Mobility Of Sb Research Articles

Decomposition of waterside plants greatly affects the transformation and mobility of sedimentary antimony in water–sediment systems after emergency treatment: A microcosm study

Polyferric sulfate (PFS) coagulation has proven to be effective in addressing antimony (Sb) water pollution accidents; however, the impact of waterside plant decomposition on its effectiveness has not been adequately elucidated. This study investigated the effects of Alternanthera philoxeroides (AP) and Digitaria sanguinalis (DS) decomposition on Sb cycling after PFS treatment. Without plant decomposition, the Fe(OH)3 hydrolysate-associated Sb remained stable, and the sediment continued to exhibit Sb sink properties. Plant residue decomposition facilitated sedimentary Sb release, and DS decomposition had a greater impact than AP decomposition. The strong decomposition phases triggered abiotic/biotic reduction processes, leading to Fe(OH)3 dissolution and subsequent Sb(V) release. Concurrently, sulfate reduction and dissolved organic matter (DOM) release regulated Sb mobility. In addition, Sb(V) reduction occurred, and Sb(III) was elevated in the overlying water. The Sb(III) levels gradually decreased during the later aerobic stages, however, did not completely disappear within a short timeframe. Furthermore, the role of the sediment as an Sb sink was significantly hindered, maintaining relatively high levels of dissolved Sb. Sedimentary Sb speciation analysis revealed that plant decomposition induced a shift in Fe-oxyhydroxide-bound Sb to more bioavailable and stable fractions. Our results indicate that plant residue decomposition easily deteriorates PFS efficiency and increases the risk of secondary Sb pollution in water–sediment systems.

Antimony sorption to schwertmannite in acid sulfate environments

Schwertmannite is a poorly-crystalline Fe(III) oxyhydroxysulfate mineral that may control Sb(V) mobility in acid sulfate environments, including acid mine drainage and acid sulfate soils. However, the mechanisms that govern uptake of aqueous Sb(V) by schwertmannite in such environments are poorly understood. To address this issue, we examined Sb(V) sorption to schwertmannite across a range of environmentally-relevant Sb(V) loadings at pH 3 in sulfate-rich solutions. Antimony K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy revealed that Sb(V) sorption (at all loadings) involved edge and double-corner sharing linkages between SbVO6 and FeIIIO6 octahedra. The coordination numbers for these linkages indicate that sorption occurred by Sb(V) incorporation into the schwertmannite structure via heterovalent Sb(V)-for-Fe(III) substitution. As such, Sb(V) sorption to schwertmannite was not limited by the abundance of surface complexation sites and was strongly resistant to desorption when exposed to 0.1 M PO43-. Sorption of Sb(V) also conferred increased stability to schwertmannite, based on changes in the schwertmannite dissolution rate during extraction with an acidic ammonium oxalate solution. This study provides new insights into Sb(V) sorption to schwertmannite in acid sulfate environments, and highlights the role that schwertmannite can play in immobilizing Sb(V) within its crystal structure.

Activated carbon as a strong DOM adsorbent mitigates antimony and arsenic release in flooded mining-impacted soils

In Southern China, the co-occurrence of arsenic (As) and antimony (Sb) contamination in soils around Sb mines presents an environmental challenge. During the flooding period of mining-impacted soils, anaerobic reduction of iron (Fe) oxides enhances the mobilization and bioavailability of Sb and As, further elevating the risk of Sb and As entering the food chain. To address this problem, activated carbon (AC) and biochar (BC) were applied to remediate flooded mining-impacted soils. Our results explored that AC can significantly decrease mobilization by 9–97 % for Sb and 9–67 % for As through inhibiting Fe(III) mineral reduction and dissolution in flooded soils. In contrast, there was no significant effect of BC. This was attributed to the strong adsorption of soil dissolved organic matter (DOM) by AC compared to BC, while DOM as electron shuttle is crucial for microbial Fe(III) reduction. Consequently, the DOM sequestration by AC effectively mitigates Sb and As leaching in contaminated mining soils.

Mobilization and transformation of antimony in stibnite by microbial induced oxidation in mining environment

Elevated concentrations of antimony (Sb) in environmental and biological systems due to mining activities are of particular global concern. Microorganisms play a crucial role in the oxidation process of metallic sulfide minerals, leading to the release of metal ions into surrounding soil or water systems. However, the mechanisms and potential environmental effects of microbial induced oxidation of stibnite (Sb2S3) in mine environment remain unclear. In this study, compared with the abiotic controls, the microbial community screened from the highly contaminated soil of the Xikuangshan antimony mine in aerobic experiments did not promote Sb mobilization as expected. However, they had a significant effect on the morphology and species of oxidation products of Sb2S3 by mediating the oxidation of Sb(III) and sulfide on surface and in solution. These naturally coexisting bacteria could partially oxidize Sb2S3 to Sb(V) and SO42− directly on the mineral surface, completely oxidize the dissolved Sb(III) to Sb(V), facilitate the oxidation of S0 to S2O32−, and form the secondary Sb(V)-bearing mineral [NaSb(OH)6]. These findings support the important role of microorganisms in the mobilization and transformation of Sb from minerals/rocks in the mining environment and provide further insight into their potential environmental impacts and effective mitigation strategies.

Manganese reductive dissolution coupled to Sb mobilization in contaminated shooting range soil

A “redox-stat” RMnR bioreactor was employed to simulate moderately reducing conditions (+ 420 mV) in Sb-contaminated shooting range soils for approximately 3 months, thermodynamically favoring Mn(IV) reduction. The impact of moderately reducing conditions on elemental mobilization (Mn, Sb, Fe) and speciation [Sb(III) versus Sb(V); Fe2+/Fe3+] was compared to a control bioreactor RCTRL without a fixed redox potential. In both bioreactors, reducing conditions were accompanied by an increase in effluent Sb(V) and Mn(II) concentrations, suggesting that Sb(V) was released through microbial reduction of Mn oxyhydroxide minerals. This was underlined by multiple linear regression analysis showing a significant (p < 0.05) relationship between Mn and Sb effluent concentrations. Mn concentration was the sole variable exhibiting a statistically significant effect on Sb in RMnR, while under the more reducing conditions in RCTRL, pH and redox potential were also significant. Analysis of the bacterial community composition revealed an increase in the genera Azoarcus, Flavisolibacter, Luteimonas, and Mesorhizobium concerning the initial soil, some of which are possible key players in the process of Sb mobilization. The overall amount of Sb released in the RMnR (10.40%) was virtually the same as in the RCTRL (10.37%), which underlines a subordinate role of anoxic processes, such as Fe-reductive dissolution, in Sb mobilization. This research underscores the central role of relatively low concentrations of Mn oxyhydroxides in influencing the fate of trace elements. Our study also demonstrates that bioreactors operated as redox-stats represent versatile tools that allow quantifying the contribution of specific mechanisms determining the fate of trace elements in contaminated soils.Key points• “Redox-stat” reactors elucidate Sb mobilization mechanisms• Mn oxyhydroxides microbial reductive dissolution has a major role in Sb mobilization in soils under moderately reducing conditions• Despite aging the soil exhibited significant Sb mobilization potential, emphasizing persistent environmental effects

Effect of freeze-thaw frequency plus rainfall on As and Sb metal(loid)s leaching from the solidified/stabilized soil remediated with Fe-based composite agent

The composite agent of ferrous sulfate, fly ash, and calcium lignosulfonate (FFC) can remediate the soil contaminated by As and Sb under cyclic freeze-thaw (F-T) via stabilization/solidification (S/S). However, the impact of high-frequency F-T cycles on the leaching behavior and migration of As and Sb in FFC-treated soils remains unclear. Here the leaching concentrations, heavy metal speciation (Wenzel's method), and Hydrus-1d simulations were investigated. The results showed that FFC effectively maintained the long-term S/S efficiency of arsenic remediation subject to an extended rainfall and freeze-thaw cycles, and stabilized the easily mobile form of As. The short-term S/S effect on Sb in the remediated soils suffering from F-T cycles was demonstrated in the presence of FFC. In a 20-year span, the mobility of Sb was affected by the number of F-T cycles (FT60 > FT20 > FT40 > FT0) in soil with a depth of 100 cm. As leaching progressed, FFC slowed the upward proportion of adsorbed As fractions but converted parts of the residual Sb to the form of crystalline Fe/Al (hydro) oxide. Moreover, the adsorption rate and capacity of As also preceded that of Sb. Long-term curative effects of FFC could be observed for As, but further development of agents capable of remedying Sb under cyclic F-T and long-term rainfall was needed. The predictive results on the migration and leaching behavior of heavy metals in S/S remediated soils may provide new insight into the long-term assessment of S/S under natural conditions.

Antimony mobility in soil near historical waste rock at the world's largest Sb mine, Central China

Soil near waste rock often contains high concentrations of antimony (Sb), but the mechanisms that mobilize Sb in a soil closely impacted by the waste rock piles are not well understood. We investigated these mobility mechanisms in soils near historical waste rock at the world's largest Sb mine. The sequential extraction (BCR) of soil reveal that over 95 % Sb is present in the residual fraction. The leached Sb concentration is related to the surface protonation and deprotonation of soil minerals. SEM-EDS shows Sb in the soil is associated with Fe and Ca. Moreover, X-ray absorption spectroscopy (XAS) results show Sb is predominantly present as Sb(V) and is associated with Fe in the form of tripuhyite (FeSbO4) as well as edge- and corner-sharing complexes on ferrihydrite and goethite. Thus, Fe in soils is important in controlling the mobility of Sb via surface complexation and co-precipitation of Sb by Fe oxides. The initially surface-adsorbed Sb(V) or co-precipitation is likely to undergo a phase transformation as the Fe oxides age. In addition, Sb mobility may be controlled by small amounts of calcium antimonate. These results further the understanding of the effect of secondary minerals in soils on the fate of Sb from waste rock weathering and inform source treatment for Sb-contaminated soils.

Functional features of a novel Sb(III)- and As(III)-oxidizing bacterium: Implications for the interactions between bacterial Sb(III) and As(III) oxidation pathways

Antimony (Sb) and arsenic (As) share similar chemical characteristics and commonly coexist in contaminated environments. It has been reported that the biogeochemical cycles of antimony and arsenic affect each other. However, there is limited understanding regarding microbial coupling between the biogeochemical processes of antimony and arsenic. Here, we aimed to solve this issue. We successfully isolated a novel bacterium, Shinella sp. SbAsOP1, which possesses both Sb(III) and As(III) oxidase, and can effectively oxidize both Sb(III) and As(III) under aerobic and anaerobic conditions. SbAsOP1 exhibits greater aerobic oxidation activity for the oxidation of As(III) or Sb(III) compared to its anaerobic activity. SbAsOP1 also significantly catalyzes the oxidative mobilization of solid-phase Sb(III) under aerobic conditions. The activity of SbAsOP1 in oxidizing solid Sb(III) is 3 times lower than its activity in oxidizing soluble form. It is noteworthy that, in the presence of both Sb(III) and As(III) under aerobic conditions, either As(III) or Sb(III) significantly inhibits the oxidation of Sb(III) or As(III), respectively. In comparison, under anaerobic conditions and in the coexistence of Sb(III) and As(III), As(III) significantly inhibits Sb(III) oxidation, whereas Sb(III) almost completely inhibits As(III) oxidation. These findings suggest that under both aerobic and anaerobic conditions, SbAsOP1 demonstrates a partial preference for Sb(III) oxidation. Additionally, bacterial oxidations of Sb(III) and As(III) mutually inhibit each other to varying degrees. These observations gain a novel understanding of the interplay between the biogeochemical processes of antimony and arsenic.

Biogeochemical mechanisms of zero-valent iron and biochar for synergistically mitigating antimony uptake in rice

Antimony (Sb) contamination in paddy fields can lead to its accumulation in rice grains, posing a threat to food safety. To address this issue, the combined use of zero-valent iron (ZVI) and biochar (BC) were applied to decrease the uptake of Sb in Sb-polluted soils, and their effects on Sb uptake from soil to rice grains were investigated. Our results showed that the combination treatment of 0.05 % ZVI and 0.095% BC resulted in a significant decrease (42.8%) in Sb accumulation in rice grains that was comparably more efficient than that by 0.05% ZVI (decrease of 15.8% Sb accumulation) or 0.095% BC (decrease of 12.7% Sb accumulation) alone, demonstrating the synergistic effect of ZVI and BC on mitigating Sb uptake by rice plants. ZVI presence resulted in the formation of iron oxides in the soil and on root surfaces, and the S2−/S22− ascent also increased by 58.7% on day 75 compared with that of the control, facilitating the reduction of Sb(V) to less mobile Sb(III), thereby decreasing Sb accumulation in rice plants. BC initially increased the mobility of Sb owing to its alkaline nature, whereas the electron shuttle properties of BC contributed to a decrease in Sb mobility. The abundance of the arsenite-reducing gene arrA ultimately increased by 203.2% on day 120 compared with the initial phase on day 5, and BC caused a remarkable increase in arrA gene abundance. This study revealed the synergistic mechanisms by combining ZVI and BC to mitigate Sb uptake by rice, which may be useful for the sustainable remediation of contaminated rice paddies.

Antimony isotope fractionation during Sb(V) and Sb(III) adsorption on secondary Fe-minerals (schwertmannite, ferrihydrite) typical of mine waters

The application of antimony (Sb) isotopes as tracers for Sb environmental cycling is currently limited. Indeed, there is a lack of knowledge of isotope fractionation factors associated with key (bio-) geochemical processes controlling its behaviour in surface environments. This study investigated the equilibrium isotope fractionation generated by Sb(V) and Sb(III) sorption on two iron minerals typical of acid mine drainage (AMD) impacted streams, ferrihydrite and schwertmannite, under controlled conditions of pH and solid to liquid ratio. Sorption behaviour and Sb isotope fractionation were similar for the different mineral phases and Sb oxidation degrees, with fractionation factors Δ123Sbsolid-solution of −0.25 ± 0.08 ‰ for Sb(III) and −0.34 ± 0.08 ‰ for Sb(V) adsorbed on ferrihydrite and −0.36 ± 0.06 ‰ for Sb(III) and −0.27 ± 0.03 ‰ for Sb(V) adsorbed on schwertmannite. The pH and initial Fe:Sb ratio did not significantly affect the Δ123Sbsolid-solution value under the experimental conditions. The light 121Sb isotope was preferentially adsorbed on the mineral phases, following an equilibrium closed system between dissolved and adsorbed Sb species. This fractionation may be related to the apparition of iron as the second closest neighbour which distorts the Sb(OH)3 or Sb(OH)6- atomic polyhedron. This study confirms that Sb equilibrium isotope fractionation occurs during sorption of Sb(III) and Sb(V) onto secondary iron minerals and suggests that the pH and redox of Sb do not exert significant effect. pH and redox conditions are important parameters which control Sb mobility in AMD streams, therefore, the study provides data for interpreting Sb isotope signatures in mine waters.

Enhanced magnetic anisotropy and high hole mobility in magnetic semiconductor Ga1-x-y Fe x Ni y Sb

(Ga,Fe)Sb is a promising magnetic semiconductor (MS) for spintronic applications because its Curie temperature (T C) is above 300 K when the Fe concentration is higher than 20%. However, the anisotropy constant K u of (Ga,Fe)Sb is below 7.6 × 103 erg/cm3 when Fe concentration is lower than 30%, which is one order of magnitude lower than that of (Ga,Mn)As. To address this issue, we grew Ga1-x-y Fe x Ni y Sb films with almost the same x (≈24%) and different y to characterize their magnetic and electrical transport properties. We found that the magnetic anisotropy of Ga0.76-y Fe0.24Ni y Sb can be enhanced by increasing y, in which K u is negligible at y = 1.7% but increases to 3.8 × 105 erg/cm3 at y = 6.1% (T C = 354 K). In addition, the hole mobility (µ) of Ga1-x-y Fe x Ni y Sb reaches 31.3 cm2/(V∙s) at x = 23.7%, y = 1.7% (T C = 319 K), which is much higher than the mobility of Ga1-x Fe x Sb at x = 25.2% (µ = 6.2 cm2/(V∙s)). Our results provide useful information for enhancing the magnetic anisotropy and hole mobility of (Ga,Fe)Sb by using Ni co-doping.

Effect of uniaxial strain on Hole mobility of Sb&lt;sub&gt;2&lt;/sub&gt;Se&lt;sub&gt;3&lt;/sub&gt;

Antimony selenide (Sb&lt;sub&gt;2&lt;/sub&gt;Se&lt;sub&gt;3&lt;/sub&gt;) is a simple-phase, element-rich, and economically friendly material for solar cell absorption layers, with broad application prospects. However, the weak conductivity of Sb&lt;sub&gt;2&lt;/sub&gt;Se&lt;sub&gt;3&lt;/sub&gt; has become a significant factor limiting the performance of solar cell devices. Carrier mobility is an important electrical parameter for both materials and devices, and strain can change carrier mobility. Therefore, studying the effect of strain on the carrier mobility of Sb&lt;sub&gt;2&lt;/sub&gt;Se&lt;sub&gt;3&lt;/sub&gt; is of practical significance. In this work, using density functional theory and deformation potential theory, we systematically investigate the influence of uniaxial strain on the band structure, bandgap width, iso-surface, and effective mass of Sb&lt;sub&gt;2&lt;/sub&gt;Se&lt;sub&gt;3&lt;/sub&gt;. We analyze the effects of three types of uniaxial strains along the &lt;i&gt;x-&lt;/i&gt;, &lt;i&gt;y-&lt;/i&gt;, and &lt;i&gt;z-&lt;/i&gt;direction on the carrier mobilities along the &lt;i&gt;x-&lt;/i&gt;, &lt;i&gt;y-&lt;/i&gt;, and &lt;i&gt;z-&lt;/i&gt;direction, which are denoted by &lt;i&gt;μ&lt;/i&gt;&lt;sub&gt;&lt;i&gt;x&lt;/i&gt;&lt;/sub&gt;, &lt;i&gt;μ&lt;/i&gt;&lt;sub&gt;&lt;i&gt;y&lt;/i&gt;&lt;/sub&gt;, and &lt;i&gt;μ&lt;/i&gt;&lt;sub&gt;&lt;i&gt;z&lt;/i&gt;&lt;/sub&gt;, respectively. It is found that under these strains, the valence band maximum (VBM) position of Sb&lt;sub&gt;2&lt;/sub&gt;Se&lt;sub&gt;3&lt;/sub&gt; remains unchanged, and the bandgap decreases with the increase of strain along the &lt;i&gt;y&lt;/i&gt;- and &lt;i&gt;z&lt;/i&gt;-direction, while it increases along the &lt;i&gt;x-&lt;/i&gt;direction. The variation in bandgap may be related to the coupling strength between the Sb-5p orbital and Se-4p orbital of the conduction band minimum (CBM). For fully relaxed Sb&lt;sub&gt;2&lt;/sub&gt;Se&lt;sub&gt;3&lt;/sub&gt;, its iso-surface exhibits a distorted cylindrical shape, with low dispersion along the &lt;i&gt;z&lt;/i&gt;-axis and high dispersion along the &lt;i&gt;x&lt;/i&gt;- and &lt;i&gt;y&lt;/i&gt;-axis, where &lt;i&gt;μ&lt;/i&gt;&lt;sub&gt;&lt;i&gt;x&lt;/i&gt;&lt;/sub&gt; is greater than &lt;i&gt;μ&lt;/i&gt;&lt;sub&gt;&lt;i&gt;y&lt;/i&gt;&lt;/sub&gt; and &lt;i&gt;μ&lt;/i&gt;&lt;sub&gt;&lt;i&gt;z&lt;/i&gt;&lt;/sub&gt;, suggesting that the &lt;i&gt;x&lt;/i&gt;-direction should be considered as the specific growth direction for Sb&lt;sub&gt;2&lt;/sub&gt;Se&lt;sub&gt;3&lt;/sub&gt; experimentally. When the strain is applied along the &lt;i&gt;x&lt;/i&gt;- and &lt;i&gt;z&lt;/i&gt;-direction, &lt;i&gt;μ&lt;/i&gt;&lt;sub&gt;&lt;i&gt;x&lt;/i&gt;&lt;/sub&gt; gradually increases with strain increasing, while it decreases when the strain is applied along the &lt;i&gt;y-&lt;/i&gt;direction. Taking into account the combined effects of strain on bandgap, iso-surface, density of states, and mobility, this study suggests that the optimal performance of Sb&lt;sub&gt;2&lt;/sub&gt;Se&lt;sub&gt;3&lt;/sub&gt; solar cell absorber layer material can be realized when the strain is applied along the &lt;i&gt;y&lt;/i&gt;-axis, with a compressive strain of 3%.

Antimony(V) behavior during the Fe(II)-induced transformation of Sb(V)-bearing natural multicomponent secondary iron mineral under acidic conditions

Fe(II)-induced phase transformations of secondary iron minerals have attracted considerable attention due to their influence on antimony (Sb) mobility. However, Fe(II)-induced natural multicomponent secondary iron mineral (nmSIM) transformations and the corresponding repartitioning of Sb on nmSIM under acidic conditions upon Fe(II) exposure have not been systematically examined. Herein, we investigated the effect of Fe(II) on nmSIM mineralogy and Sb mobility in Sb(V)-bearing nmSIM at pH 3.8 and 5.6 at various Fe(II) concentrations over 15 d. The Sb(V)-bearing nmSIM phase transformation occurred under both strongly and weakly acidic conditions without Fe(II) exposure, while the presence of Fe(II) significantly intensified the transformation, and substantial amounts of intermediary minerals, including jarosite, ferrihydrite, lepidocrocite and fougerite, formed during the initial reaction stage, especially at pH 5.6. X-ray diffraction (XRD) analyses confirmed that goethite and hematite were the primary final-stage transformation products of Sb(V)-bearing nmSIM, regardless of Fe(II) exposure. Throughout the Sb(V)-bearing nmSIM transformation at pH 3.8, Sb release was inversely related to the Fe(II) concentration in the initial stage, and after maximum release was achieved, Sb was gradually repartitioned onto the nmSIM. No Sb repartitioning occurred in the absence of Fe(II) at pH 5.6, but the introduction of Fe(II) suppressed Sb release and improved Sb repartitioning on nmSIM. This transformation was conducive to Sb reimmobilization on Sb(V)-bearing nmSIM due to the structural incorporation of Sb into the highly crystalline goethite and hematite generated by the Sb(V)-bearing nmSIM transformation, and no reduction of Sb(V) occurred. These results imply that Fe(II) can trigger mineralogical changes in Sb(V)-bearing nmSIM and have important impacts on Sb partitioning under acidic conditions. These new insights are essential for assessing the mobility and availability of Sb in acid mine drainage areas.

The fate of Sb(V) and As(V) during the aging of ferrihydrite

Iron (oxyhydr)oxides, especially ferrihydrite (Fh), abundant in the natural environment, are frequently applied in controlling the migration of heavy metals like antimony (Sb) and arsenic (As) in contaminated soils. However, little is known about the mobility and fate of Sb and As during the aging of Fh. In this study, we investigated the competitive adsorption between Sb(V) and As(V), the mineralogical transformation of Fh, and the redistribution of Sb(V)/ As(V) during the accelerated aging process of Fh. Our results showed that As(V) inhibited Sb(V) adsorption at the same concentration, but Sb(V) had no discernable influence on As(V) adsorption, suggesting As(V) had a stronger affinity to Fe minerals. XRD patterns showed that Fh was transformed into hematite or goethite in the presence of 25 mg/L Sb(V), but the transformation was inhibited in the presence of 25 mg/L As(V). Regarding the redistribution, the mobility of Sb(V) appeared to decrease probably via incorporation into Fe minerals during aging, and Fe minerals could host at least 20 % (w/w) Sb(V) in the low-mobility pool. As for As(V), the transformation of Fh was impeded resulting in high proportions of As(V) retained in high-mobility pool, with only 1.6 % (w/w) As(V) in the low-mobility pool. Our findings highlighted the differential behaviors of Sb(V) and As(V) during the adsorption and aging process on Fe oxide materials. These insights contributed to a deeper understanding of the mobility and fate of co-existing Sb(V) and As(V) in contaminated soils and offered practical guidance for their remediation using Fe oxide materials.

Antimony isotopic fractionation during Sb(III) oxidation to Sb(V): Biotic and abiotic processes

Oxidation of antimonite (Sb(III)) to antimonate (Sb(V)) plays an important role in the control of Sb mobility in aquatic systems. Fractionation of Sb isotopes (123Sb/121Sb) during Sb(III) oxidation has been investigated in the present study at concentrations relevant to mining environments. The isotopic composition (δ123Sb) of dissolved Sb(III) and Sb(V) species was analysed during biotic oxidation of Sb(III) at pH 6 and ∼ 0.1 mM Sb. Biotic experiments used a aioA gene carrier bacterial strain of the genus Ensifer isolated from Sb-rich river sediments. Chemical oxidation experiments with H2O2 were also conducted either in NaNO3 or HCl medium. During biotic oxidation, the Sb(V) produced was enriched in the light isotope compared to Sb(III), with an apparent fractionation factor Δ123SbSb(V)-Sb(III) of −0.20 ± 0.07 ‰. The Δ123Sb value was independent of the oxidation kinetics within the range 0.03 to 0.05 μmol.L−1.min−1; the fractionation observed was rather attributed to kinetic effect that weakens over time in the experiments, although this hypothesis would require further investigation. During abiotic experiments in NaNO3 medium, the Sb(V) produced was not isotopically fractionated relatively to Sb(III), while in HCl medium, the Sb(V) produced was enriched with the heavier isotope relatively to Sb(III), with a Rayleigh fractionation factor ε123Sb of +0.30 ± 0.05 ‰. These differences were attributed to different reaction pathways involving multi-step reactions and either hydroxy- or chloride-Sb species. Altogether, these results showed a low fractionation of Sb isotopes during Sb(III) oxidation, although significant variability occurred according to experimental conditions. Further experimental research and confrontation with natural systems is necessary before applying Sb isotopes as process tracer in water.

Antimony and arsenic behaviour in lead/zinc mine tailings during storage under vegetation cover

The high-volume, fine grained tailings produced from Pb/Zn ore processing need to be carefully managed. Metalloid elements, As and Sb, are present in tailings at ∼800 and ∼80 mg kg−1 respectively, and in neutral pH leachates at 5–50 μg L−1. Despite these relatively low leachate concentrations, As and Sb can cause regulatory concern due to their high toxicity and propensity for bioaccumulation. As and Sb mobility in tailings are controlled by their chemical speciation and associations with mineral phases. Changes in As and Sb speciation were, therefore, determined in depth profile samples taken from an active tailings management facility during waste storage up to 8 years since deposition. At this site, primarily to prevent dust formation, a vegetation cover was established by addition of organic compost to surface layers and seeding grasses. Over time a robust vegetation cover was established consisting of perennial grasses, clovers, and after 8 years, small trees and shrubs. The surface layer of the tailings also became progressively more oxidised over time producing a substrate more suitable for plant growth enabling the establishment of beneficial vegetation cover and the development of a thin soil-like surface layer. As and Sb were both present in predominately reduced 3+ forms in freshly deposited tailings but were converted to oxidised 5+ forms in older samples. Oxidation of Fe(II) in pyrite also occurred, producing increased amounts of weak acid leachable Fe(III)-oxides in the tailings. Sorption of As to neoformed iron oxides in leachate drains reduced concentrations in leachates to below regulatory limits, but Sb sorption was relatively ineffective resulting in higher Sb concentration in site drainage waters, which may require specific treatments to reduce Sb concentrations prior to discharge.

Compost, plants and endophytes versus metal contamination: choice of a restoration strategy steers the microbiome in polymetallic mine waste

Finding solutions for the remediation and restoration of abandoned mining areas is of great environmental importance as they pose a risk to ecosystem health. In this study, our aim was to determine how remediation strategies with (i) compost amendment, (ii) planting a metal-tolerant grass Bouteloua curtipendula, and (iii) its inoculation with beneficial endophytes influenced the microbiome of metal-contaminated tailings originating from the abandoned Blue Nose Mine, SE Arizona, near Patagonia (USA). We conducted an indoor microcosm experiment followed by a metataxonomic analysis of the mine tailings, compost, and root samples. Our results showed that each remediation strategy promoted a distinct pattern of microbial community structure in the mine tailings, which correlated with changes in their chemical properties. The combination of compost amendment and endophyte inoculation led to the highest prokaryotic diversity and total nitrogen and organic carbon, but also induced shifts in microbial community structure that significantly correlated with an enhanced potential for mobilization of Cu and Sb. Our findings show that soil health metrics (total nitrogen, organic carbon and pH) improved, and microbial community changed, due to organic matter input and endophyte inoculation, which enhanced metal leaching from the mine waste and potentially increased environmental risks posed by Cu and Sb. We further emphasize that because the initial choice of remediation strategy can significantly impact trace element mobility via modulation of both soil chemistry and microbial communities, site specific, bench-scale preliminary tests, as reported here, can help determine the potential risk of a chosen strategy.

Mobility of antimony in contrasting surface environments of a mine site: influence of redox conditions and microbial communities.

Microbial processes can influence the complex geochemical behaviour of the toxic metalloid antimony (Sb) in mining environments. The present study is aimed to evaluate the influence of microbial communities on the mobility of Sb from solid phases to water in different compartments and redox conditions of a mining site in southwest (SW) Spain. Samples of surface materials presenting high Sb concentrations, from two weathered mining waste dumps, and an aquatic sediment were incubated in slurries comparing oxic and anoxic conditions. The initial microbial communities of the three materials strongly differed. Incubations induced an increase of microbial biomass and an evolution of the microbial communities' structures and compositions, which diverged in different redox conditions. The presence of active bacteria always influenced the mobility of Sb, except in the neutral pH waste incubated in oxic conditions. The effect of active microbial activities in oxic conditions was dependent on the material: Sb oxic release was biologically amplified with the acidic waste, but attenuated with the sediment. Different bacterial genera involved in Sb, Fe and S oxidation or reduction were present and/or grew during incubation of each material. The results highlighted the wide diversity of microbial communities and metabolisms at the small geographic scale of a mining site and their strong implication in Sb mobility.

Antimony contamination sources and alteration pathways of Sb mineral phases in an abandoned mining area: The role of secondary mopungite [NaSb(OH)6

Antimony pollution caused by mining activities is a current environmental concern. This study investigates the processes involved in the Sb release and mobility in the abandoned Sb mine of Su Suergiu (SE Sardinia, Italy). Analyses of outcropping rocks, mine wastes and smelting slags by means of X-Ray Powder Diffraction, Scanning Electron Microscopy - Energy Dispersive Spectroscopy and Electron Microprobe – Wavelength Dispersive Spectroscopy provided mineralogical and compositional data which contributed to the discussion about the oxidation pathways of Sb phases. The main Sb sources are metallic Sb and Sb2O3 (valentinite/senarmontite), dumped in the smelting slag heaps as residues of metallurgical processes, and primary stibnite (Sb2S3) found in natural outcrops and mine wastes. These minerals, subjected to weathering processes, release Sb in solution where it is oxidized and remains as dissolved Sb(OH)6−. Carbonates and Na phases, like hydrate NaAl-silicate derived from metallurgical processes, influence the geochemical equilibria of the smelting slag heaps, where the precipitation of the rare mopungite, Na[Sb(OH)6], has been observed. At Su Suergiu, mopungite originates from a dissolution-precipitation process as the last forming mineral of the oxidation pathways, limiting the Sb mobility by bonding the Sb(OH)6− in solution. Among the detected Sb secondary phases (e.g., Sb-oxides, FeSb-oxides, etc.), mopungite is the prevalent Sb binder although it acts as a temporary sink because its stability is influenced by the hydrological regime, its solubility, and the water physicochemical parameters. Secondary Sb-bearing minerals can control the dispersion of Sb in contaminated area. At Su Suergiu the role of Fe-bearing compounds on Sb mobility is subordinate to that of mopungite due to the specific geochemical conditions related to the metallurgical activities. The relevance of this study arises from the known toxicity of Sb and from its worldwide diffuse mining, that results in the widespread occurrence of Na–Sb-rich residues produced by Sb smelting plants.

Novel insights into the mechanisms for Sb mobilization in groundwater in a mining area: A colloid field study

Colloids may play an important role in the geochemical cycle of antimony (Sb). However, the controlling behaviors of colloids on Sb fate in contaminated groundwater are not available. To investigate the effects of colloids on Sb mobility, groundwater samples from Xikuangshan Sb Mine's two main aquifers (the D3s2 aquifer and the D3x4 aquifer) were successively (ultra)filtered through progressively decreasing pore sizes (0.45 µm, 100 kDa, 50 kDa and 5 kDa). The results showed that 0.1–84.1% of Sb was adsorbed or carried by colloids, which corresponded to Sb concentration ranging between 0 and 2973 μg/L in the colloids (0.45 µm - 5 kDa). In both aquifers, Sb was closely associated with organic colloids (r = 0.72 p < 0.05 for the D3x4 aquifer, r = 0.94 p < 0.01 for the D3s2 aquifer). Parallel factor analysis of the three-dimensional fluorescence spectra determined that the protein-like substances in the D3x4 aquifer and the humus-like substances in the D3s2 aquifer controlled Sb behavior. X-ray absorption spectroscopy confirmed Sb complexing with organic substances. Competitive adsorption of As and Sb suppressed the complexation of colloids with Sb, particularly in the D3x4 aquifer (r = –0.71, p < 0.05). Sb mobility was also influenced by the redox of the groundwater system. As the oxidation-reduction potential and dissolved oxygen increased, Sb in the colloidal fractions decreased. These findings provide new insights into the mechanisms involved in Sb fate affected by colloids, establishing the theoretical basis for developing effective Sb and even metalloid pollution remediation strategies.