Application In Defluoridation Research Articles

Electrochemically generated adsorbent synthesis using reverse osmosis reject and its application in defluoridation with significant parameter optimization

Electrochemically generated adsorbent synthesis using reverse osmosis reject and its application in defluoridation with significant parameter optimization

Saw dust-derived activated carbon in different impregnation ratios and its application in de-fluoridation of waste water using IT2FLC and RSM

Saw dust-derived activated carbon in different impregnation ratios and its application in de-fluoridation of waste water using IT2FLC and RSM

Preparation and Characterization of Biogenic Chitosan-Hydroxyapatite Composite: Application in Defluoridation

ABSTRACTIn Northern Tanzania, high levels of fluoride in community drinking water supply is recognized as one of the major public health concern, the problem is further ameliorated by presence Escherichia coli and fecal coliform bacteria in surface water and shallow wells. Efforts to decontaminate the water involve mostly the use of low efficient bone char for fluoride removal without disinfecting the pathogens. To address this problem, a robust adsorbent which is capable of removing fluoride and microbes simultaneously with minimal diverse impact on the treated water is necessary. Here we highlight development of composite material developed from recycling of crustacean biomass waste from sea food industry. Chitosan polymer, isolated from prawns shell was composited with crab shell derived brushite (CaHPO4.2H2O) to form chitosan-hydroxyapatite composite. XRD and FT-IR analysis confirmed transformation of brushite phases into hydroxyapatite and formation hybrid composite. Fluoride adsorption tests were performed in batch mode to evaluate effectiveness. Defluoridation capacity of up to 6.4 mg/g in field water containing fluoride concentration of 5-70 mg/L was achieved. The best performance was observed with fluoride concentration of 10 mg/L and below. Apart from fluoride removal, the composite also reduced color tint and microbes from surface water samples. The pH of the treated water in most samples remained around 6.5-8.5, which is acceptable for drinking water.

Performance of Mn2+ modified Bentonite Clay for the Removal of Fluoride from Aqueous Solution

Alow-cost adsorbent produced from Mn 2+ -modified bentonite clay was evaluated for groundwater defluoridation. Batch experiments were used to evaluate the effect of contact time at various adsorbent dosages, adsorption isotherms and the effect of pH on fluoride removal. The results showed that the optimum F – uptake occurred within the first 30 min contact time and the percentage removal increased with increasing adsorbent dosage. The data fitted better to pseudo-second-order reaction indicating that F – adsorption occurred via chemisorption. The Weber-Morris model of intra-particle diffusion revealed that both surface and intra-particle diffusion processes were involved during the F – adsorption process. Furthermore, the batch results showed that pH of the solution governed the percentage of fluoride removal with the optimum of 75.2 % fluoride removal achieved at pH 4. The adsorbent chemical stability assessment showed that chemical species were leached at trace concentrations which are within the South African National Standards (SANS) limits. Electrostatic attraction and ion-exchange were established as the major mechanisms responsible for fluoride adsorption at acidic pH and at moderate to alkaline pH levels, respectively. The study demonstrated that Mn 2+ intercalated bentonite clay has potential for application in defluoridation of groundwater. Keywords: Adsorption, defluoridation, ion exchange, ligand exchange, intra-particle diffusion

Crustacean derived calcium phosphate systems: Application in defluoridation of drinking water in East African rift valley

Calcium phosphate adsorbents, derived from prawns and crabs shell biomass wastes have been developed using wet chemistry and low temperature treatment. The adsorbents were characterized by X-ray diffractometry and Fourier transform infrared spectroscopy. Batch adsorption test were carried out to investigate their effectiveness in adsorption of fluoride from ground and surface waters. Adsorption capacities were compared with bone char and synthetic hydroxyapatite (CCHA). Results indicate that prawns derived adsorbent (PHA) formed hexagonal structure with phases identifiable with hydroxyapatite while crabs based adsorbent (CHA) formed predominantly monoclinic structure with crystalline phase characteristic of brushite. Vibrational analysis and kinetic studies predicted defluoridation occurred mainly by ion exchange and ion adsorption mechanisms. Defluoridation capacity of the adsorbents was found to be superior compared to bone char and CCHA. CHA was the most effective with efficiencies above 92% and highest capacity of 13.6 mg/g in field water with fluoride concentration of 5–70 mg/L. PHA had highest capacity of 8.5 mg/g which was still better than 2.6 mg/g recorded by CCHA and bone char. Adsorption was best described by pseudo 2nd order kinetics. The findings indicate that crustacean derived calcium phosphate systems have better potential for defluoridation than traditional bone char and synthetic systems.

Synthesis, characterization, and potential application of Mn2+-intercalated bentonite in fluoride removal: adsorption modeling and mechanism evaluation

The study synthesizes a low-cost adsorbent made from Mn2+-modified bentonite clay for groundwater defluoridation. The clays were characterized using X-ray diffraction, X-ray fluorescence, scanning electron microscopy, and Fourier transform infrared techniques. The fluoride adsorption capacity of the modified clay was evaluated using batch experiments. The adsorption kinetics results showed that the optimum fluoride (F−) uptake was achieved within the 30 min’ contact time. The data fitted well to pseudo-second-order of reaction kinetics indicating that adsorption of F− occurred via chemisorption. In addition, the adsorption isotherm data fitted well to Langmuir isotherm model indicating that adsorption occurred on a mono-layered surface. Maximum F− removal of 57% was achieved from groundwater with an initial F− concentration of 5.4 mg L−1 and natural pH of 8.6 using adsorbent dosage of 1 g/100 mL. Fluoride adsorption occurred through ligands and ion exchange mechanisms. The synthesized adsorbent was successfully regenerated for up to five times. The study shows that Mn2+-intercalated bentonite clay has potential for application in defluoridation of groundwater.

Synthesis of graphene oxide using tea-waste biochar as green substitute of graphite and its application in de-fluoridation of contaminated water

In the present study, pyrolysis of domestic tea waste was carried out to yield bio-char. The biochar obtained was further used as a substitute for graphite in synthesis of graphene oxide (GO) in the conventional process. GO obtained was further applied for fluoride removal from simulated effluents. The prepared adsorbent was characterized using SEM, XRD and FTIR analysis. Effect of different experimental parameters on the de-fluoridation efficiency of the reported adsorbent was investigated. Data obtained was further used for determination of process isotherms, kinetics and thermodynamics. The regeneration potential of the reported adsorbent was also determined. The experimental results suggested that equilibrium adsorption data was strongly guided by the Langmuir isotherm and pseudo-second-order kinetics. Analysis of process thermodynamics also revealed that the adsorption reaction was spontaneous chemisorption in nature. Significant process parameters including GO dosage, ambient temperature and contact time were optimized using Response surface methodology (RSM) and artificial neural network (ANN). Results of RSM and ANN analysis indicated good correlation between experimentally recorded and theoretically predicted % fluoride removals. Under optimized conditions, fluoride removal efficiency was found to be 98.31%. Therefore, it can be inferred that tea waste derived biochar may be accepted as a sustainable alternative of graphite for GO synthesis. Moreover GO so obtained has immense potential for de- fluoridation of effluents in highly reduced dosage and treatment time.

Characterisation of smectite-rich clay soil: Implication for groundwater defluoridation


 
 
 Groundwater is a widely used and affordable source of drinking water in most of the rural areas of South Africa. Several studies have indicated that groundwater in some boreholes in South Africa has a fluoride concentration above the level recommended by the World Health Organization (1.5 mg/L). Fluoride concentrations above the permissible limit (>1.5 mg/L) lead to dental fluorosis, with even higher concentrations leading to skeletal fluorosis. In the present work, we evaluate the application of smectite-rich clay soil from Mukondeni (Limpopo Province, South Africa) in defluoridation of groundwater. The clay soil was characterised by mineralogy using X-ray diffraction, by elemental composition using X-ray fluorescence and by morphology using scanning electron microscopy. Surface area and pore volume was determined by the Brunauer–Emmett–Teller surface analysis method. Cation exchange capacity and pHpzc of the soil were also evaluated using standard laboratory methods. Batch experiments were conducted to evaluate and optimise various operational parameters such as contact time, adsorbent dose, pH and initial adsorbate concentration. It was observed that 0.8 g/100 mL of smectite-rich clay soil removed up to 92% of fluoride from the initial concentration of 3 mg/L at a pH of 2 with a contact time of 30 min. The experimental data fitted well to a Langmuir adsorption isotherm and followed pseudo second order reaction kinetics. Smectite-rich clay soil showed 52% fluoride removal from field groundwater with an initial fluoride concentration of 5.4 mg/L at an initial pH of 2 and 44% removal at a natural pH of 7.8. Therefore smectite-rich clay soil from Mukondeni has potential for application in defluoridation of groundwater. Chemical modification is recommended to improve the defluoridation capacity.
 
 
 
 
 Significance: 
 
 
 
 Physicochemical and mineralogical characterisation of smectite-rich clay soil
 Defluoridation of groundwater using smectite-rich clay soil
 Adsorption modelling using adsorption isotherms and kinetic models
 
 
 

Sol–gel synthesis of nanoparticles of gamma alumina and their application in defluoridation of water

Water solvent-based sol–gel process was employed in the synthesis of nanoparticles of gamma alumina (NPGA) which were used for the removal of fluoride from water of neutral pH. Different techniques like thermogravimetric analysis, Fourier transform infrared spectroscopy, X-ray diffraction, and field emission scanning electron microscopy were employed for the characterization of the synthesized particles. Batch adsorption studies were performed for the optimization of contact time and adsorbent doses to obtain maximum fluoride removal and understanding of the adsorption kinetics and mechanism. The maximum adsorption capacity of NPGA for fluoride removal was estimated to be nearly 14 mg/g at room temperature (30 °C) which is better than fluoride removal reported by earlier using of commercial-grade NPGA. Adsorption kinetics measurement indicated that Langmuir equilibrium model is found to be more suitable for describing the fluoride adsorption mechanism.

A low cost approach to synthesize sand like AlOOH nanoarchitecture (SANA) and its application in defluoridation of water

This paper describes a chitosan template assisted synthesis of nanocrystalline aluminium oxyhydroxide (γ-AlOOH) at an ambient temperature (30±2°C) and atmospheric pressure. High ability of the composite in removing fluoride from water has been demonstrated. The structural, morphological and compositional characteristics of the composite were studied using various spectroscopic and microscopic techniques. The results showed that the composite has nanoarchitecture comprising a number of γ-AlOOH nanoparticles of size less than 10nm attached to the fibrils of chitosan. Batch and continuous flow adsorption experiments were conducted to assess the parameters that influence the adsorption process. The parameters investigated include contact time, initial fluoride concentration, adsorbent dose, pH of the solution, co-existing ions in water, and size of the adsorbent granules. The composite showed good affinity to fluoride and the maximum uptake capacity was 13.47 (mg/g) (mg/L)−1/n as described by Freundlich isotherm model. The kinetics of adsorption was affected by the size of the granules and the kinetic data followed pseudo-second-order rate equation. Except bicarbonate and sulfate, other competing ions studied did not affect the uptake of fluoride significantly. The high affinity to fluoride, simple and eco-friendly synthesis approach demonstrate the utility of the material for defluoridation of water.

Initial fluoride concentration and loading capacity in defluoridation with bauxite, gypsum, magnesite and their composite

One of the parameters that impact on fluoride sorption capacities of materials in water defluoridation is initial concentration. Water from various sources will have different fluoride concentrations; as such the employment of a particular media in defluoridation requires information on how the media will perform in different concentrations. Consequently, research was carried out to determine how initial fluoride concentrations in raw water affect capacity in defluoridation with bauxite, gypsum, magnesite and their composite, and to investigate the possibility of predicting loading capacity of their composite filter through initial fluoride concentration to optimize their application in defluoridation. The results showed that sorption capacities increased with increase in initial concentrations. However, higher starting concentrations resulted in larger residual fluoride concentrations; as such the benefit of large sorption capacities obtained was overshadowed. Polynomial relations of capacity (Cs, mg/g) and initial concentration (Co, mg/l), were obtained for bauxite and gypsum. Magnesite obtained a logarithmic relation for Cs and Co. A power relation was obtained between Cs and Co for their composite, Cs = 0.0328C1.20160. Approximation of capacities of this composite from initial fluoride concentrations was feasible. Water defluoridation has become important as a result of dental and skeletal fluorosis.

Removal of Fluoride from Water by Adsorption onto Lanthanum Oxide

Rare earth mineral based adsorbent viz. lanthanum oxide was investigated for potential application in defluoridation of drinking water for isolated and rural communities. Results of batch experiments indicated about 90% removal in 30 min from a 4 mg L−1 synthetic fluoride solution. The effects of various parameters like contact time, pH, initial concentration, and sorbent dose on sorption efficiency were investigated. Adsorption efficiency was dependent on initial fluoride concentration and the sorption process followed BET model. Variation of pH up to 9.5 has insignificant effect on sorption and beyond a pH of 9.5, the effect was drastic. Among anions investigated, carbonates exhibited high detrimental effect on fluoride adsorption while anions like bicarbonates, chlorides, and sulfates did not seriously affect the process. Adsorbent showed negligible desorption of fluoride in distilled water. Alum was more effective regenerant than HCl and NaOH. Results of cyclic regeneration with alum indicated that the sorbent could be regenerated for ten cycles without significant loss of sorption capacity. Studies with upflow fixed-bed continuous flow columns indicated the usefulness of sorbent for fluoride removal in continuous flow process.