Volcanic Rock Materials for Defluoridation of Water in Fixed-Bed Column Systems

Consumption of drinking water with a high concentration of fluoride (>1.5 mg/L) causes detrimental health problems and is a challenging issue in various regions around the globe. In this study, a continuous fixed-bed column adsorption system was employed for defluoridation of water using volcanic rocks, virgin pumice (VPum) and virgin scoria (VSco), as adsorbents. The XRD, SEM, FTIR, BET, XRF, ICP-OES, and pH Point of Zero Charges (pH_PZC) analysis were performed for both adsorbents to elucidate the adsorption mechanisms and the suitability for fluoride removal. The effects of particle size of adsorbents, solution pH, and flow rate on the adsorption performance of the column were assessed at room temperature, constant initial concentration, and bed depth. The maximum removal capacity of 110 mg/kg for VPum and 22 mg/kg for VSco were achieved at particle sizes of 0.075–0.425 mm and <0.075 mm, respectively, at a low solution pH (2.00) and flow rate (1.25 mL/min). The fluoride breakthrough occurred late and the treated water volume was higher at a low pH and flow rate for both adsorbents. The Thomas and Adams–Bohart models were utilized and fitted well with the experimental kinetic data and the entire breakthrough curves for both adsorbents. Overall, the results revealed that the developed column is effective in handling water containing excess fluoride. Additional testing of the adsorbents including regeneration options is, however, required to confirm that the defluoridation of groundwater employing volcanic rocks is a safe and sustainable method.     

Optimization of Fluoride Adsorption on Acid Modified Bentonite Clay Using Fixed-Bed Column by Response Surface Method

Using small-scale batch tests, various researchers investigated the adsorptive removal of fluoride using low-cost clay minerals, such as Bentonite. In this study, Column adsorption studies were used to investigate the removal of fluoride from aqueous solution using acid-treated Bentonite (ATB). The effects of initial fluoride concentration, flow rates, and bed depth on fluoride removal efficiency (R) and adsorption capability (qe) in continuous settings were investigated, and the optimal operating condition was determined using central composite design (CCD). The model’s suitability was determined by examining the relationship between experimental and expected response values. The analysis of variance was used to determine the importance of independent variables and their interactions. The optimal values were determined as the initial concentration of 5.51 mg/L, volumetric flow rate of 17.2 mL/min and adsorbent packed-bed depth of 8.88 cm, with % removal of 100, adsorptive capacity of 2.46 mg/g and desirability of 1.0. This output reveals that an acid activation of Bentonite has made the adsorbent successful for field application.     

磷酸铝吸附除水中氟的研究

采用静态吸附法研究了比表面为308m2/g的无定形磷酸铝吸附除氟性能,研究了接触时间、pH值、吸附剂量等对吸附的影响。结果表明,磷酸铝吸附除氟高效、迅速,30min内可以接近最大吸附量。对含氟50mg/g的溶液,优化条件下的最大除氟率约93%。研究了吸附与溶液pH的关系,得到了优化pH值并解释了吸附机理。吸附的最佳pH值约为5.5。用拟二级动力学方程描述了吸附速率并计算了速率常数。用Langmuir方程拟合了吸附等温线,计算的饱和吸附量为53.5mg/g。吸附剂量对分配系数的影响表明吸附剂表面是不均匀的。     

Synthesis and performance evaluation of chitosan/zinc oxide nanocomposite as a highly efficient adsorbent in the removal of reactive red 198 from water

In this study, Chitosan and Chitosan-zinc oxide (ZnO) nanocomposite were prepared and applied as a low-cost adsorbent with high adsorption capacity for removing reactive red 198 (RR 198) dye from contaminated water. After preparation, it was characterized using FT-IR, XRD, and SEM. The effect of pH, temperature, time, adsorbent amount, and initial dye concentration were investigated in the removal efficiency of RR 198. The maximum adsorption capacity (q_m) obtained from the Langmuir equation was 172.41 mg/g in adsorbent dose of 0.1 g/L, pH: 4, temperature of 25°C, adsorption time of 40 min. The thermodynamic parameters demonstrated the spontaneous and endothermic nature of the adsorption process. Due to the high efficiency of chitosan/ZnO nanocomposite in removal of RR 198 from water and advantages such as high adsorption capacity, simple synthesis, and easy application, it can be used as an effective method in the removal of RR 198 from water.     

载铁(β-FeOOH)球形棉纤维素吸附剂去除地下水砷(Ⅲ)的研究

制备了一种载铁(β-FeOOH)球形棉纤维素吸附剂,并用于地下水中As(Ⅲ)的去除.吸附剂对As(Ⅴ)和As(Ⅲ)在吸附容量、选择性和速率等方面都具有良好的性能,无需预氧化As(Ⅲ),其适用pH范围宽,不必调节原水的pH.吸附剂孔隙度大,机械强度好,活性成分铁的载入量高,吸附As(Ⅲ)的活性好.Langmuir和Freundlich方程能较好地描述吸附平衡方程,其吸附动力学符合Lagergren准二级方程.吸附As(Ⅲ)的最佳pH范围为6-9.SO42-和Cl-等干扰离子均不影响As(Ⅲ)的去除.柱吸附实验表明,即使在较高流速和As(Ⅲ)进水浓度下,吸附剂对As(Ⅲ)的去除依然具有很高的穿透容量和饱和容量.吸附剂可以用NaOH溶液再生,洗脱和再生效率较高.活性成分β-FeOOH形态稳定,柱实验和再生时铁均无泄漏.     

Performance and Mechanisms of Fluoride Removal from Groundwater by Lanthanum-aluminum-loaded Hydrothermal Palygorskite Composite

Lanthanum-aluminum loaded hydrothermal palygorskite(La-Al-HP) composite was prepared and selected as adsorbent for the fluoride removal from simulated groundwater. The adsorbent was characterized by scanning electron microscopy(SEM), Brunauer-Emmet-Teller(BET) analysis, X-ray diffraction(XRD) analysis and X-ray photoelectron spectroscopy(XPS). SEM visualization shows that the dense surface structure of raw HP appeared loose and presented micro canals after modification. The BET analysis also proved the specific surface area of La-Al-HP composite(95.58 m²/g) was higher than that of the raw HP(34.31 m²/g). Subsequently, the adsorption capacity of La-Al-HP composite was demonstrated in adsorption experiments. The kinetics of fluoride ion adsorption into La-Al-HP composite followed the pseudo-second order with a correlation coefficient of 0.997. The isotherm data was well fitted with the Langmuir model. The monolayer adsorption capacity of La-Al-HP composite was 1.30 mg/g. The XRD and XPS results reveal that the La³⁺ and Al³⁺ ions were loaded on the surface of modified HP and the fluoride ion was adsorbed onto the La-Al-HP composite. A large amount of La-Al-O composite oxide existing on the surface of La-Al-HP composite might be the immanent cause for the excellent adsorption capacity of fluoride ions.     

Elimination of fluoride ions in water for human consumption using hydroxyapatite as an adsorbent

In this work, a synthetic hydroxyapatite, Bio-gel HTP, marketed by BIO-RAD®, has been studied in order to propose a method to remove the excess fluoride present in drinking water. The removal of fluoride ions by this adsorbent has been studied as a function of solution pH, and fluoride ion concentration. Experiments of fluoride ions sorption have been carried out with the use of ¹⁸F radiotracer in solutions of NaF at several concentrations with an ion selective electrode used for fluoride analysis. The adsorption isotherms show that the best fluoride adsorption on hydroxyapatite occurs at a pH range of 7.0–7.5. At this pH value the solid presents an important capacity of subtraction of fluoride, of around of 100 mmol/100 g.     

Adsorptive removal of arsenic from water by an iron-zirconium binary oxide adsorbent

Arsenate and arsenite may exist simultaneously in groundwater and have led to a greater risk to human health. In this study, an iron-zirconium (Fe-Zr) binary oxide adsorbent for both arsenate and arsenite removal was prepared by a coprecipitation method. The adsorbent was amorphous with a specific surface area of 339 m(2)/g. It was effective for both As(V) and As(III) removal; the maximum adsorption capacities were 46.1 and 120.0 mg/g at pH 7.0, respectively, much higher than for many reported adsorbents. Both As(V) and As(III) adsorption occurred rapidly and achieved equilibrium within 25 h, which were well fitted by the pseudo-second-order equation. Competitive anions hindered the sorption according to the sequence PO(4)(3-)>SiO(3)(2-)>CO(3)(2-)>SO(4)(2-). The ionic strength effect experiment, measurement of zeta potential, and FTIR study indicate that As(V) forms inner-sphere surface complexes, while As(III) forms both inner- and outer-sphere surface complexes at the water/Fe-Zr binary oxide interface. The high uptake capability and good stability of the Fe-Zr binary oxide make it a potentially attractive adsorbent for the removal of both As(V) and As(III) from water.     

Preparation and Defluorination Performance of Activated Cerium(IV) Oxide/SiMCM-41 Adsorbent in Water

By using the wetness impregnation-coprecipitation method, a new adsorbent, cerium(IV) oxide coated on SiMCM-41 ((Ce)SiMCM-41), was prepared for removal of fluoride ions from water. Factors investigated were number of impregnations, Ce/Si ratios, concentrations of F(-) ions, pH values, and calcination temperatures. The dynamics, isotherms, and mechanism of adsorption of F(-) ions were discussed. Copyright 2001 Academic Press.     

Novel reusable sulfate-type zirconium alginate ion-exchanger for fluoride removal

It is still a challenge to eliminate efficiently fluoride ion from groundwater, especially to design and synthesis an adsorbent possessing high adsorption capacity, recyclability and wide pH application conditions. Herein we present millimeter-sized sulfate-type zirconium alginate hydrogel beads with 3D network structure (AHB@Zr-SO₄²⁻) that exhibited a maximum adsorption capacity of 101.3 mg/g with wide pH applicability (pH 3−9). This material have ~2.5 times higher adsorption capacity than that of pure zirconium alginate hydrogel beads (AHB@Zr) and it was ascribed to ion exchange between SO₄²⁻ and F⁻ on the surface of AHB@Zr-SO₄²⁻, which was verified via ion chromatography measurement coupled with X-ray photoelectron spectroscopy (XPS) and Fourier Transform Infrared Spectrometer (FTIR Spectrometer) analysis. Density functional theory (DFT) calculations indicated that the ion exchange process between SO₄²⁻ and F⁻ in AHB@Zr-SO₄²⁻ was energetically favorable than OH⁻ and F⁻ in AHB@Zr. In addition, 310 bed volumes (BV) of effluent was realized via column adsorption of groundwater containing fluoride on AHB@Zr-SO₄²⁻ and indicated that it is a promising candidate for mitigating the problem of fluoride-containing groundwater.     

Adsorption kinetics of fluoride on iron(III)-zirconium(IV) hybrid oxide

Fluoride occurs in some drinking water sources at levels that are hazardous to health. Tests were conducted to assess the ability of a mineral-based adsorbent to take-up fluoride ion. Consequently, in search of novel adsorbent media, crystalline and hydrous iron(III)-zirconium(IV) hybrid oxide (IZHO) was synthesized, and tested to determine its capacity and kinetics for fluoride adsorption. The Fourier Transform Infrared (FTIR) spectrum of IZHO indicated the presence of Fe–O–Zr linkage which showed hybrid nature of the synthetic oxide. The optimum pH range for fluoride adsorption was ranged between 4.0 and 7.0. The analyses of the isotherm equilibrium data using the Langmuir and the Redlich–Peterson model equations by linear and non-linear methods showed that the data fitted better with latter model than the former. Thermodynamic analysis showed spontaneous nature of fluoride adsorption, and that took place with the increase of entropy. The kinetic data obtained for fluoride adsorption on IZHO at pH 6.8 (±0.1) and room temperature (303±2 K) described both the pseudo-first order and the reversible first-order equations equally well (r ²= ∼0.98–0.99), and better than pseudo second order equation (r ²= ∼0.96–0.98) for higher concentrations (12.5 and 25.0 mg/dm³) of fluoride. The kinetics of fluoride adsorption on the mixed oxide took place with boundary layer diffusion. External mass transport with intra-particle diffusion phenomena governed the rate limiting process, which has been confirmed from the Boyd poor non-linear kinetic plots.     

Gamma irradiation induced preparation of poly(acrylamide–itaconic acid)/zirconium hydrous oxide for removal of Cs-134 radionuclide and methylene blue

Adsorption experiments were carried out to investigate the removal of Cs-134 radionuclide and methylene blue (MB) from aqueous solution using poly(acrylamide–itaconic acid)/N,N′-methelyenediacrylamide/zirconium hydrous oxide composite [poly(AM–IA)/DAM/Zr(OH)₄] as an adsorbent. The effects of initial pH value, initial concentration of Cs or MB, adsorbent dose, contact time and temperature on adsorption were investigated. Characterization of the prepared composite was carried out using FT-IR, XRD, TGA, DTA, and SEM. The adsorption behaviors showed that the adsorption kinetics and isotherms were in good agreement with the pseudo-second-order and the Langmuir models indicating the chemosorption mechanism. Thermodynamic studies were carried out and it was found that the process was spontaneous exothermic in nature. Discussion of the results of the adsorption behavior showed that the prepared composite can be used as a promising adsorbent for removal of Cs-134 or MB.     

Use of ferric-impregnated volcanic ash for arsenate (V) adsorption from contaminated water with various mineralization degrees

Ferric-impregnated volcanic ash (FVA) which consisted mainly of different forms of iron and aluminum oxide minerals was developed for arsenate (V) removal from an aqueous medium. The adsorption experiments were conducted in both DI water samples and actual water (Lake Kasumigaura, Japan) to investigate the effects of solution mineralization degree on the As(V) removal. Kinetic and equilibrium studies conducted in actual water revealed that the mineralization of water greatly elevated the As(V) adsorption on FVA. The experiment performed in DI water indicated that the existence of multivalence metallic cations significantly enhanced the As(V) adsorption ability, whereas competing anions such as fluoride and phosphate greatly decreased the As(V) adsorption. It is suggested that FVA is a cost-effective adsorbent for As(V) removal in low-level phosphate and fluoride solution. It was important to conduct the batch experiment using the actual water to investigate the arsenic removal on adsorbents.     

Efficient removal of chlorophenols from water with a magnetic reduced graphene oxide composite

A magnetic reduced graphene oxide composite (MRGO) was successfully prepared by a simple and green method. MRGO was then used as an adsorbent and found to exhibit enhanced removal efficiency for various chlorophenols (CPs) from water compared with its precursors, graphene oxide (GO) and reduced graphene oxide. The CPs were o-chlorophenol, p-chlorophenol, 2,4-dichlorophenol, and 2,4,6-trichlorophenol. Among them, 2,4,6-trichlorophenol, which exhibited the lowest water solubility and highest molecular weight, most easily bound to MRGO. The preferential interactions between MRGO and CPs were hydrophobic interactions (π-π stacking and hydrophobic effect). This result was confirmed by the equilibrium adsorption behavior in which isotherms were all well described by Freudlich model, indicating heterogeneous and multilayer adsorption. Therefore, CP adsorption was more favored under neutral and acidic conditions, and the decreased removal efficiency of MRGO at higher pH levels was due to the improved hydrophilicity of CPs for deprotonation effect. Moreover, MRGO showed fast removal of each CP, achieving adsorption equilibrium within 10.0 min, presented efficient separation from water under an external magnetic field, and was easily regenerated using dilute NaOH aqueous solution after reaching saturated adsorption. Adsorption capacity of the regenerated MRGO had almost no loss until after five cycles. In summary, MRGO was an efficient adsorbent for the removal of various CPs and had considerable application potential in water treatment.     

Defluoridation in aqueous solution by a composite of reduced graphene oxide decorated with cuprous oxide via sonochemical

The World Health Organization (WHO) has recommended the fluoride level in drinking water (1.5 mg/L) and defluoridation of water is an essential to remove of fluoride from contaminated water. Hence, the effective and rapid adsorbent Cuprous oxide-reduced graphene oxide (Cu₂O-RGO) composite was developed to overwhelm this concern. Sonochemical approach was adopted for the synthesis of desirable composite which was further characterized by XRD, FTIR, SEM, and EDS. The optimized composite (30 mg) shown the significant adsorption capacity of 34 mg/g of F⁻ solution (pH = 9), 70% removal of F⁻ solution from real experiment and Freundlich model was fitted than Langmuir and Temkin isotherms. The experimental results corroborate that adsorbent is the most effective for removal of fluoride from its polluted water.     

Fluoride wastewater treatment by adsorption onto metallurgical grade alumina

The adsorption of fluoride onto metallurgical grade alumina (to produce Al) was investigated under different conditions: pH, contact time and adsorbent concentration. Data were evaluated with the aim of developing an alternative treatment technology for washing wastewater arising from an Aluminum can production plant. Kinetics and adsorption isotherms data have been also produced Sorption is greatly affected by pH and the best condition for fluoride removal are obtained at pH 5-6 and alkalinity competes successfully with fluoride ions for the exchange sites. Experiments with fixed beds indicate that fluoride is removed from wastewater by metallurgical-grade alumina with a capacity of 12.21 mg of F per gram and adsorption increases of about 25% at appropriate pH. The Mass Transfer Zone at 5% of the breakthrough occupies 70.6% of the total column length. The optimization of aluminum precipitation by pH adjustment and with different precipitant agents has been done.     

聚离子液体水凝胶用于中性水中Cr(VI)的去除

随着经济的快速发展,水污染已成为全球关注的紧迫问题。其中,Cr（VI）在废水中含量较高且毒性较强,可引起多种严重疾病。而大多数污染地表水和地下水的pH往往是接近中性的。因此,开发具有近中性pH值下有效去除Cr（VI）的吸附剂对生态系统和公众健康至关重要。本文设计并制备了具有不同结构的三氮唑鎓聚离子液体水凝胶,并将其应用于CrO42-的吸附和释放。该水凝胶可在中性条件下实现水中CrO42-的100%去除,最大吸附量高达356 mg/g。等温吸附结果表明,在较低浓度下CrO42-在聚离子液体水凝胶中为单层吸附。此外,可进一步通过离子交换将吸附于水凝胶中的CrO42-释放出来,实现吸附剂的再生。     

Efficient Removal of Pb(II) from Aqueous Medium Using Chemically Modified Silica Monolith

The adsorptive removal of lead (II) from aqueous medium was carried out by chemically modified silica monolith particles. Porous silica monolith particles were prepared by the sol-gel method and their surface modification was carried out using trimethoxy silyl propyl urea (TSPU) to prepare inorganic–organic hybrid adsorbent. The resultant adsorbent was evaluated for the removal of lead (Pb) from aqueous medium. The effect of pH, adsorbent dose, metal ion concentration and adsorption time was determined. It was found that the optimum conditions for adsorption of lead (Pb) were pH 5, adsorbent dose of 0.4 g/L, Pb(II) ions concentration of 500 mg/L and adsorption time of 1 h. The adsorbent chemically modified SM was characterized by scanning electron microscopy (SEM), BET/BJH and thermo gravimetric analysis (TGA). The percent adsorption of Pb(II) onto chemically modified silica monolith particles was 98%. An isotherm study showed that the adsorption data of Pb(II) onto chemically modified SM was fully fitted with the Freundlich and Langmuir isotherm models. It was found from kinetic study that the adsorption of Pb(II) followed a pseudo second-order model. Moreover, thermodynamic study suggests that the adsorption of Pb(II) is spontaneous and exothermic. The adsorption capacity of chemically modified SM for Pb(II) ions was 792 mg/g which is quite high as compared to the traditional adsorbents. The adsorbent chemically modified SM was regenerated, used again three times for the adsorption of Pb(II) ions and it was found that the adsorption capacity of the regenerated adsorbent was only dropped by 7%. Due to high adsorption capacity chemically modified silica monolith particles could be used as an effective adsorbent for the removal of heavy metals from wastewater.     

Size-dependent defluoridation properties of synthetic hydroxyapatite

Batch adsorption experiments were conducted to investigate the removal of fluoride from aqueous solution by the addition of synthetic hydroxyapatites (HAps) with different particle sizes. Results showed that size-dependent defluoridation properties of HAps. Better performances were obtained with smaller particle sized HAps, which presented higher adsorption efficiency. Bulk HAp, the HAp sample with the largest particle size, presented the lowest percentage of fluoride removal. The isotherm studies showed that the Freundlich model was the best choice to describe the adsorption behaviors of nanosized HAps. However, the adsorption pattern of the bulk sample followed both Langmuir and Freundlich isotherms. All parameters that might influence the defluoridation process were assessed, which included the effect of adsorbent dose, initial fluoride concentration, contact time and the effect of temperature. The removal efficiency of fluoride increased with increasing adsorbent dose. Decrease of the initial fluoride concentration resulted in the increase of fluoride removal efficiency. The percentage of fluoride removal increased as the ambient pH decreased. Thermodynamic parameters suggested that the adsorption of fluoride onto HAp samples was physisorption and endothermic in nature. Moreover, adsorption kinetic study revealed that the adsorption process followed pseudo-second-order kinetics. This work indicated that synthetic hydroxyapatites, especially the smaller particle sized HAps, were efficient defluoridation materials.