Optimization of fluoride adsorption onto natural and modified pumice using response surface methodology: Isotherm, kinetic and thermodynamic studies

Deep insight on mechanism and contribution of arsenic removal and heavy metals remediation by mechanical activation phosphogypsum

Arsenic-containing wastewater and arsenic-contaminated soil can cause serious environmental pollution. In this study, phosphogypsum with partial mechanical activation of calcium oxide was used to prepare a new phosphogypsum-based passivate (Ca-mPG), and its remediation performance on arsenic-contaminated soil was evaluated in terms of both effectiveness and microbial response. The results showed that the optimum conditions for the preparation of the passivate were optimized in terms of single factor and response surface with a ball milling speed of 200 r/min, a material ratio of 6:4 and a ball milling time of 4 h. Under these conditions, the adsorption capacity was 37.75 mg/g. The leaching concentration of arsenic (As) in the contaminated soil after Ca-mPG modification decreased from 25.75 μg/L to 5.88 μg/L, which was lower than the Chinese national standard (GB/T 5085.3-2007); Ca-mPG also showed excellent passivation effect on other heavy Metals (copper, nickel, cadmium, zinc). In addition, As-resistant bacteria and passivators work together to promote the stabilization effect of contaminants during the remediation of As-contaminated soil. The mechanisms of Cu, As(III)/As(V), Zn, Cd, and Ni removal were related to ion exchange, electrostatic adsorption of substances on heavy metals, calcium binding to other substances to produce precipitation; and microbially induced stabilization of HMs, oxidized. Overall, this study demonstrates an eco-friendly "waste-soil remediation" strategy to solve problems associated with solid waste reuse and remediation of HM-contaminated soils.

Adsorptive removal of acid red 18 dye from aqueous solution using hexadecyl-trimethyl ammonium chloride modified nano-pumice

Discharging untreated dye-containing wastewater gives rise to environmental pollution. The present study investigated the removal efficiency and adsorption mechanism of Acid Red 18 (AR18) utilizing hexadecyl-trimethyl ammonium chloride (HDTMA.Cl) modified Nano-pumice (HMNP), which is a novel adsorbent for AR18 removal. The HDTMA.Cl is characterized by XRD, XRF, FESEM, TEM, BET and FTIR analysis. pH, contact time, initial concentration of dye and adsorbent dose were the four different parameters for investigating their effects on the adsorption process. Response surface methodology-central composite design was used to model and improve the study to reduce expenses and the number of experiments. According to the findings, at the ideal conditions (pH = 4.5, sorbent dosage = 2.375 g/l, AR18 concentration = 25 mg/l, and contact time = 70 min), the maximum removal effectiveness was 99%. The Langmuir (R2 = 0.996) and pseudo-second-order (R2 = 0.999) models were obeyed by the adsorption isotherm and kinetic, respectively. The nature of HMNP was discovered to be spontaneous, and thermodynamic investigations revealed that the AR18 adsorption process is endothermic. By tracking the adsorption capacity of the adsorbent for five cycles under ideal conditions, the reusability of HMNP was examined, which showed a reduction in HMNP's adsorption effectiveness from 99 to 85% after five consecutive recycles.

Experimental and Modeling Optimization of Strontium Adsorption on Microbial Nanocellulose, Eco-friendly Approach

Green synthesized cellulose nanocrystals (CNCs) was prepared using Neurospora intermedia, characterized, and used to remove Strontium ions (Sr2+) from an aqueous solution with high efficiency. The characterization of CNCs was performed using a UV-Vis Spectrophotometer, Dynamic Light Scattering (DLS), Zeta Potential (ZP), Fourier Transform Infrared Spectroscopy (FTIR), X-Ray Diffraction (XRD), and Scanning Electron Microscopy (SEM) mapping, EDX elemental analysis and BET surface analyzer. In this study, Response Surface Methodology (RSM) based on Box-Behnken Design (BBD) was successfully applied for the first time to optimize the dynamic adsorption conditions for the maximum removal of Sr2+ ions from aqueous solutions using CNCs as adsorbent. The effects of parameters, such as initial concentration of Sr2+ (50–500 ppm), adsorbent dosage (0.05–0.2 g/50ml), and contact time (15–120 min.) on removal efficiency were investigated. A mathematical model was studied to predict the removal performance. The significance and adequacy of the model were surveyed using the analysis of variance (ANOVA). The results showed that the second-order polynomial model is suitable for the prediction removal of Sr2+ with regression coefficient (R2 = 97.41%). The highest sorption capacity value of Sr2+ was obtained (281.89 mg/g) at the adsorbent dosage of 0.05 g/50 ml, contact time of 120 min., and the pollutant (Sr2+) concentration of 275 ppm.

In-Situ SERS Detection of Hg2+/Cd2+ and Congo Red Adsorption Using Spiral CNTs/Brass Nails

Brass spiral nails were functionalized with CoFe₂O₄ nanoparticles and utilized as a substrate for the growth of extremely long CNTs with helical structures and diameters smaller than 20 nm. Different methods were used to characterize the grown CNTs' structures and morphologies. The characteristic Raman peaks of CNTs were amplified four times after being uploaded on the spiral nail, making the substrates for surface-enhanced Raman spectroscopy (SERS) more sensitive. To detect Hg²⁺ and Cd²⁺ at concentrations ranging from 1 to 1000 ppb, a CNT/spiral brass nail was used as a SERS substrate. The proposed sensor demonstrated high sensitivity and selectivity between these heavy metal ions. As a result, the proposed CNTs/spiral brass sensor can be an effective tool for identifying heavy metal ions in aqueous solutions. In addition, Congo red (CR) adsorption as a function of initial dye concentration and contact time was investigated. For CR dye solutions with concentrations of 5, 10, and 20 mg/L, respectively, the highest removal percentage was determined to be ~99.9%, 85%, and 77%. According to the kinetics investigation, the pseudo-first-order and pseudo-second-order models effectively handle CR adsorption onto CNTs/spiral nails. The increase in the dye concentration from 5 ppm to 20 ppm causes the rate constant to drop from 0.053 to 0.040 min^-1. Therefore, our sample can be employed for both the effective degradation of CR dye from wastewater and the detection of heavy metals.

Synergistic Fluoride Adsorption by Composite Adsorbents Synthesized From Different Types of Materials—A Review

The reduction of fluoride concentrations in water is one of many concerns. Adsorption is the most widely used technology for fluoride removal and the center to development of adsorption technology is the improvement of adsorbents. This review classifies the typical fluoride removal adsorbents into four types: metal oxides/hydroxides, biopolymers, carbon-based, and other adsorbents. The exploitation of new materials and the synthesis of composite materials are two ways of developing new adsorbents. In comparison to the discovery of novel adsorbents for fluoride adsorption, research into the composite synthesis of different types of conventional adsorbents has proliferated in recent years. The traditional adsorbents used the earliest, metal oxides, can act as active centers in a wide range of applications for modifying and compounding with other types of adsorbents. This study emphasizes reviewing the research on fluoride removal by composite adsorbents synthesized from different types of metal-modified materials. Seven factors were compared in terms of material characterization, initial fluoride concentration, adsorbent dose, pH, temperature, reaction time, and maximum adsorption capacity. The modification of composite adsorbents is facile and the synergistic effect of the different types of adsorbents significantly improves fluoride adsorption capacity. Metal composite adsorbents are synthesized by facile coprecipitation, hydrothermal, or impregnation modification methods. The adsorption mechanisms involve electrostatic attraction, ion exchange, complexation, and hydrogen bonding. The fluoride adsorption capacity of composite adsorbents has generally improved, indicating that most modifications are successful and have application prospects. However, to achieve significant breakthroughs in practical applications, numerous issues such as cost, separation/regeneration performance, and safety still need to be considered.

Fixed-Bed Adsorption: Comparisons of Virgin and Zirconium Oxide-Coated Scoria for the Removal of Fluoride from Water

Many people worldwide are exposed to extreme levels of fluoride in drinking water. It is, therefore, critical to develop inexpensive, locally available, and environmentally friendly adsorbents for fluoride-laden water defluoridation. In the current study, virgin scoria (volcanic rock) from Ethiopia, was modified with zirconium oxide and used as an adsorbent in a fixed-bed column aiming at the removal of fluoride from water. The adsorption capability of zirconium oxide-coated scoria (ZrOCSc) was compared with unmodified virgin scoria (VSco). XRD, FTIR, XRF, SEM, ICP-OES, and the pH_PZC tests were evaluated to explore the adsorption mechanisms. Thermal analysis of VSco and ZrOCSc revealed lower total weight losses of 2.3 and 3.2 percent, respectively, owing to the removal of water molecules and OH species linked to metal oxides contained in the material. The effect of test conditions such as the pH of the solution and the influent flow rate on the adsorption capacity of the adsorbent was carefully studied. ZrOCSc exhibited the maximum removal capacity of 58 mg/kg, which was 4.46 times higher than the observations for VSco (13 mg/kg) at pH 2, and an initial flow rate of 1.25 mL/min. Breakthrough time increased with decreasing initial pH and flow rate. The adsorption experimental data under various test conditions were examined by the Thomas and Adams–Bohart models. Both models were found very effective in describing the experimental data with a correlation coefficient (R²) of ≥0.976 (ZrOCSc) and ≥0.967 (VSco). Generally, coating VSco with zirconium oxide improved the adsorption performance of VSco; hence, a ZrOCSc-packed fixed bed could be employed for the decontamination of high levels of fluoride from groundwater. However, further examination of the adsorbent using natural groundwater is advisable to produce a definitive conclusion.

Adsorption of norfloxacin from aqueous solution on biochar derived from spent coffee ground: Master variables and response surface method optimized adsorption process

In this study, biochar derived from spent coffee grounds (SCGB) was used to adsorb norfloxacin (NOR) in water. The biochar properties were interpreted by analysis of the specific surface area, morphology, structure, thermal stability, and functional groups. The impacts of pH, NOR, and ion's present on SCGB performance were examined. The NOR adsorption mode of SCGB is best suited to the Langmuir model (R² = 0.974) with maximum absorption capacity (69.8 mg g^-1). By using a Response Surface Method (RSM), optimal adsorption was also found at pH of 6.26, NOR of 24.69 mg L^-1, and SCGB of 1.32 g L^-1. Compared with biochars derived from agriculture such as corn stalks, willow branches, potato stem, reed stalks, cauliflower roots, wheat straw, the NOR adsorption capacity of SCGB was 2-30 times higher, but less than 3-4 times for biochars made from Salix mongolica, luffa sponge and polydopamine microspheres. These findings reveal that spent coffee grounds biochar could effectively remove NOR from aqueous solutions. Approaching biochar derived from coffee grounds would be a promising eco-friendly solution because it utilizes solid waste, saves costs, and creates adsorbents to deal with emerging pollutants like antibiotics.

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.

Enhanced Defluoridation of Water Using Zirconium-Coated Pumice in Fixed-Bed Adsorption Columns

Millions of people across the globe suffer from health issues related to high fluoride levels in drinking water. The purpose of this study was to test modified pumice as an adsorbent for the purification of fluoride-containing waters. The adsorption of fluoride onto zirconium-coated pumice (Zr–Pu) adsorbent was examined in fixed-bed adsorption columns. The coating of zirconium on the surface of VPum was revealed by X-ray diffractometer (XRD), Inductively coupled plasma-optical emission spectroscopy (ICP-EOS), and X-ray fluorescence (XRF) techniques. The degree of surface modification with the enhanced porosity of Zr–Pu was evident from the recorded scanning electron microscope (SEM) micrographs. The Brunauer-Emmett-Teller (BET) analysis confirmed the enhancement of the specific surface area of VPum after modification. The Fourier transform infrared (FTIR) examinations of VPum and Zr–Pu before and after adsorption did not reveal any significant spectrum changes. The pH drift method showed that VPum and Zr–Pu have positive charges at pH_PZC lower than 7.3 and 6.5, respectively. Zr–Pu yielded a higher adsorption capacity of 225 mg/kg (2.05 times the adsorption capacity of VPum: 110 mg/kg), at pH = 2 and volumetric flow rate (Q_O) of 1.25 mL/min. Breakthrough time increases with decreasing pH and flow rate. The experimental adsorption data was well-matched by the Thomas and Adams-Bohart models with correlation coefficients (R²) of ≥ 0.980 (Zr–Pu) and ≥ 0.897 (VPum), confirming that both models are suitable tools to design fixed-bed column systems using volcanic rock materials. Overall, coating pumice with zirconium improved the defluoridation capacity of pumice; hence, a Zr–Pu-packed fixed-bed can be applied for defluoridation of excess fluoride from groundwater. However, additional investigations on, for instance, the influences of competing ions are advisable to draw explicit conclusions.

Preparation, characterization serpentine-loaded hydroxyapatite and its simultaneous removal performance for fluoride, iron and manganese

Aiming at the problem of excessive fluorine, iron, and manganese pollution in groundwater in mining areas, a serpentine-loaded hydroxyapatite (Srp/HAP) composite adsorbent was prepared by wet chemical coprecipitation. The preparation conditions of the Srp/HAP composite adsorbent were explored, Srp/HAP was microscopically characterized, and the adsorption performance and adsorption mechanism of the Srp/HAP composite adsorbent for F⁻, Fe²⁺ and Mn²⁺ were analyzed. The results showed that the optimal preparation conditions for the composite particles were as follows: solid–liquid ratio of Srp to calcium nitrate solution 20%, aging time 20 h, calcination temperature 180 °C, and calcination time 90 min. Compact Srp/HAP composite adsorbent particles were successfully prepared, and both the lamellar crimp structure of the Srp surface and the problem of HAP surface agglomeration were resolved. After loading, the specific surface area and pore volume of the particles significantly increased, and the surface pore structure improved, which is conducive to the simultaneous adsorption and removal of fluorine, iron and manganese. The optimal reaction conditions for Srp/HAP treatment of composite water samples with F⁻, Fe²⁺ and Mn²⁺ mass concentrations of 5 mg L⁻¹, 20 mg L⁻¹ and 5 mg L⁻¹, respectively, are as follows: dosage of Srp/HAP 3 g L⁻¹, pH 7, temperature 35 °C, and reaction time 150 min. Under these conditions, the removal rates of F⁻, Fe²⁺ and Mn²⁺ were 98.6%, 99.9% and 99.8%, respectively. The quasi-second-order kinetic model and Langmuir isothermal adsorption model described the adsorption process of F⁻, Fe²⁺ and Mn²⁺ by the composite particles well. The adsorption process includes both surface physical adsorption and chemical adsorption. Chemical adsorption is mainly characterized by ion exchange and surface complexation. The Srp/HAP composite particles can be used as an excellent adsorbent for the treatment of groundwater containing fluorine, iron and manganese ions in mining areas.

A new adsorbent Srp/HAP for simultaneous removal of fluoride, iron and manganese was prepared, characterized and analyzed.

Treatment of gold ore cyanidation wastewater by adsorption onto a Hydrotalcite-type anionic clay as a novel adsorbent

The treatment of cyanide contaminated wastewater from a gold processing plant was performed by the synthesized nanostructured Layered Double Hydroxide (LDH) which has known as a Hydrotalcite-type anionic clay. LDH was synthesized by the co-precipitation process, characterized by X-ray fluorescence (XRF), X-ray powder diffraction (XRD), scanning electron microscope (SEM) Brunauer-Emmett-Teller (BET), Fourier-transform infrared spectroscopy (FTIR) and Wavelength Dispersive X-ray analysis (WDX) and applied for removal of free cyanide from both synthetic solution and mining effluent. The maximum particle size of synthesized LDH was determined to be 4 nm based on the Scherrer's equation. The maximum loading capacity of LDH, 60 mg/g, indicates that LDH is an interesting adsorbent for cyanide removal. The data modeling showed that the kinetic and equilibrium data best fitted by FPKM and RPIM, respectively, also, rate-controlling step in the adsorption process is intra-particle diffusion based on Weber-Morris plot, and the adsorption of CN^- onto LDH is a two-step process. The thermodynamic studies confirm that the adsorption of free cyanide on Mg/Al LDH is a spontaneous and endothermic process. The energy of activation for adsorption of free cyanide on Mg/Al LDH was determined to be 6.14 kJ/mol, which is in the range physicochemical sorption. The mining wastewater treatment was performed by the synthesized LDH. The adsorption experiments showed that more than 90% of free cyanide was removed from the real solution during a short period of contact time, which confirms the ability of LDH for the treatment of industrial cyanide contaminated wastewater. Graphical abstract.

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.

Removal of boron and silicon by a modified resin and their competitive adsorption mechanisms

Boron and silicon are essential trace elements for living organisms. However, these are undesirable in excess amounts owing to the toxic effects of boron on plants, animals, and humans, and the silica scale formation by silicon in water treatment processes. Herein, a new diol-type adsorbent (T-resin) was synthesized by grafting tiron (disodium 4,5-dihydroxy-1,3-benzenedisulfonate) onto an ion-exchange resin (grafting amount is 1.2 mmol/g dry) to separate boron and silicon from a solution. The effects of pH, initial concentration, and coexisting anions, particularly, the effect of the coexistence of silicate ion on the adsorption of boron, were investigated. T-resin showed good adsorption properties for both boron and silicon in a wide pH range (pH 2-10). The adsorption of boron and silicon was effectively described by the Langmuir isotherm, and the maximum adsorption capacities of boron and silicon were 21.25 mg/g and 8.36 mg/g, respectively. In a competitive adsorption system, boron and silicon were simultaneously adsorbed on the T-resin, but the adsorption rate of boron was faster than silicon. However, silicon could replace the boron adsorbed on the resin, indicating that the adsorption of silicon was more stable than boron. ¹¹B and ²⁹Si solid state NMR data confirmed the different adsorption mechanisms of the two elements. Boron was adsorbed via two types of complexes, a triangular complex of [LB(OH)], as well as 1:1 tetrahedral complex of [LB(OH)₂] and 1:2 tetrahedral complex of [BL₂], whereas silicon was only adsorbed via a 1:3 octahedral complex of [SiL₃]. Graphical abstract A new diol-type absorbent was synthesized by grafting tiron onto an ion-exchange resin to separate boron and silicon from a solution. Boron and silicon competitively adsorbed on the T-resin, and silicon could replace the boron adsorbed on the resin. ¹¹B and ²⁹Si solid state NMR data confirmed the different adsorption mechanisms of the two elements. Boron was adsorbed via two types of complexes, a triangular complex of [LB(OH)], as well as 1:1 tetrahedral complex of [LB(OH)₂] and 1: 2 tetrahedral complex of [BL₂], whereas silicon was only adsorbed via a 1:3 octahedral complex of [SiL₃].

Microporous carbon material from fish waste for removal of methylene blue from wastewater

Microporous fish waste-based activated carbon material (MFC) was prepared, with a large surface area of 2,193.52 m²/g, a pore size of 2.67 nm and micropore and total pore volumes of 0.9168 cm³/g and 0.9975 cm³/g, respectively. Adsorption efficiency of MFC was investigated by removal of methylene blue dye from wastewater. The Langmuir model and pseudo-second-order kinetics adequately described the adsorption process. MFC exhibited a high adsorption capacity of 476.19 mg/g at 30 °C, and reached equilibrium within 1 h. MFC could be an efficient and low-cost adsorbent for cationic dye removal during wastewater treatment.

Hydrothermal synthesis of LaFeO3 nanoparticles adsorbent: Characterization and application of error functions for adsorption of fluoride

The adsorption of fluoride from aqueous solution by lanthanum ferrite nanoparticles (LaFeO₃ NPs) synthesized by the hydrothermal method has been investigated. This experimental study was conducted on a laboratory scale. The effects of various operating parameters such as pH (3-11), LaFeO₃ NPs dosage (0.1-1.0 g/L), contact time (15-120 min), temperature (303-318 K), and initial concentration of fluoride (15-40 mg/L) on fluoride adsorption were studied. The results showed that under optimal conditions of fluoride concentration of 20 mg/L, pH of 5, LaFeO₃ NPs dosage of 0.9 g/L, temperature of 308 K, and contact time of 60 min, maximum percentage removal of 94.75 % was obtained. The process of fluoride adsorption on LaFeO₃ NPs was found to depend on the Freundlich adsorption and Koble-Corrigan isotherm models. The monolayer adsorption capacity of LaFeO₃ NPs was 2.575 mg/g. The kinetic data fitted best into the pseudo-second-order model considering the values of the regression coefficients (r²) and error functions used. The thermodynamics study indicated that the adsorption process was exothermic (ΔH°< 0) and spontaneous (ΔG°< 0) in nature. It could be concluded that the synthesized LaFeO₃NPs can be used as an effective adsorbent for fluoride ions removal from aqueous solutions.

Adsorption of cephalexin in aqueous media by graphene oxide: kinetics, isotherm, and thermodynamics

The present study proposes the synthesis and characterization of graphene oxide (GO) and its application in the adsorption of the antibiotic cephalexin (CFX) in aqueous solution. The characterization of graphene oxide was obtained by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and zeta potential. The influence of pH on the batch adsorption process was investigated by analysing adsorption equilibrium isotherms and adsorption kinetics. The images obtained by SEM and TEM presented the typical morphology attributed to GO sheets. The kinetic adsorption tests showed that equilibrium was reached in 420 min, and an adsorption capacity of 164 mg g^-1 was obtained. The models that best fit the experimental data were pseudo-second as well as the Langmuir isotherm. Therefore, GO was effective for removing the CFX antibiotic from aqueous solution by using a batch adsorption process.

Synthesis and characteristics of a novel FeNi3/SiO2/TiO2 magnetic nanocomposites and its application in adsorption of humic acid from simulated wastewater: study of isotherms and kinetics

The presence of natural organic matter such as humic acid in water creates various problems in water purification. Humic acid can react with chlorine in the disinfection step and lead to the production of trihalomethanes and haloacetic acids that these compounds have carcinogenic and mutagenic properties; therefore, they must be removed before arriving to the disinfection stage. The purpose of this research was adsorption of humic acid from simulated wastewater by synthesized FeNi₃/SiO₂/TiO₂ magnetic nanocomposites. FeNi₃/SiO₂/TiO₂ magnetic nanocomposites were synthesized by sol-gel procedure and its characteristics were determined by TEM, VSM, BET, FESEM, and XRD techniques. Then, the effects of such pH (3-11), FeNi₃/SiO₂/TiO₂ dosage (0.005-0.1 g/L), contact time (0-200 min), and initial concentration (2-15 mg/L) were studied on humic acid adsorption using FeNi₃/SiO₂/TiO₂. The results of adsorption experiments revealed that the highest percentage of humic acid removal (94.4%) was achieved at pH 3, initial concentration of 5 ppm, FeNi₃/SiO₂/TiO₂ dose of 0.1 g/L, and contact time of 90 min. The analyses of experimental isotherm data showed that the humic acid adsorption was described by Langmuir model and also the kinetic studies represented that the process of adsorption of humic acid on FeNi₃/SiO₂/TiO₂ was followed by the pseudo-second kinetic. According to the results, it can be concluded that FeNi₃/SiO₂/TiO₂ magnetic nanocomposites have a high ability to absorb humic acid from simulated wastewater.

Data on the removal of fluoride from aqueous solutions using synthesized P/γ-Fe2O3 nanoparticles: A novel adsorbent

High concentration of fluoride above the optimum level can lead to dental and skeletal fluorosis. The data presents a method for its removal from fluoride-containing water. P/γ-Fe₂O₃ nanoparticles was applied as an adsorbent for the removal of fluoride ions from its aqueous solution. The structural properties of the P/γ-Fe₂O₃ nanoparticles before and after fluoride adsorption using the Fourier transform infrared (FTIR) technique were presented. The effects of pH (2–11), contact time (15–120 min), initial fluoride concentration (10–50 mg/L) and P/γ-Fe₂O₃ nanoparticles dosage (0.01–0.1 g/L) on the removal of F⁻ on P/γ-Fe₂O₃ nanoparticles were presented with their optimum conditions. Adsorption kinetics and isotherm data were provided. The models followed by the kinetic and isotherm data were also revealed in terms of their correlation coefficients (R²).

Data on fluoride concentration in drinking water resources in Iran: A case study of Fars province; Larestan region

Fluoride is a natural element among minerals, geochemical sediments and natural water systems which is entered to body chain by drinking water. Groundwater is the main and the best source of drinking water in southern areas of Iran especially in the cities of Lar and Gerash (Fars province). So due to the health significance fluoride including dental and skeletal fluorosis, fertility, abortion and thyroid diseases, etc., measuring has high importance in the water resources of this region of Iran. Fluoride concentration was 0.35–3.46 mg/L and 78.26% drinking water sources contains fluoride concentration above the WHO guideline.

Response surface methodology (RSM) modeling to improve removal of ciprofloxacin from aqueous solutions in photocatalytic process using copper oxide nanoparticles (CuO/UV)

Ciprofloxacin (CIP) antibiotic is considered as an emerging and biological resistant pollutant. This study aimed to improve of the removal of CIP from synthetic aqueous solutions in photocatalytic process through copper oxide nanoparticles as catalyst (CuO/UV). The effect of CIP concentration (10–200 mg/l), catalyst dosage included CuO (0.01–0.1 g/l) and pH (3–11) as independent variables on the COD removal efficiency as response in photocatalytic process using UV-C lamps with three different powers of 8, 15 and 30-W were optimized through the central composite design in response surface method using design-expert software. A second order model was selected as the best model with R² values and lack of fit as 0.85 and 0.06 for lamp 8-W, 0.89 and 0.11 for lamp 15-W, and 0.86 and 0.19 for lamp 30-W, respectively. Optimum conditions were obtained in CIP concentration of 11.2 (mg/l), CuO dosage of 0.08 (g/l), and pH value of 8.17. In this condition, predicted maximum COD removal was respectively found 83.79, 93.18, and 98.90% for lamps 8, 15 and 30-W. According to the results, photocatalytic process using copper oxide nanoparticles can effectively compose CIP in aqueous solutions.

Adsorption Behavior and Mechanism for the Uptake of Fluoride Ions by Reed Residues

The adsorption behavior and mechanism for the uptake of fluoride ions by untreated and desugared reed residues (roots, stems and leaves) were studied through adsorption experiments, elemental analysis, infrared spectroscopy and surface area analysis. The results showed that the adsorption capacity of untreated and desugared reeds followed the order: desugared roots 2136 mg/kg > desugared leaves 1825 mg/kg > desugared stems 1551 mg/kg > untreated roots 191 mg/kg > untreated stems 175 mg/kg > untreated leaves 150 mg/kg, so adsorption capacity of desugared reeds was larger than that of the untreated reeds. The adsorption kinetic of fluoride ions followed a pseudo-first-order model. A Langmuir model could be used to fit the isothermal adsorption process which was a spontaneous endothermic reaction involving mainly physical adsorption. The ΔG for the uptake of fluoride by the desugared reeds was more negative, so the degree of spontaneity was higher than for the use of the untreated reeds. After samples were desugared, the specific surface area and aromaticity of the reed increased, while the polarity and hydrophilicity decreased, which explained the adsorption amount of desugared reed was higher than that of the untreated. This study enriches techniques and methods of removing fluoride ions from water.

Response surface methodology modeling to improve degradation of Chlorpyrifos in agriculture runoff using TiO2 solar photocatalytic in a raceway pond reactor

This paper deals with the use of a raceway pond reactor (RPR) as an alternative photoreactor for solar photocatalytic applications. Raceway pond reactors are common low-cost reactors which can treat large volumes of water. The experiments were carried out with TiO₂ in the agriculture effluent spiked with Chlorpyrifos (CPF) at circumneutral pH. The Response Surface Methodology (RSM) was used to find the optimum process parameters to maximize CPF oxidation from the mathematical model equations developed in this study using R software. By ANOVA, p-value of lack of fit > 0.05 indicated that, the equation was well-fitted. The theoretical efficiency of CPF removal, under the optimum oxidation conditions with UV solar energy of around 697 ± 5.33 lux, was 84.01%, which is in close agreement with the mean experimental value (80 ± 1.42%) confirming that the response model was suitable for the optimization. As far as the authors know, this is the first study of CPF removal using RPR in agriculture runoff at circumneutral pH.

Predicting the capability of carboxymethyl cellulose-stabilized iron nanoparticles for the remediation of arsenite from water using the response surface methodology (RSM) model: Modeling and optimization

This study aimed to investigate the feasibility of carboxymethyl cellulose-stabilized iron nanoparticles (C-nZVI) for the removal of arsenite ions from aqueous solutions. Iron nanoparticles and carboxymethyl cellulose-stabilized iron nanoparticles were freshly synthesized. The synthesized nanomaterials had a size of 10nm approximately. The transmission electron microscope (TEM) images depicted bulkier dendrite flocs of non-stabilized iron nanoparticles. It described nanoscale particles as not discrete resulting from the aggregation of particles. The scanning electron microscopy (SEM) image showed that C-nZVI is approximately discrete, well-dispersed and an almost spherical shape. The energy dispersive x-ray spectroscopy (EDAX) and X-ray diffraction (XRD) spectrum confirmed the presence of Fe⁰ in the C-nZVI composite. The central composite design under the Response Surface Methodology (RSM) was employed in order to investigate the effect of independent variables on arsenite removal and to determine the optimum condition. The reduced full second-order model indicated a well-fitted model since the experimental values were in good agreement with it. Therefore, this model is used for the prediction and optimization of arsenite removal from water. The maximum removal efficiency was estimated to be 100% when all parameters are considered simultaneously. The predicted optimal conditions for the maximum removal efficiency were achieved with initial arsenite concentration, 0.68mgL^-1; C-nZVI, 0.3 (gL^-1); time, 31.25 (min) and pH, 5.2.