Sb Adsorption Research Articles

Antimony immobilization mechanism on schwertmannite: Insights from the microstructure of schwertmannite

Schwertmannite affects the mobility of antimony (Sb) in acid mine drainage, yet the Sb sorption mechanism remains elusive. In this study, the molecular-level mechanism and the driving force of Sb(V) immobilized on schwertmannite were investigated by a combination of wet chemistry, extended X-ray absorption fine structure (EXAFS) analysis, density functional theory (DFT) calculations, and a surface complexation model (SCM). The observed sorption capacity for Sb(V) was as high as 235.63 mg/g. Such remarkable sorption capacity is primarily achieved by the anion exchange reaction and surface complexation reaction of Sb(V) with sulfate and surface/tunnel inner-surface hydroxyl groups, respectively, and the contribution of the anion exchange reaction to Sb(V) immobilization decreases markedly with increasing Sb(V) loading or pH. The loading of Sb(V) appears to be the key parameter controlling its immobilization mechanism on schwertmannite. Low-loaded Sb(V) primarily generates bidentate-mononuclear and bidentate-binuclear surface complexes (adsorption products) and is concurrently partly incorporated into the Fe-O framework of schwertmannite to form a hexadentate-hexanuclear complex (incorporation product). With increasing Sb(V) loading, Sb is primarily adsorbed on the surface and in the tunnel of schwertmannite with the formation of bidentate-mononuclear (dominant) and bidentate-binuclear complexes without incorporation. The inconsistency of the immobilization mechanism is controlled by the amount of released sulfate induced by Sb(V). The substantial system energy reduction caused by the formation of Sb(V) adsorption and incorporation products on the surface and in the tunnel of schwertmannite is the driving force for the stable immobilization of Sb(V) by schwertmannite, and the energy reduction caused by tunnel complexes is far more obvious than that caused by surface complexes. A charge distribution multisite complexation model was established based on bidentate-mononuclear and bidentate-binuclear surface complexes with fitted Log K values of 21.99 ± 0.18 and 12.84 ± 0.92, respectively, which consistently predicted Sb(V) sorption across pH 3.0–9.0 for all involved Sb(V) loadings. In addition, Sb(V) has a strong stabilizing effect on the schwertmannite structure and broadens its pH stability window (pH 3.0–9.0). This study facilitates elucidation of the fate and geochemical cycling of Sb in the mining environment and helps to promote the application of the microstructure of schwertmannite in other studies of microscopic interface chemistry.

Separable alginate gel spheres encapsulated with La-Fe modified biochar for efficient adsorption of Sb(III) with high capacity

Sb and its compounds have been widely used in various industrial applications. Therefore, the preparation of Sb adsorbents with easy recovery and excellent adsorption levels is an urgent problem that must be resolved. By calcining and treating La/Fe metal–organic frameworks (MOF) biochar as a precursor, a loaded La-Fe-modified water hyacinth biochar was synthesised and used as a filler to synthesise iron alginate composite gel spheres, MBC/algFe. Through a series of static adsorption experiments, the effects of different filler addition ratios, solution pH, reaction time, coexisting ions, and other factors on the adsorption of Sb(III) were investigated. According to the Langmuir model, the maximum adsorption capacity of MBC/algFe at 25 ℃ was 277.8 mg·g−1. The adsorption mechanism mainly involved hydrogen bonding and metal-organic complexation interactions.

Antimony(III) removal by biogenic manganese oxides formed by Pseudomonas aeruginosa PA-1: kinetics and mechanisms.

In this study, Pseudomonas aeruginosa PA-1, a manganese-oxidizing bacterium screened from the soil at a manganese mining area, was found to be tolerated to Sb(III) stress during the Mn(II) oxidation, and the generated biological manganese oxide (BMO) outperformed the identical type of Abiotic-MnOX in terms of oxidation and adsorption of Sb(III). Adsorption kinetics and isotherm experiments indicated that Sb(III) was primarily adsorbed through chemisorption and multilayer adsorption on BMO; the maximum adsorption capacity of BMO was 143.15mg·g-1. Removal kinetic studies showed that the Sb(III) removal efficiency by BMO was 72.38-95.71% after 15min, and it could be up to 96.32-98.31% after 480min. The removal procedure could be divided into two stages, fast (within 15min) and slow (15 ~ 480min), both of which exhibited first-order kinetic behavior. Dynamic fitting in two steps revealed that the removal speed correlated to the level of dissolved Sb(III) with low Sb(III) concentrations, but with the initial concentration being high, the removal speed rate was independent of dissolved Sb(III). During the whole process, the Sb(III) removal speed by BMO was also higher than that by the Abiotic-MnOX. Combining multiple spectroscopic techniques revealed that Sb(V) was generated through the Sb(III) oxidation by BMO and replacing surface metal hydroxyl groups to form the complex internal Mn-O(H)-Sb(V) or generating stable Mn(II)-antimonate precipitates on the surface. In addition, microbial metabolites, including tryptophan and humus, in BMO may be complex with Sb(III) and Sb(V) to achieve the treatment of Sb(III). This research investigates the factors and mechanisms influencing the adsorption and removal of Sb(III) by BMO, which could aid in its future engineering applications for the BMO.

Enhance antimony adsorption from aquatic environment by microwave-assisted prepared Fe3O4 nanospherolites.

A novel hierarchically nanostructured magnetite (Fe3O4) was manufactured using microwave-assisted reflux method without surfactants. The nanostructured Fe3O4 is formed via the co-precipitation of Fe(III) and Fe(II), followed by a nanocrystal aggregation-based mechanism. Moreover, the effects of solution pH, contact time, initial Sb concentration, coexisting anions, and recycle numbers on the adsorption of nanostructured Fe3O4 toward Sb were extensively examined in the batch adsorption tests. The results demonstrated that the obtained Fe3O4 exhibited excellent adsorption ability toward Sb with the maximum adsorption capacities of 154.2 and 161.1 mg.g-1 for Sb(III) and Sb(V), respectively. The prepared Fe3O4 could be easily regenerated and reused for adsorption/desorption studies multiple times without compromising the Sb adsorption ability. Further exploration indicated that the oxidation or reduction reactions infrequently occurred during Sb adsorption processes. The proposed hierarchically nanostructured Fe3O4 thus could be potentially used for sustainable and efficient antimony removal.

Autonomous enrichment and deep removal of heavy metals by salt-tolerant gradient polyelectrolyte hydrogels

The integration of nanostructured materials into hydrogel matrix with chemical gradient holds great promise in gathering the pollutants and enhancing their adsorption or photocatalytic performance. However, the electric potentials rooting in the common gradient polyelectrolyte hydrogel are almost completely shielded by the co-existing counter-ions. In this study, a salt-tolerant gradient polycationic electrolyte hydrogel was fabricated by free radical copolymerization under the induction of unilateral UV illumination, which was used as nanofillers matrix. The cation-π interactions between the adjacent cations and aromatic rings endow the gradient polycationic electrolyte hydrogels deserving the salt-tolerant properties. Thus, the build-in electric potentials are still reactive on enrichment of the anionic heavy metals in highly concentrated salt solutions, altering the defects of the common gradient polyelectrolyte hydrogel. Using Sb(V) adsorption and Cr(VI) photocatalytic reduction as target reactions, the gradient composite hydrogels always display fast and high removal capacities towards these anionic pollutants in the saline solutions of 500 mM, as well as good stability and reusability. This salt-tolerant hydrogel matrix provides a smart material platform with self-driven forces in the fields of pollutant enrichment and removal.

Investigating the potential of structurally defective UiO-66 for Sb (V) removal from tailing wastewater

Antimony contamination of tailings from the mining process remain attracted a great amount of concern. In this study, defective UiO-66-X crystal materials are rationally constructed using trifluoroacetic acid and hydrochloric acid as modulators for the removal of Sb(V) from actual tailing sand leachates. XRD and TG characterizations reveal that the number and kind of defects in UiO-66 are influenced by the type of modulators and the addition of trifluoroacetic acid makes UiO-66-TFA contain both cluster and ligand defects. Adsorption experiments show that UiO-66 and UiO-66-HCl achieve 100% removal of Sb(V) at pH 7.5 of the tailing sand leachate, and up to 90% removal of Sb(V) by the three materials at pH 2.5. It is noteworthy that the removal rate of Sb(V) by UiO-66-HCl is still satisfactory even under strongly acidic conditions at pH 0.5, with good potential for practical applications. Four kinetic models are used to fit the adsorption data and the analysis shows that the mechanism of Sb(V) adsorption by three adsorbent is all pseudo-second order and chemisorption acts as an important role in the adsorption process. In addition, the fixed bed adsorption experiments show that the material exhibit good prospects for practical applications.

Performance and mechanism of simultaneous Sb(III) and Cd(II) removal from water by Fe-Mn binary oxide/bone char.

A novel Fe-Mn binary oxide (FMBO)/bone char composite (FMBC) was synthesized and utilized to simultaneously adsorb Sb(III) and Cd(II) from aqueous phase in this study. The successful loading of Fe-Mn binary oxide on the bone char surface was revealed by the results of scanning electron microscope, X-ray diffraction patterns, and energy dispersive spectroscopy of FMBC. The FMBC exhibited remarkable ability of simultaneous removing Sb(III) and Cd(II) from aqueous, and the presence of Cd(II) enhanced Langmuir theoretical maximum adsorption capacity for Sb(III) significantly from 67.8 to 209.0mg/g. Besides, FMBC could efficiently remove Sb(III) and Cd(II) in the wide initial pH range of 2-7. The influences of ionic strength, co-existing anions, humic acid, and temperature on the adsorption of Sb(III) and Cd(II), and the application potential of FMBC in actual groundwater were investigated. The main mechanisms of Sb(III) and Cd(II) adsorption onto FMBC involved redox, electrostatic interaction, surface complexation, ion exchange, and precipitation. The result of X-ray photoelectron spectroscopy and mapping spectrum analysis revealed that Mn(III) on FMBC played the key role in the Sb(III) oxidation, while FeOOH worked as the adsorption sites of FMBC. Meanwhile, the hydroxyapatite on FMBC also contributed to the removal of Cd(II). The presence of Cd(II) not only increased the positive charge on the surface of FMBC but also formed the Fe-Sb-Cd ternary complex, promoting the removal of Sb. This work provides valuable information for the application of FMBO/bone char as a cost-effective adsorbent to remediate co-pollution of Sb(III) and Cd(II) in aqueous environment.

Antimony Isotope Fractionation Revealed from EXAFS during Adsorption on Fe (Oxyhydr)oxides.

A lack of knowledge about antimony (Sb) isotope fractionation mechanisms in key geochemical processes has limited its environmental applications as a tracer. Naturally widespread iron (Fe) (oxyhydr)oxides play a key role in Sb migration due to strong adsorption, but the behavior and mechanisms of Sb isotopic fractionation on Fe (oxyhydr)oxides are still unclear. Here, we investigate the adsorption mechanisms of Sb on ferrihydrite (Fh), goethite (Goe), and hematite (Hem) using extended X-ray absorption fine structure (EXAFS) and show that inner-sphere complexation of Sb species with Fe (oxyhydr)oxides occurs independent of pH and surface coverage. Lighter Sb isotopes are preferentially enriched on Fe (oxyhydr)oxides due to isotopic equilibrium fractionation, with neither surface coverage nor pH influencing the degree of fractionation (Δ123Sbaqueous-adsorbed). Limited Fe atoms are present in the second shell of Hem and Goe, resulting in weaker surface complexes and leading to greater Sb isotopic fractionation than with Fh (Δ123Sbaqueous-adsorbed of 0.49 ± 0.004, 1.12 ± 0.006, and 1.14 ± 0.05‰ for Fh, Hem, and Goe, respectively). These results improve the understanding of the mechanism of Sb adsorption by Fe (oxyhydr)oxides and further clarify the Sb isotope fractionation mechanism, providing an essential basis for future application of Sb isotopes in source and process tracing.

Removal of antimonite and antimonate in aqueous solution by mugwort biochar modified by Acidithiobacillus ferrooxidans after pyrolysis

In the research, iron oxides-biochar composites (ALBC) were prepared from pristine biochar modified by Acidithiobacillus ferrooxidans (A. ferrooxidans) and pyrolyzed at 500 °C and 700 °C in order to remove antimonite (Sb(III)) and antimonate (Sb(V)) from water. The results indicated that biochar prepared at 500 °C and 700 °C (ALBC500 and ALBC700) were loaded with Fe2O3 and Fe3O4, respectively. In bacterial modification systems, ferrous iron and total iron concentrations decreased continuously. The pH values of bacterial modification systems including ALBC500 increased first and then decreased to a stable state, while the pH values of bacterial modification systems with ALBC700 continued to decrease. The bacterial modification systems can facilitate the formation of more jarosites by A. ferrooxidans. ALBC500 had optimal adsorbing capacities for Sb(III) (18.81 mg·g−1) and Sb(V) (14.64 mg·g−1). The main mechanisms of Sb(III) and Sb(V) adsorption by ALBC were electrostatic interaction and pore filling.

Enhanced adsorption-oxidation of Sb(III) over chitosan bimetallic beads: In-situ generated O2•– and autocatalytic effect of Sb(III)

Recently, the oxidation-coupled adsorption technologies for Sb(III) detoxification as well as adsorption are of great concern. To develop a kind of material for not only improving the Sb(III) adsorption efficiency but also enabling the oxidation of the adsorbed Sb(III) with low reagent or energy consumption, we prepared a magnetite-cuprite@chitosan bead adsorbent (nMC@CS) using a one-step method. Batch experiments and characterization of the beads demonstrated that Sb(III) adsorption was highly dependent on the Fe3O4 nanoparticles in the beads, and the adsorbed Sb(III) was oxidized by the reactive oxygen species (ROS) generated in-situ upon activation of the dissolved oxygen by Cu(I). Importantly, the Sb(III) adsorbed onto the surface of the beads could effectively catalyze the redox cycles of Fe(III)/Fe(II) and Cu(II)/Cu(I) in the system through the generation of O2•– while being oxidized to Sb(V), forming a closed-loop circulation of electrons. This cyclic electron transfer facilitated the adsorption-oxidation process of Sb and further improved their synergistic efficiency. Under the optimal adsorption conditions, 97.4% of the Sb(III) in solution was adsorbed onto the nMC@CS, 84.3% of which was oxidized to Sb(V), providing a simple and promising strategy for efficient Sb(III) adsorption and simultaneous detoxification.

Adsorption capacity of Penicillium amphipolaria XK11 for cadmium and antimony

Heavy metal pollution is a global problem that affects both the environment and human health. Microorganisms play an important role in remediation. Most studies on the use of microorganisms for heavy metal remediation focus on single heavy metals. In this study, a strain of Penicillium amphipolaria, XK11 with high resistance to both antimony (Sb III) and cadmium (Cd II) was screened from the mineral slag. The strain also had a high phosphate solubilization capacity. The single-factor adsorption experiment results showed that the initial pH (pH0), adsorption time (T), and initial solution concentration (C0) all affected the adsorption of Sb and Cd by XK11. When the initial pH0 (Cd = 6, Sb = 4) and adsorption time (T = 7 d) were constant, XK11 achieved the maximum removal rate of Cd (45.6%) and Sb (34.6%). These results confirm that XK11 has potential as a biomaterial or remediation of Sb and Cd pollution.

Influential antimony removal from Aquatic Solution using Graphene Nanoplatelet/ Staphylococcus aureus as Novel Composite Adsorbent

Antimony (Sb) is one of the primary pollutants and its compounds and therefore its removal from wastewater and natural waters is significant using effective and eco-friendly adsorbents. Graphene nanoplatelets (GNP) are an important graphene derivative with a varying number of exfoliation cycles which is referred to as multi-layered or few-layered graphene. In this study, Staphylococcus aureus (S. aureus) was immobilized with GNP for adsorption of Sb(III) from the aquatic system. The batch study conditions, composite dosage (100–300 mg/L), Sb(III) initial concentration (1–300 mg/L), pH level (2–8), contact time (10–50 min), and temperature (24–60 °C) were optimized. The adsorption efficiency of the composite was also investigated for wastewater samples including ions K+, Cl−, Na+, Mg2+, Ca2+, NO3−, PO43−, SO42-, and several heavy metal ions. The factorial design is broadly utilized to estimate the statistical correlation among experimental variables and responses. The equilibrium data were studied for Langmuir and Freundlich isotherms under optimized adsorption conditions and the Langmuir adsorption capacity of (qm) of GNP/S. aureus composite was estimated as 116.1 mg g−1. The adsorption kinetic mechanism well followed the pseudo-second order model with a non-linear correlation coefficient (R2 = 0.999). The electrostatic, π–π interactions, and hydrogen bonding interactions as well as surface adsorption make feasible removal of Sb(III) ions onto GNP/S. aureus composite sorbent. The prepared GNP/S. aureus composite is a promising adsorbent to remove Sb(III) ions from aquatic systems.

Remediation of Sb-Contaminated Soil by Low Molecular Weight Organic Acids Washing: Efficiencies and Mechanisms

Low molecular weight organic acids (LMWOAs) are promising agents in the remediation of heavy metal contaminated soil with strong complexing ability and less environmental impact. However, the application of LMWOAs for washing the Sb-contaminated soil still faces great challenges, such as the selection of suitable washing agents, optimal washing parameters, and the unclear Sb removal mechanism. In this study, five suitable LMWOAs were screened from ten common washing agents and their optimum washing parameters were determined. The results showed that oxalic acid (OA) and HEDP were the top two outstanding agents, and the removal efficiencies of Sb were 68.79% and 49.73%, respectively, under optimal parameters (OA at 0.5 mol/L, HEDP at 0.2 mol/L, washing for 480 min, and the liquid-to-solid ratio of 15). The soil was analyzed for chemical speciation, morphology, functional groups, and mineralogy before and after washing. The results indicated that Fe/Al minerals in the soil are the main reason for the adsorption of Sb, and the possible mechanisms of Sb removal by LMWOAs included the dissolution of minerals, complexation reaction, and ligand exchange. Our findings highlight the potential application of LMWOAs as efficient washing agents to remove Sb from contaminated soils.

Insight into the reactions of antimonite with manganese oxides: Synergistic effects of Mn(III) and oxygen vacancies

Manganese oxides (MnxOy) are critical for determining the environmental behaviors and fate of antimonite (Sb(III)). However, little is known about the qualitative/quantitative connection between MnxOy structures and Sb(III) fate. Herein, the reactions of Sb(III) and six MnxOy with different structures were systematically investigated. The initial oxidation rates of Sb(III) (rinit) on six MnxOy decreased in the order of γ-MnO2>δ-MnO2>α-MnO2>γ-MnOOH>Mn3O4>β-MnO2 (pHinitial=7.0), from 0.32 ± 0.04 to 11.17 ± 1.61 mmol/min/mol-Mn. The amounts of antimony retained (i.e., the sum of Sb(III) and antimonate (Sb(V))) on these MnxOy followed the same trend as that of oxidation. Oxidation of Sb(III) released Mn(II) and created more sites for adsorption. Outwardly, MnxOy with higher reduction potential (E0) and specific surface area (SSA) favored faster Sb(III) oxidation. Inwardly, Mn(III) and oxygen vacancies (Ov) exhibited a synergistic effect on Sb(III) oxidation. Mn(III) can easier accept electron than Mn(IV) based on the change in Gibbs free energy calculation. Ov can adsorb free oxygen to form surface oxygen (Osur) which is much more reactive than lattice oxygen (Olatt). Moreover, Ov is in close proximity to Mn(III) in high-valent MnxOy which facilitated the reactions between Sb(III) and Mn(III) through the enhancement of Sb(III) adsorption and electron transfer. Ov in low-valent MnxOy is adjacent to Mn(II), thus it showed weaker enhancement than that in high-valent MnxOy. Part of δ-MnO2 and almost all Mn3O4 were converted to γ-MnOOH during their reaction with Sb(III), while the other four MnxOy were barely changed. The results obtained provide mechanistic insight into the reactions occurring within Sb(III) and MnxOy, which are helpful for better understanding and prediction of the fate of Sb(III) in Mn-rich environments.

Hierarchical Encapsulation and Rich sp2 N Assist Sb2Se3‐Based Conversion‐Alloying Anode for Long‐Life Sodium‐ and Potassium‐Ion Storage

Sodium‐ and potassium‐ion batteries have exhibited great application potential in grid‐scale energy storage due to the abundant natural resources of Na and K. Conversion‐alloying anodes with high theoretical capacity and low‐operating voltage are ideal option for SIBs and PIBs but suffer the tremendous volume variations. Herein, a hierarchically structural design and sp2 N‐doping assist a conversion‐alloying material, Sb2Se3, to achieve superior life span more than 1000 cycles. It is confirmed that the Sb2Se3 evolves into nano grains that absorb on the sp2 N sites and in situ form chemical bonding of C‐N‐Sb after initial discharge. Simulation results indicate that sp2 N has more robust interaction with Sb and stronger adsorption capacities to Na+ and K+ than that of sp3 N, which contributes to the durable cycling ability and high electrochemical activity, respectively. The ex situ transmission electron microscopy and X‐ray photoelectron spectroscopy results suggest that the Sb2Se3 electrode experiences conversion‐alloying dual mechanisms based on 12‐electron transfer per formula unit.

Efficient removal of antimonate and antimonite by a novel lanthanum-manganese binary oxide: Performance and mechanism.

Antimony is a highly toxic pollutant and its removal from water gains increasing attention. To effectively remove both Sb(III) and Sb(V), a novel lanthanum-manganese binary oxide (L1M2BO) adsorbent was synthesized by a simple oxidation coupled with precipitation method. The as-prepared L1M2BO was detailedly characterized by the XRD, SEM, TEM, BET, FTIR and XPS techniques. It is amorphous and irregular in shape, with a particle size of 50-100nm and a specific surface area of 180.4m2/g. A remarkable synergistic effect between the lanthanum hydroxide and Mn oxide in improving antimony adsorption is shown. The maximum adsorption capacities of Sb(III) and Sb(V) are 364.6mg/g and 131.1mg/g at pH 7.0, respectively, which outcompete most of reported adsorbents. The adsorption behaviors of antimony fitted well the pseudo-second-order kinetic and Freundlich models. The adsorption mechanism of Sb(V) involves mainly the replacement of surface metal hydroxyl and forming inner-sphere complex. While the Sb(III) removal is a more complicated process, containing both Sb(III) adsorption and oxidation to Sb(V). Furthermore, the spent L1M2BO sorbent can be regenerated and reused. The L1M2BO could be used as an attractive adsorbent for antimony removal, owing to its easily fabrication, high effectiveness and reusability.

Highly efficient adsorption of Sb(iii) and Sb(v) from water using a hybrid functional Zr–Fe metallic oxide composite

For the removal of highly toxic and non-degradable Sb(iii/v), one novelty hybrid functional Zr–Fe metallic oxide (HF-ZFOs) composite was successfully prepared, which exhibited high adsorption performance for the removal of Sb(iii/v) from water.

Antimony (Sb) isotopic signature in water systems from the world’s largest Sb mine, central China: Novel insights to trace Sb source and mobilization

The Xikuangshan (XKS) mine, the world’s largest antimony (Sb) mine, was chosen for a detailed Sb isotopic signature study owing to its historical Sb contamination of water systems. Hydrochemical data, in particularδ123Sb values, were analyzed to identify the Sb source and predominant geochemical processes that affect Sb mobilization in different waters. The δ123Sb values of waters from the XKS Sb mine range from − 0.20‰ to + 0.73‰. In particular, the δ123Sb values of the main Feishuiyan stream do not significantly vary (+0.19‰-+0.24‰), while those of groundwater in different aquifers (−0.08‰ to +0.73‰) and mine water in different adits (−0.20‰ to +0.37‰) vary over a wide range. The relationships between δ123Sb values and Sb concentrations indicate that a simple dilution of Sb and a weak Sb adsorption onto Fe/Mn suspended particles and sediments in the Feishuiyan stream may occur, oxidative weathering and leaching infiltration of Sb-containing waste rocks and slags may cause variations in the δ123Sb values in groundwater, and Sb mobilization in the mine water is influenced by a combination of processes (oxidative dissolution, adsorption of Fe/Mn (hydr)oxides, and mixing). A conceptual hydrogeochemical model was summarized to elucidate the Sb source and mobilization in water systems from the XKS Sb mine.

Fate of antimony contamination generated by road traffic – A focus on Sb geochemistry and speciation in stormwater ponds

Although antimony (Sb) contamination has been documented in urban areas, knowledge gaps remain concerning the contributions of the different sources to the Sb urban biogeochemical cycle, including non-exhaust road traffic emissions, urban materials leaching/erosion and waste incineration. Additionally, details are lacking about Sb chemical forms involved in urban soils, sediments and water bodies. Here, with the aim to document the fate of metallic contaminants emitted through non-exhaust traffic emissions in urban aquatic systems, we studied trace element contamination, with a particular focus on Sb geochemistry, in three highway stormwater pond systems, standing as models of surface environments receiving road-water runoff. In all systems, differentiated on the basis of lead isotopic signatures, Sb shows the higher enrichment factor with respect to the geochemical background, up to 130, compared to other traffic-related inorganic contaminants (Co, Cr, Ni, Cu, Zn, Cd, Pb). Measurements of Sb isotopic composition (δ123Sb) performed on solid samples, including air-exposed dusts and underwater sediments, show an average signature of 0.07 ± 0.05‰ (n = 25, all sites), close to the δ123Sb value measured previously in certified reference material of road dust (BCR 723, δ123Sb = 0.03 ± 0.05‰). Moreover, a fractionation of Sb isotopes is observed between solid and dissolved phases in one sample, which might result from Sb (bio)reduction and/or adsorption processes. SEM-EDXS investigations show the presence of discrete submicrometric particles concentrating Sb in all the systems, interpreted as friction residues of Sb-containing brake pads. Sb solid speciation determined by linear combination fitting of X-Ray Absorption Near Edge Structure (XANES) spectra at the Sb K-edge shows an important spatial variability in the ponds, with Sb chemical forms likely driven by local redox conditions: “dry” samples exposed to air exhibited contributions from Sb(V)–O (52% to 100%) and Sb(III)–O (<10% to 48%) species whereas only underwater samples, representative of suboxic/anoxic conditions, showed an additional contribution from Sb(III)–S (41% to 80%) species. Altogether, these results confirm the traffic emission as a specific source of Sb emission in surface environments. The spatial variations of Sb speciation observed along the road-to-pond continuum likely reflect a high geochemical reactivity, which could have important implications on Sb transfer properties in (sub)surface hydrosystems.

Adsorption and immobilization performance of pine-cone pristine and engineered biochars for antimony in aqueous solution and military shooting range soil: An integrated novel approach

Antimony (Sb–V), a carcinogenic metalloid, is becoming prevalent in water and soil due to anthropogenic activities. Biochar could be an effective remedy for Sb(V)-contaminated water and soil. In this study, we used pristine and engineered pinecone-derived biochar as an innovative approach for treating Sb(V)-contaminated water and shooting range soil. Biochar was produced from pine–cone waste (pristine biochar) and enriched with Fe and Al salts via saturation (engineered biochar). Adsorption tests in water revealed that iron-modified biochar showed higher adsorption capacity (8.68 mg g−1) than that of the pristine biochar (2.49 mg g−1) and aluminum-modified biochar (3.40 mg g−1). Isotherm and kinetic modeling of the adsorption data suggested that the adsorption process varied from monolayer to multilayer, with chemisorption as the dominant interaction mechanism between Sb(V) and the biochars. The post-adsorption study of iron-modified biochar by Fourier Transform Infrared (FTIR) and X-ray diffraction (XRD) further supported the chemical bonding and outer-sphere complexation of Sb(V) with Fe, N–H, O–H, C–O and CC components. The pristine and iron-modified biochars also successfully immobilized Sb(V) in a shooting range soil, more so in the latter. Subsequent sequential extractions and post-analysis by scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), and elemental dot mapping revealed that Sb in the treated soil transformed to a more stable form. It was concluded that iron-modified biochar could act as an efficient material for the adsorption and immobilization of Sb(V) in water and soil, respectively.