING OF FLUORIDE REMOVAL BY ELECTROCOAGULATION IN A CONTINUOUS FLOW BIPOLAR REACTOR

In this study an experimental design was employed to investigate the effects of different operating conditions on the removal of fluoride by electrocoagulation with aluminum electrodes. Box-Behnken design was then used for optimizing and modeling the electrocoagulation process and for evaluating the effects and interactions of variables: current density (i, A/m2), flow rate (Q, mL/min), and initial fluoride concentration (C0, mg/L). The proposed model fitted very well with the experimental data. R2 adjusted correlation coefficients (AdjR2: 0.98) for fluoride removal efficiency showed a high significance of the model. The model predicted for a maximum removal of fluoride (95.07%) at the optimum operating conditions (120 A/m2, 120 mL/min and 30 mg/L) after the EC process was 94.76% at the same optimum operating conditions.

Activated tamarind seed coat: a green biosorbent to remove fluoride from aqueous solutions

Abstract A novel, inexpensive, easily available and eco-friendly biosorbent, Tamarindus indica activated seed coat, has been evaluated for its capability to remove fluoride from water. Batch experiments were carried out to study the effect of various parameters affecting the biosorption such as pH (2–10), biosorbent dose (0.05 g/L to 0.35 g/L), contact time (10–80 min) and initial fluoride concentration (0.001–0.006 g/L) for the biosorption of fluoride at room temperature. The maximum removal of fluoride was found at pH 6, biosorbent dose 0.3 g and contact time 60 min. Physicochemical characterization studies revealed the suitable morphology and chemical functional groups present on the biosorbent. Isothermal data agreed well with the Langmuir isotherm adsorption model with R2 value 0.976 and KL 0.1. The biosorption interface of fluoride onto Tamarindus indica activated seed coat obeyed the pseudo-second-order rate equation with R2 0.976. The present study demonstrates that Tamarindus indica activated seed coat can effectively remediate fluoride-contaminated water.

Simultaneous adsorption of manganese and fluoride from aqueous solution via bimetal impregnated activated carbon derived from waste tire: Response surface method modeling approach

AbstractAdsorptive removal of manganese and fluoride from wastewater by waste tire‐derived activated carbon impregnated with iron and cobalt has been presented in this article. The surface properties of bimetallic activated carbon were characterized in scanning electron microscopy (SEM), Brunauer–Emmett–Teller (BET), and X‐ray diffraction (XRD). The newly developed adsorbent was used for simultaneous removal of fluoride and manganese from aqueous solution. Present work focuses on the optimization of process parameters using response surface method (RSM) technique employing significant parameters, namely, adsorbent dosage, initial fluoride and manganese concentrations, contact time and pH. Central composite design in RSM was utilized for the levels of adsorbent dosage (0.5–1 g/L), initial fluoride concentration (20–40 ppm), initial manganese concentration (30–50 ppm), time (15–35 min), and pH (4–8) of the solution. The R2 value obtained from the statistics data was 96.25 and 97.57% for fluoride and manganese, respectively. The optimal values were determined as the adsorbent dosage of 1.25 g/L, initial fluoride concentration of 10 ppm, initial manganese concentration of 25.25 ppm, the contact time of 30.9 min and pH of solution of 2.0, under which 99.96% manganese and 85.34% fluoride removal efficiency could be accomplished.