Arsenic Removal Research Articles

The Adsorption of Arsenate and Arsenite Ions on Oxidic Substrates Prepared with a Variable-Charge Lithological Material

The adsorption of As(V) and As(III) (0.01–1 mM) on a calcined oxidic lithologic material substrate with pH-dependent surface variable charges, chemically modifiable, was investigated. The substrate was prepared via thermal treatment using a natural lithologic material rich in amphoteric oxides of Fe, Al, Mn and Ti. The calcined substrate was treated with acid media (HCl 0.1) to homogenize the positive charge density on the oxide surface via oxide protonation so that anion adsorption would be favored. A batch experiment was performed on the acid-treated substrate (activated) and non-activated substrate. L-type isotherms were obtained, which fit the Freundlich model. Isotherm constants showed that there was a greater affinity between the activated substrate and As(V) (K = 10.58) compared to As(III) (K = 5.45). The adsorption capacity of the activated substrate was two times greater than that of the non-activated substrate, As(V) (Kact = 10.58 and Knoact = 5.45) vs. As(III) (Kact = 5.45 y Knoact = 2.44), which was due to the greater positive charge density on the activated surface, created by the protonation of the surface oxides. Protons were liberated during the adsorption reaction (As(V): 2.17×10−3 and As(III): 0.96×10−3 mmol/mL). The forms H2AsO4− and H3AsO3 deprotonated when adsorbed by the surface groups (M: Fe, Al). Kinetic data showed a second-order process for As(V) adsorption and a first-order process for As(III) adsorption. The adsorption rate on the activated substrate was two times greater compared with the non-activated substrate: As(V) (kact = 3.78×10−5 L/mg×min and knoact = 2.16×10−5 L/mg×min) vs. As(III) (kact = 0.055 h−1 and knoact = 0.027 h−1). The tested substrate is potentially useful as a low-cost natural material for arsenic removal from contaminated water.

Arsenite removal by using ZnAlFe mixed metal oxides derived from layered double hydroxides.

ZnAlFe mixed metal oxides (ZnAlFe-MMOs) were synthesized from layered double hydroxides (LDHs) prepared by the coprecipitation method at pH 9 using an initial weight composition of Zn2+ = 75%, Al3+ = 15% and Fe3+ = 10%, with or without the addition of citric or oxalic acid. The solids were calcined at 400 °C to obtain the respective MMOs, which exhibited relatively high specific surface areas (165.3 - 63.8 m2 g-1) and semiconductor properties active in the visible region (bandgap values (Eg) of 2.42 - 1.77 eV). The synthesized materials were tested for the removal of trivalent arsenic by adsorption and by photocatalysis under visible light irradiation (λ ≥ 420 nm). The best removal of As(III) by adsorption (65.9%) and by photocatalysis (99.9%) was obtained with the ZnAlFe-MMOs prepared in the absence of organic acids. The XPS results indicate the coexistence of As3+ and As5+ over ZnAlFe-MMOs after the photocatalytic reaction and also confirm the formation of Fe2+ sites on the hematite surface that enhances the removal of As(III). Raman measurements confirmed that, in the photocatalytic experiments, As is largely retained as As(V) on ZnAlFe-MMOs, bound to Fe. The results of fluorescence of 7-hydroxycoumarin suggest that the photocatalyst produces HO•, which can be the main species for As(III) oxidation under UV-Vis irradiation. Moreover, ZnAlFe-MMOs exhibited a good reusability after regeneration making ZnAlFe-MMOs a promising material for arsenic decontamination in polluted water.

Mineral Heterostructures for Simultaneous Removal of Lead and Arsenic Ions

This study focuses on Pb2+ and As(V) adsorption on mineral heterostructures based on a mixture of Si, Fe, and Ti oxides (MOHs). Various techniques were performed to analyze the morphological and structural properties of the synthesized metal oxide samples. In addition to the experimental optimization of the parameters determined by the response surface method (RSM), the effects of pH, adsorbent dosage, temperature, and contact duration on the batch and column system adsorption efficiency of single-component and simultaneous lead and arsenate removal were tested. The pseudo-second-order kinetic model and Weber–Morris model were more relevant to the adsorption on the metal(loid)s. The adsorption of Pb2+ was related to the Langmuir isotherm model, while the adsorption of As(V) was fitted to the Freundlich isotherm model. The thermodynamic parameters indicate the spontaneity of the adsorption process with a low endothermic character. The MOHs were more effective in removing Pb2+ and As(V) in the multi-component system (87.7 and 46.1%, respectively) than in the single-component system (56.3 and 23.4%, respectively). This study demonstrates that mineral heterostructures can be effectively used to remove cations and anions from water systems, and due to their fast kinetics, they can be applied to the needs of rapid interventions after pollution.

Removal of hexavalent chromium and pentavalent arsenic from aqueous solutions by adsorption on polyethylenimine-modified silica nanoparticles.

Chromium and arsenic are commonly found in water and wastewater as hexavalent chromium, Cr(VI), and inorganic arsenic species, such as pentavalent arsenic, As(V). In aqueous media, both Cr(VI) and As(V) exist predominantly in the form of oxy-anions. In our study, we prepared a polyethylenimine-silica composite material (SiO₂-PEI) as an adsorbent to study the adsorption capacity for chromate and arsenate ions. Polyethylenimine (PEI) can effectively bind negatively charged species through electrostatic interactions. The parameters that were evaluated, regarding the adsorption capacity were the effect of pH, the effect of the initial concentration of Cr(VI) and As(V), and the presence of other anions. Also, we examined the effect of Cr(VI) and As(V) on each other by studying the simultaneous removal of chromate and arsenate ions. Isotherm, kinetic, and thermodynamic analyses on the experimental data obtained were conducted. The results showed that the pH of the solution is affecting the charge density of PEI, and at pH 4, the lower value that was examined, the SiO₂-PEI exhibited higher adsorption capacity. The presence of other anions, such as phosphate, nitrate, and sulfate ions, had an adverse effect on the adsorption capacity of the SiO₂-PEI material for both chromate and arsenate ions. The adsorption capacity of arsenate was more affected by the presence of other anions compared to the chromate, and the higher impact was observed by the sulfate ions at pH 4, on the contrary for the chromate ions the higher impact was observed by the sulfate ions at pH 7 and by the phosphate ions at pH 4. Concerning the effect of temperature, the adsorption is an exothermic process and it was more favorable at lower environmental temperature. The study of simultaneous removal of Cr(VI) and As(V) declares the material's ability to accommodate both types of ions without requiring separate treatment steps. Addressing the simultaneous removal is essential for reducing the complexity of water treatment systems, lowering operational costs, and improving the safety of treated water.

Simultaneous Removal of Strontium, Manganese, Lead and Arsenate from Wastewaters Using a Green and Low-Cost Adsorbent Derived from Nut Residues

The potential of a nut residue, activated only by physical means, to simultaneously adsorb Sr2+, Mn2+, Pb2+ and As5+ from contaminated waters was investigated. Mono-metal and multi-metal adsorption behavior and adsorption capacities by the solid material were compared for a range of initial metals concentrations, adsorbent dose, contact time and solution pH. The mechanisms of adsorption were examined by conducting structural, mineralogical and chemical analyses and applying two isotherm models to simulate experimental data. In the case of mono-metal adsorption, the maximum uptake of Sr2+ by the biochar was 12.3, of Mn2+ 23.8, of Pb2+ 24.7 and of As5+ 12.4 mg/g. In the case of multi-metal adsorption, the uptake of each metal was enhanced as the total ion flux density increased, revealing that there was no competition between these ions for biochar’s sorption sites. For an adsorbent dose of 2 g/L, the maximum adsorption capacity of biochar for Sr2+, Mn2+, Pb2+ and As5+ could be raised up to 47.6, 49.9, 25 and 48.7 mg/g, respectively. Potential adsorption mechanisms were chemical complexation or electron coordination between the metals and the biochar matrix, as well as mineral precipitation on the adsorbent surface.

Discussion on arsenic removal in arsenic-containing copper concentrate

Discussion on arsenic removal in arsenic-containing copper concentrate

Numerical Approximation Tool Prediction on Potential Broad Application of Subsurface Vertical Flow Constructed Wetland (SSVF CW) Using Chromium and Arsenic Removal Efficiency Study on Pilot Scale

\noindent {\bf Abstract:} This study investigates the potential broad application of Subsurface Vertical Flow Constructed Wetlands (SSVF CWs) for heavy metal remediation, focusing on Chromium (Cr) and Arsenic (As) removal efficiency. A pilot-scale experimental setup was employed, utilizing a SSVF CW filled with 12 mm gravel and 2 mm coarse sand, planted with Phragmites Australis. The research, conducted over 366 days, aimed to develop a numerical approximation tool to predict the performance and applicability of SSVF CWs in various environmental conditions. The experimental system operated at a hydraulic loading rate of $98-111 \mathrm{~mm} / \mathrm{d}$ and a hydraulic retention time of 6 days. Results showed average removal efficiencies of $44.87 \pm 9.52 \%$ for Cr and $43.16 \pm 9.43 \%$ for As. A mass balance analysis revealed that substrate accumulation was the primary mechanism for heavy metal removal, accounting for $29 \%$ of Cr and $26 \%$ of As removal. Plant uptake contributed to $3.5-9.9 \%$ of Cr and $0.3-$ $8.8 \%$ of As removal. Based on these findings, a numerical model was developed to simulate SSVF CW performance under varying environmental and operational parameters. The model incorporated factors such as influent concentrations, hydraulic loading rates, substrate composition, and plant species. Validation against experimental data showed good agreement, with an $\mathrm{R}^{2}$ value of 0.89 . The numerical tool was then used to predict SSVF CW performance across a range of scenarios, indicating potential broad applications in industrial wastewater treatment, mine drainage remediation, and contaminated groundwater cleanup. This study provides valuable insights into the scalability and versatility of SSVF CWs for heavy metal removal, offering a sustainable and cost-effective solution for water treatment challenges.\\

Predicting removal of arsenic from groundwater by iron based filters using deep neural network models

Arsenic (As) contamination in drinking water has been highlighted for its environmental significance and potential health implications. Iron-based filters are cost-effective and sustainable solutions for As removal from contaminated water. Applying Machine Learning (ML) models to investigate and optimize As removal using iron-based filters is limited. The present study developed Deep Learning Neural Network (DLNN) models for predicting the removal of As and other contaminants by iron-based filters from groundwater. A small Original Dataset (ODS) consisting of 20 data points and 13 groundwater parameters was obtained from the field performances of 20 individual iron-amended ceramic filters. Cubic-spline interpolation (CSI) expanded the ODS, generating 1600 interpolated data points (IDPs) without duplication. The Bayesian optimization algorithm tuned the model hyper-parameters and IDPs in a Stratified fivefold Cross-Validation (CV) setup trained all the models. The models demonstrated reliable performances with the coefficient of determination (R2) 0.990–0.999 for As, 0.774–0.976 for Iron (Fe), 0.934–0.954 for Phosphorus (P), and 0.878–0.998 for predicting manganese (Mn) in the effluent. Sobol sensitivity analysis revealed that As (total order index (ST) = 0.563), P (ST = 0.441), Eh (ST = 0.712), and Temp (ST = 0.371) are the most sensitive parameters for the removal of As, Fe, P, and Mn. The comprehensive approach, from data expansion through DLNN model development, provides a valuable tool for estimating optimal As removal conditions from groundwater.

ZnFe-LDH synthesized by seed-induced method to simultaneous enhance arsenic removal, stabilization and sludge reduction

To simultaneously enhance arsenic removal, stabilization and sludge reduction, a seed-induced method was applied to in-stiu synthesize ZnFe-LDH containing arsenic (ZnFe-As-LDH). The optimal seed was determined to be ZnFe-LDH by analyzing the effects of the unseeded system and seed-induced system (FeⅡFeⅢ-LDH, ferrihydrite and ZnFe-LDH). In the ZnFe-LDH seed system, the arsenic removal efficiency increased and the arsenic leaching concentration were drastically reduced by 91.33% under the optimal conditions as the seeds dosage of 2.5g/L, pH 10 and Zn/Fe ratio of 1.5. The addition of seed crystals promoted crystal growth and aggregation and finally regulated the formation of dense bulk LDH with fewer pores and smaller pore sizes. The arsenic removal and stabilization were achieved by converting active arsenic into more stable crystalline bound arsenic through coprecipitation, ion exchange and complexation. The SV30 was reduced by 73.68% and it was due to reduction of unstable surface water and interspace and crystallinity enhancement. The formation pathway of ZnFe-As-LDH by seed-induced was elucidated. The seed-induced method promoted the formation of arsenic-containing ferrihydrite and Zn(OH)2 coprecipitations on the surface of ZnFe-LDH seed, and led to a structural rearrangement to generate ZnFe-As-LDH.

Arsenic(V) removal from water using polyelectrolyte enhanced ultrafiltration with poly(dimethyldiallylammonium chloride) (PDADMAC): Ion-selectivity based modeling and electric field influence

Polyelectrolyte enhanced ultrafiltration (PEUF) shows promise for arsenic removal. However, competing ions may serve as potential limiting factors, and membrane fouling caused by aggregation of polyelectrolytes may impact PEUF performance. This study employed poly(dimethyldiallylammonium chloride) (PDADMAC) for arsenate (As(V)) removal via ultrafiltration, and the electric field assistance was investigated on the PEUF performance. Ion exchange experiments between Cl-, and typical anions were conducted in a binary system to determine the selectivity coefficients (Ksel) of PDADMAC for different anions. The affinity of PDADMAC towards common monovalent anions was found to be Br->NO3->Cl->H2PO4->HCO3->H2AsO4-, while its affinity for divalent anions decreased in the order SO42-> HPO42-> HAsO42-. By determining the selectivity coefficients of various anions with PDADMAC and utilizing mass conservation models, a phase distribution model for anions during PEUF process was developed to predict As(V) removal. Predictions were made regarding the enhanced ultrafiltration efficiency for As(V) under different conditions (pH, ionic strength, and competing anions) in complex water environments. As the dosage of PDADMAC increased, the removal of As(V) from the actual water sample spiked with an initial concentration of 0.2mM exceeded 90%, and the experimental results closely matched the model predictions. The impact of electric field on the PEUF process was investigated by placing electrodes on both sides of the ultrafiltration membrane. Results showed that the ultrafiltration membrane, when positively charged by an electric field, repelled cationic PDADMAC, thereby alleviating membrane fouling. However, a cleaner membrane led to increased leakage of PDADMAC molecules, resulting in the co-loss of As with PDADMAC and consequently reducing the overall As removal.

Arsenic Removal using De-oiled Mentha Biomass Biochar: Adsorption Kinetics and the Role of Iron Modification

Arsenic Removal using De-oiled Mentha Biomass Biochar: Adsorption Kinetics and the Role of Iron Modification

Sintered Clays: Application in the Removal of Arsenic from Water by Filter Beds

Objectives: The main objective of the research was to build a ceramic filter bed, using red clay and diatomite, for the removal of arsenic in aqueous media and to propose an environmentally friendly and low-cost technique for rural communities in Peru that consume water contaminated with arsenic. Theoretical framework: Arsenic is a common contaminant in the drinking water of many rural communities in Peru, exceeding the limits allowed by the WHO. Prolonged exposure to arsenic can cause serious health problems. The use of low-cost non-metallic materials, such as thermally activated clay and diatomite, is proposed for its adsorption. Method: A filter bed composed of 5 cm layers of red clay and diatomite with particle sizes of 0.81, 0.31 and 0.20 mm was used. Both materials were thermally activated at 900°C and placed on a stainless steel support. The arsenic removal process was evaluated by passing a synthetic solution with 13.99 ppm of arsenic through the bed. Material characterization analyses were performed before and after the adsorption process, using techniques such as ICP-OES, SEM, FTIR, among others. Results and discussion: The filter bed composed of diatomite (83.31% SiO2) and red clay (8.23% Fe2O3) achieved an arsenic removal of up to 99.99%, highlighting the efficiency of particles with a size of 0.20 mm. This shows that the combination of these materials can be highly effective in removing arsenic in water, which is promising for its implementation in rural areas. Research implications: This research has important implications for water treatment in rural communities facing arsenic contamination problems. The technique developed is low-cost and uses abundant resources, which facilitates its application at the local level and promotes sustainable solutions for access to safe drinking water. Originality/Value: The research provides a novel approach through the use of red clay and diatomite, accessible resources, thermally activated for the removal of arsenic in water. In addition, the high removal effectiveness achieved provides a potentially scalable and replicable solution in other rural communities with similar problems.

Adsorption Performance of Fe-Mn Polymer Nanocomposites for Arsenic Removal: Insights from Kinetic and Isotherm Models.

Global concern over arsenic contamination in drinking water necessitates innovative and sustainable remediation technologies. This study evaluates the adsorption performance of Fe-Mn binary oxide (FMBO) nanocomposites developed by coating polyethylene (PE) and polyethylene terephthalate (PET) with FMBO for the removal of As(III) and As(V) from water. Adsorption kinetics were rapid, with equilibrium achieved within 1-4 h depending on the material and pH. PET-FMBO and FMBO exhibited faster rates and higher arsenic removal (up to 96%) than PE-FMBO. Maximum As(III) adsorption capacities ranged from 4.76 to 5.75 mg/g for PE-FMBO, 7.2 to 12.0 mg/g for PET-FMBO, and up to 20.8 mg/g for FMBO, while capacities for As(V) ranged from 5.20 to 5.60 mg/g, 7.63 to 18.4 mg/g, and up to 46.2 mg/g, respectively. The results of the Dubinin-Radushkevich isotherm model, with free energy (Ea) values exceeding 16 kJ/mol, suggest chemisorption is the dominant mechanism, which is supported by the kinetics data. Given the effective removal of As(III), chemisorption likely proceeds through ligand exchange during the Mn oxide-mediated oxidation of As(III) and complexation with hydroxyl groups on the nanocomposite. These findings highlight the strong potential of Fe-Mn polymer nanocomposites, particularly PET-FMBO, for efficient arsenic removal during practical water treatment applications.

Arsenic Removal from Water by Using Bacterial Dry Biomasses

Arsenic Removal from Water by Using Bacterial Dry Biomasses

Genipin Nanoparticles-Doped Reduced Graphene Oxide Membranes: A Promising Solution for Arsenic Ion Removal From Wastewater

Genipin Nanoparticles-Doped Reduced Graphene Oxide Membranes: A Promising Solution for Arsenic Ion Removal From Wastewater

Implementation and performance monitoring of the treatment system to remove arsenic from dam water in a full-scale urban water treatment plant

Nowadays, health and environmental problems caused by elevated arsenic concentration in water sources have become a major concern for researchers and environmental experts. Therefore, it is necessary to study processes that significantly reduce the arsenic content in aqueous solutions, which is of great interest to environmental experts. This work aimed to evaluate the effect of the pre-oxidation/coagulation process with commercially available coagulants (FeCl3, Al2 (SO4)3·18H2O, and PACl) on the efficiency of arsenic removal (with initial concentration of 73 ± 2.5 μg/L) from Talvar Dam entering the Sheikhi Jan Hamadan water treatment plant. This was demonstrated on a laboratory and operational scale at the water treatment plant under different scenarios (pre-oxidant agents, type of coagulant, solution pH, and different coagulant dosages). It should be noted that, as part of an emergency project, the possibility of arsenic removal at the Sheikhi Jan water treatment plant, which receives Talvar Dam water at a flow rate of 1800 L/s, was investigated. The priority of the researchers and city officials in the present study was to use the potential of the water treatment plant and the existing equipment so that they could remove arsenic quickly and without additional costs. This study was conducted in three stages: laboratory scale, implementation of the process in the water treatment plant, and monitoring of the treatment plant's performance, which continues to this day. The results of this project showed that the pre-oxidation/coagulation process can effectively reduce the concentration of arsenic at the inlet of the treatment plant from to less than national and international recommended values.

Green synthesis of graphene oxide and magnetite nanoparticles and their arsenic removal efficiency from arsenic contaminated soil

Graphene-based nanomaterials have been proved to be robust sorbents for efficient removal of environmental contaminants including arsenic (As). Biobased graphene oxide (bGO-P) derived from sugarcane bagasse via pyrolysis, GO-C via chemical exfoliation, and magnetite nanoparticles (FeNPs) via green approach using Azadirachta indica leaf extract were synthesized and characterized by Ultraviolet-Visible Spectrophotometer (UV-vis.), Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), mean particle size and Scanning electron microscopy (SEM) along with Energy dispersive spectroscopy (EDX) analysis. Compared to cellulose and hemicellulose, the lignin fraction was less in the precursor material. The GOC, bGO-P and FeNPs displayed maximum absorption at 230, 236, and 374 nm, respectively. FTIR spectrum showed different functional groups (C-OH, C-O-C, COOH and O-H) modifying the surfaces of synthesized materials. Graphene based nanomaterials showed clustered dense flakes of GO-C and thin transparent flakes of bGO-P. Elemental composition by EDX analysis of GO-C (71.26% C and 27.36% O), bGO-P (74.54% C and 24.61% O) and FeNPs (55.61% Fe, 4.1% C and 35.72% O) confirmed the presence of carbon, oxygen, and iron in synthesized nanomaterials. Sorption study was conducted with soil amended with different doses of synthesized nanomaterials (10, 50 and 250 mg) and exposed to 100, 300 and 500 ppm of As. Arsenic concentrations were estimated by colorimetry and atomic absorption spectroscopy (AAS). GO-C, bGO-P, and FeNPs showed substantial As removal efficiency i.e., 81 to 99.3%, 65 to 98.8% and 73.1–89.9%, respectively. Green synthesis of bGO-P and magnetite nanoparticles removed substantial amounts of As compared to GO-C and can be effectively deployed for As removal or immobilization. Higher and medium sorbent doses (250 and 50 mg) exhibited greater As removal and data was best fitted for Freundlich isotherm evidencing favorable sorption. Nevertheless, at low sorbent doses, data was best fitted for both models. Newly synthesized nanomaterials emerged as promising materials for As removal strategy for soil nano-remediation and can be effectively deployed in As contaminated soils.

Techno-economic analysis of arsenic (III) removal using spiral wound polyethersulfone nanofiltration membrane at pilot scale

In this work, the influence of initial solution pH on membrane performance was carried out for arsenic (III) removal using spiral wound polyethersulfone (HFN300) Nanofiltration membrane at pilot scale. The rejection percentage was found to increase from 49 % to 96 % while increasing initial solution pH from 4 to 10. Speciation of arsenic, solute-membrane affinity, electric-migration effect along with convection and diffusion were found to be dominant mechanisms for arsenic removal. Donnan Steric Pore Model was selected to estimate the membrane parameters including pore radius (0.313 nm), membrane thickness (2.17 μm), and membrane charge density (−3.56 mol/m3).Excellent agreements were found between the experimental and simulated values for all the studied pH range. Selected model works satisfactorily within 10 % of error for both rejection percentage and permeate flow. Economic feasibility study was carried out for the rural population (India) and total annualized cost was found to be USD 0.90/m3 that seems both reasonable and affordable for arsenic free drinking water. It can be concluded that annualized production cost was dependent on membrane lifespan, electricity tariff, per capita, population size, arsenic feed concentration, etc. The result obtained in the study suggests the feasibility of using the NF process in removing arsenic from contaminated water. Overall, the study provides valuable insights into the mechanisms governing arsenic (III) removal through nanofiltration process using spiral wound polyethersulfone nanofiltration membrane at pilot scale, demonstrating the effectiveness of pH optimization and membrane modelling in improving removal efficiency, which can contribute to the development of cost-effective solutions for safe drinking water in arsenic-affected rural areas.

Designing of a proficient macro porous metallo-polymer of iron with anion functionality: A sustainable approach for arsenic remediation from water

In this study, a novel porous metallo-polymeric network named poly(Ferric trimethacrylate-co-4-Vinyl benzyl chloride), incorporating an iron moiety, was developed for arsenic remediation from water. The synthesis of crosslinked q(pFeVBC) was carried out via suspension polymerization and functionalizing it with hexamethylenetetramine, resulting in a porous three-dimensional structure. Characterization using FTIR, FESEM, XPS, XRD, and BET-SA analysis confirmed its properties. Various monomer ratios were tested to optimize q(pFeVBC) for arsenic removal. The q(pFeVBC) exhibited significant adsorption capacities (qe max exp) of 8.33 mg g−1 for As(V) and 7.9 mg g−1 for As (III), owe to its unique architecture (integrated iron moiety and anion functionality) and porous texture (SA: 112 m2 g−1, pore size: 1.27–2.07 µm), which is close to the capacity calculated by Langmuir model (qe max theo) 8.719 mg g−1 for As (V) and 8.463 mg g−1 for As (III). The PSO kinetic model showed excellent fitting for both arsenic forms. Thermodynamic studies indicated a spontaneous and endothermic adsorption process. Additionally, a 4:10:1 ANN model accurately predicted adsorption behavior.

Removal of arsenic from aqueous solution using magnetic biochar derived from Spirulina platensis

Arsenic contamination in surface waters and groundwater affects millions of people on a daily basis. Oxidation of As(III) to less toxic As(V) is a widely used strategy to enhance the removal of As from solution. This study developed and evaluated a Fe-modified biochar (FeSP600). Spirulina platensis (SP) is one of the most promising microalgae because of its physicochemical properties and potential applications. The high N content of SP may affect the physicochemical properties of the biochar, which could be used as an inherent N source for N doping biochar by carbonization. After Fe modification, the formed Fe species and N-containing components of SP were used to introduce pyridinic N, which can be coordinated with Fe to form Fe-N. We demonstrated that the formed Fe species (Fe0, Fe2+ and Fe3+) and the defective structures in FeSP600 could act as active sites for surface catalytic reactions. FeSP600 not only had magnetic properties but also could effectively remove As from an aqueous solution. These properties were attributed to the release of Fe2+ and the reactive oxygen species (ROSs) generated by the γ-Fe2O3 particles on the crystalline defect structure. As(III) and As(V) removal were affected by the initial pH values. The removal efficiencies for As(III) increased from 57.2 % to 94.9 % as the pH increased from 3 to 9, whereas that for As(V) decreased from 80.1 % to 46.8 %. The presence of coexisting ions either completely (PO43−) or partially (Cl−, CO32− and SO42−) inhibited As removal. The removal of As(V) depended on electrostatic interactions, but As(III) removal was a complex process, including both oxidation and surface adsorption, as the ROSs were able to oxidize As(III) to As(V). Our study demonstrates that FeSP600 has properties that are beneficial for the removal of As(III) and As(V) from aqueous environments. The findings of this study have potential for real-world application in treating As-contaminated water sources, particularly in improving drinking water purification systems in developing countries. More importantly, an assessment of the impact of FeSP600 usage on aquatic ecosystems is required to ensure the safe application of this technology. Therefore, developing methods for mass production of FeSP600 is essential for the commercialization of this technology, necessitating process engineering studies in this area.