Removal of phosphate and fluoride from wastewater by a hybrid precipitation–microfiltration process

Controllable and selective fluoride precipitation from phosphate-rich wastewater

Industrial wastewater containing high levels of fluoride and phosphate poses significant environmental challenges and results in the waste of non-renewable resources. This study investigates the use of La(OH)3 as a precipitating agent to selectively remove and separate fluoride from phosphate in such wastewater. The findings indicate that fluoride removal efficiency is highly dependent on the pH level and La(OH)3 dosage. Using Response Surface Methodology, the optimal conditions for fluoride precipitation were identified as a pH range of 1.0 to 2.5, a reaction time of 60-80 min, a La/3F molar ratio of 2.0, and reaction temperature of 25 °C. Under these parameters, the fluoride removal efficiency exceeded 96.9 %, while phosphate removal remained around 7.2 %. Further Density Functional Theory calculations and characterization confirmed La(OH)3 has a strong affinity for fluoride than phosphate under acidic conditions, leading to the formation of a LaF3 precipitate without forming LaPO4, effectively separating fluoride from phosphate. These results demonstrate an efficient strategy for treating wastewater with high fluoride and phosphate content, enabling the selective precipitation and recovery of these elements for sustainable management.

Phosphorus Removal from Dirty Farmyard Water by Activated Anaerobic-Digestion-Derived Biochar

The management of anaerobic digestate is important to realize the value of the waste and enhance the whole system sustainability of anaerobic digestion. In this study, the phosphorus treatment of dirty irrigation water by biochar samples derived from digestate of anaerobic digestion were investigated. The biochars were further activated by steam activation with different duration time and KOH activation with different introducing ratios; the textural properties of biochars were optimized after activation from the aspect of biochar characterization. Notably, AD-N2 demonstrates a remarkable adsorption effect of phosphorus, with an adsorption efficiency of 8.99 mg g-1. Besides the effect of biochar dosage on phosphorus removal, adsorption kinetics and thermodynamic isotherms are studied. According to the adsorption kinetics, the adsorption of phosphorus from dirty water fits the Elovich equation (R2 = 0.95). Furthermore, the thermodynamic isotherm results illustrate the process of phosphorus removal by biochar is endothermic (ΔH0 = 17.93 kJ mol-1) and spontaneous (ΔS = 96.24 J mol-1 K-1). Therefore, this work suggests a promising solution to phosphorus-related environmental challenges in industry and agriculture.

Quantitative Analysis of Camellia oleifera Seed Saponins and Aqueous Two-Phase Extraction and Separation

At present, the technology used for the extraction and purification of Camellia oleifera saponins generally has the problems of high cost and low purity, and the quantitative detection of Camellia oleifera saponins also has the problems of low sensitivity and easy interference from impurities. To solve these problems, this paper aimed to use liquid chromatography for the quantitative detection of Camellia oleifera saponins, and to adjust and optimize the related conditions. In our study, the average recovery of Camellia oleifera saponins obtained was 100.42%. The RSD of precision test was 0.41%. The RSD of the repeatability test was 0.22%. The detection limit of the liquid chromatography was 0.06 mg/L, and the quantification limit was 0.2 mg/L. In order to improve the yield and purity, the Camellia oleifera saponins were extracted from Camellia oleifera Abel. seed meal by methanol extraction. Then, the extracted Camellia oleifera saponins were extracted with an ammonium sulfate/propanol aqueous two-phase system. We optimized the purification process of formaldehyde extraction and aqueous two-phase extraction. Under the optimal purification process, the purity of Camellia oleifera saponins extracted by methanol was 36.15%, and the yield was 25.24%. The purity of Camellia oleifera saponins obtained by aqueous two-phase extraction was 83.72%. Thus, this study can provide a reference standard for rapid and efficient detection and analysis of Camellia oleifera saponins for industrial extraction and purification.

Effective Removal of Phosphate from Waste Water Based on Silica Nanoparticles

This study explored the potential application of silica nanoparticles (SiNPs) prepared from rice husk ash (RHA) to reuse phosphate from aqueous solution. The physicochemical analysis illustrated that the SiNPs, which were extracted from waste biomass, have a nonuniform shape with a size range of a few nanometer to hundreds of nanometers, a surface area of 15.56 m2·g−1, and an adsorption pore width of 4.06 nm. Those results carried out the possibility to utilize the SiNPs for removal of phosphate. Findings from the batch sorption experiments showed that the phosphate adsorption was controlled by experimental parameters, i.e., pH, adsorbent dosage, concentration of adsorbate, and adsorption time. The experimental results showed that the maximum phosphate adsorption capacity of SiNPs was achieved at around 9.08 mg·g−1 at adsorption conditions, i.e., pH 7, SiNPs dosage of 0.3 g, and adsorption time of 90 min. The phosphate removal based on SiNPs will offer several benefit such as an effective and low cost method, reliable to reuse as an effective slow release phosphate fertilizer.

State-of-the-art of research progress on adsorptive removal of fluoride-contaminated water using biochar-based materials: Practical feasibility through reusability and column transport studies

Fluoride (F^-) is one of the essential elements found in soil and water released from geogenic sources and several anthropogenic activities. Fluoride causes fluorosis, dental and skeletal growth problems, teeth mottling, and neurological damage due to prolonged consumption, affecting millions worldwide. Adsorption is an extensively implemented technique in water and wastewater treatment for fluoride, with significant potential due to efficiency, cost-effectiveness, ease of operation, and reusability. This review highlights the current state of knowledge for fluoride adsorption using biochar-based materials and the limitations of biochar for fluoride-contaminated groundwater and industrial wastewater treatment. Biochar materials have shown significant adsorption capacities for fluoride under the influence of low pH, biochar dose, initial concentration, temperature, and co-existing ions. Modified biochar possesses various functional groups (-OH, -CC, -C-O, -CONH, -C-OH, X-OH), in which enhanced hydroxyl (-OH) groups onto the surface plays a significant role in fluoride adsorption via electrostatic attraction and ion exchange. Regeneration and reusability of biochar sorbents need to be performed to a greater extent to improve removal efficiency and reusability in field conditions. Furthermore, the present investigation identifies the limitations of biochar materials in treating fluoride-contaminated drinking groundwater and industrial effluents. The fluoride removal using biochar-based materials at an industrial scale for understanding the practical feasibility is yet to be documented. This review work recommend the feasibility of biochar-based materials in column studies for fluoride remediation in the future.

Robust strategies to eliminate endocrine disruptive estrogens in water resources

The widespread occurrence and ubiquitous distribution of estrogens, i.e., estrone (E1), estradiol (E2), and estriol (E3) in our water matrices, is an issue of global concern. Public and regulatory authorities are concerned and placing joint efforts to eliminate estrogens and related environmentally hazardous compounds, due to their toxic influences on the environmental matrices, ecology, and human health, even at low concentrations. However, most of the available literature is focused on the occurrence of estrogens in different water environments with limited treatment options. Thus, a detailed review to fully cover the several treatment processes is needed. This review comprehensively and comparatively discusses many physical, chemical, and biological-based treatments to eliminate natural estrogens, i.e., estrone (E1), estradiol (E2), and estriol (E3) and related synthetic estrogens, e.g., 17α-ethinylestradiol (EE2) and other related hazardous compounds. The covered techniques include adsorption, nanofiltration, ultrafiltration, ultrasonication, photocatalysis of estrogenic compounds, Fenton, Fenton-like and photo-Fenton degradation of estrogenic compounds, electro-Fenton degradation of estrogenic compounds, ozonation, and biological methods for the removal of estrogenic compounds are thoroughly discussed with suitable examples. The studies revealed that treatment plants based on chemical and biological approaches are cost-friendly for removing estrogenic pollutants. Further, there is a need to properly monitor and disposal of the usage of estrogenic drugs in humans and animals. Additional studies are required to explore a robust and more advanced oxidation treatment strategy that can contribute effectively to industrial-scale applications. This review may assist future investigations, monitoring, and removing estrogenic compounds from various environmental matrices. In concluding remarks, a way forward and future perspectives focusing on bridging knowledge gaps in estrogenic compounds removal are also proposed.

Applications of Nano Hydroxyapatite as Adsorbents: A Review

Nano hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂, HAp) has aroused widespread attention as a green and environmentally friendly adsorbent due to its outstanding ability in removing heavy metal ions, radio nuclides, organic pollutants and fluoride ions for wastewater treatment. The hexagonal crystal structure of HAp supports the adsorption mechanisms including ionic exchange reaction, surface complexation, the co-precipitation of new partially soluble phases and physical adsorption such as electrostatic interaction and hydrogen bonding. However, nano HAp has some drawbacks such as agglomeration and a significant pressure drop during filtration when used in powder form. Therefore, instead of using nano HAp alone, researchers have worked on modificationsand composites of nano HAp to overcome these issues and enhance the adsorption capacity. The modification of cationic doping and organic molecule grafting for nano HAp can promote the immobilization of ions and then increase adsorption capacity. Developing nano HAp composite with biopolymers such as gelatin, chitosan and chitin has proven to obtain a synergetic effect for improving the adsorption capacity of composites, in which nano HAp fixed and dispersed in polymers can playmuch more of a role for adsorption. This review summarizes the adsorption properties and adsorbent applications of nano HAp as well as the methods to enhance the adsorption capacity of nano HAp.

MF–NF Treatment Train for Pig Manure: Nutrient Recovery and Reuse of Product Water

The livestock industry negatively impacts the environment by producing high organic and mineral loaded manure and wastewater. On the contrary, manure is also considered as the major focal point of resource recovery. The microfiltration (MF) process in manure treatment is well known for being the least complex and highly energy efficient. However, the major fraction of the dissolve nutrients easily bypasses the MF membranes. In this research work, we reported the efficiency of using MF–nanofiltration (NF) treatment train in a dead-end filtration system for the treatment of raw manure. The objectives were to produce nutrient rich separate streams in reduced volumes and a particle and pathogen-free product water. MF removed TSS above 98% and the COD and phosphorus (P) retention were noticed above 60 and 80%, respectively, within a reduced MF concentrate volume, which accounted for 40% of the initial feed volume. The NF of MF permeate by NF270 showed most promising results by concentrating overall 50 and 70% of the total nitrogen (TN) and potassium (K) within a reduced NF concentrate volume, which accounted for 30% of the initial MF feed volume. Finally, the MF–NF treatment train of raw pig manure could produce a particle-free product water that can be reused in farms to wash barns, to irrigate nearby cultures, or can be applied to specific fields based on the demand.

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

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

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Iron-based oxides and hydroxides from the EC sludge were recovered and prepared for fluoride ion adsorption.

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EC sludge as an iron-based adsorbent was synthesized by thermal activation at 500 °C.

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Iron oxide adsorbents could efficiently remove fluoride ions from synthetically prepared water solutions.

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The adsorption of fluoride followed a Langmuir isotherm pseudo-Second-order kinetic model.

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The prepared adsorbents were regenerated in an aqueous solution and the reusability efficiency was up to the 4th cycle.

Tricks and tracks in removal of emerging contaminants from the wastewater through hybrid treatment systems: A review

In recent years, many biological and physicochemical treatment technologies have been investigated for the removal of the emerging contaminants (ECs) from the wastewater matrix. However, due to the deficiency of these treatments to completely degrade the ECs in wastewater, hybrid systems were explored using the distinguishing removal potential of the different treatment processes. This review gives an insight on such hybrid systems combining several physical, chemical and biological treatments for the fast and eco-efficient removal of ECs from wastewater. Most of the hybrid systems have applied biological treatments first and then physical or chemical treatments. The hybrid system of membrane bioreactor (MBR) followed by membrane filtrations (RO/NF) effectively removed a suite of ECs such as pharmaceuticals, beta blockers, pesticides and EDCs. Some of the hybrid systems of constructed wetlands and waste stabilization ponds showed promising potential for the biosorptive removal of pharmaceuticals and some beta blockers. The hybrid systems combining activated sludge process and physical processes such as ultrafiltration (UF), reverse osmosis (RO) and gamma radiations are considered as the cost effective technologies and had better removal of trace organic pollutants. The hybrid system of MBR coupled with UV oxidation, activated carbon and ultrasound, and ozonation followed by ultrasounds, completely degraded some ECs and many pharmaceuticals. The review also synthesizes the trend followed by the hybrid system processes for the removal of various categories of ECs. The future research directions for the ECs removal utilizing hybrid nanocomposites and green sustainable technology have been suggested.

Removal of fluoride from water using activated carbon fibres modified with zirconium by a drop-coating method

Metal-modified carbon materials have been widely used for fluoride removal, but the traditional impregnation by soaking method suffers from low loading of metals and substantial use of chemicals. This study proposed a new approach to prepare zirconium modified activated carbon fibres (Zr-ACF) by a drop-coating method. Using the same amount of chemicals, the drop-coating method yielded a 5.5 times higher fluoride adsorption capacity than the soaking method due to more effective loading of Zr(IV) onto ACF. The effects of various preparation conditions, including the addition of a complexing agent (oxalic acid) and Zr/ACF mass ratio (0.2-1), were investigated. Zr-ACF prepared by drop-coating was characterised by SEM and BET, and the functional groups involved in the anchoring of Zr(IV) on ACF and the adsorption of fluoride onto Zr-ACF were identified by FTIR and XPS. Adsorption experiments at pH between 3 and 11 revealed that ion exchange and electrostatic attraction were the main adsorption mechanisms at different pH levels. Co-existing anions such as CO₃^2-, HCO₃^- and Cl^- had an insignificant negative impact (<5%) on fluoride adsorption capacity while SO₄^2- decreased fluoride adsorption capacity by 11.5%. The adsorption kinetics followed the pseudo-second-order model. The adsorption isotherms followed the Langmuir isotherm model with a maximum fluoride adsorption capacity of 28.50 mg/L at 25 °C, which was higher than other carbon-based materials in the literature. The remarkable improvement of adsorption capacity and reduced chemical consumption demonstrate that Zr-ACF prepared by drop-coating is a promising adsorbent for fluoride removal.

Membrane-Based Processes Used in Municipal Wastewater Treatment for Water Reuse: State-Of-The-Art and Performance Analysis

Wastewater reuse as a sustainable, reliable and energy recovery concept is a promising approach to alleviate worldwide water scarcity. However, the water reuse market needs to be developed with long-term efforts because only less than 4% of the total wastewater worldwide has been treated for water reuse at present. In addition, the reclaimed water should fulfill the criteria of health safety, appearance, environmental acceptance and economic feasibility based on their local water reuse guidelines. Moreover, municipal wastewater as an alternative water resource for non-potable or potable reuse, has been widely treated by various membrane-based treatment processes for reuse applications. By collecting lab-scale and pilot-scale reuse cases as much as possible, this review aims to provide a comprehensive summary of the membrane-based treatment processes, mainly focused on the hydraulic filtration performance, contaminants removal capacity, reuse purpose, fouling resistance potential, resource recovery and energy consumption. The advances and limitations of different membrane-based processes alone or coupled with other possible processes such as disinfection processes and advanced oxidation processes, are also highlighted. Challenges still facing membrane-based technologies for water reuse applications, including institutional barriers, financial allocation and public perception, are stated as areas in need of further research and development.

Phosphorus recovery from process waste water made by the hydrothermal carbonisation of spent coffee grounds

This study investigates the recovery of phosphorus from the process water obtained through hydrothermal carbonisation (HTC) of a 'wet' biomass waste, namely spent coffee grounds. HTC was shown to liberate more than 82% of the total phosphorus in the grounds in the form of dissolved ortho-phosphate. Nanofiltration was used to concentrate the inorganic nutrients of the HTC process water, achieving a mass concentration factor of 3.9 times. The natural stoichiometry of phosphorus, magnesium and ammoniacal nitrogen in the nanofiltration retentate was favourable for struvite precipitation. 92.8% of aqueous phosphorus was recovered as struvite through simple pH adjustment, yielding a total phosphorus recovery of 75% from the feedstock spent coffee grounds.

Synthesis optimisation and characterisation of chitosan-calcite adsorbent from fishery-food waste for phosphorus removal

Here, Box-Behnken design (BBD) approaches were utilised to optimise synthesis methodology for the chitosan-calcite rich adsorbent (CCM) made from fishery-food waste material (crab carapace), using low-temperature activation and potassium hydroxide (KOH). The effect of activation temperature, activation time and impregnation ratio was studied. The final adsorbent material was evaluated for its phosphorus (P) removal efficiency from liquid phase. Results showed that impregnation ratio was the most significant individual factor as this acted to increase surface deacetylation of the chitin (to chitosan) and increased the number of amine groups (-NH₂) in the chitosan chain. P removal efficiency approached 75.89% (at initial P concentration of 20 mg/L) under optimised experimental conditions, i.e. where the impregnation ratio for KOH:carapace (g/g) was 1:1, the activation temperature was 105 °C and the activation time was 150 min. Predicted responses were in good agreement with the experimental data. Additionally, the pristine and CCM material were further analysed using scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM/EDX), Brunauer-Emmett-Teller technique (BET), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and thermal gravimetric analysis (TGA). Characterisation showed enhancements in surface chemistry (introducing positively charged amine groups), textural properties and thermal stability of the CCM.

Zero-Liquid Discharge Treatment of Wastewater from a Fertilizer Factory

This article describes the improvement of wastewater treatment in a fertilizer plant located in Central Italy (municipality of Vasto). In this facility, water is used for the removal of dust and fluorinated gases from the air. The resulting wastewater contains fluorides and phosphates in hazardous forms. Its treatment ordinarily does not result in a Zero-Liquid Discharge (ZLD) process. To achieve this purpose, several reagents were tested, focusing on the correlation linking pH, type of reagent and the effect on the separation of fluorides and phosphates from the wastewater. It was eventually found, and explained with a model, that hydrated lime at pH = 12 was so effective as a precipitating agent that phosphate and fluoride separation reached a value of 99.9%, thus allowing for reuse of the water in the plant process. Furthermore, phosphates and fluorides precipitated in a non-hazardous form, so that the material could also be recycled. In synthesis, wastewater treatment of the fertilizer plant was upgraded so that it became a ZLD process coupled with the recovery and recycling of fluorides and phosphates.

Hydrothermal synthesis of a mineral-substituted hydroxyapatite nanocomposite material for fluoride removal from drinking water

Mineral substituted hydroxyapatite (mHAp) nanocomposite was synthesized and it shows high fluoride adsorption capacity.

The utilization of waste by-products for removing silicate from mineral processing wastewater via chemical precipitation

This study investigates an environmentally friendly technology that utilizes waste by-products (waste acid and waste alkali liquids) to treat mineral processing wastewater. Chemical precipitation is used to remove silicate from scheelite (CaWO₄) cleaning flotation wastewater and the waste by-products are used as a substitute for calcium chloride (CaCl₂). A series of laboratory experiments is conducted to explain the removal of silicate and the characterization and formation mechanism of calcium silicate. The results show that silicate removal reaches 90% when the Ca:Si molar ratio exceeds 1.0. The X-ray diffraction (XRD) results confirm the characterization and formation of calcium silicate. The pH is the key factor for silicate removal, and the formation of polysilicic acid with a reduction of pH can effectively improve the silicate removal and reduce the usage of calcium. The economic analysis shows that the treatment costs with waste acid (0.63 $/m³) and waste alkali (1.54 $/m³) are lower than that of calcium chloride (2.38 $/m³). The efficient removal of silicate is confirmed by industrial testing at a plant. The results show that silicate removal reaches 85% in the recycled water from tailings dam.

Recovery of phosphorus from synthetic wastewaters by struvite crystallization in a fluidized-bed reactor: Effects of pH, phosphate concentration and coexisting ions

The crystallization of struvite in fluidized-bed crystallizer (FBC) was performed to treat synthetic wastewaters that contain phosphorous. Under optimal conditions (pH 9.5, molar ratio Mg/N/P = 1.3/4/1, struvite seed dose (53-297 μm) = 30 g L^-1, total flow rate = 12 ml min^-1, reflux = 120 ml min^-1), the removal of phosphate (PR) and the crystallization ratio (CR) were 95.8% and 93.5%, respectively. Based on a thermodynamic prediction, the supersaturation, which was obtained from the difference between the theoretical solubility and phosphate concentration, predominated the crystallization efficiency and the properties of the struvite pellets, such as their morphology, particle size and apparent density. Coexisting ions NO₃^- (80, 160 ppm), CH₂COOH^- (260, 520 ppm), F^- (650, 1300 ppm) and SO₄^2- (650, 1300 ppm), were utilized to prepare P-containing wastewaters. Of these ions, SO₄^2- (1300 ppm) remarkably reduced the capability of FBC to remove phosphate from solution. In the presence of NO₃^- and CH₃COO^- (for synthesizing TFT-LCD wastewater), and F^- and SO₄^2- (for synthesizing semiconductor wastewater), CR% was lower than in pure water, although the ultimate PR% did not differ significantly.

Adsorption of fluoride at the interface of water with calcined magnesium–ferri–lanthanum hydrotalcite-like compound

A new calcined Mg/Fe/La hydrotalcite-like compound was prepared and showed a good performance for fluoride adsorption. The “memory effect” of the adsorbent and lanthanum played a great role for fluoride adsorption.

An unprecedented bacterial cellulosic material for defluoridation of water

Defluoridation of water using bacterial cellulosic membrane.

Simultaneous adsorptive removal of fluoride and phosphate by magnesia–pullulan composite from aqueous solution

The presence of fluoride and phosphate could affect the adsorption rate of another one while simultaneous adsorption on MgOP.

Study on an effective industrial waste-based adsorbent for the adsorptive removal of phosphorus from wastewater: equilibrium and kinetics studies

In this work, an effective adsorbent for removing phosphate from aqueous solution was developed from modifying industrial waste--lithium silica fume (LSF). The characterization of LSF before and after modification was investigated using an N2 adsorption-desorption technique (Brunauer-Emmett-Teller, BET), scanning electron microscopy (SEM) and X-ray diffraction (XRD). Studies were conducted to investigate the effect of adsorbent dose, initial solution pH, contact time, phosphate concentration, and temperature on phosphate removal using this novel adsorbent. The specific surface area for modified LSF (LLSF) is 24.4024 m(2)/g, improved 69.8% compared with unmodified LSF. XRD result suggests that the lanthanum phosphate complex was formed on the surface of LLSF. The maximum phosphate adsorption capacity was 24.096 mg P/g for LLSF, and phosphate removal was favored in the pH range of 3-8. The kinetic data fitted pseudo-second-order kinetic equation, intra-particle diffusion was not the only rate controlling step. The adsorption isotherm results illustrated that the Langmuir model provided the best fit for the equilibrium data. The change in free energy (△G(0)), enthalpy (△H(0)) and entropy (△S(0)) revealed that the adsorption of phosphate on LLSF was spontaneous and endothermic. It was concluded that by modifying with lanthanum, LSF can be turned to be a highly efficient adsorbent in phosphate removal.

Al2O3–Fe3O4–expanded graphite nano-sandwich structure for fluoride removal from aqueous solution

In this study, a novel Al₂O₃–Fe₃O₄–expanded graphite nano-sandwich adsorbent was prepared to remove fluoride from aqueous solutions.

Fractionation and release behaviors of metals (In, Mo, Sr) from industrial sludge

Little is known on the fate of rare metals in the environment and the associated risks. The fractionation and release of three metals of an industrial sludge were assessed. The average concentration ranges from 39.3 to 41.5 mg/kg for indium (In), 43.1-77.8 mg/kg for molybdenum (Mo), and 131.1-376.4 mg/kg for strontium (Sr). Sequential extraction results implied that In was mobile, while Mo and Sr were immobile. However, experimental results from effects of Eh/pH revealed that In was slightly mobile under acidic (pH 4.5) in Eh range of 210-260 mV, and immobile under alkaline conditions (9.0) in Eh range of -250 to 125 mV. The release of Mo was slightly mobile under acidic conditions. However, Mo was very mobile under alkaline conditions and it increased with decreasing Eh. The release of Sr was significant under acidic conditions; however, it was immobile under alkaline conditions. Solubility and adsorption as affected by pH, and speciation could explain their release behaviors. Discrepancy in predictions from sequential extraction and actual observation from Eh/pH experiments was discussed.

Enhanced defluoridation and facile separation of magnetic nano-hydroxyapatite/alginate composite

In this research study, a new magnetic biosorbent was developed by the fabrication of magnetic Fe3O4 particles on nano-hydroxyapatite(n-HAp)/alginate (Alg) composite (Fe3O4@n-HApAlg composite) for defluoridation in batch mode. The synthesized Fe3O4@n-HApAlg biocomposite possess an enhanced defluoridation capacity (DC) of 4050 mgF(-)/kg when compare to n-HApAlg composite, Fe3O4@n-HAp composite, n-HAp and Fe3O4 which possesses the DCs of 3870, 2469, 1296 and 1050 mgF(-)/kg respectively. The structural changes of the sorbent, before and after fluoride sorption were studied using FTIR, XRD and SEM with EDAX techniques. There are various physico-chemical parameters such as contact time, pH, co-existing anions, initial fluoride concentration and temperature were optimized for maximum fluoride removal. The equilibrium data was well modeled by Freundlich, Langmuir, Dubinin-Radushkevich (D-R) and Temkin isotherms. The present system follows Dubinin-Radushkevich isotherm model. The thermodynamic parameters reveals that the feasibility, spontaneity and endothermic nature of fluoride sorption. The performance and efficiency of the adsorbent material was examined with water samples collected from fluoride endemic areas namely Reddiyarchatram and Ammapatti in Dindigul District of Tamil Nadu using standard protocols.