Removal of arsenic from groundwater using low cost ferruginous manganese ore

Arsenite oxidation and adsorptive arsenic removal from contaminated water: a review

Arsenic poisoning of groundwater is one of the most critical environmental hazards on Earth. Therefore, the practical and proper treatment of arsenic in water requires more attention to ensure safe drinking water. The World Health Organization (WHO) sets guidelines for 10 μg/L of arsenic in drinking water, and direct long-term exposure to arsenic in drinking water beyond this value causes severe health hazards to individuals. Numerous studies have confirmed the adverse effects of arsenic after long-term consumption of arsenic-contaminated water. Here, technologies for the remediation of arsenic from water are highlighted for the purpose of understanding the need for a single-point solution for the treatment of As(III)-contaminated water. As(III) species are neutral at neutral pH; the solution requires transformation technology for its complete removal. In this critical review, emphasis was placed on single-step technologies with multiple functions to remediate arsenic from water.

Arsenic Contamination in Groundwater: Geochemical Basis of Treatment Technologies

Arsenic (As) is abundant in the environment and can be found in both organic (e.g., methylated) and inorganic (e.g., arsenate and arsenite) forms. The source of As in the environment is attributed to both natural reactions and anthropogenic activities. As can also be released naturally to groundwater through As-bearing minerals including arsenopyrites, realgar, and orpiment. Similarly, agricultural and industrial activities have elevated As levels in groundwater. High levels of As in groundwater pose serious health risks and have been regulated in many developed and developing countries. In particular, the presence of inorganic forms of As in drinking water sources gained widespread attention due to their cellular and enzyme disruption activities. The research community has primarily focused on reviewing the natural occurrence and mobilization of As. Yet, As originating from anthropogenic activities, its mobility, and potential treatment techniques have not been covered. This review summarizes the origin, geochemistry, occurrence, mobilization, microbial interaction of natural and anthropogenic-As, and common remediation technologies for As removal from groundwater. In addition, As remediation methods are critically evaluated in terms of practical applicability at drinking water treatment plants, knowledge gaps, and future research needs. Finally, perspectives on As removal technologies and associated implementation limitations in developing countries and small communities are discussed.

Optimization of multiple parameters for adsorption of arsenic (III) from aqueous solution using Psidium guajava leaf powder

The conventional method of water treatment using activated carbon from several sources has been focused on extensively in the last two decades. However, rare attention has been noticed on natural adsorbents such as plant leaves. Therefore, the Psidium guajava (guava) leaf has been investigated to understand its adsorption efficacy for Arsenic (III) [As(III)] in this study. The effect of process variables, e.g., pH, concentration of metal ion, adsorbent's particle size, and dosages, are evaluated. Experiments are carried out in batch mode, and the individual and combined parameter's impact on adsorption have been discussed. Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) is used to characterize the adsorbent's surface. Freundlich and Langmuir's isotherms are used for adsorption equilibrium study. The adsorption parameters are optimized by establishing a regression correlation using central composite design (CCD) of response surface methodology (RSM). The analysis of variance (ANOVA) suggests a high regression coefficient (R² = 0.9249) for the removal of As(III). Particle size of 0.39 mm; adsorbent's height of 10 cm; metal ion concentration of 30 ppm, and pH 6 are optimized to remove 90.88% As(III) from aqueous solution. HCl is evaluated as a potential solvent for desorption of arsenic from the desorption study.

Bioaccumulation of arsenic(V) from wastewater by live and dead Spirogyra sp

Contaminated water with arsenic causes a negative impact on socioeconomic status in the concerned area. Existing methods are not much adequate, efficient, and appropriate. Bioremediation of heavy metals with microalgae seems to be a promising and holistic approach to counter the pre-existing associated with heavy metal toxicity. A pure culture of live and dead Spirogyra sp. was tested for its ability to adsorb arsenic(V) and modeling of experimental data was used to interpret the mechanism of bioaccumulation. Langmuir and Freundlich isotherm models were used to explain the sorption of arsenic. The maximum sorption capacity of live Spirogyra sp. was 315 mg/g and dead Spirogyra sp. was 207 mg/g. Mechanism of bioaccumulation for As(V) ions by live and dead Spirogyra sp. were studied using several advanced techniques including Fourier-transform infrared, fluorescence microscopy, and scanning electron microscope. The study summarizes, bioaccumulation of AsO₄ ^-3 by live and dead cells of Spirogyra sp. seems to be promising. The pseudo-second-order rate equation described better the kinetics of As(V) adsorption with good correlation coefficients. The results suggested that live Spirogyra sp. was more suitable to remove As(V) as compared to dead Spirogyra sp.

Insights into the underlying mechanisms of stability working for As(III) removal by Fe-Mn binary oxide as a highly efficient adsorbent

Fe-Mn binary oxide has received increasing interest in treating As(III)-containing polluted groundwater due to its low cost and environmental friendliness. Although the stability of Fe-Mn binary oxide is as important as its adsorption ability, little is known about whether and why Fe-Mn binary oxide is stable during As(III) removal. In this study, five successive cycles were conducted to evaluate the stability of Fe-Mn binary oxide for As(III) removal. As(III) oxidation/adsorption kinetics and the speciation distribution of the released Fe and Mn elements within single Fe oxide, Mn oxide, and Fe-Mn binary oxide were investigated by using characterization techniques of TEM-EDS mapping, selected area electron diffraction (SAED), and XPS combined with a binary component reactor, where Fe and Mn oxides were separated by a semipermeable membrane. The results revealed that Fe-Mn binary oxide could maintain excellent stability, although As(III) oxidation/adsorption behavior was coupled with the release of Fe and Mn ions from its surface. The great stability of Fe-Mn binary oxide for As(III) removal was attributed to the rapid return of aqueous Fe(II) and Mn(II) to the solid surface, which subsequently formed new mineral phases mediated by Fe and Mn oxides, thus considerably decreasing the loss of released Mn(II) and Fe(II).

Research and application of arsenic-contaminated groundwater remediation by manganese ore permeable reactive barrier

Arsenic pollution in the water environment is one of the important environmental problems at present. High arsenic groundwater and its resulting local arsenic poisoning have caused a great threat to human life and health. The permeable reactive barrier (PRB) is an underground in-situ remediation technology, which has the advantages of high efficiency, low energy consumption, long aging, low operating and maintenance costs. By studying the arsenic removal effects of different materials, this paper selected natural manganese ore, manganese ore granulation, loaded manganese ore and mixed manganese ore as fillers for PRB. And it conducted a simulated experiment to study the feasibility of actual PRB engineering to repair arsenic-containing groundwater. The experiment proves that the removal rate of arsenic by four manganese ore materials exceeds 90%. After examining the geographical location and hydrogeological conditions of the PRB project, the Dengjiatang area of Chenzhou City, Hunan Province was selected as the construction area. Studies show that after the completion of PRB, the arsenic content of the effluent at each monitoring point is below 10 μg/L. It indicates that all four fillers achieve the purpose of removing arsenic, and can be applied to the project according to actual needs. Finally, the safety evaluation of the PRB project was carried out. And FeCl₃·6H₂O was selected as the base curing material and cement was as the process auxiliary stabilizer to solidify the arsenic-containing waste residue. The arsenic concentration in the leaching solution of the arsenic slag after curing is only 1 μg/L.

Highly enhanced oxidation of arsenite at the surface of birnessite in the presence of pyrophosphate and the underlying reaction mechanisms

Manganese(IV) oxides, and more especially birnessite, rank among the most efficient metal oxides for As(III) oxidation and subsequent sorption, and thus for arsenic immobilization. Efficiency is limited however by the precipitation of low valence Mn (hydr)oxides at the birnessite surface that leads to its passivation. The present work investigates experimentally the influence of chelating agents on this oxidative process. Specifically, the influence of sodium pyrophosphate (PP), an efficient Mn(III) chelating agent, on As(III) oxidation by birnessite was investigated using batch experiments and different arsenic concentrations at circum-neutral pH. In the absence of PP, Mn(II/III) species are continuously generated during As(III) oxidation and adsorbed to the mineral surface. Field emission-scanning electron microscopy, synchrotron-based X-ray diffraction and Fourier transform infrared spectroscopy indicate that manganite is formed, passivating birnessite surface and thus hampering the oxidative process. In the presence of PP, generated Mn(II/III) species form soluble complexes, thus inhibiting surface passivation and promoting As(III) conversion to As(V) with PP. Enhancement of As(III) oxidation by Mn oxides strongly depends on the affinity of the chelating agent for Mn(III) and from the induced stability of Mn(III) complexes. Compared to PP, the positive influence of oxalate, for example, on the oxidative process is more limited. The present study thus provides new insights into the possible optimization of arsenic removal from water using Mn oxides, and on the possible environmental control of arsenic contamination by these ubiquitous nontoxic mineral species.

Aspergillus niger Decreases Bioavailability of Arsenic(V) via Biotransformation of Manganese Oxide into Biogenic Oxalate Minerals

The aim of this work was to evaluate the transformation of manganese oxide (hausmannite) by microscopic filamentous fungus Aspergillus niger and the effects of the transformation on mobility and bioavailability of arsenic. Our results showed that the A. niger strain CBS 140837 greatly affected the stability of hausmannite and induced its transformation into biogenic crystals of manganese oxalates—falottaite and lindbergite. The transformation was enabled by fungal acidolysis of hausmannite and subsequent release of manganese ions into the culture medium. While almost 45% of manganese was bioextracted, the arsenic content in manganese precipitates increased throughout the 25-day static cultivation of fungus. This significantly decreased the bioavailability of arsenic for the fungus. These results highlight the unique A. niger strain’s ability to act as an active geochemical factor via its ability to acidify its environment and to induce formation of biogenic minerals. This affects not only the manganese speciation, but also bioaccumulation of potentially toxic metals and metalloids associated with manganese oxides, including arsenic.

Review: Efficiently performing periodic elements with modern adsorption technologies for arsenic removal

Arsenic (As) toxicity is a global phenomenon, and it is continuously threatening human life. Arsenic remains in the Earth's crust in the forms of rocks and minerals, which can be released into water. In addition, anthropogenic activity also contributes to increase of As concentration in water. Arsenic-contaminated water is used as a raw water for drinking water treatment plants in many parts of the world especially Bangladesh and India. Based on extensive literature study, adsorption is the superior method of arsenic removal from water and Fe is the most researched periodic element in different adsorbent. Oxides and hydroxides of Fe-based adsorbents have been reported to have excellent adsorptive capacity to reduce As concentration to below recommended level. In addition, Fe-based adsorbents were found less expensive and not to have any toxicity after treatment. Most of the available commercial adsorbents were also found to be Fe based. Nanoparticles of Fe-, Ti-, Cu-, and Zr-based adsorbents have been found superior As removal capacity. Mixed element-based adsorbents (Fe-Mn, Fe-Ti, Fe-Cu, Fe-Zr, Fe-Cu-Y, Fe-Mg, etc.) removed As efficiently from water. Oxidation of AsO₃^3- to AsO₄^3-and adsorption of oxidized As on the mixed element-based adsorbent occurred by different adsorbents. Metal organic frameworks have also been confirmed as good performance adsorbents for As but had a limited application due to nano-crystallinity. However, using porous materials having extended surface area as carrier for nano-sized adsorbents could alleviate the separation problem of the used adsorbent after treatment and displayed outstanding removal performances.

Electrochemical adsorption of cadmium and arsenic by natural Fe-Mn nodules

Fe-Mn nodules are widely distributed and regarded as excellent adsorbents for heavy metals. Their adsorption-desorption reactions with heavy metal ions are usually accompanied by redox processes. Herein, Fe-Mn nodules were used as adsorbents for Cd(II) and As(III,V) at a constant cell voltage under electrochemically controlled reduction and oxidation, respectively. The results showed that the adsorption performance for Cd(II) and As(III,V) was enhanced respectively due to the decrease and increase of Mn average oxidation state (Mn AOS) in Fe-Mn nodules. High birnessite content and Mn average oxidation state (Mn AOS) improved the adsorption of Cd(II) and As(III,V). The adsorption capacity for Cd(II) and total As increased with increasing voltage. With increasing pH, the adsorption capacity for Cd(II) increased first and then reached equilibrium, and that of total As decreased and then increased. The Cd(II) electrochemical adsorption capacity (129.9 mg g^-1) and the removal efficiency for total As at 1.2 V (83.6 %) in As-containing wastewater at an initial concentration of 4.068 mg L^-1 were remarkably higher than the corresponding inorganic adsorption performance (9.46 mg g^-1 and 70.5 %, respectively). This work may further promote the application of natural Fe-Mn nodules in the adsorption of heavy metals from wastewaters.

Application of recycling waste products for ex situ and in situ water treatment methods

The specific objectives of the study were to determine the approximate design parameters for filter bed and highlight the possible scope of using mixed iron oxides rich smelter slag for in situ or ex situ treatment. The batch and column study was conducted to assess the As removal capacities from contaminated water. X-ray fluorescence (XRF) analysis of the slag waste product determined the presence of large quantities of iron (Fe). In this study, the maximum removal capacities were found to be approximately 1.78 mg As per g of slag and 100% removal of As(V) was achieved during the first 30 days of three column operations. The changes in redox potential (E_h) values and the changes in effluent pH throughout the column operation period indicated redox reactions occurring in the system. The column experiments were modelled using a semi-analytic solution to the advection-dispersion-adsorption equation incorporated in the commercial software, Pollute V7. From the best-fit of the modelling results to the experimental breakthrough curves, the hydrodynamic dispersion coefficient (D) was found to be 0.0115 and 0.00775 m²/day for column 1 and column 2, respectively, and 0.00862 m²/day for column 3. The values of the distribution coefficient (K_D) were 0.18, 0.173 and 0.171 m³/kg or L/g for the three columns and 0.24 L/g from the batch test. The results from the experiments may be used to aid the design of a filter bed or reactive barrier in a scenario where the mixed iron oxides rich smelter waste product is used as a candidate reactive medium.

Synthesis, Characterization and DNA Binding Investigations of a New Binuclear Ag(I) Complex and Evaluation of Its Anticancer Property

Aim

A new Ag(I) complex (A₃) was synthesized and evaluated for its anticancer activity against human cancer cell lines.

Materials and Methods

The complex A₃ was characterized by ¹H, ¹³C, and ³¹P nuclear magnetic resonance (NMR), infrared (IR) spectra, elemental analysis, and X-ray crystallography. The interaction of the complex with CT-DNA was studied by electronic absorption spectra, fluorescence spectroscopy, and cyclic voltammetry; cell viability (%) was assessed by absorbance measurement of the samples.

Results

The interaction mode of the complex A₃ with DNA is electrostatic, and this complex shows good potential in anticancer properties against HCT 116 (human colorectal cancer cells) and MDA-MB-231 (MD Anderson-metastatic breast) cell lines with 0.5 micromolar concentrations.

Conclusion

The Ag(I) complex could interact with DNA noncovalently and has anticancer properties.

Influence of the structure and composition of Fe-Mn binary oxides on rGO on As(III) removal from aquifers

Fe-Mn binary oxide (FMBO) possesses high efficiency for As(III) abatement based on the good adsorption affinity of iron oxide and the oxidizing capacity of Mn(IV), and the composition and structure of FMBO play important roles in this process. To compare the removal performance and determine the optimum formula for FMBO, magnetic graphene oxide (MRGO)-FMBO and MRGO-MnO₂ were synthesized with MRGO as a carrier to improve the dispersity of the adsorbents in aquifers and achieve magnetic recycling. Results indicated that MRGO-FMBO had higher As(III) removal than that of MRGO-MnO₂, although the ratios of Fe and Mn were similar, because the binary oxide of Fe and Mn facilitated electron transfer from Mn(IV) to As(III), while the separation of Mn and Fe on MRGO-MnO₂ restricted the process. The optimal stoichiometry x for MRGO-FMBO (Mn_xFe_3-xO₄) was 0.46, and an extraordinary adsorption capacity of 24.38 mg/g for As(III) was achieved. MRGO-FMBO showed stable dispersive properties in aquifers, and exhibited excellent practicability and reusability, with a saturation magnetization of 7.6 emu/g and high conservation of magnetic properties after 5 cycles of regeneration and reuse. In addition, the presence of coexisting ions would not restrict the practical application of MRGO-FMBO in groundwater remediation. The redox reactions of As(III) and Mn(IV) on MRGO-FMBO were also described. The deprotonated aqueous As(III) on the surface of MRGO-FMBO transferred electrons to Mn(IV), and the formed As(V) oxyanions were bound to ferric oxide as inner-sphere complexes by coordinating their "-OH" groups with Mn(IV) oxides at the surface of MRGO-FMBO. This work could provide new insights into high-performance removal of As(III) in aquifers.

Removing arsenic from water with an original and modified natural manganese oxide ore: batch kinetic and equilibrium adsorption studies

Arsenic contamination of drinking water is a serious water quality problem in many parts of the world. In this study, a low-cost manganese oxide ore from Vietnam (Vietnamese manganese oxide (VMO)) was firstly evaluated for its performance in arsenate (As(V)) removal from water. This material contains both Mn (25.6%) and Fe (16.1%) mainly in the form of cryptomelane and goethite minerals. At the initial As(V) concentration of 0.5 mg/L, the adsorption capacity of original VMO determined using the Langmuir model was 0.11 mg/g. The modified VMOs produced by coating VMO with iron oxide (Fe^a-VMO) and zirconium oxide (Zr^a-VMO) at 110 °C and 550 °C achieved the highest As(V) adsorption capacity when compared to three other methods of VMO modifications. Langmuir maximum adsorption capacities of Fe^a-VMO and Zr^a-VMO at pH 7.0 were 2.19 mg/g and 1.94 mg/g, respectively, nearly twenty times higher than that of the original VMO. Batch equilibrium adsorption data fitted well to the Langmuir, Freundlich, and Temkin models and batch kinetics adsorption data to pseudo-first order, pseudo-second order, and Elovich models. The increase of pH progressively from 3 to 10 reduced As(V) adsorption with a maximum reduction of 50-60% at pH 10 for both original and modified VMOs. The co-existing oxyanions considerably weakened the As(V) removal efficiency because they competed with As(V) anions. The competition order was PO₄^3- > SiO₃^2- > CO₃^2- > SO₄^2-. The characteristics of the original and modified VMOs evaluated using SEM, FTIR, XRD, XRF, surface area, and zeta potential explained the As(V) adsorption behaviour.

Mining Rock Wastes for Water Treatment: Potential Reuse of Fe- and Mn-Rich Materials for Arsenic Removal

The worldwide mining industry produces millions of tons of rock wastes, raising a considerable burden for managing both economic and environmental issues. The possible reuse of Fe/Mn-rich materials for arsenic removal in water filtration units, along with rock properties, was evaluated. By characterizing and testing 47 samples collected from the Joda West Iron and Manganese Mine in India, we found As removal up to 50.1% at 1 mg/L initial As concentration, with a corresponding adsorption capacity of 0.01–0.46 mgAs/g mining waste. The As removal potential was strictly related to spectral, mineralogical, and elemental composition of rock wastes. Unlike rock crystallinity due to quartz and muscovite, the presence of hematite, goethite, and kaolinite, in association with the amorphous fractions of Fe and Al, enhanced the As adsorption. The natural content of arsenic indicated itself the presence of active sorptive sites. The co-occurrence of site-specific competitors (i.e., phosphate) represented a consequent limitation, whereas the content of Ce, Cu, La, and Pb contributed positively to the As adsorption. Finally, we proposed a simplified multiple linear model as predictive tool to select promising rock wastes suitable for As removal by water filtration in similar mining environments: As predicted = 0.241 + 0.00929[As] + 0.000424[La] + 0.000139[Pb] − 0.00022[P].

Treatment of Contaminated Groundwater via Arsenate Removal Using Chitosan-Coated Bentonite

In the present research, treatment of contaminated groundwater via adsorption of As(V) with an initial concentration of 50.99 µg/L using chitosan-coated bentonite (CCB) was investigated. The effect of adsorbent mass (0.001 to 2.0 g), temperature (298 to 328 K), and contact time (1 to 180 min) on the removal efficiency was examined. Adsorption data was evaluated using isotherm models such as Langmuir, Freundlich, and Dubinin-Radushkevich. Isotherm study showed that the Langmuir (R2 > 0.9899; χ2 ≤ 0.91; RMSE ≤ 4.87) model best correlates with the experimental data. Kinetics studies revealed that pseudo-second order equation adequately describes the experimental data (R2 ≥ 0.9951; χ2 ≤ 0.8.33; RMSE ≤ 4.31) where equilibrium was attained after 60 min. Thermodynamics study shows that the As(V) adsorption is non-spontaneous (ΔG0 ≥ 0) and endothermic (ΔH0 = 8.31 J/mol) that would result in an increase in randomness (ΔS0 = 29.10 kJ/mol•K) within the CCB-solution interface. FT-IR analysis reveals that hydroxyl and amino groups are involved in the adsorption of As(V) from groundwater. Results of the present research serve as a tool to determine whether CCB is an environmentally safe and cost effective material that could be utilized in a permeable reactive barrier system for the remediation of As(V) from contaminated groundwater.

Impact of different amendments on biochemical responses of sesame (Sesamum indicum L.) plants grown in lead-cadmium contaminated soil

Soil co-contamination with lead (Pb) and cadmium (Cd) is a tenacious risk to crop production globally. The current experiment observed the roles of amendments [biochar (BC), slag (SL), and ferrous manganese ore (FMO)] for enhancing Pb and Cd tolerance in sesame (Sesamum indicum L.). Our results revealed that application of amendments significantly enhanced the nutrient level of sesame seedlings developed under extreme Pb and Cd conditions. The higher Pb and Cd-tolerance in sesame encouraged by amendments might be credited to its capability to restrict Pb and Cd uptake and decreased oxidative damage induced by Pb and Cd that is also demonstrated by lesser production of hydrogen peroxide (H₂O₂), malondialdehyde (MDA), and reduced electrolyte leakage (EL) in plant biomass. The added amendments relieved Pb and Cd toxicity and improved photosynthetic pigments, soluble protein, and proline content. Not only this amendments also decreased the antioxidant bulk, such as superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) in sesame plants compared to control when exposed to Pb and Cd. Moreover, the added amendments = down-regulated the genes expression which regulate the SOD, POD, and CAT activity in sesame under Pb and Cd-stress. Furthermore, supplementation of amendments to the soil, reduced the bio accessibility (SBET), leachability (TCLP), and mobility (CaCl₂) of Pb and Cd. Collectively, our findings conclude that the application of amendments enhanced sesame tolerance to Pb and Cd stress by restricting Pb and Cd accumulation, maintained photosynthetic presentation and dropped oxidative loss through enhanced antioxidant system, thus signifying amendments as an operational stress regulators in modifying Pb and Cd-toxicity that is highly important economically in all crops including sesame.

Investigation of a novel pyrolusite particle electrode effects in the chlorine-containing wastewater

Research on three-dimensional electrode system mainly focuses on the material of plate electrode and catalytic activity, and minimal attention is provided to particle electrode. Pyrolusite was prepared as a novel particle electrode with high active chlorine (ACl) yield. The particle electrode was characterised by scanning electrode microscopy (SEM), X-ray diffraction (XRD), X-ray fluorescence (XRF) and electrochemical properties. Results show that the intended pyrolusite particle electrode was prepared successfully. These pyrolusite particle electrodes were applied to degrade sulphonated phenolic resin in chlorine-containing wastewater and displayed an excellent catalytic activity. A total of 68.76 mg/L ACl was produced, and the COD_Cr removal rate was 49.55%. These results indicated that pyrolusite particle electrode is much more effective than the reference material, that is, granular activated carbon. Furthermore, the product of electrolytic process was characterised by gas chromatography-mass spectrometry (GC-MS) and ultraviolet visible spectrometry (UV-vis). The enhanced mechanism was proposed that the high degradation efficiency could be ascribed to the increase of ACl.

Enhanced oxidation of arsenite to arsenate using tunable K+ concentration in the OMS-2 tunnel

Cryptomelane-type octahedral molecular sieve manganese oxide (OMS-2) possesses high redox potential and has attracted much interest in its application for oxidation arsenite (As(III)) species of arsenic to arsenate (As(V)) to decrease arsenic toxicity and promote total arsenic removal. However, coexisting ions such as As(V) and phosphate are ubiquitous and readily bond to manganese oxide surface, consequently passivating surface active sites of manganese oxide and reducing As(III) oxidation. In this study, we present a novel strategy to significantly promote As(III) oxidation activity of OMS-2 by tuning K+ concentration in the tunnel. Batch experimental results reveal that increasing K+ concentration in the tunnel of OMS-2 not only considerably improved As(III) oxidation kinetics rate from 0.027 to 0.102 min-1, but also reduced adverse effect of competitive ion on As(III) oxidation. The origin of K+ concentration effect on As(III) oxidation was investigated through As(V) and phosphate adsorption kinetics, detection of Mn2+ release in solution, surface charge characteristics, and density functional theory (DFT) calculations. Experimental results and theoretical calculations confirm that by increasing K+ concentration in the OMS-2 tunnel not only does it improve arsenic adsorption on K+ doped OMS-2, but also accelerates two electrons transfers from As(III) to each bonded Mn atom on OMS-2 surface, thus considerably improving As(III) oxidation kinetics rate, which is responsible for counteracting the adverse adsorption effects by coexisting ions.

Development of bark-based magnetic iron oxide particle (BMIOP), a bio-adsorbent for removal of arsenic (III) from water

Novel low-cost bark-based magnetic iron oxide particles (BMIOPs) were synthesized and investigated for the removal of As(III) in drinking water. The synthesized BMIOP had a saturation magnetization value of 38.62 emug^-1 which was found to be enough for the magnetic separation of exhausted BMIOP after As(III) adsorption. Parameters like agitation speed, adsorbent dosage, contact time, pH, temperature, and initial concentration were thoroughly investigated. Langmuir, Freundlich, and Dubinin-Radushkevich isotherms were used for the modeling of experiments and observed a maximum adsorption (19.61 mg g^-1) of As(III) by Langmuir isotherm. Kinetics of As(III) sorption were well correlated with the coefficients in pseudo-first-order than the pseudo-second-order rate equation. Thermodynamic parameter investigation revealed that As(III) sorption process is endothermic, feasible, and spontaneous. BMIOP emerged as less expensive adsorbent for the abatement of arsenic ion from the drinking water. BMIOP showed 13.58 mg g^-1 adsorption capacity when As(V) alone is present, while it is 9.43 and 7.04 mg g^-1 for As(V) and As(III), respectively, when present together in the water. Graphical Abstract ᅟ.

Chemical and toxicological assessment of arsenic sorption onto Fe-sericite composite powder and beads

Batch sorption and leaching of arsenic (1-30mgL^-1) on Fe-sericite composite powder and beads were investigated in this study. Fe-sericite composite powder was made from natural sericite modified with iron, and alginate was used to transform the powder into beads. The maximum sorption capacities of the Fe-sericite composite powder (15.04 and 13.21mgg^-1 for As(III) and As(V), respectively) were higher than those of the corresponding beads (9.02 and 7.11mgg^-1 for As(III) and As(V), respectively) owing to the higher specific surface area of the powder. In addition, the leaching amounts of As(III) from Fe-sericite composite beads (≤ 15.03%) were higher than those of the corresponding powder (≤ 5.71%). However, acute toxicity of As(III)-sorbed Fe-sericite composite beads toward Daphnia magna was not significantly different from that of the corresponding powder (p > 0.05). Considering higher uptake of the powder particles by the daphnids, Fe-sericite composite beads seem to be a more appropriate and safer sorbent for arsenic removal in practical application. Based on Fe content, Fe-sericite composite beads had similar or higher maximum sorption capacities (71.19 and 56.11mgg^-1 Fe for As(III) and As(V), respectively) than those of previously reported sorbents.

Arsenic removal methods for drinking water in the developing countries: technological developments and research needs

Arsenic pollution of drinking water is a concern, particularly in the developing countries. Removal of arsenic from drinking water is strongly recommended. Despite the availability of efficient technologies for arsenic removal, the small and rural communities in the developing countries are not capable of employing most of these technologies due to their high cost and technical complexity. There is a need for the "low-cost" and "easy to use" technologies to protect the humans in the arsenic affected developing countries. In this study, arsenic removal technologies were summarized and the low-cost technologies were reviewed. The advantages and disadvantages of these technologies were identified and their scopes of applications and improvements were investigated. The costs were compared in context to the capacity of the low-income populations in the developing countries. Finally, future research directions were proposed to protect the low-income populations in the developing countries.

Equilibrium and kinetics study on removal of arsenate ions from aqueous solution by CTAB/TiO2 and starch/CTAB/TiO2 nanoparticles: a comparative study

We present a comparative study on the efficacy of TiO₂ nanoparticles for arsenate ion removal after modification with CTAB (N-cetyl-N,N,N-trimethyl ammonium bromide) followed by coating with starch biopolymer. The prepared nanoparticles were characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray diffractometry (XRD), thermogravimetry, scanning electron microscopy (SEM) and electron dispersive X-ray analysis (EDX). The removal efficiency was studied as a function of contact time, material dose and initial As(V) concentration. CTAB-modified TiO₂ showed the highest arsenate ion removal rate (∼99% from 400 μg/L). Starch-coated CTAB-modified TiO₂ was found to be best for regeneration. For a targeted solution of 400 μg/L, a material dose of 2 g/L was found to be sufficient to reduce the As(V) concentration below 10 μg/L. Equilibrium was established within 90 minutes of treatment. The sorption pattern followed a Langmuir monolayer pattern, and the maximum sorption capacity was found to be 1.024 mg/g and 1.423 mg/g after starch coating and after CTAB modification, respectively. The sorption mechanisms were governed by pseudo second order kinetics.

Adsorption of As(III) on porous hematite synthesized from goethite concentrate

Arsenite (As(III)) is toxic in drinking water, which becomes an environmental concern worldwide. This work was to synthesize porous hematite through the calcination of natural goethite concentrate for As(III) adsorption, including adsorption kinetics, isotherms and the influence of pH and temperature. The calcination was performed at 300 °C for 180 min, producing porous hematite with large amount of micropores. The maximum adsorption capacity of As(III) on porous hematite was achieved at pH 6.0 and 25 °C, about 14.46 mg g^-1, compared with 2.965 mg g^-1 on the original goethite concentrate. The improvement might be attributed to the formation of micropores and thus the increase in the surface area. Also, it was found that the adsorption was strongly pH dependent and reduced with increasing temperature. It is indicated that the low-cost porous hematite has great potential in As(III) removal from contaminated water.

Simultaneously removal of inorganic arsenic species from stored rainwater in arsenic endemic area by leaves of Tecomella undulata: a multivariate study

In the present study, an indigenous biosorbent (leaves of Tecomella undulata) was used for the simultaneous removal of inorganic arsenic species (As(III) and As(V)) from the stored rainwater in Tharparkar, Pakistan. The Plackett-Burman experimental design was used as a multivariate strategy for the evaluation of the effects of six factors/variables on the biosorption of inorganic arsenic species, simultaneously. Central composite design (CCD) was used to found the optimum values of significant factors for the removal of As(III) and As(V). Initial concentrations of both inorganic As species, pH, biosorbent dose, and contact time were selected as independent factors in CCD, while the adsorption capacity (q e) was considered as a response function. The separation of inorganic As species in water samples before and after biosorption was carried out by cloud point and solid-phase extraction methods. Theoretical values of pH, concentration of analytes, biosorbent dose, and contact time were calculated by quadratic equation for 100 % biosorption of both inorganic As species in aqueous media. Experimental data were modeled by Langmuir and Freundlich isotherms. Thermodynamic and kinetic study indicated that the biosorption of As(III) and As(V) was followed by pseudo second order. It was concluded that the indigenous biosorbent material efficiently and simultaneously removed both As species in the range of 70.8 to 98.5 % of total contents in studied ground water samples. Graphical abstract Optimizing the significant varable by central 2(3) + star orthogonal composite design.

Biosorptive removal of inorganic arsenic species and fluoride from aqueous medium by the stem of Tecomella undulate

Simultaneous removal of fluoride (F(-)), inorganic arsenic species, As(III) and As(V), from aqueous samples has been performed using an economic indigenous biosorbent (Stem of Tecomella undulata). The inorganic As species in water samples before and after biosorption were determined by cloud point and solid phase extraction methods, while F(-) was determined by ion chromatography. Batch experiments were carried out to evaluate the equilibrium adsorption isotherm studies for As(III), As(V) and F(-) in aqueous solutions. Several parameters of biosorption were optimized such as pH, biomass dosage, analytes concentration, time and temperature. The surface of biosorbent was characterized by SEM and FTIR. The FTIR study indicated the presence of carbonyl and amine functional groups which may have important role in the sorption/removal of these ions. Thermodynamic and kinetic study indicated that the biosorption of As(III), As(V) and F(-) were spontaneous, exothermic and followed by pseudo-second-order. Meanwhile, the interference study revealed that there was no significant effect of co-existing ions for the removal of inorganic As species and F(-) from aqueous samples (p > 0.05). It was observed that the indigenous biosorbent material simultaneously adsorbed As(III) (108 μg g(-1)), As(V) (159 μg g(-1)) and F(-) (6.16 mg g(-1)) from water at optimized conditions. The proposed biosorbent was effectively regenerated and efficiently used for several experiments, to remove the As(III), As(V) and F(-) from real water sample collected from endemic area of Pakistan.

Porous graphene oxide based inverse spinel nickel ferrite nanocomposites for the enhanced adsorption removal of arsenic

Porous nanocomposites, graphene oxide based-inverse spinel nickel ferrite (GONF) and reduced graphene oxide based-inverse spinel nickel ferrite (rGONF), were prepared by co-precipitation of graphene oxide (GO) with nickel and iron salts at one pot.

Utilization of natural hematite as reactive barrier for immobilization of radionuclides from radioactive liquid waste

Potential utilization of hematite as a natural material for immobilization of long-lived radionuclides from radioactive liquid waste was investigated. Hematite ore has been characterized by different analytical tools such as Fourier transformer infrared (FTIR), X-ray fluorescence (XRF), powder X-ray diffraction (XRD), thermogravimetry (TG) and differential thermal (DT) analysis, scanning electron microscopy (SEM) and BET-surface area. In this study, europium was used as REEs(III) and as a homolog of Am(III)-isotopes (such as (241)Am of 432.6 y, (242m)Am of 141 y and (243)Am of 7370 y). Micro particles of the hematite ore were used for treatment of radioactive waste containing (152+154)Eu(III). The results indicated that 96% (4.1 × 10(4) Bq) of (152+154)Eu(III) was efficiently retained onto hematite ore. Kinetic experiments indicated that the processes could be simulated by a pseudo-second-order model and suggested that the process may be chemisorption in nature. The applicability of Langmuir, Freundlich and Temkin models was investigated. It was found that Langmuir isotherm exhibited the best fit with the experimental results. It can be concluded that hematite is an economic and efficient reactive barrier for immobilization of long-lived radio isotopes of actinides and REEs(III).

Magnetic iron oxide and manganese-doped iron oxide nanoparticles for the collection of alpha-emitting radionuclides from aqueous solutions

Magnetic nanoparticles are well known to possess chemically active surfaces and large surface areas that can be employed to extract a range of ions from aqueous solutions. Additionally, their superparamagnetic properties provide a convenient means for bulk collection of the material from solution after the targeted ions have been adsorbed. Herein, two nanoscale amphoteric metal oxides, each possessing useful magnetic attributes, were evaluated for their ability to collect trace levels of a chemically diverse range of alpha emitting radioactive isotopes (polonium (Po), radium (Ra), uranium (U), and americium (Am)) from a wide range of aqueous solutions. The nanomaterials include commercially available magnetite (Fe₃O₄) and magnetite modified to incorporate manganese (Mn) into the crystal structure. The chemical stability of these nanomaterials was evaluated in Hanford Site, WA ground water between the natural pH (~8) and pH 1. Whereas the magnetite was observed to have good stability over the pH range, the Mn-doped material was observed to leach Mn at low pH. The materials were evaluated in parallel to characterize their uptake performance of the alpha-emitting radionuclide spikes from ground water across a range of pH (from ~8 down to 2). In addition, radiotracer uptake experiments were performed on Columbia River water, seawater, and human urine at their natural pH and at pH 2. Despite the observed leaching of Mn from the Mn-doped nanomaterial in the lower pH range, it exhibited generally superior analyte extraction performance compared to the magnetite, and analyte uptake was observed across a broader pH range. We show that the uptake behavior of the various radiotracers on these two materials at different pH levels can generally be explained by the amphoteric nature of the nanoparticle surfaces. Finally, the rate of sorption of the radiotracers on the two materials in unacidified ground water was evaluated. The uptake curves generally indicate that equilibrium is obtained within a few minutes, which is attributed to the high surface areas of the nanomaterials and the high level of dispersion in the liquids. Overall, the results indicate that these nanomaterials may have the potential to be employed for a range of applications to extract radionuclides from aqueous solutions.

Rational design of nanomaterials for water treatment

The ever-increasing human demand for safe and clean water is gradually pushing conventional water treatment technologies to their limits. It is now a popular perception that the solutions to the existing and future water challenges will hinge upon further developments in nanomaterial sciences. The concept of rational design emphasizes on 'design-for-purpose' and it necessitates a scientifically clear problem definition to initiate the nanomaterial design. The field of rational design of nanomaterials for water treatment has experienced a significant growth in the past decade and is poised to make its contribution in creating advanced next-generation water treatment technologies in the years to come. Within the water treatment context, this review offers a comprehensive and in-depth overview of the latest progress in rational design, synthesis and applications of nanomaterials in adsorption, chemical oxidation and reduction reactions, membrane-based separation, oil-water separation, and synergistic multifunctional all-in-one nanomaterials/nanodevices. Special attention is paid to the chemical concepts related to nanomaterial design throughout the review.

Synthesis of iron oxyhydroxide-coated rice straw (IOC-RS) and its application in arsenic(V) removal from water

Because of the recognition that arsenic (As) at low concentrations in drinking water causes severe health effects, the technologies of As removal have become increasingly important. In this study, a simplified and effective method was used to immobilize iron oxyhydroxide onto a pretreated naturally occurring rice straw (RS). The modified RS adsorbent was characterized, using scanning electron microscope, Fourier transform infrared spectroscopy, thermogravimetric analyzer, and surface area analyzer. Experimental batch data of As(V) adsorption were modeled by the isotherms and kinetics models. Although all isotherms, the Langmuir model fitted the equilibrium data better than Freundlich and Dubinin-Radushkevich models and confirmed the surface homogeneity of adsorbent. The iron oxyhydroxide-coated rice straw (IOC-RS) was found to be effective for the removal of As(V) with 98.5% sorption efficiency at a concentration of <50 mg/L of As(V) solution, and thus maximum uptake capacity is ∼22 and 20 mg As(V)/g of IOC-RS at pH 4 and 6, respectively. The present study might provide new avenues to achieve the As concentrations required for drinking water recommended by the World Health Organization.

Carbon dots from PEG for highly sensitive detection of levodopa

Fluorescent carbon dots (CDs)/tyrosinase hybrid as a fluorescent probe for efficient, fast and sensitive detection of levodopa.

Closer look at As(III) and As(V) adsorption onto ferrihydrite under competitive conditions

Batch experiments were conducted in order to investigate the competitive interaction of arsenite (As(III)) and arsenate (As(V)) onto ferrihydrite as a function of initial pH, adsorbent dosage, concentration of coexisting ligands, and order of addition. The pH generally had a great impact on adsorption under both single ion and competitive conditions. However, the amount of As(V) in solution was the controlling factor of adsorption behavior, and As(III) more or less outcompeted As(V) across the pH scale from 4 to 10. Under competitive conditions, i.e., both species were present at the same time, As(III) and As(V) were adsorbed almost equally up to a pH of 5 at an adsorbent dosage of 0.5 g/L and up to a pH of 6 at an adsorbent dosage of 1 g/L. This was contrary to the theoretical prediction that As(V) should adsorb more strongly than As(III) at pH values below the point of zero charge (pzc) of ferrihydrite of about 7 to 8. At low pH, As(V) impedes the adsorption of As(III) but to lesser degree than As(III) impedes As(V) adsorption at a pH above 6. The effect of As(III) on the adsorption of As(V) increased with an increase in pH, and the adsorption of As(V) was almost absent at pH 9 at an adsorbent dosage of 1 g/L and at pH 8 at an adsorbent dosage of 0.5 g/L. In the range of ferrihydrite dosages from 0.2 to 1.6 g/L, As(III) was adsorbed preferentially over As(V) under the availability of less adsorbent. The order of anion addition also had significant effects on their competitive adsorption behavior: the first species was always more favored to compete for the adsorbing sites than when the two species were added to the suspensions simultaneously.

Arsenic(V) Removal in Wetland Filters Treating Drinking Water with Different Substrates and Plants

Constructed wetlands are an attractive choice for removing arsenic (As) within water resources used for drinking water production. The role of substrate and vegetation in As removal processes is still poorly understood. In this study, gravel, zeolite (microporous aluminosilicate mineral), ceramsite (lightweight expanded clay aggregate) and manganese sand were tested as prospective substrates while aquatic Juncus effuses (Soft Rush or Common Rush) and terrestrial Pteris vittata L. (Chinese Ladder Brake; known as As hyperaccumulator) were tested as potential wetland plants. Indoor batch adsorption experiments combined with outdoor column experiments were conducted to assess the As removal performances and process mechanisms. Batch adsorption results indicated that manganese sand had the maximum As(V) adsorption rate of 4.55 h^-1 and an adsorption capacity of 42.37 μg/g compared to the other three aggregates. The adsorption process followed the pseudo-first-order kinetic model and Freundlich isotherm equations better than other kinetic and isotherm models. Film-diffusion was the rate-limiting step. Mean adsorption energy calculation results indicated that chemical forces, particle diffusion and physical processes dominated As adsorption to manganese sand, zeolite and gravel, respectively. During the whole running period, manganese sand-packed wetland filters were associated with constantly 90% higher As(V) reduction of approximate 500 μg/L influent loads regardless if planted or not. The presence of P. vittata contributed to no more than 13.5% of the total As removal. In contrast, J. effuses was associated with a 24% As removal efficiency.

Naturally dissolved arsenic concentrations in the Alpine/Mediterranean Var River watershed (France)

A detailed study on arsenic (As) in rocks and water from the Var River watershed was undertaken aiming at identifying (i) the origin and the distribution of As in this typical Alpine/Mediterranean basin, and (ii) As input into the Mediterranean Sea. Dissolved As concentrations in the Var River range from 0.1 to 4.5 μg⋅L(-1), due to high hydrological variability and the draining through different geological formations. In the upper part of the Var drainage basin, in the Tinée and the Vésubie valleys, high levels of dissolved As concentrations occur (up to 263 μg⋅L(-1)). The two main sources of As in rocks are the Hercynian metamorphic rocks and the Permian argilites. Highly heterogeneous distribution of As in waters draining through metamorphic rocks is probably related to ore deposits containing arsenopyrite. As, U, W and Mo concentrations in water and rocks correspond to the formation of As-rich ore deposits around Argentera granite by hydrothermal fluids deposited at the end of the Hercynian chain formation, which occurred about 300 My ago. In 2009, weekly monitoring was performed on the Var River (15 km upstream of the mouth), highlighting an average dissolved As concentration (<0.45 μm) of 2.7 ± 0.9 μg⋅L(-1), which is significantly higher than the world-average baseline for river water (0.83 μg⋅L(-1)). Taking the average annual discharge (49.4 m(3)⋅s(-1)) into account and the As levels in the dissolved phase and in deposits of the Var River, dissolved As input into the Mediterranean Sea would be 4. 2± 1.4 tons⋅year(-1) which represents 59% of the total As flux. This study also reveals a probable non-conservative As behaviour, i.e., possible transfer between aqueous and solid phases, during the mixing of the Var River with a tributary.