Arsenic and antimony in water and wastewater: overview of removal techniques with special reference to latest advances in adsorption

One-step Sb(III) decontamination using a bifunctional photoelectrochemical filter

Developing advanced technologies to achieve decontamination of emerging contaminants such as antimony (Sb) is highly demanded. Herein, we successfully designed a dual-functional photoelectrochemical filter system for "one-step" detoxification and sequestration of highly toxic Sb(III). The key to this technology is a photoelectrical-responsive CNT filter functionalized with nanoscale MIL-88B(Fe) photocatalysts. At 2.5 V and under illumination, a 97.7 ± 1.5 % Sb(III) transformation and a 92.9 ± 2.3 % Sb_total removal efficiency can be obtained using an optimal hybrid filter (e.g. CM(50:3)) over 2 h continuous filtration. This can be explained by the synergistic effects of the filter's flow-through design, photoelectrochemical reactivity, fine pore size, and plentiful exposed sorption sites. Various advanced characterization techniques validated the system efficacy. Improved Sb(III) removal kinetics were observed when compared with conventional batch system (97.5 % vs 75.8 %). A synergistic effect between photocatalytic (PC) and electrochemical (EC) process were identified (k_PEC =0.99 h^-1 >k_PC=0.21 h^-1 + k_EC =0.30 h^-1). EPR and photochemical characterizations suggested that hydroxyl radicals dominated the Sb(III) conversion. The proposed technology works effectively across a wide range of pH values and water matrixes. The outcomes of this study can facilitate mechanistic insights into photoelectrocatalysis and provide a promising nanotechnology for efficient Sb(III) decontamination.

Synthesis of novel adsorbent by intercalation of biopolymer in LDH for the removal of arsenic from synthetic and natural water

This study focuses on the synthesis of nanocomposites named CCA and CZA that were prepared by the incorporation of cellulose (CL) in the Ca/Al and Zn/Al layered double hydroxide (LDH), respectively. These materials were then used for the uptake of As(III) and As(V) from aqueous medium. Characterization of both nanocomposites (CCA and CZA) was done using FTIR and Raman analysis to identify the functional groups, N₂ adsorption-desorption isotherms to determine the specific surface area and pore geometry and XPS analysis to obtain the surface atomic composition. Some other characters were investigated using simultaneous TGA and DTA and elemental chemical analysis (CHNS/O). The crystallinity of the prepared nanocomposites was displayed by XRD patterns. Furthermore, the sheet-like structure of the LDHs and the irregularity of surface morphology with porous structure were observed by TEM and SEM microphotographs. Optimization of maximum adsorption capacity was adjusted using different parameters including pH, contact time and adsorbent dosage. The pseudo-second-order model was in good fitting with kinetics results. The adsorption isotherm results showed that CZA exhibits better adsorption capacity for As(III) than CCA and the Langmuir isotherm model described the data well for both nanocomposites. Thermodynamic studies illustrated the endothermic nature of CCA and exothermic nature on CZA, as well as the fact that the adsorption process is spontaneous. A real water sample collected from well located in Gabes (Tunisia), has also been treated. The obtained experimental results were confirmed that these sorbents are efficient for the treatment of hazardous toxic species such as.

Arsenic removal from groundwater in Kütahya, Turkey, by novel calcined modified hydrotalcite

Since arsenic is highly toxic and carcinogenic, it now causes serious health problems all over the world. Therefore, there is an urgent need to develop new techniques that are cost-effective and easily applicable to remove arsenic from contaminated waters. Layer double hydroxides have the potential to be a good adsorbent to remove arsenic from contaminated waters due to high surface area and high anion exchange capacity. In this paper, arsenic removal from water by calcined Fe-hydrotalcite (CFeHT) known as layered double hydroxide and prepared synthetically with coprecipitation method was researched. The study brings out that the effect of initial solution pH values was limited for the adsorption. The experimental study indicates that the adsorption of arsenic rapidly occured in comparison with other studies. It was determined that the pseudo-second-order kinetic model was more suitable than the first order. In isotherm studies, it was seen that the experimental data were compatible with Langmuir model. In this study was determined that CFeHT has a high arsenic removal potential. And also the concentration of the arsenic solution (600 µg/L) has been reduced below the allowable value by the World Health Organization (< 10 µg/L). The desorption test indicates that the desorption ratio of As(V) was obtained as 72.7.

Adsorption of antimonite and antimonate from aqueous solution using modified polyacrylonitrile with an ultrahigh percentage of amidoxime groups

Porous modified polyacrylonitrile (PAN) with an ultrahigh percentage of amidoxime groups (UAPAN) was synthesized for the first time and used to adsorb antimonite (Sb(III)) and antimonate (Sb(V)) from aqueous solution. Fourier transform infrared (FT-IR), Zeta potential, X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT) were adopted to characterize UAPAN and explore adsorption mechanism. Moreover, batch experiments were performed to investigate the influence of various adsorption parameters, including initial pH, contact time, temperature, coexisting ions and reusability on adsorption capacities. Results showed that the maximum adsorption capacities for Sb(III) and Sb(V) were 125.4 and 177.3 mg g^-1, respectively, which were much higher than those of other adsorbents reported in literature. The adsorption thermodynamics was evaluated, indicating the spontaneous and endothermic adsorption. The adsorption isotherm was suitable to be modeled by Langmuir isotherm (R² > 0.96). Results of FT-IR, Zeta potential and XPS indicated that adsorption was involved with electric charge attraction and ligand exchange. DFT further explained that better adsorption of Sb(V) on UAPAN than that of Sb(III) was caused by the higher adsorption energy, more favorable bond lengths and atom charge density. Accordingly, UAPAN is expected to be a compelling candidate for antimony decontamination from aqueous environment.

A review of removal technology for antimony in aqueous solution

Antimony (Sb) and its compounds, toxic metalloid, have been classified as high-priority pollutants. Increasing Sb released into the water environment by natural processes and anthropogenic activities, which exposure threatens to human health and ecosystems. Therefore, it is of unquestionable importance to remove Sb from polluted water. Keeping in view the extreme importance of this issue, we summarize the source, chemistry, speciation, distribution, toxicity, and polluted situation of Sb about aqueous solution. Then, we provide the recent and common technology to remove Sb, which are based on adsorption, coagulation/flocculation, electrochemical technology, membrane technology, ion exchange, etc. In this review, we focus in detail on the adsorption method, researchers at present have been investigating to discover more advanced, cost-effective, eco-friendly, reusable adsorbents. However, to date the Sb-containing wastewater treatment technologies are not sufficiently developed and most of research have been tested only in controlled lab conditions. Few reports are available that include field studies and applications. We critically analyzed the salient features and removal mechanisms, evaluating benefits and limitations of these technologies, hoping to provide more references for further research. Finally, we considered the Fe- or Mn-based technologies was the most promising technique to remove Sb for field application.

Synthesis of Fe3O4 magnetic nanoparticles coated with cationic surfactants and their applications in Sb(V) removal from water

Antimony (Sb) pollution was an emerging environmental risk in several contaminated waters, whereas its removal still presented as a severe challenge due to the lack of efficient adsorbent and its further removal mechanism. In this study, synthesized absorbents, Fe₃O₄ magnetic nanoparticles (Fe-MNPs) modified and dispersed with commonly used cationic surfactants, were applied to remove Sb contamination in real surface waters, its synthesized conditions, removal performance and mechanism were investigated by using batch experiments and characterization analyses. Optimum conditions on Sb(V) (the dominant form is Sb(OH)₆^-) removal by modified adsorbents were obtained as: cetylpyridinium chloride (CPC) coated on Fe-MNPs, mass ratio of Fe-MNPs: CPC = 4:1 and pH = 3-5. Magnetic properties of synthesized adsorbent were not affected, dispersibility was enhanced after fabrication of CPC, that indicated the Fe-MNPs@CPC could be separated and reused with external magnetic field. The adsorption efficiency of this low-cost adsorbent coated with CPC was superior than several traditional adsorbents. The practical application of Fe-MNPs@CPC in five types real waters from the Xikuangshan (XKS) Sb mine area and regeneration experiments by 1 M (mol/L) NaOH solution further confirm its practicability and reusability. Removal experiment results, X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FT-IR) spectra suggested that electrostatic attraction and surface bonding might responsible for the Sb(V) removal by Fe-MNPs modified with cationic surfactants.

Sustainable Low-Concentration Arsenite [As(III)] Removal in Single and Multicomponent Systems Using Hybrid Iron Oxide-Biochar Nanocomposite Adsorbents-A Mechanistic Study

Rice and wheat husks were converted to biochars by slow pyrolysis (1 h) at 600 °C. Iron oxide rice husk hybrid biochar (RHIOB) and wheat husk hybrid biochar (WHIOB) were synthesized by copyrolysis of FeCl₃-impregnated rice or wheat husks at 600 °C. These hybrid sorbents were characterized using X-ray photoelectron spectroscopy, X-ray diffraction, scanning electron microscopy (SEM), SEM-energy-dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy, transmission electron microscopy, physical parameter measurement system, and Brunauer-Emmett-Teller (BET) surface area techniques. Fe₃O₄ was the predominant iron oxide present with some Fe₂O₃. RHIOB and WHIOB rapidly chemisorbed As(III) from water (∼24% removal in first half an hour reaching up to ∼100% removal in 24 h) at surface Fe-OH functions forming monodentate ≡Fe-OAs(OH)₂ and bidentate (≡Fe-O)₂AsOH complexes. Optimum removal occurred in the pH 7.5-8.5 range for both RHIOB and WHIOB, but excellent removal occurred from pH 3 to 10. Batch kinetic studies at various initial adsorbate-adsorbent concentrations, temperatures, and contact times gave excellent pseudo-second-order model fits. Equilibrium data were fitted to different sorption isotherm models. Fits to isotherm models (based on R ² and χ²) on RHIOB and WHIOB followed the order: Redlich-Peterson > Toth > Sips = Koble-Corrigan > Langmuir > Freundlich = Radke-Prausnitz > Temkin and Sips = Koble-Corrigan > Toth > Redlich-Peterson > Langmuir > Temkin > Freundlich = Radke-Prausnitz, respectively. Maximum adsorption capacities, Q _RHIOB ⁰ = 96 μg/g and Q _WHIOB ⁰ = 111 μg/g, were obtained. No As(III) oxidation to As(V) was detected. Arsenic adsorption was endothermic. Particle diffusion was a rate-determining step at low (≤50 μg/L) concentrations, but film diffusion controls the rate at ≥100-200 μg/L. Binding interactions with RHIOB and WHIOB were established, and the mechanism was carefully discussed. RHIOB and WHIOB can successfully be used for As(III) removal in single and multicomponent systems with no significant decrease in adsorption capacity in the presence of interfering ions mainly Cl^-, HCO₃ ^-, NO₃ ^-, SO₄ ^2-, PO₄ ^3-, K⁺, Na⁺, Ca²⁺. Simultaneous As(III) desorption and regeneration of RHIOB and WHIOB was successfully achieved. A very nominal decrease in As(III) removal capacity in four consecutive cycles demonstrates the reusability of RHIOB and WHIOB. Furthermore, these sustainable composites had good sorption efficiencies and may be removed magnetically to avoid slow filtration.

Industrial waste materials as adsorbents for the removal of As and other toxic elements from an abandoned mine spoil heap leachate: a case study in Asturias

The purpose of this study is to determine the capacity of four industrial waste materials originate from steelmaking processes and from gas treatment at a thermal power plant to remove As and other contaminants from a leachate from the spoil heap of an abandoned mercury mine. Arsenic removal is faster in the first minutes, then increases only slightly over time reaching equilibrium in 8 hours. As removal efficiency increased with increasing adsorbent concentration. As removal efficiency was found to be 82.7%, 71%, 37.2% and 27.2% for EA, FA, HA and G, respectively, when employing 80 g/dm³ of adsorbent concentration. The main mechanism of As removal appears to be the results show that Hg and Pb are completely removed using low concentrations of adsorbents regardless of the waste material used in the treatment. FA removed more than 82% of other toxic elements such as Ni, Cu and Cd. EA is the most effective byproduct of the four employed in this study for removing pollutants, while G is the least effective. The present study shows it is possible to carry out an efficient and economical treatment of mine leachate using these byproducts.

LC-ICP-OES method for antimony speciation analysis in liquid samples

A method for the analysis of different species of antimony (Sb) that couples liquid chromatography with an inductively coupled plasma-optical emission spectrometry (LC-ICP-OES) system is presented. The method is simple and reliable to separate and quantify directly and simultaneously Sb(III) and Sb(V) in aqueous samples. The calibration curves showed high linearity at the three wavelengths tested. The limits of detection ranged from 24.9 to 32.3 μg/L for Sb(III) and from 36.2 to 46.0 μg/L for Sb(V), at the three wavelengths evaluated. The limit of detection for this method varied depending on the wavelength used. The lowest limit of quantification for Sb(V) (49.9 μg/L) and Sb(III) (80.7 μg/L) was obtained at a wavelength of 217.582 nm. The method sensitivity for Sb(V) was higher compared to Sb(III) at all the wavelengths considered. Samples containing different concentrations of Sb(III) and Sb(V) in three different matrices, i.e., water, basal culture medium, and anaerobic sludge plus basal medium, were analyzed. The coefficients of variation were low and ranged from 0.1 to 5.0 depending on the sample matrix. Recoveries of Sb(III) and Sb(V) were higher than 90% independently of the matrix analyzed and the wavelength used in the analysis.

A polythreaded MnII-MOF and its super-performances for dye adsorption and supercapacitors

One new polythreaded Mn^II-MOF was successfully prepared by employing a tridentate N-donor ligand with three long arms. Its excellent performances in dye adsorption and supercapacitor have been investigated in detail.

Enhancing the Removal of Sb (III) from Water: A Fe3O4@HCO Composite Adsorbent Caged in Sodium Alginate Microbeads

To remove antimony (Sb) ions from water, a novel composite adsorbent was fabricated from ferriferous oxide and waste sludge from a chemical polishing process (Fe3O4@HCO) and encapsulated in sodium alginate (SAB). The SAB adsorbent performed well with 80%–96% removal of Sb (III) ions within a concentration range of 5–60 mg/L. The adsorption mechanism of Sb (III) was revealed to be the synergy of chemisorption (ion exchange) and physisorption (diffusion reaction). The adsorption isotherms and kinetics conformed to the Langmuir isotherm and the pesudo-second-order kinetic model. Both initial pH and temperature influenced the adsorption performance with no collapse of microbeads within solution pH range 3–7. Most importantly for practical applications, these microspheres can be separated and recovered from aqueous solution by a magnetic separation technology to facilitate large-scale treatment of antimony-containing wastewater.

The synthesis of calcium arsenate@iron arsenate coating materials and their application for arsenic-containing wastewater treatment

The current method of treating arsenic-containing wastewater is mainly to use a calcium method to synthesize stable calcium arsenate. It is easy to cause reverse dissolution by rain or other erosion, releasing arsenic into the natural world and polluting soil and groundwater. So, calcium arsenate is not an ideal material for removing and immobilizing arsenic. Iron arsenate (FeAsO₄) is much better than calcium arsenate because of its stability and acid resistance. In this study, calcium arsenate@iron arsenate coating materials were synthesized. From the results of the XRD and SEM analyses, it was shown that calcium arsenate was coated by an iron arsenate shell which consisted of nanoparticles. The stability of the coating materials was determined using the Toxicity Characteristic Leaching Procedure (TCLP). The results showed that the concentrations of As for CaHAsO₄ and Ca₃(AsO₄)₂ were 744 mg L⁻¹ and 302.2 mg L⁻¹, respectively. Arsenic was not detected through the TCLP tests for CaHAsO₄@FeAsO₄ and Ca₃(AsO₄)₂@FeAsO₄ coating materials, and the best coating condition was confirmed to be an Fe/As molar ratio of 4 : 1, pH of 4, and temperature of 50 °C. The stability of the materials showed a significant improvement. The results indicated that calcium arsenate materials could be converted to coating materials by using ferric salts. The coating materials had excellent stability in an aqueous solution. Thus, the coating was suitable for the removal and immobilization of arsenic in industrial applications. This work provided a new way to treat arsenic-containing wastewater, which was simple and economical. This method has potential for use in the field of wastewater treatment containing arsenic.

Calcium arsenic salts converted to coating materials by ferric salts. The coating materials can be used for arsenic immobilization.

Sb(III)-resistance mechanisms of a novel bacterium from non-ferrous metal tailings

Understanding the mechanism(s) of microbial resistance to antimony (Sb) is critical in the bioremediation of Sb polluted environments. Here a novel bacterium (Acinetobacter sp. JH7) isolated from mine tailings decreased the Microtox toxicity of a Sb(III)-containing medium. DNA sequencing and physiological testing were employed for the identification and characterization of strain JH7. Following a batch experiment, Fourier transform infrared spectroscopy (FTIR) and antimony speciation analyses determined the adsorption and oxidation of antimony. Analyses of Sb(III) distribution revealed that extracellular polymeric substances and cell walls inhibited Sb(III) entry into JH7 cells. FTIR studies indicated that key functional groups including -OH, C-N, and C-O likely participated in Sb(III) biosorption. Isothermal and kinetic studies revealed that Sb(III) sorption to viable JH7 cells fitted the Langmuir model (R² = 0.99) and could be described by pseudo-second order kinetics (R² = 0.99). Furthermore, the increase of anti-oxidative enzymatic activity of JH7 enhanced the intracellular detoxification of Sb(III), which would indirectly contribute to the Sb(III) resistance ability of strain JH7. Our results indicate that biosorption and ROS oxidation of Sb(III) were likely responsible for the decreased toxicity of Sb. The greater understanding how Acinetobacter sp. JH7 lowers the environmental Sb(III) toxicity could provide a basis for future research and subsequent development of technologies for the remediation of Sb contaminated sites.

Risk Assessment of Potentially Toxic Elements Pollution from Mineral Processing Steps at Xikuangshan Antimony Plant, Hunan, China

We evaluated the direct release to the environment of a number of potentially toxic elements (PTEs) from various processing nodes at Xikuangshan Antimony Mine in Hunan Province, China. Sampling wastewater, processing dust, and solid waste and characterizing PTE content (major elements Sb, As, Zn, and associated Hg, Pb, and Cd) from processing activities, we extrapolated findings to assess wider environmental significance using the pollution index and the potential ecological risk index. The Sb, As, and Zn in wastewater from the antimony benefication industry and a wider group of PTEs in the fine ore bin were significantly higher than their reference values. The content of Sb, As, and Zn in tailings were relatively high, with the average value being 2674, 1040, and 590 mg·kg−1, respectively. The content of PTEs in the surface soils surrounding the tailings was similar to that in tailings, and much higher than the background values. The results of the pollution index evaluation of the degree of pollution by PTEs showed that while dominated by Sb, some variation in order of significance was seen namely for: (1) The ore processing wastewater Sb > Pb > As > Zn > Hg > Cd, (2) in dust Sb > As > Cd > Pb > Hg > Zn, and (3) surface soil (near tailings) Sb > Hg > Cd > As > Zn > Pb. From the assessment of the potential ecological risk index, the levels were most significant at the three dust generation nodes and in the soil surrounding the tailings reservoir.

Emerging technologies for arsenic removal from drinking water in rural and peri-urban areas: Methods, experience from, and options for Latin America

Providing drinking water with safe arsenic levels in Latin American (LA) countries (a total of 22 countries) is a major current challenge. Arsenic's presence in water has been neglected for many decades since it was first reported ~100 years ago in Argentina. The major arsenic source in this region is geogenic. So far, arsenic has been reported in 15 LA countries. Arsenic concentrations in drinking water have been reported up to >200 fold (2000 μg/L) the WHO limit of 10 μg/L. About 14 million people in the arsenic affected LA countries depend on contaminated water characterized by >10 μg/L of arsenic. Low-cost, easy to use, efficient, and sustainable solutions are needed to supply arsenic safe water to the rural and peri-urban population in the affected areas. In the present study, >250 research articles published on various emerging technologies used for arsenic remediation in rural and peri-urban areas of LA countries are critically reviewed. Special attention has been given to arsenic adsorption methods. The manuscript focuses on providing insights into low cost emergent adsorbents with an implementation potential in Latin America. Natural, modified and synthetic adsorbents used for arsenic decontamination were reviewed and compared. Advantages and disadvantages of treatment methods are summarized. Adsorbent selection criteria are developed. Recommendations concerning emerging adsorbents for aqueous arsenic removal in LA countries have also been made.

As(III) and As(V) removal by using iron impregnated biosorbents derived from waste biomass of Citrus limmeta (peel and pulp) from the aqueous solution and ground water

Now a day's biosorbents with magnetic properties have been applied for water and wastewater treatment process, because of its magnetic nature it can be easily separated and can be reused more than one time. In the present study, two magnetic biosorbents were synthesized from waste biomass of Citrus limetta (peel and pulp) at 500 °C temperature represented as PAC-500 and PPAC-500. These biosorbents were effectively used for the removal of As(III) and As(V) from an aqueous solution and groundwater samples. The prepared biosorbents were characterized by using Brunauer Emmett Teller (BET), Zeta potential, Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM), Energy Disperssive X-ray (EDS), X-ray Diffraction (XRD) and Particle Size Analyzer (PSA). Isotherms, kinetics and thermodynamics were also applied to the obtained experimental data. The regeneration study revealed that the biosorbent can be recycled up to four cycles. The adsorbent capacity of PAC-500 and PPAC-500 for the sorption of As(III) was 714.28 μg/g and 526.31 μg/g, respectively, whereas the q_max value for As(V) sorption was 2000 μg/g for both the biosorbents (PAC-500 and PPAC-500). The effect of competitive ions was also studied that shows that the presence of H₂PO₄^- and CO₃² have negative effects on the sorption of As(III) and As(V). Arsenic is very toxic and it is a more important subject for consideration, therefore it is necessary to develop a low cost material that is very efficient in removing As from ground water contaminated with As water.

Novel electroblowing synthesis of submicron zirconium dioxide fibers: effect of fiber structure on antimony(v) adsorption

Both stable and radioactive antimony are common industrial pollutants. For antimonate (Sb(v)) removal from industrial waste water, we synthesized submicron zirconium dioxide (ZrO₂) fibers by electroblowing and calcination of the as-electroblown fibers. The fibers are amorphous after calcination at 300 and 400 °C and their average diameter is 720 nm. The fibers calcined at 500 to 800 °C have an average diameter of 570 nm and their crystal structure transforms from tetragonal to monoclinic at the highest calcination temperatures. We investigated Sb(v) adsorption capacity of the synthesized ZrO₂ fibers as a function of pH, adsorption isotherm at pH 6 and adsorption kinetics at pH 7. The tetragonal ZrO₂ fibers calcined at 500 °C exhibited the best potential for Sb(v) remediation with Sb(v) uptake of 10 mg g^-1 at pH 2 and a maximum Sb(v) uptake of 8.6 mg g^-1 in the adsorption isotherm experiment. They also reached 30% of 7 days' Sb(v) uptake in only a minute. The adsorption kinetics followed the Elovich model.

Preparation of a novel Fe3O4/HCO composite adsorbent and the mechanism for the removal of antimony (III) from aqueous solution

A novel adsorbent (Fe3O4/HCO) was prepared via co-precipitation from a mix of ferriferrous oxide and a Ce-rich waste industrial sludge recovered from an optical polishing activity. The effect of system parameters including reaction time, pH, dose, temperature as well as initial concentration on the adsorption of Sb(III) were investigated by sequential batch tests. The Sb(III)/Fe3O4/HCO system quickly reached adsorption equilibrium within 2 h, was effective over a wide pH (3-7) and demonstrated excellent removal at a 60 mg/L Sb(III) concentration. Three isothermal adsorption models were assessed to describe the equilibrium data for Sb(III) with Fe3O4/HCO. Compared to the Freundlich and dubinin-radushkevich, the Langmuir isotherm model showed the best fit, with a maximum adsorption capacity of 22.853 mg/g, which exceeds many comparable absorbents. Four kinetic models, Pseudo-first-order, Pseudo-second-order, Elovich and Intra-particle, were used to fit the adsorption process. The analysis showed that the mechanism was pseudo-second-order and chemical adsorption played a dominant role in the adsorption of Sb(III) by Fe3O4/HCO (correlation coefficient R2 = 0.993). Thermodynamic calculations suggest that adsorption of Sb(III) ions was endothermic, spontaneous and a thermodynamically feasible process. The mechanism of the adsorption of Sb(III) on Fe3O4/HCO could be described by the synergistic adsorption of Sb (III) on Fe3O4, FeCe2O4 and hydrous ceric oxide. The Fe3O4/HCO sorbent appears to be an efficient and environment-friendly material for the removal of Sb(III) from wastewater.

Arsenic adsorption and removal by a new starch stabilized ferromanganese binary oxide in water

A new starch stabilized ferromanganese binary oxide (starch-FMBO) with an Fe/Mn ratio of 1.00-2.00 and a synthetic pH of 2 was prepared using an organic polymer (starch) as the stabilizing dispersant. The maximum arsenic adsorption capacity of starch-FMBO was 161.29 mg/g. Adsorption optimization was also conducted, which revealed that starch-FMBO had a high adsorption capacity over a wide pH range (pH 3.0 to pH 11.0) and in the presence of some common anions (HCO₃^-, SO₄^2-, Cl^-, and NO₃^-). Arsenic removal by FMBO and starch-FMBO followed pseudo-second-order dynamics (R² ≥ 0.99), indicating that the adsorption rate depended on the chemical adsorption process. Through the analysis of X-ray photoelectron spectroscopy (XPS), and Fourier-transform infrared spectroscopy (FTIR), it was shown that hydroxyl was continuously produced and complexated with As(III) and As(V) during the adsorption process. Thus, the reaction of iron oxide and manganese oxide with arsenic was inferred and explained. The developed starch-FMBO shows promise for its application in the treatment of arsenic-contaminated water.

Fruit waste management by pigment production and utilization of residual as bioadsorbent

Dry powder of fruit wastes including pomegranate, grapes, lime, apple, and papaya was used to examine their pigment extraction capability. Solvent combination of hexane and acetone (1:1) produced the maximum extraction for lime waste with a yield of 1.65%. Gas Chromatography and Mass Spectrometry analysis of the crude pigment of lime exhibited the abundance of compounds like chlorogenic acid, caffeic acid, and coumaric acid. Three major bands were obtained in Thin Layer Chromatography. Column Chromatographic purification using ethyl acetate and hexane mixture as eluting phase showed a retention factor of 0.62 for the major band. Nuclear Magnetic Resonance revealed the final structure of the compound as chlorogenic acid. Slight inhibition was exhibited by the compound against Escherichia coli. Adsorption of arsenate by residual fruit waste revealed the highest adsorption in grapes with 92% efficiency. This study enlightens an alternative approach of fruit waste management with the production of value-added products and its utilization of residue as bioadsorbent.

Sequential determination and chemical speciation analysis of inorganic As and Sb in airborne particulate matter collected in outdoor and indoor environments using slurry sampling and detection by HG AAS

In this work, fast sequential determination and chemical speciation analysis of inorganic arsenic and antimony in airborne particulate matter collected in outdoor and indoor environments using slurry sampling and detection by hydride generation atomic absorption spectrometry (HG-AAS) is proposed. A Doehlert design was applied to optimise the hydride generation conditions of As and Sb for fast sequential determination in the same aliquot of particulate matter samples after preparation of the slurry. The limits of quantification (LoQ) obtained for As and Sb were 0.3 and 0.9 ng m^-3, respectively. The accuracy of the analytical method was confirmed by analysis of the certified reference material of urban particulate matter (SRM NIST 1648a), presenting concordance with certified values of 92.7±7.7% for As and 91.2±9.5% for Sb. Precision was expressed as relative standard deviation (% RSD, n=3), with our results presenting values better than 3.4% and 4.2% for total inorganic As and Sb, respectively. For all analysed samples, total As concentrations and its inorganic species were below the LoQ of the analytical method (<0.3 ng m^-3). However, the averages of total inorganic Sb concentrations in airborne particulate matter, collected as total suspended outdoor particles (TSP_outdoor), inhalable particulate matter (PM₁₀), and total suspended indoor particles (TSP_indoor), were 3.1±0.5, 2.4±0.6, and 2.6±0.4 ng m^-3, respectively. Trivalent Sb (Sb³⁺) was the predominant inorganic species in all samples investigated, with mean percentages of 76%, 72%, and 73% in TSP_outdoor, PM₁₀, and TSP_indoor, respectively. The presence of Sb and its predominant inorganic form (Sb³⁺) can be attributed to vehicular traffic close to the sampled urban areas. Therefore, fast sequential determination of As and Sb and their inorganic species in particulate matter samples prepared as slurry by FS-HG-AAS is an efficient, accurate, and precise method and can be successfully applied to routine analysis.

Effect of Water Chemistry on Antimony Removal by Chemical Coagulation: Implications of ζ-Potential and Size of Precipitates

The process of coagulation and precipitation affect the fate and mobility of antimony (Sb) species in drinking water. Moreover, the solubility and physico-chemical properties of the precipitates may be affected by the media chemistry. Accordingly, the present study aimed to investigate the removal of Sb(III, V) species by ferric chloride coagulation under various water chemistry influences with a particular focus on the role of the properties of the precipitates. The results indicated that the amount of Sb(III) removed increased with increasing solution pH, showing the insignificant effects of the hydrodynamic diameter (HDD) and ζ-potential of the precipitates. However, no Sb(V) removal occurred at alkaline pH values, while a highly negative ζ-potential and the complete dissolution of precipitates were observed in the aqueous solution. The solution pH was also useful in determining the dominant coagulation mechanisms, such as co-precipitation and adsorption. The Fe solubility substantially affects the Sb removal at a certain pH range, while the HDD of the precipitates plays an insignificant role in Sb removal. The presence of divalent cations brings the ζ-potential of the precipitates close to point of zero charge (pzc), thus enhancing the Sb(V) removal at alkaline pH conditions. Pronounced adverse effects of humic acid were observed on Sb removal, ζ-potential and HDD of the precipitates. In general, this study may provide critical information to a wide group of researchers dealing with environmental protection from heavy metal pollution.

Evaluation of hybrid anion exchanger containing cupric oxide for As(III) removal from water

The aim of this study was investigate of arsenite adsorption on a hybrid polymer based on a polystyrene/divinylbenzene macroporous anion exchanger containing cupric oxide deposited within its porous structure. The study included batch kinetic and equilibrium experiments, and investigation of influence of the pH, regeneration of spent adsorbent and the column process on arsenic(III) adsorption. The experimental data were evaluated using kinetic, isotherm and fixed-bed column models. The adsorption capacity calculated from the Langmuir model was 6.61 mg As(III) g^-1. The adsorption rate was controlled by both chemisorption of arsenic on the adsorbent surface and external diffusion, and at a higher initial As(III) concentration also by intraparticle diffusion. The spent adsorbent was easily regenerated with 1.0 M NaOH solution. Based on batch adsorption studies and X-ray photoelectron spectroscopic analyses a mechanism of As(III) adsorption was proposed. Arsenite removal proceeded in two stages: oxidation to arsenate on the CuO surface, followed by an ion exchange reaction. The studied hybrid polymer also showed very good adsorption characteristics under the dynamic regime. The S-shape of breakthrough curves and insignificant influence of bed height, initial concentration and flow rate on the adsorption capacity confirmed its applicability in water treatment.

Novel nanostructured Fe-Cu-Al trimetal oxide for enhanced antimony(V) removal: synthesis, characterization and performance

Given the adverse health effects of antimony (Sb), there is an increased focus on developing methods to remove this toxic metal from contaminated water bodies. To effectively remove Sb(V), a new nanostructured Fe-Cu-Al trimetal oxide was fabricated using co-precipitation method at ambient temperature. The Fe-Cu-Al trimetal oxide was very effective at removing Sb(V) from water; it had a maximal adsorption capacity of 169.1 mg/g at pH 7.0, a capacity that was competitive with most other reported adsorbents. The obtained amorphous oxide had a high pH point of zero charge (pH_pzc = 8.8) and good adsorption Sb(V) efficiency over a wide pH range (4.0-8.0). Sb(V) uptake was achieved mainly through an ion-exchange reaction between Sb(V) ions and hydroxyl groups on the surface of the oxide. Given its good removal performance, high selectivity, and simple synthesis, this novel Fe-Cu-Al trimetal oxide offers a promising alternate for removing antimony contamination from aquatic environments.

Interaction of Arsenic Species with Organic Ligands: Competitive Removal from Water by Coagulation-Flocculation-Sedimentation (C/F/S)

The co-occurrence of arsenic (As) and organic ligands in water bodies has raised environmental concerns due to their toxicity and adverse effects on human health. The present study aims to elucidate the influences of hydrophobic/hydrophilic organic ligands, such as humic acid (HA) and salicylic acid (SA), on the interactive behavior of As species in water. Moreover, the competitive removal behaviors of As(III, V) species and total organic carbon (TOC) were systematically investigated by coagulation-flocculation-sedimentation (C/F/S) under various aqueous matrices. The results showed the stronger binding affinity of As(V) than As(III) species, with a higher complexation ability of hydrophobic ligands than hydrophilic. The media containing hydrophilic ligands require smaller ferric chloride (FC) doses to achieve the higher As(III, V) removal, while the optimum FC dose required for As(III) removal was found to be higher than that for As(V). Moreover, hydrophobic ligands showed higher TOC removal than hydrophilic ligands. The pronounced adverse effect of a higher concentration of hydrophobic ligands on the removal efficiencies of As(V) and TOC was observed. The adsorption of As(V) on Fe precipitates was better fitted with the Langmuir model but the Freundlich isotherm was more suitable for As(III) in the presence of hydrophilic SA. Moreover, TOC removal was substantially decreased in the As(V) system as compared to the As(III) system due to the dissolution of Fe precipitates at higher As(V) concentrations. The results of FC composite flocs demonstrated that the combined effect of oxidation, charge neutralization and adsorption played an important role in the removal of both toxicants during the C/F/S process. In summary, the findings of the present study provide insights into the fate, mobility and competitive removal behavior of As(III, V) species and organic ligands in the water treatment process.

Recyclable polyvinyl alcohol sponge containing flower-like layered double hydroxide microspheres for efficient removal of As(V) anions and anionic dyes from water

Layered double hydroxides (LDHs) are very promising adsorbents for the removal of anionic pollutants from water. However, the low adsorption efficiency and recycling difficulty of conventional LDH powders are obstacles to practical applications. Herein, a novel Zn/Fe-LDH composite sponge was successfully fabricated using a simple in-situ hydrothermal method. Characterization studies revealed that the composite sponge contained flower-like Zn/Fe LDH microspheres uniformly dispersed throughout a poly vinyl alcohol (PVA) sponge matrix. The specific surface area of the Zn/Fe-LDH composite sponge was 42.5 m² g^-1, approximately 5 times higher than the pristine PVA sponge (8.9 m² g^-1). Adsorption experiments revealed that Zn/Fe-LDH composite sponge exhibited a much higher adsorption ability for As(V) anions and methyl orange (MO) compared with a Zn/Fe-LDH powder or the pristine PVA sponge. The maximum adsorption capacity for As(V) was found to be 85.7 mg g^-1. Furthermore, the Zn/Fe-LDH composite sponge showed high thermal stability, good mechanical stability and easy recoverability, thereby allowing reuse. Results guide the development of improved, low cost water treatment materials.

Seasonal antimony pollution caused by high mobility of antimony in sediments: In situ evidence and mechanical interpretation

Antimony (Sb) mobilization in sediments and its impact on water quality remained to be studied. In this study, high-resolution dialysis (HR-Peeper) and diffusive gradients in thin films (DGT) technique were used to measure soluble Sb and labile Sb in sediment-overlying water profiles for a full year in a eutrophic region of Lake Taihu. Results showed that the highest mean concentrations of soluble Sb in overlying water (11.27 and 6.99 μg/L) appeared in December 2016 and January 2017, due to oxidation of Sb(III) to Sb(V) by Mn and Fe oxides, all of which exceeded the surface or drinking water limits set by China, United States and European Union. From April to November 2016, the concentrations of soluble Sb remained low with small monthly fluctuations and mean values ranging from 1.79 to 2.93 μg/L. This was attributed to the predominance of insoluble Sb(III) in sediments under anoxic conditions. The concentration of soluble Sb was slightly higher in summer than in autumn, due to the complexation of Sb(III) with DOM, as shown under anaerobic incubation. The mobility of inorganic Sb in sediments was mostly determined by the transition between Sb(III) and Sb(V), with Sb pollution in bottom water during winter being of concern.

Complexation of Antimony with Natural Organic Matter: Performance Evaluation during Coagulation-Flocculation Process

The presence of natural organic matter (NOM) in drinking water sources can stabilize toxic antimony (Sb) species, thus enhancing their mobility and causing adverse effects on human health. Therefore, the present study aims to quantitatively explore the complexation of hydrophobic/hydrophilic NOM, i.e., humic acid (HA), salicylic acid (SA), and L-cysteine (L-cys), with Sb in water. In addition, the removal of Sb(III, V) species and total organic carbon (TOC) was evaluated with ferric chloride (FC) as a coagulant. The results showed a stronger binding affinity of hydrophobic HA as compared to hydrophilic NOM. The optimum FC dose required for Sb(V) removal was found to be higher than that for Sb(III), due to the higher complexation ability of hydrophobic NOM with antimonate than antimonite. TOC removal was found to be higher in hydrophobic ligands than hydrophilic ligands. The high concentration of hydrophobic molecules significantly suppresses the Sb adsorption onto Fe precipitates. An isotherm study suggested a stronger adsorption capacity for the hydrophobic ligand than the hydrophilic ligand. The binding of Sb to NOM in the presence of active Fe sites was significantly reduced, likely due to the adsorption of contaminants onto precipitated Fe. The results of flocs characteristics revealed that mechanisms such as oxidation, complexation, charge neutralization, and adsorption may be involved in the removal of Sb species from water. This study may provide new insights into the complexation behavior of Sb in NOM-laden water as well as the optimization of the coagulant dose during the water treatment process.

Arsenic, antimony, and nickel leaching from northern peatlands treating mining influenced water in cold climate

Increased metal mining in the Arctic region has caused elevated loads of arsenic (As), antimony (Sb), nickel (Ni), and sulfate (SO₄^2-) to recipient surface or groundwater systems. The need for cost-effective active and passive mine water treatment methods has also increased. Natural peatlands are commonly used as a final step for treatment of mining influenced water. However, their permanent retention of harmful substances is affected by influent concentrations and environmental conditions. The effects of dilution, pH, temperature, oxygen availability, and contaminant accumulation on retention and leaching of As, Sb, Ni, and sulfate from mine process water and drainage water obtained from treatment peatlands in Finnish Lapland were studied in batch sorption experiments, and discussed in context of field data and environmental impacts. The results, while demonstrating effectiveness of peat to remove the target contaminants from mine water, revealed the risk of leaching of As, Sb, and SO₄^2- from treatment peatlands when diluted mine water was introduced. Sb was more readily leached compared to As while leaching of both was supported by higher pH of 9. No straightforward effect of temperature and oxygen availability in controlling removal and leaching was evident from the results. The results also showed that contaminant accumulation in treatment peatlands after long-term use can lead to decreased removal and escalated leaching of contaminants, with the effect being more pronounced for As and Ni.

Removal efficiency of As(V) and Sb(III) in contaminated neutral drainage by Fe-loaded biochar

Performance of raw and two Fe-loaded biochars, produced either by evaporation (E-product, 26.9% Fe) or precipitation (P-product, 12.6% Fe), was evaluated in batch and column testing for As(V) and Sb(III) removal from contaminated neutral drainage (CND). Batch testing results showed that sorption capacity of the E-product tripled for As(V) and quintupled for Sb(III), whereas for the P-product, it doubled for both contaminants, relative to the raw biochar. Moreover, As(V) removal by the E-product reached 90% in less than 8 h, for initial concentrations up to 50 mg/L. In column testing, the E-product efficiently treated the influent [pH 6; 1 mg/L As(V)] for more than 286 days. The pH of the final effluent was within the legally allowed limits (6-9.5) while less than 0.3 mg/L Fe leached out. Based on these findings, Fe-loaded biochar by evaporation (E-product) seems promising for As(V) treatment in CND.

Antimony Removal from Water by a Chitosan-Iron(III)[ChiFer(III)] Biocomposite

The presence of antimony(III) in water represents a worldwide concern, mainly due to its high toxicity and carcinogenicity potential. It can be separated from water by the use of sustainable biopolymers such as chitosan or its derivatives. The present study applied chitosan modified with iron(III) beads to Sb(III) removal from aqueous solutions. The resulting material performed with a high adsorption capacity of 98.68 mg/g. Material characterization consisted of Raman spectroscopy (RS), X-ray diffraction (XRD), scanning electron microscope observations (SEM-EDX), Fourier transform infrared spectroscopy (FTIR) and point of zero charge (pHpzc). The adsorption study included pH study, effect of initial concentration, kinetics, ion effect, and reusability assessment. The RS, XRD, and FTIR results indicated that the main functional groups in the composite were related to hydroxyl and amino groups, and iron oxyhydroxide species of α-FeO(OH). The pHpzc was found to be 7.41. The best adsorption efficiency was set at pH 6. The equilibrium isotherms were better fitted with a non-linear Langmuir model, and the kinetics data were fitted with a pseudo-second order rate equation. The incorporation of iron into the chitosan matrix improved the Sb(III) uptake by 47.9%, compared with neat chitosan (CS). The material did not exhibit an impact in its performance in the presence of other ions, and it could be reused for up to three adsorption⁻desorption cycles.

Adsorptive removal of lead from acid mine drainage using cobalt-methylimidazolate framework as an adsorbent: kinetics, isotherm, and regeneration

In this work, cobalt-methylimidazolate framework has been used as an adsorbent in the removal of Pb(II) from acid mine drainage in adsorption batch system. X-ray diffraction, Fourier-transform infrared spectroscopy, Brunauer-Emmet-Teller and transmission electron microscope were used for structural, morphological, and surface characteristics of cobalt-methylimidazolate framework. The concentration of heavy metal ions in water samples was measured by inductively coupled plasma optical emission spectrometry. Different experimental factors/variables (such as contact time, dosage, and pH) affecting the adsorption of Pb(II) from acid mine drainage were optimized by response surface methodology based on central composite design. Under optimized experimental parameters, the maximum adsorption capacity of Pb(II) was found to be 105 mg g^-1. The nature of the adsorption process was investigated using Langmuir and Freundlich isotherm models. The obtained data best fitted Langmuir isotherm model suggesting a homogeneous adsorption process. Furthermore, the adsorption mechanism was investigated using five kinetic models, that is, pseudo-first order, pseudo-second order, intraparticle diffusion and Elovich model. The adsorption data fitted better to pseudo-second-order followed by intra-particle diffusion kinetic models suggesting that the adsorption mechanism is dominated by both chemical and physical adsorption processes. The adsorbent could be regenerated up to 8 cycles and it was successfully used in the removal of lead in real acid mine drainage samples.

Uptake of Sb(V) by Nano Fe3O4-Decorated Iron Oxy-Hydroxides

The presence of antimony in water remains a major problem for drinking water technology, defined by the difficulty of available adsorbents to comply with the very low regulation limit of 5 μg/L for the dominant Sb(V) form. This study attempts to develop a new class of water adsorbents based on the combination of amorphous iron oxy-hydroxide with Fe3O4 nanoparticles and optimized to the sufficient uptake of Sb(V). Such a Fe3O4/FeOOH nanocomposite is synthesized by a two-step aqueous precipitation route from iron salts under different oxidizing and acidity conditions. A series of materials with various contents of Fe3O4 nanoparticles in the range 0–100 wt % were prepared and tested for their composition, and structural and morphological features. In order to evaluate the performance of prepared adsorbents, the corresponding adsorption isotherms, in the low concentration range for both Sb(III) and Sb(V), were obtained using natural-like water. The presence of a reducing agent such as Fe3O4 results in the improvement of Sb(V) uptake capacity, which is found around 0.5 mg/g at a residual concentration of 5 μg/L. The intermediate reduction of Sb(V) to Sb(III) followed by Sb(III) adsorption onto FeOOH is the possible mechanism that explains experimental findings.

Antimony speciation in the environment: Recent advances in understanding the biogeochemical processes and ecological effects

Antimony (Sb) is a toxic metalloid, and its pollution has become a global environmental problem as a result of its extensive use and corresponding Sb-mining activities. The toxicity and mobility of Sb strongly depend on its chemical speciation. In this review, we summarize the current knowledge on the biogeochemical processes (including emission, distribution, speciation, redox, metabolism and toxicity) that trigger the mobilization and transformation of Sb from pollution sources to the surrounding environment. Natural phenomena such as weathering, biological activity and volcanic activity, together with anthropogenic inputs, are responsible for the emission of Sb into the environment. Sb emitted in the environment can adsorb and undergo redox reactions on organic or inorganic environmental media, thus changing its existing form and exerting toxic effects on the ecosystem. This review is based on a careful and systematic collection of the latest papers during 2010-2017 and our research results, and it illustrates the fate and ecological effects of Sb in the environment.

Simultaneous removal of arsenic and antimony from mining wastewater using granular TiO2: Batch and field column studies

Coexisting arsenic (As) and antimony (Sb) in mining wastewater is a common and great concern. On-site simultaneous removal of As and Sb from mining wastewater was achieved by using a reusable granular TiO₂ column in this study. To evaluate the accuracy of the scale-up procedure, As and Sb adsorption from wastewater was studied in both large (600g TiO₂) and small columns (12g TiO₂) based on the proportional diffusivity rapid small-scale column tests (PD-RSSCTs) design. The comparable As and Sb breakthrough curves obtained from small and large columns confirmed the accuracy of the PD-RSSCT theory in the design of large-scale columns. Meanwhile, the consistent As and Sb adsorption results from batch and column experiments suggested that TiO₂ adsorption for As and Sb can be predicted from bench-scale tests. Charge distribution multi-site complexation (CD-MUSIC) and one-dimensional transport modeling integrated in the PHREEQC program were performed to study the adsorption behaviors of As and Sb on the TiO₂ surface. Coexisting ions, such as Ca²⁺, Mg²⁺, and Si⁴⁺, play an important role in As and Sb adsorption, and the breakthrough curves were well simulated after considering the compound ion effects. The results from this study highlight the surface reactions of As and Sb on TiO₂ and provide a practical way for on-site remediation of industrial wastewater.

Influences of As(v), Sb(iii), and Hg(ii) ions on the nucleation and growth of akaganeite

The physico-chemical properties of akaganeite are known to be modified when formed in the presence of ions, but there are no reports on these effects for arsenic, antimony and mercury.

Submicron fibers as a morphological improvement of amorphous zirconium oxide particles and their utilization in antimonate (Sb(v)) removal

Zirconium oxide was formed into submicron fibers to improve the Sb(v) separation performance compared to a conventional aggregate material.

Adsorption performance of antimony by modified iron powder

Antimony pollution resulting from industrial production is a great threat to the environment, ecology and the human body. Zero-valent iron powder is low-cost and easy to obtain. Nevertheless, the lower adsorption capacity limits its application when it is used as an adsorbent. In the present study, ball-milling and acid modification were developed to change its surface characteristics and γ-Fe₂O₃, γ-FeOOH and Fe₃O₄ were obtained after treatment, which promoted its adsorption capacity. Compared with the raw iron powder, the adsorption capacities for Sb(iii) and Sb(v) using the modified material were increased from 12.93 mg g⁻¹ and 5.47 mg g⁻¹ to 17.96 mg g⁻¹ and 10.58 mg g⁻¹, respectively. The study showed that the experimental data fitted the Langmuir model and the pseudo-first-order kinetic model better; the adsorption process was monolayer and chemically controlled at pH 5.0 ± 0.2. XPS and FT-IR analysis showed that Fe–O–Sb bonds arose during the adsorption process. The effect of pH on the adsorption capacity was also studied and the pH affected the adsorption of Sb(v) more than the adsorption of Sb(iii). In addition, the modified iron powder presented better efficiency when applied to the removal of low levels of antimony in drinking water. Based on the increase of adsorption capacity and low cost, iron powder should be a promising adsorbent for aqueous antimony removal.

Modified iron powders were obtained by ball-milling and acid modification and the adsorption behavior and mechanism for Sb(iii) and Sb(v) analyzed. The improved adsorption capacity and low cost show the application potential of the modified material.

An overview of main arsenic removal technologies

Arsenic (As) is metalloid, naturally present in the environment but also introduced by human activities. It is toxic and carcinogenic and its exposure to low or high concentrations can be fatal to human health. Arsenic contamination in drinking water threatens more than 150 million peoples all over the world. Therefore, treatment of As contaminated water is of unquestionable importance. The present review begins with an overview of As chemistry, distribution and toxicity, which are relevant aspects to understand and develop remediation techniques. The most common As removal processes (chemical precipitation, adsorption, ion exchange, membrane filtration, phytoremediation and electrocoagulation) are presented with discussion of their advantages, drawbacks and the main recent achievements.