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Granulation of Fe–Al–Ce nano-adsorbent for fluoride removal from drinking water by spray coating on sand in a fluidized bed
Abstract
A technology for the granulation of Fe–Al–Ce nano-adsorbent (Fe–Al–Ce) in a fluidized bed was developed. The coating reagent, a mixture of Fe–Al–Ce and a polymer latex, was sprayed onto sand in a fluidized bed. The granule morphology, coating layer thickness, granule stability in water and adsorption capacity for fluoride was investigated by analyzing samples for different coating time. The coating amount was from 3% to 36%. With increasing coating amount, granule stability decreased and adsorption capacity increased. FTIR analysis showed that the latex can react with active hydroxyl on the Fe–Al–Ce adsorbent, which led to a decrease of the adsorption capacity. Coated granules with a coating amount of 27.5% had a fluoride adsorption capacity of 2.22 mg/g (coated granules) at pH 7 and initial fluoride concentration of 0.001 M. A column test showed that 300 bed volumes can be treated with the effluent under 1.0 mg/L at an initial fluoride concentration of 5.5 mg/L, space velocity of 5 h− 1 and pH of 5.8. The coating granulation of the Fe–Al–Ce adsorbent can produce granules that can be used in a packed bed for the removal of fluoride from drinking water.Graphical AbstractA technology for the granulation of Fe–Al–Ce nano-adsorbent by spray coating on sand with an acrylic-styrene copolymer latex as a binder in a fluidized bed was developed. The effects of coating amount on adsorption capacity and the stability of the granules were investigated. Using the coated granules as adsorbent, high stability and fluoride adsorption capacity was achieved.
... Chen et al. [98] developed a method for granulation of nano-Fe-Al-Ce coated sand to use in a fluidized bed for defluoridation to produce drinking water. Polymer latex was used as a coating agent. ...
... These modified Fe-Al-Ce nanoadsorbent coated sand granules showed a maximum fluoride adsorption capacity of 2.8 mg/g . [98,99] Kuang et al. [100] anchored iron oxide nanoparticles on graphene oxide surface with (FeOOH +Ac/GO) and without acetic acid (FeOOH/GO). They investigated the effect of acetate as a novel crystal modifier during the synthesis of metal-based adsorbents. ...
... Nanomaterials coated or anchored on support/ matrix tend to block some fraction of the adsorbent surface area. This may explain the low adsorption capacity of some non-porous composite nanoadsorbents [96][97][98][99] compared to nanoparticle loaded porous support-based composite adsorbents . [29,46,47,49] However, some non-porous nanoadsorbents (nanoparticles coated on support medium) [96] have also demonstrated better adsorption capacities than porous nanocomposite materials [79,80] because fluoride removal not only depends on the porous nature of nanocomposite but also on the ion specificity of the adsorbent material. ...
In groundwater, excess fluoride concentration (>1.5 mg/L) is a primary concern for various countries. Nanoadsorbents have been proven to possess higher adsorption capacity than conventional adsorbents. This review aims to provide insights into recent advancements in the adsorption of fluoride using various nanoadsorbents. Nanoparticles have very high specific surface area but are usually found unsuitable for real field applications as they tend to agglomerate. They are also difficult to recover after use and pose a significant threat to the environment through leaching. These limitations have given rise to the trend of the development of nanocomposites for defluoridation. Nanocomposites often involve a polymeric matrix that serves as a medium for their homogenous dispersion. This reduces agglomeration and leaching into the surroundings without altering the original activities of the nanoadsorbent. This review classifies the fluoride nanoadsorbents into three categories: bare nanoparticles, nanocomposites with nanoparticles inside the porous matrix, and nanocomposites with nanoparticles coated with or anchored on the matrix surface. Critical analyses of the importance and shortcomings of these classes have been presented. In general, bare nanocomposites show the best fluoride adsorption performance compared to other classes of nanoadsorbents.
... In recent years, considerable attention has been paid to synthesizing composites, especially tri-metal composites of rare earth-based adsorbents, because the amounts of rare earths used can be significantly reduced in the composites, thus resulting in relatively low cost. Several tri-metal nanocomposites such as Fe-Al-Ce nanocompsites, 12 Fe-Mg-La composites, 7 Ca-Al-La hydroxides 13 and Al-Zr-La hydroxides have been developed. 14 Unfortunately, the F − adsorption capacity of most of them is not satisfactory. ...
... 14 Unfortunately, the F − adsorption capacity of most of them is not satisfactory. 7,[12][13][14] It is well known that size and shape are important for nanomaterial properties; [15][16][17] however, morphology control has not been paid enough attention in most of these tri-metal adsorbents, because most previously reported tri-metal F − adsorbents were amorphous. 7,[12][13][14] Therefore regular control of their morphology may be one effective way to improve their adsorption performance. ...
... 7,[12][13][14] It is well known that size and shape are important for nanomaterial properties; [15][16][17] however, morphology control has not been paid enough attention in most of these tri-metal adsorbents, because most previously reported tri-metal F − adsorbents were amorphous. 7,[12][13][14] Therefore regular control of their morphology may be one effective way to improve their adsorption performance. 18 In order to investigate morphological effects on fluoride adsorption, a novel La-Zr-Ce tri-metal adsorbent was prepared in this study. ...
BACKGROUND
Composites of defluoridation adsorbents based on rare earths have attracted increasing interest recently, but most of them were amorphous. The main reason for this situation is that morphology control has not been paid enough attention, because the related preparation methods are relatively sparse. Consequently, novel preparation methods are urgently needed.
RESULTS
In this study, a novel La‐Zr‐Ce tri‐metal adsorbent with regular morphology was facilely synthesized. There were two morphological shapes in the composite. Nanoprisms of La2(C2O4)3 were decorated with mesoporous nanospheres of Fe3O4@m(ZrO2‐CeO2). The samples were investigated by energy‐dispersive spectroscopy (EDS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X‐ray diffraction (XRD), vibrating sample magnetometer (VSM) and X‐ray photoelectron spectroscopy (XPS). Several affecting factors such as initial fluoride concentration, contact time, coexisting anions and pH were studied in detail. The balance data were analyzed by Langmuir, Freundlich and Langmuir–Freundlich isotherm models. The nanocomposite had a maximum sorption capacity of 117.3 mg g⁻¹ toward fluoride, which is among the highest ever reported for fluoride adsorbents. Furthermore, it had a wide applicable pH range of 2–10 and high anti‐interference ability. The different functions of La2(C2O4)3 nanoprisms and Fe3O4@m(ZrO2‐CeO2) nanospheres in the composite have been elucidated. These two components were found to synergistically improve F⁻ adsorption performance via their individual merits.
CONCLUSION
The adsorbent had high potential to treat F⁻ contaminants in real application, and the method reported here is considered to be helpful for developing more highly effective adsorbents. © 2019 Society of Chemical Industry
... Few studies related to spray coating in the production of adsorbent coating have been stated. Chen et al. (2009) and Wu et al. (2008) share similar studies regarding fluoride treatment from water using adsorbent coating prepared by the spray-drying method. The adsorbent coating solution was formulated from iron-aluminum-cerium tri-metal hydroxide (Fe/Al/Ce) suspension, added with acrylic-styrene (copolymer latex) in the form of a binding agent. ...
... The sand was placed in a fluidized bed and sprayed. The coated sand was dried at 35°C to complete the process [71,132]. ...
“Drink up” wastewater using adsorption technology is considered an effective tactic to switch water scarcity. A proactive environmental strategy has to be established in order to increase the environmental sustainability performance particularly in obtaining cleaner wastewater discharges as well as reducing the operating cost. The adsorption process has proven efficient in eliminating the pollutants, only if the suitable adsorbent is obtained in terms of high removal rate, high adsorption capacity, and sustainability. In this regard, an innovative low-cost adsorbent coating technology has been investigated to treat industrial wastewater. The classic form of adsorbent (powder, pellet, or bead) has been improvised in terms of its flexibility along with chemical and thermal stability in the wastewater treatment plant. The present review outlines the current research of adsorbent coating in wastewater treatment by holistically highlighting the advantages of adsorbent in a way of coating (lower energy usage, flexible design, simple yet efficient procedure, etc.). Among different adsorbents, clay-modified adsorbents have generated an innovative alternative to design flexible coatings. Moreover, it has a significant adsorption potential in dye treatment which is anticipated to demonstrate its industrial application. The use of common components in synthesizing the adsorbent coating along with the adsorption mechanism between the adsorbent and targeting pollutants have also been discussed in detail. Additionally, challenges and possible future direction on the development of flexible adsorbent coating to be handled in real wastewater treatment issues are also delineated.
... Ce, Mn-Ce, La-Ce and Fe-Al-Ce, Al-Ce Mn-Ce and Fe-Al-Ce as hybrid absorbents have also been investigated as potential absorbent materials because of their strong affinity to fluoride. ( (Chen J et al. 2013;Morales et al. 2020;Wang J et al.2018, Liu H et al. 2010, Deng S et al. 2011, Wu X et al. 2007, Chen L et al. 2009). ...
Fluoride concentration greater than 1.5 mg/L in drinking water affects more than 748 million of the global population causing life-threatening diseases like fluorosis amongst many others. In the present study, activated graphite incorporated with ceria nanocrystals was synthesized by simple two step wet chemical route for fluoride removal and subsequently characterized to define its physical and chemical properties based on analytical tools like SEM–EDX, FTIR, XRD, XPS and BET. The sorption experiments were carried out in batch mode for analyte concentration of 5 mg/L, and the obtained optimized parameters were pH 3, stirring time 10 min followed by static contact time of 1 h and adsorbent dosage 0.1 g in total aqueous volume of 50 ml at ambient temperature. The maximum adsorption capacity of the adsorbent was 7.6 mg/g towards fluoride which was comparable with various other adsorbents suggested in the literature. Langmuir and Temkin isotherms were the best-suited models for the equilibrium data at room temperature, Freundlich being more favourable with increase in temperature suggesting initial monolayer adsorption followed by multilayer adsorption with rise in temperature. The kinetics of adsorption appeared to follow pseudo-second-order model with intraparticle diffusion and boundary mass transfer also significantly influencing the rate-limiting step. Thermodynamic studies showed the adsorption process to be exothermic and spontaneous. From the interference studies based on commonly occurring anions and cations, sulphate exhibited adverse effect on adsorption. The synthesized adsorbent could be used for fluoride removal studies on real samples over five cycles and was successfully regenerated for reuse. The scaling up possibilities of the present methodology for defluoridation application appear impressive based on features like efficiency, selectivity, environmentally benign nature and economic viability of the ceria-impregnated activated graphite composite.
... Chen et al. have examined trimetal named Fe-Al-Ce NPs that are used acrylicstyrene copolymer latex to spray coating on the sand in a fluidized bed. The adsorption capacity was 2.22 mg/g in a coated granular at pH 7 (Chen et al., 2009). However, the mentioned adsorbents have major drawbacks, like regeneration of the adsorbent often required, less adsorption efficiency, and less surface area because of the agglomeration. ...
In this research article, a novel adsorbent (Zn-Fe-Al) was synthesized successfully by a simple chemical route where three oxides combined to enhance affinity towards fluoride. The physicochemical properties of the adsorbent were used to characterize and assess its effectiveness in defluoridation with both synthetic and groundwater. The TEM results demonstrated the overlapping of metals, and EDX shows the metals present in the adsorbent. The maximum defluoridation efficiency (97%) of Zn-Fe-Al was obtained at an optimized initial pH 7 and adsorbent dose 0.08 g L⁻¹. The fluoride adsorption on Zn-Fe-Al followed the D-R isotherm and intraparticle diffusion. The maximum adsorption capacity of Zn-Fe-Al was found to be 187 mg g⁻¹. The adsorption of fluoride on Zn-Fe-Al was found to be endothermic and spontaneous. The Zn-Fe-Al adsorbent exhibited satisfactory defluoridation performance on real groundwater. The co-existing ions were also investigated. The adsorption mechanisms for fluoride were electrostatic interaction and ion exchange. These results demonstrated that Zn-Fe-Al adsorbent was considered high potential for effective defluoridation of groundwater.
... However, due to their hydraulic conductivity, they are with inorganic or organic latex rather than packed beds. Fluoride adsorption capacity of Fe-Al-Ce nanoadsorbent was developed and investigated (Chen et al. 2009). A fluidized bed was covered with polymer latex containing this nanoadsorbent. ...
Groundwater has traditionally been recognized as a reliable, safe, and essential source of drinking water. Rapid population growth increases groundwater demand, resulting in overexploitation. The quality of groundwater is deteriorating day by day due to geogenic forces and pollutants. Fluoride is one of the biggest worries about groundwater contamination, which can have serious consequences for human health mainly as fluorosis. WHO has set a global rejection limit of 1.5 mg/l for fluoride; however, it is exceeded in many places of the world. Where no other source of safe drinking water is available, removing fluoride from drinking water is the only option for obtaining safe drinking water. This review discusses various removal options, based on a number of laboratory experiments and recognized literature. The findings show that the majority of removal methods are based on adsorption processes and suit well in bench scale conditions, but hybrid and real-world application-oriented economic strategies are still being developed. The ineffective removal of fluoride from water by a single treatment has led researchers to look for hybrid approaches. Bioremediation, a usually disregarded approach, is also offered for temporarily relieving fluoride levels due to a lack of wastewater treatment facilities that need large construction costs and phytoremediation is gaining popularity owing to its advantages.
... The IR band at 1650 cm − 1 due to H-O-H bending vibrations confirms the presence of surface-adhered water on ≡ Al y (OH) 3x [66]. The bands at 3676 cm − 1 and 3448 cm − 1 persist even after the evacuation, can be ascribed to -OH stretching and H-bonded -OH vibrations of ≡ AlOH [67]. Further, the appearance of a band at 1524 cm − 1 suggests the presence of surface ≡ AlOH bending vibrations. ...
Water treatment based on electrocoagulation (EC) is attractive since required chemicals and colloids are produced in-situ. However, optimization of EC operation parameters is necessary to enhance its efficiency. We optimized EC cell parameters by the response surface method (RSM). The optimal removal efficiencies of hardness (63%) and fluoride (97%) were achieved at 1.98 kWh/m³. With the removal of divalent cations, some anionic species concurrently remove via an energetically feasible route to adjust the charge balance. When simulated water is used (450 mg/L TDS, 580 mg/L CaCO3, 10 mg/L fluorides and pH 6.50), 83% hardness and 99% fluoride are removed with 0.69 kWh/m² energy consumption. The chemical species in the solution matrix, particularly SO42, significantly affect the hardness and fluoride removal efficiencies. The contaminated EC sludge resulted from feed water is characterized by spectroscopic methods to probe hardness and fluoride removal mechanisms. In the presence of Mg²⁺, F⁻ interacts with Al-sludge sites forming≡MgF−OH. When Ca²⁺ and F⁻ are present, both ≡CaF−OH and ≡CaF are formed. In Ca²⁺, Mg²⁺ and F⁻ treated Al-sludge dominates , CaF−OH and ≡CaF over ≡MgF−OH.
... Nano-hydroxyapatite (NHA), which is a major inorganic segment of human bone (Michael et al. 2016a, b), could also play a significant role in wastewater treatment. Nano-hydroxyapatite (Sairam et al. 2008), polypyrrole (PPy)/Fe 3 O 4 magnetic nanocomposites (Bhaumika et al. 2011) and Fe-Al-Ce nanoadsorbent (Chen et al. 2009) were used for defluoridation of water. Nano-hydroxyapatite showed a defluoridation capacity of 1845 mg/kg. ...
Day by day, the water sources are increasingly being adulterated due to various reasons including the uncontrolled discharge of pollutants from the point and nonpoint sources. Therefore, it is a timely need to develop suitable, inexpensive and efficient treatment techniques for water purification. This review aims at evaluating different water treatment technologies, their basic principles, cost and suitability for pollutants’ removal from wastewater. Among various water treatment technologies, adsorption technique appears to be techno-economically more attractive due to its inexpensiveness, universality and environment friendliness. Here, wide varieties of adsorbents (silica gel, activated alumina, clays, limestone, chitosan, activated carbon, zeolite, etc.) and their capacities for pollutant removal are described. The limitations of conventional adsorbent applications for water treatment are also discussed. Recently, nanotechnology has introduced nanoadsorbents, which have drawn additional attention due to their unique properties and are considered to be the viable alternative to conventional adsorbents. The potential applications, separation and regeneration of nanoadsorbents for wastewater treatment are also included in this review. Furthermore, prospects including commercial and health aspects of nanoadsorbents are also added.
... The granulation method allows both the structure of solid fine powders in agglomerated particles of almost specific shapes, and ameliorates the physical properties in terms of density, porosity, hardness, compressibility, and thus facilitates their use in the field of water treatment by adsorption in dynamic mode [31][32][33][34][35][36][37][38][39]. Furthermore, it avoids the production of undesirable non-pulp and which may form for injection in the case of a wet granulation between gluten and water. ...
A series of novel resistant granular sorbents based on iron granular surfactant modified pillared montmorillonite and gluten as binder noted (Fe-GSMPM) are prepared and used in adsorption towards
hydrosoluble micropollutants. The batch sorption of Malachite Green (MG) and/or Rhodamine B (RB) both on single and binary component systems from aqueous solutions was investigated. In all
used component systems, sorption capacities were depending both on the pH and the granule size. In single-component systems, results showed that sorption on Fe-GSMPM are very effective and more quickly with MG than RB with obtained amounts reached more than 9 and 6 mg/g at pH = 6 and strongly decreased more than 3 mg/g for both solutes at pH = 3, respectively. In binary component systems at different weight ratios r (MG/RB = 1/9, 1/3, 1, 3 and 9) and at pH 6, the sorption capacities decreased significantly with values lower than those obtained in single-component systems. Isotherms were best described using the Freundlich model in single component systems with R² reach 0.9. In binary mixture systems, results indicate that the Sheindorf–Rebhun–Sheintuch (SRS) model provides the best correlation of the experimental data by the higher competition coefficients, which increase with decreasing weight MG/RB ratio.
... The maximum adsorption capacity of fluoride by using the Langmuir model was obtained 163.3 mg/g at the pH range of 2-8. An acrylic-styrene copolymer latex incorporated with binder Fe-Al-Ce and spray-coated onto sand in a fluidised bed by Chen et al. [74]. Latex was observed to rise stability of coated layer. ...
The demand for pure and clean water increased in the developing states due to their growing population. Hence, the treatment of toxic elements especially fluoride in aqueous solution has emerged a major issue of their public concern. The fluoride pollution in the aqueous system is due to natural and anthropogenic activities which cause several diseases, i.e. Arthritis, cancer, brittle bones, brain damage. The present review article highlights different types of removal techniques including Adsorption, Ion exchange, Membrane filtration and Electrocoagulation used for the elimination of fluoride from aqueous media. The maximum removal capacity of fluoride by fly ash adsorbent was obtained up to 332.5 mg/g. However, the removal efficiency using other technologies such as ion exchange, membrane filtration and electrocoagulation was achieved up to 90–95%, 99% and 85.5%. Among them, adsorption has been explored widely as a very effective and efficient method due to its easy operation, low cost and give satisfactory results. In this perspective, various adsorbents are discussed in this review, i.e. activated carbon, activated alumina, bio-sorbents, natural-based sorbents, agricultural waste sorbents, nano-sorbents and industrial waste sorbents but still there is need to develop such type of materials on a marketable scale for the control of pollution. It is evident from the literature review that every technique showed novel potential for the remediation of toxic fluoride ion.
This study investigates the synthesis and characterization of Al2O3 nanoparticles derived from multilayered packaging (MLP) waste, specifically postconsumer coffee capsules, and evaluates their efficacy in fluoride adsorption from aqueous solutions. The nanoparticles were synthesized using a facile thermal degradation technique followed by leaching and precipitation processes. Characterization techniques, including inductively coupled plasma‐mass spectroscopy, XRF, Fourier transform infrared spectroscopy, X‐ray diffraction, and transmission electron microscope, confirmed the formation of γ‐Al2O3 nanoparticles with a cubic crystal structure. The adsorption process was found to be endothermic and spontaneous, with a maximum adsorption capacity of 9.60 mg/g. Kinetic studies revealed that the pseudo‐second order model best described the adsorption process, indicating a complex multistep mechanism involving both physisorption in the initial rapid adsorption and chemisorption in the latter slower phase. The Freundlich–Langmuir isotherm provided the best fit for equilibrium data suggesting a complex adsorption mechanism involving both homogeneous and heterogeneous surface interactions. The presence of competing anions, particularly carbonate and phosphate, significantly affected the adsorption efficiency. This research demonstrates the potential of upcycling MLP waste into valuable adsorbents for wastewater treatment applications, offering both environmental and economic benefits.
Hydroxyapatite is the one of the promising defluoridating material. For easy separation and to enhance defluoridation capacity (DC), magnetic iron oxide cum β‐ cyclodextrin functionalized hydroxyapatite was prepared and because of its powder form it cannot be used in column studies. To make functionalized magnetic hydroxyapatite in usable bead form it was encapsulated using hybrid biopolymers chitosan and gelatin named as magnetic iron oxide/gelatin‐chitosan/hydroxyapatite/ β‐ cyclodextrin (MGCHC) composite beads were fabricated and utilized for rapid fluoride removal. The obtained MGCHC hybrid beads exhibited DC of 4985 mgF ⁻ kg ⁻¹ within 30 min. In co‐anions studies, Cl ⁻ , SO 4 ²⁻ and NO 3 ⁻ had little influence on fluoride adsorption, whereas HCO 3 ⁻ had major influence on fluoride adsorption. The isotherm and kinetic data of MGCHC beads toward fluoride removal was effectively portrayed with Langmuir and pseudo‐second order model respectively. Defluoridation mechanism of MGCHC beads were mainly followed by electrostatic attraction, ion‐exchange and complexation. This investigation using MGCHC beads affords cost‐effective and eco‐friendly for fluoride removal which gives a practicable way for the fluoride treatment from field water.
The magnetic hybrid material, namely, iron oxide/alginate–gelatin/hydroxyapatite/covalent organic framework (MAGHCOF)-based bio-hybrid beads were prepared and utilized for fluoride removal studies.
Fluoride is recognized as a vital ion for human and animal growth because of the critical role it plays in preventing skeletal and dental problems. However, when it is ingested at a higher concentration it can cause demineralization of teeth and bones resulting in fluorosis, therefore, the production of high-adsorptive capacity material which is also cost-effective is necessary for the treatment of fluorides. In this study, aluminium foil is valorised into alumina nanoparticles. The as-prepared alumina was modified with alum in two different ratios of 1:0.5 and 1:1 (alumina to alum w/w%) and later used as adsorbents for the removal of fluoride from groundwater. The adsorbents were characterized by Fourier transform infrared spectroscopy, point of zero charge and X-ray diffraction. Different factors that influence the removal efficiency of fluorides such as pH, initial concentrations, contact time and adsorbent dosage were studied and optimized using a simulated fluoride solution. The optimum conditions obtained were used to test real groundwater. The static experiment conditions were used to calibrate a PHREEQC geochemical model which was later used to simulate the fluoride sorption onto the modified alumina at different conditions. PHREEQC was also coupled with parameter estimation software to determine equilibrium constants for the surface reactions between the fluoride species and the adsorbent in a way that the simulations accurately reflect the outcomes of laboratory experiments. Isotherm studies were carried out on the adsorbents. Both Langmuir and Freundlich's non-linear models fitted well for the equilibrium data. However, with a higher coefficient of regression and low chi-square test values, the adsorption process was more of chemisorption on a monolayer surface. Kinetic studies were also carried out by using the non-linear equations from the pseudo-first-order and pseudo-second-order models. The pseudo-second-order model fitted well for the equilibrium data. The mechanism for the fluoride ion adsorption was also studied by the intraparticle (IP) diffusion model and was found that IP was not the rate-determining factor, and therefore the most plausible mechanism for the sorption process was ion exchange or attraction of fluoride ions to the sorbent surface. The findings obtained from this research show that readily available aluminium waste could be valorised into a useful product that could be employed in the removal of fluoride from water samples, including groundwater, that may contain too much fluoride and pose a risk to the general public's health.
The surplus fluoride in drinking water leads to diseases namely fluorosis (dental, skeletal, and non‐skeletal). Hence, to overcome these problems, in this study, hydrotalcite (HT) integrated La‐based metal‐organic frameworks (LaMOFs) namely HT‐LaMOFs was fabricated for fluoride removal. The fabricated HT‐LaMOFs material was well characterized by various characterization methods (x‐ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), Energy‐dispersive X‐ray spectroscopy (EDAX), thermogravimetric analysis (TGA), and differential thermal analysis (DTA)) to find the structural properties and stability of HT‐LaMOFs. To find the fluoride adsorption nature, the batch studies were employed towards fluoride adsorption such as reaction time, co‐ions, HT‐LaMOFs dosage, pH, initial fluoride concentration, selectivity, pHzpc, and temperature studies. The contact time studies results reveals that the defluoridation capacity (DC) of HT‐LaMOFs was towards fluoride was found as 4451 mgF⁻ kg⁻¹ at 30 min than HT (1030 mgF⁻ kg⁻¹ at 50 min). The DC had little influences in the presence of HCO3⁻ ion compared to other ions. Fluoride adsorption mechanism of HT‐LaMOFs was initiated to be electrostatic interaction, ion‐exchange and complexation. Fluoride adsorption onto HT‐LaMOFs was well matched and followed with Langmuir model. Thermodynamic investigations exposed that the adsorption of fluoride onto HT‐LaMOFs followed by spontaneous and endothermic nature. Kinetic studies of HT‐LaMOFs on fluoride capture followed with pseudo‐second‐order and intraparticle diffusion models. Defluoridation by HT‐LaMOFs was followed endothermic with spontaneous nature of adsorption system. The regeneration study results of HT‐LaMOFs revealed that the developed HT‐LaMOFs was regenerable up to six cycles. In addition, field study outcomes revealed that the developed HT‐LaMOFs diminished fluoride concentration under the acceptable limit as 1.5 mg/L.
Fluoride is recognized as a vital ion for human and animal growth because of the critical role it plays in preventing skeletal and dental problems. However, when it is ingested at a higher concentration it can cause demineralization of teeth and bones resulting in fluorosis, therefore, the production of high-adsorptive capacity material which is also cost-effective is necessary for the treatment of fluorides. In this study, aluminium foil is valorised into alumina nanoparticles. The as-prepared alumina was modified with alum in two different ratios of 1:0.5 and 1:1 (alumina to alum w/w%) and later used as adsorbents for the removal of fluoride from groundwater. The adsorbents were characterized by Fourier transform infrared spectroscopy (FTIR), point of zero charge and X-ray diffraction (XRD). Different factors that influence the removal efficiency of fluorides such as pH, initial concentrations, contact time and adsorbent dosage were studied and optimized using a simulated fluoride solution. The optimum conditions obtained were used to test real groundwater. The static experiment conditions were used to calibrate the PHREEQC geochemical model which was later used to simulate the fluoride sorption onto the modified alumina at different conditions. PHREEQC was also coupled with parameter estimation software (PEST) to determine equilibrium constants for the surface reactions between the fluoride species and the adsorbent in a way that the simulations accurately reflect the outcomes of laboratory experiments. Isotherm studies were carried out on the adsorbents. Both Langmuir and Freundlich's non-linear models fitted well for the equilibrium data. However, with a higher coefficient of regression and low chi-square test values, the adsorption process was more of chemisorption on a monolayer surface. Kinetic studies were also carried out by using the non-linear equations from the pseudo-first-order and pseudo-second-order models. The pseudo-second-order model fitted well for the equilibrium data. The mechanism for the fluoride ion adsorption was also studied by the intraparticle (IP) diffusion model and was found that IP was not the rate-determining factor and therefore the most plausible mechanism for the sorption process was ion exchange or attraction of fluoride ions to the sorbent surface. The findings obtained from this research show that readily available waste could be valorised into a useful product that could be employed in the removal of fluoride from water samples, including groundwater, that may contain too much fluoride and pose a risk to the general public's health.
The excess fluoride in drinking water is serious risk which leads to fluorosis. The adsorption method is facile route for defluoridation studies. Hybrid adsorbent possesses unique advantages like high surface area and high stability has been employed for water treatment. In the present work, hydrotalcite (HT) fabricated Ce-metal organic frameworks (MOFs) bridged with biopolymers (alginate and chitosan) namely HT-CeMOFs@Alg-CS cubic hybrid beads was developed and employed towards fluoride removal in batch mode. The fabricated HT-CeMOFs@Alg-CS beads were analyzed by DTA, FTIR, SEM, EDAX, TGA and XRD studies. Besides, FTIR and EDAX proved the affinity of HT-CeMOFs@Alg-CS cubic hybrid beads on fluoride was majorly attributed by electrostatic interaction, ion-exchange and complexation mechanism. To include detail insight into adsorption route; the kinetics, thermodynamic and isotherm studies were investigated for fluoride adsorption. The equilibrium data of HT-CeMOFs@Alg-CS cubic hybrid beads for fluoride adsorption was fitted with Langmuir isotherm model. Thermodynamic investigation results demonstrated that the fluoride adsorption was spontaneous with endothermic nature. The regeneration and field investigation results revealed that the developed HT-CeMOFs@Alg-CS cubic hybrid beads are reusable and more apt at field environment.
Fluoride is an essential micronutrient for humans. Nonetheless, when the amount of fluoride ion is greater than required, it will cause skeletal fluorosis and dental fluorosis to threaten human health. In this paper, a series of sodium alginate (SA)-based foam materials are prepared by freeze-drying technique and anchored with the nano-activated alumina (nAl2O3) in the SA to obtain a novel adsorbent of SA-nAl2O3 foam used for fluoride ions removal. The SA-nAl2O3 foam morphology was further explored and confirmed that nAl2O3 existed stably in the SA. The adsorption results showed that the maximal fluoride ion adsorption capacity was 5.09 mg/g with 20 mg/L fluorine solutions at a pH of 3. The adsorption isotherm fitted adequately to the Langmuir isotherm model, which demonstrated that the adsorption process is closer to monolayer adsorption. The adsorption kinetics behavior of SA-nAl2O3 foam was described by a pseudo-second-order model, and the adsorption process occurred by chemisorption. Adsorption thermodynamics analysis emphasized that the adsorption process was spontaneous and endothermic. The main mechanism of the foam is ion exchange. The SA-nAl2O3 foam exhibited excellent regeneration performance and stability after three cycles.
HIGHLIGHTS
A novel adsorption material of SA-nAl2O3 foam was obtained for fluoride ion removal.;
SA-nAl2O3 foam exhibited steady fluoride ion adsorption capacity.;
SA-nAl2O3 foam has excellent regenerability after three cycles;
Water is linked to every aspect of our life, and the nexus between water and health is well-documented. Lack of access to clean water and waterborne diseases is a significant cause of human misery. Pesticides are a group of chemicals widely detected in water bodies, mainly due to their indiscriminate use in the agricultural sector. Due to possible entry into human and animal food chains, health hazards posed by pesticides have become a considerable area of concern worldwide. Nevertheless, the production and use of pesticides are increasing, and the global pesticide market is expected to reach 24.6 billion USD by 2020–2024. Given the widespread occurrence and potential toxicity, many treatment technologies are in place to treat pesticide-contaminated water. However, the diverse chemical nature of the pesticides and the stringent regulations in drinking water standards, 0.1 μg/L for a single pesticide and 0.5 μg/L for the sum of all pesticides, limit the use of many existing treatment systems. The advancement in nanoscience and nanotechnology suggests that nanoscale materials, especially nanocarbon and its derivatives, are promising candidates for scavenging pesticides in water. This chapter reviews the literature on various nanoscale carbons with exciting properties and their applications for treating pesticide-laden drinking water. The mechanism of removal, challenges, prospects, and future development in the area is discussed. This chapter also covers the origin, occurrence of pesticides in water bodies, and their human and ecological health impacts.
Clean drinking water is an unconditional requirement to sustain life, but current human activities have posed severe threats to its quality. Fluoride contamination is one of the biggest challenges being faced by the world that is associated with deadly health problems. Hence, it is imperative to design efficacious purification technologies for its decontamination from water. Multitude of conventional methods involving basic principles of precipitation, coagulation, flocculation, ion exchange, membrane filtration, and reverse osmosis have been tested to combat fluoride pollution, but among these methods, adsorption is considered effective in terms of cost cutting and convenience. Nanomaterials have attracted paramount attention owing to their peculiar attributes, i.e., large surface area, short diffusion rate, enhanced optical, chemical, electronic, and magnetic characteristics as compared to their bulk counterparts, making them highly efficient nanoadsorbents. In this chapter, several metal-based adsorbents, biopolymers, and carbon-based nanomaterials are highlighted with special emphasis on their water defluoridation potential.
The template preparation of hydroxyapatite (HAp) layered lanthanum-benzene tricarboxylic acid based metal organic frameworks (La-BTC MOFs) abbreviated as HAp-La-BTC-MOFs has been investigated here for defluoridation of water. The nucleation and growth of La based MOFs was carried out in the prepared HAp hard template using layer-by-layer (LBL) technique. The coulomb and chelation contacts on HAp surface between Ca²⁺ ions and COO− organic ligands of La-BTC MOFs play vital roles in the preparation process. The batch experiments were employed to assess the defluoridation capacity (DC) of HAp-La based MOFs. The physicochemical properties of HAp-La based MOFs were investigated by various instrumentation techniques. To identify the nature, order and feasibility of HAp-La based MOFs towards defluoridation was examined by adsorption kinetics, isotherms and thermodynamics studies. The mechanism of defluoridation using HAp-La based MOFs were explained in detail. The field and reusability investigations of HAp-La-BTC MOFs also explored to find the potential applicability.
In this present investigation, aluminium (Al³⁺) fabricated 2-aminobenzene-1,4-dicarboxylic acid (ABDC) namely [email protected] metal organic frameworks (MOFs) was developed for defluoridation studies. The unique advantages of developed MOFs possess high selectivity, high porous and enhanced surface area but the developed powder form of [email protected] MOFs has several restrictions in field applications like slow filtration and column blockage. To prevail over these troubles, biopolymer namely chitosan (CS) supported [email protected] MOFs namely [email protected] beads for effective fluoride adsorption. The synthesized [email protected] beads were employed for the retention of fluoride in batch level. The defluoridation capacities (DCs) of [email protected] MOFs and [email protected] beads were found to be 4880 and 4900 mgF⁻ kg⁻¹ respectively. The influencing factors of adsorption method namely agitation time, sorbent dosage, initial fluoride concentration, pH, common anions and temperature were exploit to get utmost defluoridation capacity (DC) of [email protected] beads. The experimental data of [email protected] beads have been evaluated utilizing Langmuir, Fruendlich and Dubinin-Radushkevich (D-R) isotherms. The defluoridation nature of [email protected] beads was determined by the thermodynamic parameters. The order of reaction of [email protected] beads was studied using various kinetic models. The regeneration and field water studies of [email protected] beads were also carried out to check their reusability and suitability at field conditions.
The continuous growth and advancement of nanotechnology have introduced new and novel state-of-the-art multi-metallic nanostructures with well-defined morphologies and small particle size, together with high surface area, enhancing the transfer of electrons between the metal atoms. Nowadays, the combination of three metal elements in a core-shell, alloy, intermetallic, or other forms of nanostructures is under investigation. The synergistic combination of three metals in trimetallic nanostructures (TMNs) leads to extraordinary physicochemical properties, better performance, and better durability in various applications as compared to mono- and bimetallic nanostructures. The trimetallic nano-catalysts synthesized using chemical, physical, and biological methods in alloy and core-shell structures have shown promising performance in organic synthesis, environmental treatment and remediation, and health applications. Ternary systems have shown up to 100% yield, conversion, and selectivity in the catalysis of organic reactions. Similarly, 100% organic dye degradation has been recorded in a very short time. Furthermore, trimetallic nanostructures have shown excellent results in different diagnostic biomarker detections. In the present review, the synthesis strategies of TMNs are discussed using recent literature. The potential applications of TMNs in organic reactions, environmental remediation, and health-related applications are also reviewed. Finally, the conclusion and future prospects are highlighted.
In this scrutiny, the hydroxyapatite (HAp) decorated Ce-BTC metal organic frameworks (MOFs) namely HAp-Ce-BTC MOFs was prepared using a simple template-directed layer-by-layer (LBL) method for the successful capture of fluoride from water. The developed HAp-Ce-BTC MOFs were evaluated through FTIR, XRD, SEM, elemental mapping, EDAX, TGA, DTA analysis. These results were exhibited that the successful fabrication of nanocomposites with altered morphologies. The adsorption ability of HAp-Ce-BTC MOFs on fluoride removal was explored with batch mode and HAp-Ce-BTC MOFs was identified to possess versatile adsorption property broad range pH conditions and occurrence of the common ions present in water. On the whole, HAp-Ce-BTC MOFs on fluoride were spontaneous with endothermic in nature. The adsorption isotherm and kinetics were well fitted with Langmuir and pseudo-second-order kinetics respectively. The major mechanism like electrostatic interaction and complexation involved in fluoride adsorption on HAp-Ce-BTC MOFs. The reusability and field studies of HAp-Ce-BTC MOFs indicate that they are regenerable and applicable at field environment.
Making and securing safe drinking water is considered as the most important element and human right for sustainable human life. However, many countries in Africa still have low access to safe water, and in particular, fluorosis symptoms are severe from the people of Africa where there is a lot of groundwater and surface water contaminated with fluoride due to the geological natures. Fluoride is a colorless, tasteless, and odorless element with very strong reactivity and is emitted from the cleaning process of semiconductors and the fertilizer manufacturing industries. Various technologies such as chemical coagulation/precipitation, electrochemical method, ion exchange, separation membrane technology, nanotechnology, and adsorption may be proposed as a technology for removing fluoride for securing safe drinking water. The strengths and weaknesses of each element technology and recent research cases were investigated and analyzed, and an appropriate technology application plan for the sustainable development of emerging and developing countries in Africa was presented. Efficiency of fluoride removal may be important to secure drinking water for developing countries in Africa, but it is necessary to consider the local economic situation and cultural background first for sustainability of the applied technology. Therefore, animal bone-based adsorption process is advantageous in terms of sustainability and can be proposed as a fluoride removal technology suitable for the developing countries in Africa.
The optimization of fluoride removal from aqueous media was studied over the mesoporous titania-alumina composites using Taguchi method-based L25 orthogonal array experimental design. The chemical structure, surface chemistry, and morphology of as-prepared composite adsorbents were studied utilizing various analytical methods. The findings of the characterization demonstrated that the produced composites have high textural qualities, which are conducive to enhanced fluoride adsorption. The optimum conditions for maximum percentage removal of fluoride from aqueous solution were found as adsorbent type as TA75, adsorbent dose 4 g L-1, initial concentration of fluoride 40 ppm, solution pH 3 with a treatment time of 60 min. Under the optimum conditions, 98% of fluoride adsorption was achieved. Analysis of variance revealed that the solution pH followed by the adsorbent dose was the most significant for fluoride adsorption. The Langmuir model and pseudo-second-order kinetic model fit the adsorption data well, and the TA75 adsorbent had a maximum Langmuir fluoride adsorption capacity of 34.48 mg g⁻¹ at pH = 3. The thermodynamic information suggests that the adsorption was spontaneous and endothermic under the given operating conditions. The synergic combination of Ti-Al nanoparticles demonstrated a high percentage removal of fluoride under the optimized operating conditions.
Practitioner Points
• ○ Taguchi method-based design of experiment approach was implemented in optimization of the fluoride adsorption process.
• ○ Mesoporous titania-alumina composites with 0 to 100 wt. % of alumina in titania were prepared and applied in fluoride removal from an aqueous solution.
• ○ Solution pH was the most influential parameter for the fluoride adsorption process.
• ○ The synergistic combination of 75 wt.% alumina in titania showed the maximum adsorption capacity.
• ○ Equilibrium adsorption data fit well with the Langmuir model and pseudo-second-order kinetic model.
Flouride is the predominant inorganic pollutant found in groundwater. Fluorine contamination in potable water and ground water streams due to natural and anthropogenic activities has been recognised as one of the key issues .If the fluoride content is less than 0.5 ppm in drinking water it's going to reason dental caries and if the fluorine is present above 1.5 ppm it will cause osteoporosis that's a bone disease, Thyroid malfunctioning and kidney malfunctioning. So the fluorine content has be there in small amounts and it is very important .The permissible limit for fluoride is around 1.5 ppm. The major concern is in some areas like Nalgonda district and Ananthpur district the amount of flourine is very high in drinking water and this results in most of the population present in these areas are affected by fluorosis .So the fluorine content present in the water has to be removed and make the water suitable for drinking. There are many strategies to remove the fluorine content present in drinking water like coagulation, ion exchange, adsorption, membrane separation method .This article gives the information of the technology that were used for fluoride elimination and it describes the best process for the removal of fluorine through various observations. Introduction:
Three effective adsorbents are developed for the de-fluoridation of water based on nano Silica and activated carbon of Terminalia Ivorensis plant (SACTI). Nano-SiO2 particles are synthesized from the sand collected in Krishna River at Vijayawada, India, using Aloe-vera gel as a capping agent. Activated carbon (SACTI), composite of ‘nSiO2 + SACTI’ and La-alginate beads doped with ‘nSiO2 + SACTI’ are examined. The adsorbents are characterized. Optimum extraction conditions for the maximum defluoridation capacities are established. Effect of co-anions, thermodynamic and regeneration studies are also investigated. The results show the spontaneity and endothermic nature of sorption with high positive entropy values. Adsorption efficiency is restored even after fifth regeneration cycles. The Freundlich adsorption isotherm and pseudo 2nd order kinetic model describes well the sorption process. Adsorption capacities of adsorbents are: 2.02 mg/g for SACTI, 4.01 mg/g for nSiO2 + SACTI, 5.13 mg/g for nSiO2 + SACTI-La-Ali (beads). The methodologies developed are successfully applied to reduce fluoride concentration in ground water samples of Ananthapur District, Andhra Pradesh, India.
The advancement and growth of nanotechnology lead to realizing new and novel multi-metallic nanostructures with well-defined sizes and morphology, resulting in an improvement in their performance in various catalytic applications. The trimetallic nanostructured materials are synthesized and designed in different architectures for energy conversion electrocatalysis. The as-synthesized trimetallic nanostructures have found unique physiochemical properties due to the synergistic combination of the three different metals in their structures. A vast array of approaches such as hydrothermal, solvothermal, seed-growth, galvanic replacement reaction, biological, and other methods are employed to synthesize the trimetallic nanostructures. Noteworthy, the trimetallic nanostructures showed better performance and durability in the electrocatalytic fuel cells. In the present review, we provide a comprehensive overview of the recent strategies employed for synthesizing trimetallic nanostructures and their energy-related applications. With a particular focus on hydrogen evolution, alcohol oxidations, oxygen evolution, and others, we highlight the latest achievements.
Graphene oxide possesses appreciable defluoridation capacity (DC) of 2451 mgF⁻ kg⁻¹. To enhance the DC and its properties, amine functionalized graphene oxide (AGO) was developed for fluoride removal. In addition, the prepared AGO have the vital defluoridation capacity (DC) of 4001 mgF⁻ kg⁻¹. The sophisticated instrumentations techniques namely SEM, TGA, FTIR, XRD, XPS and Raman analysis were explored for AGO and individual materials. The optimization of the responsible parameters (shaking time, solution pH, AGO dosage, interfering anions, temperature and initial fluoride ion concentration) for fluoride adsorption was employed under batch condition. The influence of adsorption isotherms (Freundlich, Dubinin-Radushkevich (D-R) and Langmuir), kinetics (particle/intraparticle diffusion and pseudo-first/second-order models) and thermodynamic studies (ΔH°, ΔS° and ΔG°) of defluoridation by AGO was investigated. The fluoride removal mechanism of AGO was found to be electrostatic attraction. The reusability and field study of AGO was also scrutinized.
The leaching of fluoride in potable water leads to fluorosis. To prevail over this trouble, tunable porous metal organic frameworks (MOFs) were prepared by solvothermal method and utilized for fluoride removal. Herein, polyvalent metal ions namely Zr⁴⁺, Fe³⁺ and Al³⁺ fabricated benzene-1,3,5-tricarboxylic acid (BTC) based MOFs namely Zr-BTC, Fe-BTC, and Al-BTC MOFs exhibits higher defluoridation capacities (DCs) of 4998, 4940, and 4920 mgF⁻ kg⁻¹ respectively. The developed metal based BTC (M-BTC) MOFs were investigated by XRD, TEM, SEM, FTIR, XPS and EDAX investigation. The influencing factors of adsorption viz., solution pH, M-BTC MOFs dosage, shaking time, preliminary fluoride concentration, temperature, and challenger anions were optimized under batch scale. The fluoride adsorption ability of M-BTC MOFs was slightly affected by adsorbate pH medium and bicarbonate ion in water. In addition, the experimental data was fitted with various adsorption kinetic and isotherm models. The thermodynamic investigation shows the feasible, spontaneous and endothermic nature of fluoride adsorption. The plausible fluoride adsorption mechanism of M-BTC MOFs was majorly ruled by electrostatic attraction and complexation. Furthermore, synthesized M-BTC MOFs can be reused upto eight cycles. The field trial indicates M-BTC MOFs diminish fluoride concentration below the acceptance limit in field water which helps in supply of water with secure fluoride levels.
Arsenic is an extremely hazardous metalloid affecting the health of millions of people worldwide. Numerous technologies have been developed to remove As from drinking water/wastewater, of which adsorption is considered as the most effective technique. Nanoadsorbents such as nano scale zero valent metals, carbon nanotubes (CNTs), and biochar/biomaterial-based nanocomposites are being widely used by the researchers for water treatment. In this chapter, recent developments in the nanoadsorbents to eliminate As from water/wastewater are discussed. Application of raw and engineered nanoparticles (NPs) such as iron oxide/hydroxide, alumina, copper oxide, titanium oxide, bi-metal oxides, and carbonaceous NPs are primarily focused. Different techniques for the physico-chemical characterization of nanoadsorbents, including Fourier transform infrared (FTIR) spectroscopy, Raman spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS) have been discussed briefly. The influence of numerous factors (e.g., pH, synthesis method, initial concentration, particle size, competing ions, and contact medium) on the As adsorption capacity by nanoadsorbents are deliberated. Furthermore, the chapter also discusses As adsorption mechanisms and regeneration and separation of nanoadsorbents from water/wastewater.
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.
Fluoride ion in trace amount is essential for the growth of human bones but, the excess intake of this ion creates a toxic effect in the body. The acceptable limit for fluoride ion in the drinking water should be less than 1.5 mg/L. Over and above 200 million people all over the world are suffering severe health hazards like crippling fluorosis, mottling of teeth, anaemia due to the consumption of fluoride contaminated water. In India, more than 60 million people across 20 states are suffering from this toxicity. Several years of research shows the applicability of the adsorption process for the defluoridation of water. In recent years, ceramic adsorbents due to their better thermal and chemical stability, suitability in harsh environment attracting the research interest. However, minimum information is available regarding the type, required properties, application conditions and regeneration of this ceramic adsorbents. This paper aims to review the performance of ceramic adsorbents along with the advancement and modification in their synthesis process. It discussed the surface chemistry and mechanism of fluoride adsorption of some preferred ceramic adsorbents in an aqueous medium to understand the adsorption process. This paper also assessed the regeneration capability of the used ceramic adsorbents. Though ceramic adsorbents have good potential in fluoride removal from groundwater still, there is a need for further research on the utilization of these ceramic adsorbents in our day to day life on a commercial scale to combat with a real-life problem like water pollution.
Defluoridation plays a vital role in providing drinking water with safe fluoride levels. The present work concentrated on the development of fumaric acid-based metal-organic frameworks (MOFs) using Zr⁴⁺, La³⁺, and Fe³⁺ metal ions, viz., [email protected], [email protected], and [email protected] MOF composites by the hydrothermal method for defluoridation studies. Fluoride removal from water was investigated and optimized in batch mode. The fabricated [email protected], [email protected], and [email protected] MOF composites have the maximum defluoridation capacities (DCs) of 4920, 4925, and 4845 mgF⁻ kg⁻¹, respectively. The fluoride adsorption studies were conducted by optimizing various affecting parameters like contact time, adsorbent dosage, adsorbate pH, influence of co-ions and temperature. The fabricated [email protected], [email protected], and [email protected] MOF composites were characterized by Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), energy-dispersive X-ray analysis (EDAX), X-ray diffractometry (XRD), high-resolution transmission electron microscopy (HR-TEM), selected area electron diffraction (SAED), and atomic force microscopy (AFM) studies. The sorption data were fitted with different isotherm models. The studies of thermodynamic parameters demonstrate the feasibility and endothermic nature of the defluoridation process. The DCs of [email protected], [email protected], and [email protected] MOF composites were compared with other reported adsorbents. The regeneration and reusability studies were proposed to adequately utilize [email protected], [email protected], and [email protected] MOF composites. The field sample taken from a nearby fluoride rife village was also tested with the synthesized [email protected], [email protected], and [email protected] MOF composites, which reduce the fluoride content below the tolerance limit.
Nanotechnology has aroused as a field that has resulted in paradigm shift in agronomic practices and given a true essence to sustainable agriculture. Nanomaterials belonging in the agriculture domain are of vast variety and had find applications in crop production, soil and water management, diagnostic measurements, controlled use of chemicals, and plant protection owing to their tailored properties, small size, and surface to volume ratio. The contribution of nanotechnology in precision farming through the development of nano-based fertilizers, pesticides, herbicides, and early pathogen diagnostic can be considered as a breakthrough. The chapter will focus on the aspects of nanotechnology that have revolutionized the agriculture field, leading to better environmental management and sustainable practices.
Ground water contamination of fluoride is a serious global issue leading to its excessive intake and subsequently numerous adverse health issues. This research was designed to assess the efficiency of nano-adsorbent for removal of fluoride levels from water. For this purpose, calcium carbonate (CaCO3) nanoparticles (average particle size 14.6 nm) were prepared and later applied for effective removal of fluoride from simulated as well as real drinking water (DW) samples collected from different areas of Lahore, Pakistan. The particles were characterized by powder X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), Scanning electron microscopy (SEM)/ Energy-dispersive X-ray spectroscopy (EDX) and Atomic Force Microscopy (AFM). Physico-chemical parameters were studied in batch mode which revealed high adsorption capacity (i.e. 754.36 mg g−1) at room temperature and neutral pH within 10 minutes. The kinetic isotherms (General, pseudo-first and pseudo-second order), diffusion studies (Intra-particle diffusion and particle diffusion models) and adsorption models (Langmuir, Freundlich, Liu and Redlich-Peterson) were also applied to evaluate the suitability of adsorption process. The applicability of nano-adsorbent to fluoride contaminated real DW samples led to 98–100% efficacy of defluoridation.
Microsized layered Fe-Mg-Zr tri-metal hydroxide particles were synthesized by co-precipitation method and used for defluoridation of the groundwater. The obtained powders were characterized by various instruments such as FTIR, BET, XRD, SEM, XPS. Batch adsorption experiment showed that the composite had good defluoridation efficiency, and the experimental data fit well with the Langmuir model and the pseudo second-order kinetic model. The composite has a maximum adsorption capacity of 88.55mg/g, which is much higher than the adsorbents already reported. The adsorbent still has 85% adsorption capacity even after 5 cycles of adsorption-desorption-adsorption, showing good regenerative capacity. HPO4²⁻ and SO4²⁻ take slight interference with fluorine removal efficiency, while Cl-, CO3²⁻ and HCO3- have no effect on fluoride removal. A simultaneous feeding continuous defluoridation process was designed, and the experiments were carried out by using the actual fluorine-containing water collected from the rural areas of North China with the initial fluoride concentration of 2.71mg/L. It was found that above established setup has quite good defluoridation efficiency for real groundwater in a continuous way, providing an example for the water purification by microsized particles that are conventionally performed by using packed column with the problem of easy blocking due to the fine particle size. This work demonstrated a successful model with great potential in the defluoridation by using the fine materials on a large scale with the low cost and high efficiency.
This paper is concerned with the cross-linking of poly(vinyl alcohol) (PVA) using maleic acid as the cross-linker. The curative (maleic acid) dose and the curing temperature and time were varied between 2.5 and 60% (w/w), 120 and 160 °C and 30 and 120 min, respectively. From a thorough swelling study in both hot and cold water (percentage swelling, gel content, swelling ratio, etc-) the optimum curative dose and curing conditions have been evaluated. The molecular weight between the cross-links exhibited a sharp fall up to a maleic acid dose of 20% (w/w). A comparative evaluation of maleic acid cross-linked and heat-treated PVA films has been done. Better heat stability for maleic acid cross-linked PVA was observed from thermogravimetric analysis. A shift in glass transition temperature was observed for both heat-treated and maleic acid treated PVA compared with the virgin one. IR spectroscopic study indicated the presence of an ester linkage and an olefinic double bond in maleic acid treated and heat-treated PVA films, respectively. Maleic acid cross-linked PVA is quite stable in different polar and nonpolar solvents. A definite structural pattern has been observed in maleic acid cross-linked PVA films through scanning electron microscopy. © Springer 2005.
Collagen materials were crosslinked by 1-ethyl-3-(3-dimethyl aminopropyl) carbodiimide (EDC) in the presence of chondroitin sulfate (CS), one of glycosaminoglycans (GAGs). PVA and chitosan were also blended with collagen. The physical and chemical properties of the matrices were characterized by SEM, DSC and ESCA. L929 cells were implanted on the matrices to show the cytotoxic and the biological characters of the materials. The results indicate that EDC is an effective and non-cytotoxic cross-link reagent, which can replace the common dialdehyde reagent. The attachment of CS can improve the stability of collagen and accelerate the cell growth. The addition of PVA can prepare porous matrices with smaller bore size. There are reactions between the chitosan and the collagen, and the composite has good biological character. The presence of chitosan can also increase the amount of incorporated CS.
A new adsorbent media has been prepared consisting of iron oxide coated onto sand surfaces. The oxide coating is made by adding a solution of a ferric salt and base to a mixture of sand and applying various heating protocols. The iron oxide is an excellent, regenerable adsorbent, and the process of coating it on sand allows the media to be used in a packed column. Depending on solution pH, the media can be made to adsorb either cationic or anionic metals. In this work, the media was used to collect hexavalent chromium from a synthetic waste stream. The influent contained 20 mg/L Cr(VI), and better than 99% removal was achieved consistently. Once breakthrough occurred, the media could be regenerated by exposure to base. The pH of the regenerant solution determined the kinetics and efficiency of the regeneration process. With further development, the process represents an inexpensive and effective method for removal and recovery of metals from industrial waste streams.
The present study explores the feasibility of utilizing bauxite for fluoride removal from synthetic and natural fluoride bearing groundwater samples of Orissa, India. Adsorption experiments with respect to variation in time, pH, adsorbate and concentrations of other anions namely NO3-, SO42-, CO32- and PO43- were carried out. Characterization of bauxite before and after fluoride adsorption was studied by XRD, FTIR and SEM–EDX to get a better insight into the mechanism of adsorption. The rate of adsorption was rapid and followed first order kinetics with intraparticle diffusion as the rate determining step. The system followed the Langmuir adsorption isotherm model with adsorption capacity of 5.16mgg−1. The competition of CO32- ions for surface sites is comparatively less as compared to NO3-, SO42- and PO43- in the concentration range of 5–20mgg−1 at solution pH of 6 during fluoride adsorption. The estimated thermodynamic parameters (ΔH°, ΔS° and ΔG°) indicated that the adsorption was spontaneous and exothermic in nature.
A coating granulation technology comprising the spraying of a Fe–Al–Ce nano-adsorbent suspension onto glass beads in a fluidized bed was developed. An acrylic-styrene copolymer latex was used as a binder. The granulated adsorbent was used in a packed bed for fluoride removal from drinking water. The effects of coating temperature, latex/Fe–Al–Ce ratio, and coating amount on granule compressive strength and adsorption capacity were investigated. With increased coating temperature, cross linking in the polymer in the coated layer increased, which resulted in increased granule strength but decreased adsorption capacity. With increased latex/Fe–Al–Ce ratio, more active sites were covered by the polymer, which also resulted in increased granule strength but decreased adsorption capacity. The optimal parameters for making high performance adsorbent granules were for the granules to be coated at 65°C using a latex/Fe–Al–Ce ratio of 0.5:1 and a coating amount of 27.8%. These granules had a fluoride adsorption capacity of 2.77mg/g (coated granules) for water with an initial fluoride concentration of 0.001M that was treated at pH 7.
Nano-adsorbents of Fe–Al–Ce trimetal hydroxide (FAC) were immobilized in porous polyvinyl alcohol (PVA) via cross-linking with boric acid. Spherical composite granules of 3–5mm in size that would not cause a large pressure drop in a packed bed were obtained. SEM images showed that the FAC particles were embedded in holes of about 10μm in the PVA granules, while the surface pores of the granules were only nano-scale in size. Thermal analysis showed that the FAC and PVA in the granules combined tightly by forming a chemical bond. The mechanical stability of the granules decreased with increased FAC concentration, and increased with increased PVA concentration. The fluoride adsorption capacity of the granules increased with FAC concentration and decreased with PVA concentration. For acceptable mechanical stability and adsorption capacity, a FAC concentration of 12% and PVA concentration of 7.5% were suggested. The adsorption capacity of the granules prepared under suggested concentrations was 4.46mg/g at an initial fluoride concentration of 19mg/L and pH 6.5. Immobilization of the nano-adsorbent in porous polyvinyl alcohol granules is a promising granulation method for water treatment in packed beds.
A mathematical model of preparation of a catalyst paste was developed with allowance made for the physicochemical features of phenomena occurring at this step. This model enables one to determine the thickness of the adsorption–solvation shells on solid-phase particles and also the concentrations of the components of the dispersion (continuous) phase as functions of time. It was found how the solvation shell thickness and the volume content of the solid phase in a paste affects its rheological and deformation properties. A mathematical model of the catalyst paste flow in a ram extruder is developed. An expression was derived for the extrusion pressure as a function of the paste flow velocity in the extruder. It was shown that this expression can be used to calculate the paste flow through an extrusion die with any number of channels. It was determined how the velocity at which the paste slides along the channel wall depends on the channel diameter.
In this study, zeolite particles were charge-reversed by chemically modifying them with aluminum and it was verified by EDXS that aluminum replaced sodium from the zeolite structure. The charge-reversed zeolite particles were subsequently used in fluoride removal from aqueous solution. The influence of the experimental variables such as particle size, initial fluoride concentration and temperature on the fluoride diffusion kinetics, was investigated using a batch adsorber. A model that lumps internal mass transfer phenomenon, i.e. pore and surface diffusion, was used to describe the uptake kinetics. From the model, a diffusional time constant and a corresponding effective diffusion coefficient were determined. Results demonstrate that the internal mass transfer rate is enhanced with an increase in temperature and decreases in particle size and initial concentration. It is also found that the diffusional time constant correlates well with the reciprocal of the square of zeolite particle radius corroborating that internal mass transfer plays a limiting role in fluoride sorption. An examination of the thermodynamic parameters reveals that the interaction between fluoride and charge-reversed zeolite particles is endothermic and spontaneous in nature.
Iron–cerium hydroxide (Fe–Ce), which has shown a high arsenic (V) (As(V)) adsorption capacity in previous studies, was granulated using the vibration dropping method used to prepare small-sized fuel particles. Fabrication studies showed that the sintering process could not be used in the preparation of the granular Fe–Ce (GFC) adsorbent and that the optimum grain size was 1.0mm for As(V) removal. The optimum sized GFC (GFC-1.0mm) exhibited a Freundlich adsorption of 18.2 and 11.8mgg−1 at an equilibrium concentration of 1.0 and 0.1mgL−1, respectively. The GFC-1.0mm also showed equivalent As removal performance to READ, a commercial adsorbent with CeO2 as the sole metal oxide component (about 81%), under both space velocities of 240 and 24h−1 in column tests. The cost for the manufacturing of GFC, however, is much lower since iron is the major metal component (about 80%). Energy dispersive X-ray microanalysis (EDX) results showed that As was distributed from the surface to the center of the GFC after the As(V) adsorption experiment, suggesting that nearly all active sites inside the GFC were available for the removal of As(V). The As(V) on the used GFC could be desorbed with an efficiency of 89% using 1.0molL−1 sodium hydroxide, and the GFC after desorption showed similar As adsorption performance with the fresh GFC. In conclusion, the GFC consisting of 80% Fe and 20% Ce exhibited As removal performance equivalent to the commercial adsorbent consisting only of Ce.
The pervaporation separation of acetic acid–water mixture was carried out using poly(vinyl alcohol) (PVA) membranes modified using malic acid (MA). The effects of PVA/MA ratio, membrane thickness, operating temperature, feed concentration on the transmembrane permeation rate and separation factor were investigated. Optimum PVA/MA ratio was determined as 85/15 (v/v) for 20wt.% acetic acid mixtures at 40°C. The influence of membrane thickness on the separation factor and the permeation rate was studied in the range of 50–100μm at constant acetic acid concentration. It was observed that separation factor was independent of membrane thickness below a limit value of 70μm and permeation rate was found to be inversely proportional to the membrane thickness. The prepared membranes were also tested to separate various compositions of acetic acid–water mixtures with 20–90wt.% acetic acid content at 40°C. Typically, separation factor of 670 and total permeation rate of 4.8×10−2kg/m2h was obtained for 90wt.% acetic acid concentration in the feed. Arrhenius-type relation and activation energy of 41kJ/mol was also found for acetic acid–water mixtures.
An economic study was conducted to evaluate the costs of fluoride removal by electrodialysis on the basis of industrial and economic data. The investment and operating costs were estimated for an industrial plant with a capacity of 2200 m3/d water consumption for 50,000 per capita according to Moroccan standards for rural areas. The capital cost was estimated to be € 833,207 and the calculated operating cost to be € 0.154/m3.
A new technique based on the combination of an activated alumina column and an electrochemical system for fluoride removal from water is reported in this study. In the first step, the optimization of the process was achieved under various experimental parameters (volumetric flow, temperature, pH, initial fluoride concentration and hardness) with a synthetic solution. The comparison of the performance of the current activated alumina process and the electrosorption system proved to be more efficienct than the latter in removing fluoride from water. Thus, the fluoride sorption capacity at the breakthrough point of the activated alumina column reached 3.8 mg F−/L. It was increased by about 60% by means of the electrochemical process than the results obtained in current mode. Moreover, it was found that the electrosorption system could be utilized to regenerate the saturated activated alumina. In the second step, the electrosorption process was utilized to treat Sahara drinking water naturally contaminated with fluoride (3 mg/L) under optimum conditions previously determined. The electrosorption process coupled with activated alumina column has been successfully applied for fluoride removal from drinking water.
IR spectroscopy has shown that adsorbed water is almost completely removed from ferrihydrite by evacuation at room temperature. Absorption bands at 3615 and 3430 cm ⁻¹ appearing thereafter are interpreted as arising from OH groups located respectively at the surface and deeper in the structure. These groups are readily converted to OD on treatment with D 2 O vapour and this has allowed the OH deformation vibration to be identified at 800 cm ⁻¹ . It is proposed that OH groups in ferrihydrite are about half as numerous as those in akaganéite ( β -FeOOH) and that they may occur in environments similar to those in this mineral. The formula for ferrihydrite proposed by earlier workers, 5 Fe 2 O 3 .9H 2 O, should thus be amended to Fe 2 O 3 . 2 FeOOH.2·6H 2 O in order to indicate the presence of structural OH groups. A re-appraisal of the ferrihydrite structure appears desirable.
Sand coated with iron hydroxide was compared with uncoated sand as an adsorbent filter media for treating metalbearing wastes. The oxide-coated sand outperformed uncoated sand in removing particulate metals, as well as both uncomplexed and ammonia-complexed soluble metals. The removed metals were recovered and the adsorptive capacity of the media was regenerated by exposure to a pH-3 solution. Head loss through coated sand was comparable to that through uncoated sand, but was more strongly pH dependent. The oxide coatings were stable when exposed to acidic solutions or moderate abrasion. This process offers a promising means of obtaining high-level treatment of metal-bearing wastes.
ɛ-Caprolactam (CPL) is usually crystallized from CPL–water mixtures by reduced pressure distillation through triple-effect evaporation sets. But high energy consumption and low heat transfer coefficient limit economic profit of this process. To improve or substitute the CPL aqueous solution dehydration process, pervaporation separation of caprolactam–water system was investigated using PVA crosslinked membranes. An in-depth study of sorption, swelling, pervaporation performances of caprolactam–water mixtures and crosslinked membrane had been conducted. The experimental data demonstrated that the PVA crosslinked with glutaraldehyde showed excellent dehydration performances. The novel separation technique is feasible for application to the dehydration of CPL–water mixtures.
Cr/SBA-15 catalysts were prepared by the grafting of chromium nitrate nonahydrate [Cr(NO3)3·9H2O] complexes onto SBA-15 mesoporous materials. Shish-kebab and nanofiber polyethylenes (PEs) were prepared under different temperatures via ethylene extrusion polymerization with the Cr(NO3)3·9H2O catalytic system. The diameter of a single nanofiber was 100–250 nm. Scanning electron microscopy images showed that the polymer obtained from the SBA-15-supported catalyst under different polymerization temperatures produced nanofiber and/or shish-kebab morphologies. X-ray diffraction and differential scanning calorimetry were used to characterize microstructures of the materials. Polymers obtained with all of the catalysts showed a melting temperature, bulk density, and high load melt index; this indicated the formation of linear high-density PE. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010
Submicrometer alumina suspensions, dispersed in aqueous acidic solutions of polyvinyl alcohol (PVA) and 2,5-dimethoxy-2,5-dihydrofuran, have been evaluated for suitability as a cross-linkable binder system for casting complex-shaped ceramic components. Suspensions of up to 50 vol% solids have rheological behavior, which is suitable for pouring and filling molds. Complex-shaped green bodies are then formed by heating the suspension in the mold for a period of time (typically 15–60 min) at moderate temperature (60°–80°C) to gel the suspension. High green densities (58%–62% of full density) can be obtained. The dried green bodies have strength in excess of 1 MPa and may be readily machined. No more than 1–3 wt% PVA per weight of alumina is necessary, ensuring burnout that minimizes generation of flaws. The ceramic components can be fired to >96% of full density when fired for 2 h at 1400°–1450°C. Cross-linkable PVA may receive more widespread acceptance in ceramic processing than previous gelcasting formulations because PVA is already a common processing additive.
Aluminum-oxide-coated sand (AOCS) was evaluated for the removal of selenite (Se(IV)) and selenate (Se(VI)) from water. Quartz sand was coated at 70°C using 1 M AlCl3 solution aging for 2 d at various coating pH (pH(coating)). The characteristics of the AOCS surface were pH(coating)-dependent. The Al oxide coating was an X-ray noncrystalline, porous compound at low pH(coating), while at high pH(coating), the AOCS could better withstand acid/alkali and the coatings tended to form crystalline boehmite and bayerite. Adsorption of Se(IV) and Se(VI) was more effective using sand coated at low pH(coating) than at high pH(coating). AOCS produced at pH(coating) 5.98 had optimum properties and was employed as the adsorbent for the present adsorption studies. Adsorption experiments of Se(IV) and Se(VI) by AOCS performed as a function of pH, initial concentration, reaction time, and competing ion concentrations were examined. Removal of Se(IV) and Se(IV) increased with decreasing pH but was obviously greater for Se(IV) than Se(VI). In Se(IV) and Se(VI) mixed systems, the adsorption of Se(IV) was evidently inhibited by Se(VI) only at system pH ranging from 3 to 8, and the degree of inhibition was similar at Se(VI) to Se(IV) molar ratios of 1 and 3. However, Se(VI) adsorption significantly decreased with increasing Se(IV) concentration at all system pH. The sequence of foreign anions competing with respect to Se(IV) and Se(VI) adsorption was in the order of SO2−4>HCO−3.
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 m2 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.
An iron-aluminum-cerium trimetal hydroxide (FesAlsCe) adsorbent with an acrylic-styrene copolymer latex binder, which can cross-link and cure at room temperature, was coated on sand particles by spray coating. The adhesion of the coated layer increased with the latex/FesAlsCe ratio. A suitable latex/FesAlsCe ratio and thickness of coated adsorbent were determined to be 0.8 and 70 µm, respectively, giving good stability and adsorption capacity. The corresponding adsorption capacity of fluoride ions on the coated sand reached 3.46 mg/g at pH 7.0 and an initial fluoride concentration of 50 mg/L. Sand coated with Fe-Al-Ce is a potential adsorbent for use in a packed bed for fluoride removal from drinking water.
The molecular character of atmospheric particulate matter is of prime importance when interpreting air pollution trends and its subsequent influence on environmental monitoring and preventative conservation. The known methods of estimating the molecular composition normally involve elemental analysis of particles (both as bulk and computer controlled analyses of single particles) with subsequent multivariate analyses to clusterise the elements in groups of elements that are closely related to each other. With this approach one can at best suggest associations. Evidently the application of molecular spectroscopy in addition to elemental concentration profiles would provide intimate information regarding the nature of the particles and consequently their fate. This paper gives an overview of research performed in our laboratory and describes the optimisation of experimental parameters to use scanning electron microscopy with energy-dispersive X-ray detection (SEM/EDX) or electron probe X-ray microanalysis (EPXMA) in parallel with micro-Raman Spectrometry (MRS) to investigate single environmental particles. The challenges associated with the two stand-alone techniques are revealed and consequently those posed with an interfaced approach are discussed. Preliminary results, of an initial investigation of the SEM/EDX interfaced with MRS to ultra-fine heterogeneous environmental particles, are given.
Traditionally the manufacturing of pharmaceutical dosage forms has been a batch-wise process and continuous processes have limited applications in a pharmaceutical manufacturing plant. However, several factors (reduction of cost, improved process efficiency, optimal use of equipment, flexibility in production capacity) are stimulating the pharmaceutical industry to investigate the opportunities offered by continuous processes. This paper discusses some of the techniques which could be implemented in a continuous granulation process of pharmaceuticals.
The inherent hydrophilicity of poly(vinyl alcohol) (PVA) makes it an attractive polymer for water treatment applications based on membranes. Thermal and chemical resistance and a high anti-fouling potential are accompanied by high water permeability. The large swelling capacity requires that the PVA be adequately crosslinked to ensure that the contaminants in water can be retained, and that compaction under pressure can be minimised. There is a challenge to achieve this and still obtain economical permeate fluxes.
In the present study, the performance of Ti–Al binary metal oxide supported beads using chitosan template was studied for fluoride removal from drinking water. The adsorbent was synthesized by precipitation method and characterized using FTIR, SEM, XRD and BET. The higher surface area of the synthesized adsorbent 323.83 m2/g results in a much higher fluoride removal capacity Qmax = 2.22 mg g−1 as compared to bare chitosan. Pore size of beads is 42.97 Å, suggesting mesoporous nature of adsorbent. Material works very effectively at all pH except at pH greater than 9. The presence of carbonate and bicarbonate ions showed significant decline in the fluoride removal capacity of adsorbent. The experimental data fitted well to Langmuir adsorption model. The kinetic studies indicate that the system follows the pseudo-second-order and intra-particle diffusion model. Thermodynamic study reveals that the fluoride adsorption by Ti–Al binary metal oxide supported beads is an exothermic and spontaneous process. Alum appears to be the promising regeneration media showing 80% regeneration. The applicability of the adsorbent for fluoride removal was tested in field water collected from the Dhar district in Madhaya Pradesh, India.
Fluoride in drinking water has a profound effect on teeth and bones. Up to a small level (1–1.5 mg/L) this strengthens the enamel. Concentrations in the range of 1.5–4 mg/L result in dental fluorosis whereas with prolonged exposure at still higher fluoride concentrations (4–10 mg/L) dental fluorosis progresses to skeletal fluorosis. High fluoride concentrations in groundwater, up to more than 30 mg/L, occur widely, in many parts of the world. This review article is aimed at providing precise information on efforts made by various researchers in the field of fluoride removal for drinking water. The fluoride removal has been broadly divided in two sections dealing with membrane and adsorption techniques. Under the membrane techniques reverse osmosis, nanofiltration, dialysis and electro-dialysis have been discussed. Adsorption, which is a conventional technique, deals with adsorbents such as: alumina/aluminium based materials, clays and soils, calcium based minerals, synthetic compounds and carbon based materials. Studies on fluoride removal from aqueous solutions using various reversed zeolites, modified zeolites and ion exchange resins based on cross-linked polystyrene are reviewed. During the last few years, layered double oxides have been of interest as adsorbents for fluoride removal. Such recent developments have been briefly discussed.
In the present study, removal of fluoride ions using activated alumina (AA) was investigated in batch and continuous operations. The fluoride removal performance was investigated as a function of the fluoride concentration, flow rate, amount of adsorbent dose and pH. Sorption data have been correlated with Langmuir and Freundlich isotherms. pH was shown to be a decisive parameter on fluoride removal. Percentage fluoride removal as a function of time and uptake capacity related to flow volume were determined by evaluating the breakthrough curves.Data confirmed that early saturation and lower fluoride removal was observed at higher flow rate and at higher concentration. There was a marginal decrease in the uptake capacity after each regeneration cycle. A one-dimensional model for isothermal, axially dispersed fixed-bed adsorption has been numerically solved and compared with the experimental results. Predicted simulation results based on the assumption of pore-diffusion rate-control conditions matches with the experimental data in the initial zone of the breakthrough curve, but deviated marginally in the final tailing zone.
Zirconium impregnated cashew nut shell carbon was studied to assess its capacity for the adsorption of fluoride from aqueous solutions. The dependence of the adsorption of fluoride on the pH of the solution has been studied to achieve the optimum pH value and a better understanding of the adsorption mechanism. The influence of addition of the co-existing ions on the adsorption of fluoride was also studied. Adsorption isotherms have been modeled by Langmuir, Freundlich and Redlich–Peterson equations and their constants were determined. Pseudo-first- and second-order equations were used to describe the adsorption rate of fluoride and adsorption rate constant was calculated. A mechanism involving three stages, viz.; external surface adsorption, intra-particle diffusion and final equilibrium has been proposed for the adsorption of fluoride onto adsorbent material. Thermodynamic parameters such as ΔG°, ΔH° and ΔS° were calculated in order to understand the nature of sorption. Field studies were carried out with the fluoride containing water sample collected from a fluoride-endemic area in order to test the suitability of the sorbent at field conditions.
In this study, a granular zirconium-iron oxide (GZI) was successfully prepared using the extrusion method, and its defluoridation performance was systematically evaluated. The GZI was composed of amorphous and nano-scale oxide particles. The Zr and Fe were evenly distributed on its surface, with a Zr/Fe molar ratio of ∼2.3. The granular adsorbent was porous with high permeability potential. Moreover, it had excellent mechanical stability and high crushing strength, which ensured less material breakage and mass loss in practical use. In batch tests, the GZI showed a high adsorption capacity of 9.80 mg/g under an equilibrium concentration of 10 mg/L at pH 7.0, which outperformed many other reported granular adsorbents. The GZI performed well over a wide pH range, of 3.5-8.0, and especially well at pH 6.0-8.0, which was the preferred range for actual application. Fluoride adsorption on GZI followed pseudo-second-order kinetics and could be well described by the Freundlich equilibrium model. With the exception of HCO(3)(-), other co-existing anions and HA did not evidently inhibit fluoride removal by GZI when considering their real concentrations in natural groundwater, which showed that GZI had a high selectivity for fluoride. In column tests using real groundwater as influent, about 370, 239 and 128 bed volumes (BVs) of groundwater were treated before breakthrough was reached under space velocities (SVs) of 0.5, 1 and 3 h(-1), respectively. Additionally, the toxicity characteristic leaching procedure (TCLP) results suggested that the spent GZI was inert and could be safely disposed of in landfill. In conclusion, this granular adsorbent showed high potential for fluoride removal from real groundwater, due to its high performance and physical-chemical properties.
The present study was conducted to evaluate the feasibility of nano-alumina (Al(2)O(3)) for fluoride adsorption from aqueous solutions. The nature and morphology of pure and fluoride-sorbed nano-alumina were characterized by SEM with EDX, XRD, and FTIR analysis. Batch adsorption studies were performed as a function of contact time, initial fluoride concentration, temperature, pH and influence of competing anions. Fluoride sorption kinetics was well fitted by pseudo-second-order model. The maximum sorption capacity of nano-alumina for fluoride removal was found to be 14.0 mg g(-1) at 25°C. Maximum fluoride removal occurred at pH 6.15. The fluoride sorption has been well explained using Langmuir isotherm model. Fluoride sorption was mainly influenced by the presence of PO(4)(3-), SO(4)(2-) and CO(3)(2-) ions.
The aim of this work was to develop a continuous solid lipid extrusion process that includes post-process milling of the extrudates. Die diameters smaller than 0.5 mm should be used for taste masking of the bitter tasting anthelmintic praziquantel. During lipid extrusion with small die diameters, electrostatic charging of the extrudates occurred. This could be avoided by adding liquid polyethylene glycol (PEG) as antistatic agent. Further, extrusion with PEG as antistatic agent was possible with small diameter down to 0.2 mm and with up to 80% praziquantel load. Dissolution of praziquantel extrudates was shown to be faster with smaller extrudate diameter due to surface enlargement. Anyhow, different praziquantel extrudates with small diameter, drug load up to 70% and PEG content up to 20%, were proven to be sufficiently taste masked in a randomised palatability study with 40 cats. Within a scale-up experiment, lipid extrusion and milling of the extrudates in a centrifugal mill afterwards were conducted continuously. Extrudates from continuous and batchwise production revealed small differences in terms of size distribution and surface habit, but were similar in drug dissolution rate.
Charcoals that contain calcium compounds have been synthesized by impregnating wood with calcium chloride followed by carbonization at 500 degrees C, 650 degrees C or 900 degrees C. The charcoals were characterized by SEM, EDAX, XRD and chemical titrations. These adsorbents were porous with the wood microstructure. XRD revealed the presence of crystallized CaCO(3) and CaO. Despite this content, all the charcoals showed acidic surface properties and pH of point of zero charge (pH(PZC)) values were around 7.4-7.7. Their performance for fluoride removal from aqueous solution was evaluated by batch experiments. Fluoride adsorption kinetic followed a pseudo-second order model. Charcoal prepared at 650 degrees C exhibited the best efficiency with a fluoride sorption capacity of 19.05 mg g(-1) calculated from the Langmuir model. A fluoride residual concentration of 0.67 mg L(-1) was achieved within 24 h from a 10 mg L(-1) solution at neutral pH. The fluoride removal was not modified by the presence of NO(3)(-), SO(4)(2-) and PO(4)(3-) in the fluoride solution, while HCO(3)(-) and Cl(-) slightly affected the defluoridation capacity. The charcoals were chemically stable in solution and the amount of dissolved Ca was found to be 3.23 mg L(-1) at neutral pH.
The compression behavior of high- and low drug strength pellets containing kappa-carrageenan as pelletisation aid was investigated. Model drugs and fillers with different compression mechanisms were used and the effects of compression force and turret speed were examined. Regardless of the compression behavior of their starting components, all pellet formulations exhibited minimal to absent fragmentation and underwent compression by deformation, confirmed by increased equivalent diameter and aspect ratio and decreased roundness factor of the pellets retrieved after de-aggregation of tablets prepared from lubricated pellets. The retrieved pellets showed also higher fracture resistance in three of the tested formulations and no statistically significant difference in the remaining one thus excluding significant crack formation. A densification mechanism was suggested by decreased total porosity and reduced median pore radius of the compressed pellets. No effect of the process parameters on the degree of pellet deformation was reported. The tensile strength of the tablets prepared from unlubricated pellets increased slightly with increased compression force. Compression of pellets with high density silicified microcrystalline cellulose (SMCC HD 90) as embedding powder protected them from severe deformation and resulted in tablets with sufficient tensile strength, minimal friability, negligible elastic recovery and short disintegration time. The percentage of the pellets and the compression force affected the tensile strength of the prepared tablets whereas no influence of the turret speed and the pre-compression force was observed.
Using a redox process, granular activated carbon (GAC) was coated with manganese oxides to enhance its ability to adsorb fluoride from an aqueous solution. Compared with plain GAC, the fluoride adsorption capacity of this new adsorbent was improved and at least three times greater than that of uncoated GAC. The surface characteristics of coated GAC were observed with scanning electron microscopy. The surface area of the new adsorbent was calculated using the Brunauer-Emmett-Teller method. X-ray diffraction revealed that manganese oxides are amorphous. X-ray photoelectron spectroscopy demonstrated that manganese existed primarily in the oxidation state +IV. Kinetic and equilibrium adsorption data showed that the adsorption process follows the pseudo-second order kinetic and Freundlich equation models. The sorption data also indicated that the removal of fluoride by adsorption is a highly complex process, involving both boundary layer diffusion and intra-particle diffusion. The pH value of solution influences fluoride removal, and the optimum equilibrium pH value of fluoride adsorption is 3.0.
Zn/Al/Cl anionic clay has been synthesized by co-precipitation method and applied for adsorption of fluoride in aqueous medium. Equilibrium adsorption data were fitted to Langmuir, Freundlich, Temkin, and Generalized isotherm equations. Thermodynamic parameters like DeltaG and DeltaH values show the feasibility and exothermic nature of the adsorption process. Influence of solution pH and presence of other anions on fluoride adsorption by the clay has also been studied. Presence of carbonate in water was found to have an adverse effect on fluoride adsorption by the clay. pH(pzc) of the clay has been found to be 8.97. A two-step 1st order kinetic model was used to explain the fluoride adsorption kinetics of the as-synthesized clay. It was possible to regenerate the adsorbent with an aqueous solution of 0.01 M NaOH and the effect of regeneration on fluoride adsorption was reported up to five regeneration cycles.
Carboxylated cross-linked chitosan beads (CCB) showed a significant defluoridation capacity (DC) of 1385 mgF(-)/kg than the raw chitosan beads (CB) which displayed only 52 mgF(-)/kg. Sorption experiments were performed by varying contact time, pH, presence of co-anions and temperature. The nature and morphology of the sorbent were discussed using FTIR and SEM with EDAX analysis. The stability of the beads in solution was explained in terms of swelling ratio of the beads. The fluoride uptake onto CCB obeys both Freundlich and Langmuir isotherms. Thermodynamic studies revealed that the nature of fluoride sorption is spontaneous and endothermic. Sorption kinetics is mainly controlled by pseudo-second-order and intraparticle diffusion models. 0.1M HCl was identified as the best eluent. The suitability of CCB at field conditions has been tested with field sample collected from a nearby fluoride-endemic area.
This study was conducted to develop a heating process for coating hydrated iron oxide on the sand surface to utilise the adsorbent properties of the coating and the filtration properties of the sand. BET and scanning electron microscope (SEM) analyses were used to investigate the surface properties of the coated layer. An energy dispersive X-ray (EDAX) technique of analysis was used for characterising metal adsorption sites on the iron-coated sand surface. The results indicated that the iron-coated sand had more micropores and higher specific surface area because of the attachment of iron oxide. Copper ions could penetrate into the micropores and mesopores of iron oxide on sand surface, and the regeneration of the iron-coated sand could be achieved by soaking with pH = 3.0 acid solution. Besides, the results of EDAX analysis showed that copper ions were chemisorbed on the surface of iron-coated sand. Results of the study developed an innovative technology for coating iron oxide on sand surface for the treatment of heavy metal in water.
A very low soluble pectin-derivative (pectinic acid, degree of methoxylation 4%) was found to be well suited as an excipient for pelletisation by extrusion/spheronisation. Formulations containing pectinic acid and lactose in the following ratios were evaluated: 99/1, 80/20, 50/50 and 20/80. The capacity as an extrusion aid was found to be high; even formulations containing only 20% pectinic acid resulted in nearly spherical pellets. All pectinic acid pellets were mechanically stable, had an aspect ratio of approximately 1.15-1.20 and released 30-60% of a low solubility model drug within 15 min both in simulated gastric acid (0.1M HCl) and intestinal fluid (phosphate buffer pH 6.8).
The modification of polymeric materials (polystyrene and polyHIPE) by coating their surface with appropriate adsorbing agents (i.e. iron hydroxides) was investigated in the present work, in order to apply the modified media in the removal of inorganic arsenic anions from contaminated water sources. The method, termed adsorptive filtration, has been classified as an emerging technology in water treatment processes as it presents several advantages towards conventional technologies: the production of high amounts of toxic sludge can be avoided and it is considered as economically more efficient; whereas it has not yet been applied in full-scale treatment plants for low-level arsenic removal. The present experiments showed that both modified media were capable in removing arsenic from the aqueous stream, leading to residual concentration of this toxic metalloid element below 10 microg/L, which is the new maximum concentration limit set recently by the European Commission and imposed by the USEPA. Though, among the examined materials, polyHIPE was found to be more effective in the removal of arsenic, as far as it concerns the maximum sorptive capacity before the filtration bed reaches the respective breakthrough point.
Heat was employed to coat crystalline goethite onto a quartz sand surface so that the adsorbent properties of the coating could be utilized. The adsorption characteristics of cadmium and humic acid onto goethite-coated sand were examined. Results show that the goethite-coated sand surface had a higher specific surface area and more mesopores than the uncoated sand. The adsorption of both cadmium and humic acid was highly pH-dependent: cadmium adsorption increased with pH, but humic acid adsorption decreased as pH increased. The presence of humic acid resulted in increasing cadmium adsorption in a specific pH range. The order of reacting humic acid with cadmium was found to have a noticeable effect on the final adsorption capacity. The adsorption capacity of cadmium for humic acid that is adsorbed onto goethite-coated sand before reacting with a cadmium system, exceeds that of humic acid that is mixed with cadmium ions before goethite-coated sand is added.
The characteristics of fluoride ion adsorption onto carbonaceous materials were derived as adsorption isotherms at different temperatures and in different pH solutions. The fluoride ion was adsorbed into pores in carbonaceous materials produced from wood; the larger the specific surface area, the more fluoride ions adsorbed. Bone char was the most effective adsorbent. The composition of bone char includes calcium phosphate, calcium carbonate, and so on. This suggests that the phosphate ion in bone char was exchanged with a fluoride ion. Moreover, the mechanism of fluoride ion adsorption onto bone char is clearly chemical in nature because the amount of fluoride ion adsorbed onto bone char increased with increasing temperature and decreasing pH. The amount of fluoride ion adsorbed onto bone char was also shown to depend on the concentration of sodium chloride in solution because of the "salting-out" effect. The adsorption of fluoride ion onto bone char is endothermic. Bone char can be utilized to remove fluoride ions from drinking water.
Chitosan pellets were successfully prepared using the extrusion/spheronization technology. Microcrystalline cellulose was used as additive in concentrations from 70 to 0%. The powder mixtures were extruded using water and diluted acetic acid solution in different powder to liquid ratios. The effects on bead formation using water and different acetic acid concentrations and solution quantities were analysed. Also, the morphological and mechanical characteristics of the obtained beads were investigated. With demineralized water as granulation fluid, pellets with a maximum of 50% (m/m) of chitosan could be produced. The mass fraction of chitosan within the pellets could be increased to 100% by using diluted acetic acid for the granulation step.
A novel adsorbent, zirconium(IV)-impregnated collagen fiber, was prepared. Zr(IV) was uniformly dispersed in collagen fiber, mainly through chemical bonds, and was able to withstand the extraction of water. This adsorbent is effective for the removal of fluoride from aqueous solutions. The adsorption capacity was 2.29 mmol/g at pH = 5.5 when 5.00 mmol/L fluoride solution was adsorbed by use of 0.100 g of adsorbent, and the extent of removal was 97.4% when the adsorbent dose was 0.300 g. The adsorption isotherms were well fitted by the Langmuir equation, and the maximum adsorption capacities calculated by the Langmuir equation were close to those determined by experiment. The adsorption capacity increased with rising temperature. These facts imply that the mechanism of chemical adsorption might be involved in the adsorption process of fluoride on the absorbent and that fluorides are adsorbed in the form of monolayer coverage on the surface of the adsorbent. The adsorption kinetics of fluoride onto Zr(IV)-impregnated collagen fiber could be described by Lagergren's pseudo-first-order rate mode. The investigation on desorption indicated that this adsorbent is easily regenerated by use of dilute NaOH solution.
An Fe-Ce bimetal adsorbent was investigated with X-ray powder diffraction (XRD), transmission electron micrograph (TEM), Fourier transform infrared spectra (FTIR), and X-ray photoelectron spectroscopy (XPS) methods for a better understanding of the effect of surface properties on arsenate (As(V)) adsorption. In the adsorption test, the bimetal oxide adsorbent showed a significantly higher As(V) adsorption capacity than the referenced Ce and Fe oxides (CeO2 and Fe3O4) prepared by the same procedure and some other arsenate adsorbents reported recently. XRD measurement of the adsorbent demonstrated that the phase of magnetite (Fe3O4) disappears gradually with the increasing dosage of Ce4+ ions until reaching a molar ratio of Ce4+ to Fe3+ and Fe2+ of 0.08:0.2:0.1 (Fe-CeO8 refers to the adsorbent prepared at this ratio), and the phase of CeO2 begins to appear following a further increase of the Ce dose. Combined with the results of TEM observation, it was assumed that a solid solution of Fe-Ce is formed following the disappearance of the magnetite phase. Occurrence of a characteristic surface hydroxyl group (MOH, metal surface hydroxyl, 1126 cm(-1)), which showed the highest band intensity in the solid solution state, was confirmed on the bimetal oxide adsorbent by FTIR. Quantificational calculation from the XPS narrow scan results of O(1s) spectra also indicated that the formation of the bimetal Fe-CeO8 was composed of more hydroxyl (30.8%) than was the formation of CeO2 and Fe3O4 (12.6% and 19.6%). The results of adsorption tests on Fe-CeO8 at differentAs(V) concentrations indicated that both the integral area of the As-O band at 836 cm(-1) and the As(V) adsorption capacity increased almost linearly with the decrease of the integral area of M-OH bands at 1126 cm(-1), proving that the adsorption of As(V) by Fe-CeO8 is mainly realized through the mechanism of quantitative ligand exchange. The atomic ratio of Fe on Fe-CeOB decreased from 20.1% to 7.7% with the increase of the As atom ratio from 0 to 16% after As(V) adsorption, suggesting that As(V) adsorption might be realized through the replacement of the M-OH group of Fe (Fe-OH) with arsenate. The well splitting of three v3 bands at As-O band (836 cm(-1)) of FTIR and the hydroxyl ratio (1.7) of Fe-CeO8 calculated from the XPS results suggested that the diprotonated monodentate complex (SOAsO(OH)2) is possibly dominant on the surface of Fe-CeO8.
Excessive fluoride concentrations have been reported in groundwaters of more than 20 developed and developing countries including India where 19 states are facing acute fluorosis problems. Various technologies are being used to remove fluoride from water but still the problem has not been rooted out. In this paper, a broad overview of the available technologies for fluoride removal and advantages and limitations of each one have been presented based on literature survey and the experiments conducted in the laboratory with several processes. It has been concluded that the selection of treatment process should be site specific as per local needs and prevailing conditions as each technology has some limitations and no one process can serve the purpose in diverse conditions.
Investigations were carried out on the defluoridation of fluoride-spiked ground water in domestic defluoridation units (DDU) with activated alumina (AA). Specific safe water yield (SSY) was determined as a function of AA amount and adsorbent depth. Reuse potential of exhausted AA was assessed by regenerating and reusing AA in multiple defluoridation cycles. High fluoride uptake capacity (FUC) from ground water matrix as well as retaining approximately 95% FUC up to five cycles showed the suitability of AA for defluoridation in DDU. SSY, liters of safe water/kg AA, was dependent on the AA amount and its depth. There was a significant decrease in SSY with the decrease in AA depth in different DDUs, even though the amount was maintained constant. The derived data from four DDUs, with 3-5 kg AA and depth ranging from 5 to 13 cm, showed that DDU design is one of the most important parameter to be considered for optimizing SSY.
In this study, adsorption potential of a new sorbent manganese-oxide-coated alumina (MOCA) was investigated for defluoridation of drinking water using batch and continuous mode experiments. The effects of different parameters such as pH, initial fluoride concentration and co-existing ions (usually present in groundwater sample) were studied to understand the adsorption behavior of the sorbent under various conditions. Optimum removal of fluoride ions occurred in a pH range of 4-7. Results of the present study indicate that fluoride adsorption rate and adsorption capacity of MOCA are far superior to that of activated alumina (AA), which was used as the base material for MOCA preparation. The MOCA can be effectively regenerated using 2.5% NaOH as eluent. The Langmuir equilibrium model was found to be suitable for describing the fluoride sorption on AA and MOCA. The maximum fluoride uptake capacity for MOCA and AA was found to be 2.85 and 1.08 mg g(-1), respectively. The kinetic results showed that the fluoride sorption to MOCA followed pseudo--second-order kinetics with a correlation coefficient greater than 0.98. The fluoride sorption capacity at breakthrough point for both the adsorbents was greatly influenced by bed depth. A bed depth service time (BDST) approach was adopted to describe the continuous flow system. The batch and column studies demonstrated the superiority of MOCA over AA in removing fluoride from the drinking water system.
A trimetal oxide was developed as a fluoride adsorbent by coprecipitation of Fe(II), Al(III) and Ce(IV) salt solutions with a molar ratio of 1:4:1 under alkaline condition. The material retained amorphous structure and maintained relatively stable fluoride adsorption performance at calcination temperatures lower than 600 degrees C. The optimum pH range for fluoride adsorption was 6.0-6.5 and the adsorbent also showed high defluoridation ability around pH 5.5-7.0, which is preferable for actual application. A high fluoride adsorption capacity of 178 mg g(-1) was acquired under an equilibrium fluoride concentration of 84.5 mg l(-1), adsorbent dose of 150 mg l(-1) and pH 7.0. The adsorption isotherm could be better described by the two-site Langmuir model than the one-site model, suggesting the existence of two types of active sites on the adsorbent surface. Coexistence of high concentrations of phosphate or arsenate only led to partial inhibition of fluoride adsorption, which further suggests the existence of heterogeneous adsorption sites. Sulfate and chloride did not affect fluoride adsorption, and nitrate influenced it only when the concentration of NO(3)(-)-N exceeded 50 mg l(-1). A high desorption efficiency of 97% was achieved by treating fluoride loaded Fe-Al-Ce oxide with NaOH solution at pH 12.2. A column experiment using the adsorbent fabricated into 1mm pellets was performed at an initial fluoride concentration of 5.5 mg l(-1), space velocity of 5h(-1) and pH of 5.8, and 2240 bed volumes were treated with the effluent fluoride under 1.0 mg l(-1).
Cellulose supported layered double hydroxides (CSLDHs) were synthesized and tested for adsorption of fluoride in aqueous medium. Three samples of cellulose supported LDHs were synthesized by varying the LDH loading on cellulose. The raw cellulose, unsupported LDH and cellulose supported LDHs were characterized by XRD, SEM and BET surface area. Batch adsorption as well as fixed-bed column experiments were performed for determining the fluoride adsorption characteristics of CSLDHs. The fluoride adsorption properties of CSLDHs were found to be superior to that of reported adsorbents, including activated alumina and carbon nanotubes. Defluoridation capacity of the CSLDHs was 2-4 times higher than that of unsupported LDH. The cellulose supported LDH, CSLDH-50, having an LDH loading of 27% showed maximum fluoride uptake capacity (5.29 mg g(-1) of CSLDH, 25.18 mg g(-1) of LDH) in fixed-bed column study.
Adsorption mechanism and application study of Fe–Ce oxide adsorbent for arsenic removal
- Dou
X.M. Dou, Adsorption mechanism and application study of Fe–Ce oxide adsorbent for arsenic removal, Dr. Diss. Chin. Acad. Sci. (2006).