Initial Sb Research Articles

Efficiency and mechanisms of Sb(III/V) removal by Fe-modified biochars using X-ray absorption spectroscopy

Fe-modified biochars (FeBC) are effective antimony (Sb) removal materials; however, the removal mechanisms require further investigation. In this study, aqueous Sb(III) and Sb(V) removal by FeBC (300, 600, and 900 °C) was evaluated, with the adsorption mechanisms investigated using X-ray absorption spectroscopy (XAS). Screening results (based on removal efficiencies) using different types of FeBC indicated the 900 °C FeCl3-modified biochar (FeCl3BC900) achieved the best Sb(III/V) removal performance. The kinetics of the Sb(III/V) removal process were best fitted by a pseudo-second-order model. Additionally, the isothermal results were described by Langmuir and Redlich-Peterson models. Aqueous analysis and X-ray absorption near-edge structure data fitting indicated Sb(III) was oxidized to Sb(V) in the Sb(III)-spiked system, and the oxidation extent increased with increasing pyrolysis temperature. The oxidation process rapidly occurred in both the solution and biochar. No Sb(V) was reduced to Sb(III) in the Sb(V)-spiked system. The XAS results of the isothermal experiment indicated the oxidation capacity of FeCl3BC900 was limited for high initial Sb(III) concentrations. The Sb-Fe1 and Sb-Fe2 bonding distances were 3.05–3.10 and 3.47–3.54 Å, respectively, indicating inner-sphere complexes were formed during the Sb(III/V) removal processes. The Sb(III/V) removal mechanisms included electrostatic adsorption, inner-sphere complexes, and coprecipitation. Oxidation was also involved in Sb(III) removal.

Recycling the steel pickling waste liquor to produce a low-cost material for immobilization of heavy metal(loid)s

This work aims to demonstrate the practicability of employing Iron (Fe)-manganese (Mn) binary oxide (FMBO) synthesized from pickling wastewater to immobilize arsenic (As(V)) and antimony (Sb(V)). Visual MINTEQ software was used to simulate the speciation of As(V) and Sb(V) under different pH values. The adsorption performance of FMBO for Sb(V) and As(V) were examined by batch experiments, the pH impact, sorption kinetics, sorption isotherms and the reuse of the adsorbent were investigated. The pH impact results demonstrated that the absorption capacity decreased dramatically as the pH value increased, the maximum adsorption capacities As(V) and Sb(V) were obtained at pH value of 4 as 95.24 and 147.1 mg/g, respectively. The kinetic results indicated that the pseudo-second order model could fit the kinetic data of Sb(V) and As(V) well. Equilibrium studies displayed that the adsorption of Sb(V) and As(V) on FMBO could be appropriately described by Freundlich model. Results of the binary adsorption indicated that Sb(V) exhibited ∼ 5% improvement for As(V) when the initial Sb(V) content raised from 0 to 500 mg/L, while As(V) showed a significant hindrance for Sb(V) adsorption. Moreover, utilization of FMBO could also effectively reduce the TCLP extractable and easy mobile As and Sb in contaminated soil, thus reducing their bioavailability. In view of the advantages of cost-effective, eco-friendly and excellent sorption performance, the steel pickling waste liquor-derived FMBO could be regarded as a promising amendment for remediating As and Sb contamination in environment. • A new low-cost adsorbent (FMBO) was prepared from steel pickling waste liquor. • FMBO exhibited an excellent performance for sorption of As(V) and Sb(V). • The existence of Sb(V) favor As(V) sorption, while As(V) showed opposite effect on Sb(V). • The FMBO could also effectively reduce the bioavailability of soil As and Sb.

Biosorption of Sirius Blue azo-dye by Agaricus campestris biomass: Batch and continuous column studies

In this study, biosorption of azo-dye Sirius Blue K-CFN (SB) was investigated from aqueous solution by using Agaricus campestris biomass as a biosorbent. Operating batch system conditions like pH, temperature, initial SB concentration and biosorbent dosage were studied. Optimum initial pH was determined as pH 3.0. The percentage of biosorption was determined as 97.32% for 80 mg/L SB at 45 °C. The maximum biosorption capacity was increased with increasing initial SB concentration and temperature. The experimental results were represented by the Freundlich isotherm model. The negative values of ΔG° indicated that the biosorption process of SB onto A. campestris biomass is spontaneous. Continuous column studies were also performed to show the efficiency of fungal biomass as a biosorbent for SB. In column system, the effect of flow rate (3–7 mL/min), packing heights (3–7 cm) and dye concentration (20–80 mg/L) were studied. Since A. campestris can be effectually used as a biosorbent for the SB azo-dye biosorption.

Removal of antimonite (Sb(III)) from aqueous solution using a magnetic iron-modified carbon nanotubes (CNTs) composite: Experimental observations and governing mechanisms

In this study, a novel nanoscale iron oxide (FeOx) modified carbon nanotubes composite (FeOx@CNTs) was synthesized through a combined ball milling–hydrothermal two-step method and tested for aqueous Sb(III) removal efficiency and mechanisms. FeOx nanoparticles was successfully loaded on the surface of CNTs through functional groups such as hydroxyl (–OH), C–H, and C–O to enhance the removal efficiency of Sb(III) through adsorption and surface complexation. At a dosage of 0.02 g, a FeCl3·6H2O-to-CNTs mass ratio of 3:1, and an initial solution pH of 6.3, the amount of Sb(III) removed by the prepared FeOx@CNTs reached 172 mg/g, which was 42.9 times higher than that of the pristine CNTs (4.01 mg/g). Chemical adsorption and oxidation were the main removal mechanisms. At the equilibrium Sb(III) concentration of 6.08 mg/L, 6.56% of initial Sb(III) was adsorbed onto the surface of FeOx@CNTs, and 81.3% of initial Sb(III) was oxidized to Sb(V) with lower toxicity. The pseudo-second-order kinetic model could better describe the adsorption of Sb(III) onto the FeOx@CNTs composite, indicating that adsorption was mainly controlled by chemical sorption. In the adsorption isotherm equation, the Redlich–Peterson model provided a better fit of Sb(III) adsorption onto the FeOx@CNTs composite than the Langmuir and Freundlich models, which further indicated that the adsorption process was a hybrid removal process dominated by chemical sorption. The presence of CO32− slightly promoted the removal of Sb(III) from aqueous solution. The synthesized composite was magnetic and could be easily separated from the solution by an external magnetic field at the end of the sorption experiment. Based on these findings, the FeOx@CNTs nanocomposite is expected to provide an environmentally-friendly adsorbent with a strong sorption capacity for remediating Sb(III) in water environments.

Antimony isotope fractionation in hydrothermal systems

In order to characterize antimony (Sb) isotope fractionation in hydrothermal systems, we present Sb isotope compositions of primary stibnite ores from a large Sb deposit in south China. A total number of 39 analyses reveals a large δ123Sb range of −0.27 to +0.86‰, representing an up to 1.13‰ variation in this hydrothermal system. A gradual increase of Sb isotope ratios from the proximal to the distal parts was observed in stibnite ores. Rayleigh distillation models the systematic variation trend of the Sb isotope values, demonstrating that ore fluids are preferentially enriched in heavier Sb isotopes during the precipitation of isotopically light stibnite. In this way, we consider that separation of stibnite from a Sb-bearing fluid related to reaction kinetics as a cause for Sb isotope fractionation. The modeled data constrain a Sb isotope fractionation factor (αfluid-stibnite) between hydrothermal fluid and stibnite at approximately 0.9994. The model also constrains an initial Sb isotope value of ~0.45‰, which indicates metal sources in the basement rocks of the study area. Given that distal stibnites possess higher Sb isotopic values, Sb isotopes could be used to fingerprint hydrothermal fluid flow and unravel different processes in natural systems.

Removal mechanism of Sb(III) by a hybrid rGO-Fe/Ni composite prepared by green synthesis via a one-step method

The annual influx of antimony (Sb) into the environment due to the widespread use of Sb compounds in industry and agriculture has become of global concern. Herein, a functional nanomaterial composite based on loading bimetallic iron/nickel nanoparticles on reduced graphene oxide (rGO-Fe/Ni) was initially prepared in a one-step phytogenic synthesis using a green tea extract. Subsequently, when applied for Sb(III) removal, the removal efficiency of rGO-Fe/Ni reached 69.7% within 3 h at an initial Sb concentration of 1.0 mg·L−1. Advanced materials characterization via scanning electron microscopy-energy dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy revealed that Sb(III) was initially adsorbed onto the surface of rGO and then oxidized to Sb(V). This result was also supported by adsorption isotherm, kinetics, and thermodynamic analysis. These studies revealed that the adsorption was spontaneous and endothermic, following a Langmuir adsorption model with pseudo-second-order kinetics and allowed a Sb(III) removal mechanism based on adsorption and catalytic oxidation to be proposed. Furthermore, when rGO-Fe/Ni was practically used to remove Sb(III) in groundwater a 95.7% removal efficiency was obtained at 1 mg·L−1 Sb(III), thus successfully demonstrating that rGO-Fe/Ni has significant potential for the practical remediation of Sb contaminated groundwater.

Antimonate sequestration from aqueous solution using zirconium, iron and zirconium-iron modified biochars

Antimony (Sb) is increasingly being recognized as an important contaminant due to its various industrial applications and mining operations. Environmental remediation approaches for Sb are still lacking, as is the understanding of Sb environmental chemistry. In this study, biosolid biochar (BSBC) was produced and utilized to remove antimonate (Sb(V)) from aqueous solution. Zirconium (Zr), Zirconium-iron (Zr–Fe) and Fe–O coated BSBC were synthesized for enhancing Sb(V) sorption capacities of BSBC. The combined results of specific surface area, FTIR, SEM–EDS, TEM–EDS, and XPS confirmed that Zr and/or Zr–Fe were successfully coated onto BSBC. The effects of reaction time, pH, initial Sb(V) concentration, adsorbate doses, ionic strength, temperature, and the influence of major competitive co-existing anions and cations on the adsorption of Sb(V) were investigated. The maximum sorption capacity of Zr–O, Zr–Fe, Zr–FeCl3, Fe–O, and FeCl3 coated BSBC were 66.67, 98.04, 85.47, 39.68, and 31.54 mg/g respectively under acidic conditions. The XPS results revealed redox transformation of Sb(V) species to Sb(III) occurred under oxic conditions, demonstrating the biochar’s ability to behave as an electron shuttle during sorption. The sorption study suggests that Zr–O and Zr–O–Fe coated BSBC could perform as favourable adsorbents for mitigating Sb(V) contaminated waters.

PH-dependent doping level and optical performance of antimony-doped tin oxide nanocrystals as nanofillers of spectrally selective coating for energy-efficient windows

The optimal pH value of the titration endpoint remains uncertain for the synthesis of antimony-doped tin oxide by the co-precipitation method. In this study, the influence of the pH titration endpoint on doping level and optical performance was systematically studied. The phase composition, microstructure, the valence state of Sb ions and thermodynamic behaviors of antimony-doped tin oxide were comprehensively investigated. The UV–Vis–NIR transmittance spectra of ATO glass and SEM images of ATO coating were also studied. When the pH value of the titration endpoint was 6, the measured doping ratio of Sb was 10.81% which was close to the initial Sb doping level of 10%. In the meanwhile, the content of Sb5+ ions also reached the maximum value of 76.4%. Especially, the spectrally selective coating exhibited optimally spectral selectivity with the average visible light transmittance of 77.24% and the average near-infrared shielding ratio of 80.06% respectively. The results show that the doping level and optical properties of antimony-doped tin oxide certainly relied on the pH value of the titration endpoint. It is of great significance to scale up the production of antimony-doped tin oxide with superior near-infrared shielding performance and promote its practical application in the field of energy-efficient glazing.

Optimization of Antimony Removal by Coagulation-Flocculation-Sedimentation Process Using Response Surface Methodology

Coprecipitation-adsorption plays a significant role during coagulation-flocculation-sedimentation (C/F/S) of antimony (Sb) in water. This work uses a Box–Behnken statistical experiment design (BBD) and response surface methodology (RSM) to investigate the effects of major operating variables such as initial Sb(III, V) concentration (100–1000 µg/L), ferric chloride (FC) dose (5–50 mg/L), and pH (4–10) on redox Sb species. Experimental data of Sb(III, V) removal were used to determine response function coefficients. The model response value (Sb removal) showed good agreement with the experimental results. FC showed promising coagulation behavior of both Sb species under optimum pH (6.5–7.5) due to its high affinity towards Sb species and low residual Fe concentration. However, a high dose of 50 mg/L of FC is required for the maximum (88–93%) removal of Sb(V), but also for the highest (92–98%) removal of low initial concentrations of Sb(III). Furthermore, BBD and RSM were found to be reliable and feasible for determining the optimum conditions for Sb removal from environmental water samples by a C/F/S process. This work may contribute to a better understanding and prediction of the C/F/S behavior of Sb(III, V) species in aqueous environments, to reduce potential risks to humans.

Enhanced removal of antimony in dyeing wastewater by mixing Fe3 O4 with manganese sand filter material.

Wastewaters from the printing and dyeing industries contain many contaminants in particular antimony (Sb) that end up in the environment. Both manganese sand filter and Fe3 O4 have good removal effect on Sb, and are cheap and easy to obtain. We made a filter material by mechanically mixing the manganese sand filter material and ferro-ferric oxide (Fe3 O4 ). The Fe-Mn oxide filter material was analyzed by X-ray diffraction. We studied the filtration of real wastewater from a dyeing wastewater resource recovery facility in Suzhou, China, containing Sb at high concentration of 410μg/L, using dynamic tests in adsorption columns during 7days. We tested the effects of filter material volume filling ratio, the empty bed contact time (EBCT), pH, and back washing on the removal of Sb. Results show that the addition of Fe3 O4 enhanced the removal of Sb, reaching 85% of initial Sb. When the initial influent pH of the raw water is 3.0, the volume filling ratio of filter material is 60%, the EBCT is 20min, and the developed dynamic Fe-Mn oxide filter has the best removal effect on Sb. Daily back washing of the filter keeps a Sb removal rate of about 80%. PRACTITIONER POINTS: A novel and cheap Fe-Mn oxide was developed for Sb removal from dyeing wastewater. A self-designed filter device was designed to verify performance of the low-cost material. Optimal design and operational parameters of the filtration process were determined.

Antimonate adsorption onto Mg-Fe layered double hydroxides in aqueous solutions at different pH values: Coupling surface complexation modeling with solid-state analyses

In this study, the importance of Sb behavior under different pH conditions has been addressed with respect to its stabilization in aqueous solutions using Mg-Fe layered double hydroxides (LDHs). The Sb(V) adsorption onto Mg-Fe LDHs was performed at different initial Sb(V) concentrations and pH values (pH 5.5, 6.5 and 7.5). The removal rate and the maximal adsorbed amount increased with decreasing pH values. Moreover, the surface complexation modeling (SCM) predicted preferable formation of monodentate mononuclear and bidentate binuclear complexes on the Mg-Fe LDH surface. Spectroscopic (X-ray diffraction analysis, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy) and microscopic (scanning electron microscopy and energy-dispersive X-ray spectroscopy) techniques were used to further specify the adsorption mechanisms. The influence of chemical adsorption, surface-induced precipitation of brandholzite Mg[Sb(OH)6]2·6H2O, formation of brandholzite-like phases and/or anion exchange was observed. Moreover, Sb(V) was nonhomogeneously distributed on the Mg-Fe LDH surface at all pH values. The surface complexation modeling supported by solid-state analyses provided a strong tool to investigate the binding arrangements of Sb(V) on the Mg-Fe LDH surface. Such a complex mechanistic/modeling approach has not previously been presented and enables prediction of the Sb(V) adsorption behavior onto Mg-Fe LDHs under different conditions, evaluating their possible use in actual applications.

Removal of antimonate (Sb(V)) and antimonite (Sb(III)) from aqueous solutions by coagulation-flocculation-sedimentation (CFS): Dependence on influencing factors and insights into removal mechanisms

This study investigates the effects of different influence factors on the removal of inorganic Sb species using coagulation-flocculation-sedimentation (CFS) and establishes the mechanism of the process. Thus, the influence of pH, initial Sb concentrations, coagulant dosages and competitive matters on Sb(V) and Sb(III) removal via CFS with polymeric ferric sulfate (PFS) was investigated systemically. Competition experiments and characterization methods, including X-ray diffraction (XRD), energy dispersive spectrometry (EDS), and X-ray photoelectron spectroscopy (XPS), were performed to determine the mechanisms of the process. The main conclusions included: (i) Optimum Sb removal was observed at a pH range of 4–6 and dosages of 4 × 10−4 mol/L and 8 × 10−5 mol/L for Sb(V) and Sb(III), respectively. Additionally, both Sb(V) and Sb(III) removal could be inhibited by the presence of phosphate and humic acid (HA). (ii) A higher priority was observed for the removal of Sb(III) over Sb(V). (iii) After excluding precipitation/inclusion/occlusion, coprecipitation involving chemical bonding played a significant role in both Sb(V) and Sb(III) removal, and electrostatic force served another significant role in Sb(V) removal. The Sb(V) and Sb(III) contamination in real contaminated waters was successfully removed using PFS via CFS process. The results of this study provide insights into the removal mechanisms of inorganic Sb species via CFS.

Removal of Sb(III) and Sb(V) by Ferric Chloride Coagulation: Implications of Fe Solubility

Coagulation and precipitation appear to be the most efficient and economical methods for the removal of antimony from aqueous solution. In this study, antimony removal from synthetic water and Fe solubility with ferric chloride (FC) coagulation has been investigated. The effects of pH, FC dosage, initial antimony loading and mixed Sb(III), Sb(V) proportions on Fe solubility and antimony removal were studied. The results showed that the Sb(III) removal efficiency increased with the increase of solution pH particularly due to an increase in Fe precipitation. The Sb(V) removal was influenced by the solution pH due to a change in Fe solubility. However, the Fe solubility was only impaired by the Sb(III) species at optimum pH 7. The removal efficiencies of both Sb species were enhanced with an increase in FC dose. The quantitative analysis of the isotherm study revealed the strong adsorption potential of Sb(III) on Fe precipitates as compared to Sb(V). Furthermore, the removal behavior of antimony was inhibited in mixed proportion with high Sb(V) fraction. In conclusion, this study contributes to better understanding the fate of Sb species, their mobilities, and comparative removal behavior, with implications for Fe solubility using ferric chloride in different aqueous environments.

Active surveillance criteria in the age of targeted biopsies.

116 Background: Many urologists are now using active surveillance (AS) to manage patients with low-risk prostate cancer. A variety of criteria have been proposed to select patients for AS. A key feature of these criteria is Gleason Group as determined by systematic or “random” biopsies (SB). In this study, we examined the progression of Gleason Group (GG) detected only on SB compared to patients with positive MRI-fusion or “targeted” biopsies (FB). Methods: A prospectively maintained database was queried for all patients who underwent an MRI guided FB and SB from 2007 to 2016 and chose AS as their primary management strategy. Patents with GG 1 or 2 were eligible. Patients were then followed with yearly PSA, exam, MRI and biopsy if warranted. FBs were reviewed to determine GG progression. We divided patients into those who had cancer detected on SB only and those who had positive FBs with or without a positive SB. Results: A total of 162 patients met our criteria with 73 having an initial positive FB and 89 having cancer only on SB and a negative FB. Median follow-up was 27.62 (4.14 – 96.56) and 33.83 (3.45-99.84) months, respectively. The two groups were similar in age (64.49 ± 6.57 vs. 62.08 ± 6.92 years, p = 0.03) and PSA (6.23 ± 4.23 vs. 5.67 ± 3.98 ng/ml, p = 0.39). The median time to pathologic progression for GG 1 patients with initial FB positive was 53.88 months and those with GG 1 on initial SB was 80.81 months (p = 0.003). The median time to pathologic progression for GG 2 patients with initial FB positive was 36.26 months and those with GG 2 on initial SB was 76.01 months (p = 0.099). Conclusions: Previously accepted AS criteria have been based on SBs. However, those patients placed on AS after a positive FB progressed fast than cancer detected only on SB. With MRI and FBs more routinely used in clinical practice, clinicians could use this information from FBs to better stratify and closely monitor patients during AS. This research was supported by the Intramural Research Program of the National Cancer Institute, NIH.

Effect of Sb and As spray on emission characteristics of InAs quantum dots with AlAs capping layer

We report on the influence of an Sb/As combined spray on the physical and optical characteristics of AlAs-capped InAs/GaAs quantum dots grown by Molecular Beam Epitaxy. Photoluminescence emission from the quantum dots shows a significant peak position shift under different Sb/As spray sequences. A blue-shifted quantum dot emission peak with an initial Sb rest indicates a large-to-small quantum dots transition process, with a bi-modal quantum dot size distribution inferred. High-resolution Transmission Electron Microscopy results reveal a large density of small quantum dots when the Sb spray is treated first. Furthermore, defect passivation in the vicinity of the quantum dots by use of Sb spray was detected.

Bioremoval of antimony from contaminated waters by a mixed batch culture of sulfate-reducing bacteria

Bioremediation of metal(loid)-contaminated water could be a cost-effective process. In this work, Sb-polluted water was treated by application of a mixed batch culture of sulfate-reducing bacteria (SRB). Aqueous Sb could be efficiently removed by the SRB over an initial pH range 5–8. The SRB was tolerant of at least 50 mg L−1 Sb in solution. With an initial pentavalent Sb (Sb(V)) concentration of 5 mg L−1, batch kinetic variations of the treatment were studied over a 11 d period at an initial pH 7 at 30 °C. A high removal (93%) of the aqueous Sb was achieved. The final products were identified microscopically. Before removal of Sb from solution in this treatment, Sb(V) was first reduced to trivalent Sb (Sb(III)). Hydrogen sulfide was proven to be the reducing agent in this reaction. The SRB were not able to reduce Sb(V) enzymatically. Following the chemical reduction of Sb(V) to Sb(III), the latter reacted with excess sulfide, resulting in the formation of insoluble antimony sulfide (Sb2S3). Studies on the sorption of Sb species by dead SRB indicated that, in the batch treatment, sorption by bacteria made a relatively small contribution to the removal of Sb.

Antimony Removal from Aqueous Solutions by the Use of Zn-Al Sulphate Layered Double Hydroxide

This study tested the efficacy of Zn-Al sulphate layered double hydroxides (LDH) as sorbent to remove antimony from circum-neutral solutions. Results of experimentation showed that Sb(V) in the anionic form Sb(OH)6 − can be efficiently removed from aqueous solutions through an exchange process with the SO4 2− present in the interlayer; total removal can be achieved within 6–24 h for A ≥2, where A is the ratio of the maximum theoretical anion exchange capacity (AEC) to the initial Sb concentration, both expressed in milliequivalents per liter. The complex rearrangement of the LDH structure to host Sb(OH)6 − in the interlayer is correlated to an initial fast removal of the contaminant, followed by a progressive slowing down of the exchange process. The overall speed of the process is again a direct function of A; in practice, the sorbent dose should be carefully evaluated to balance cost/efficacy/timing of the water treatment. Comparison with previous studies documenting Zn-Al sulphate LDH efficacy as arsenate and molybdate sorbent indicates a comparable affinity for As(V) and Sb(V), higher than for Mo(VI). The results of this study reinforce the possible key role of Zn-Al sulphate LDHs in water treatment for pH ranging from circum-neutral to moderately alkaline, thanks to their capability to rearrange the original structure in order to host different-sized/charged anions.

Antimony oxyanions uptake by green marine macroalgae

The potential of green seaweeds, Cladophora sericea and Ulva rigida, to adsorb antimony(III) and antimony(V) from aqueous solution was studied in batch mode. The hydroxyl and carboxyl groups from the algae surface, responsible for Sb uptake, were quantified by potentiometric titration and a continuous model for the deprotonation of these sites was obtained. Kinetic studies using C. sericea as biosorbent were conducted using different initial Sb concentrations and solid/liquid ratios. A fast uptake process was observed with equilibrium being achieved in less than 2h. Equilibrium studies show considerable adsorbed amounts for both Sb(III) and Sb(V). Maximum biosorption capacities, predicted by Langmuir model, were 2.1mg/g, for Sb(III), and 3.1mg/g for Sb(V), at pH 2 and 22°C. A low influence of pH (range 2–8) and of ions typically present in natural waters were shown to be additional advantages of C. sericea, as a potential biosorbent for antimony.

Experimental investigation of As, Sb and Cs behavior during olivine serpentinization in hydrothermal alkaline systems

While Fluid-Mobile Elements (FMEs) such as B, Sb, Li, As or Cs are particularly concentrated in serpentinites, data on FME fluid–serpentine partitioning, distribution, and sequestration mechanisms are missing. In the present experimental study, the behavior of Sb, As and Cs during San Carlos olivine serpentinization was investigated using accurate mineralogical, geochemical, and spectroscopic characterization. Static-batch experiments were conducted at 200°C, under saturated vapor pressure (≈1.6MPa), for initial olivine grain sizes of <30μm (As), 30–56μm (As, Cs, Sb) and 56–150μm (Cs) and for periods comprised between 3 and 90days. High-hydroxyl-alkaline fluid enriched with 200mgL−1 of a single FME was used and a fluid/solid weight ratio of 15. For these particular conditions, olivine is favorably replaced by a mixture of chrysotile, polygonal serpentine and brucite. Arsenic, Cs or Sb reaction product content was determined as a function of reaction advancement for the different initial olivine grain sizes investigated. The results confirm that serpentinization products have a high FME uptake capacity with the partitioning coefficient increasing such as CsDp/fl=1.5–1.6<AsDp/fl=3.5–4.5<SbDp/fl=28 after complete reaction of the 30–56μm grain-sized olivine. The sequestration pathways of the three elements are however substantially different. While the As partition coefficient remains constant throughout the serpentinization reaction, the Cs partition coefficient decreases abruptly in the first stages of the reaction to reach a constant value after the reaction is 40–60% complete. Both As and Cs partitioning appear to decrease with increasing initial olivine grain size, but there is no significant difference in the partitioning coefficient between the 30–56 and 56–150μm grain size after complete serpentinization. X-ray absorption spectroscopy (XAS) measurements combined with X-ray chemical measurements reveal that the As(V) is mainly adsorbed onto the serpentinization products, especially brucite. In contrast, mineralogical characterization combined with XAS spectroscopy reveal redox sensitivity for Sb sequestration within serpentine products, depending on the progress of the reaction. When serpentinization is <50%, initial Sb(III) is oxidized into Sb(V) and substantially adsorbed onto serpentine. For higher degrees of reaction, a decrease in Sb sequestration by serpentine products is observed and is attributed to a reduction of Sb(V) into Sb(III). This stage is characterized by the precipitation of Sb–Ni-rich phases and a lower bulk partitioning coefficient compared to that of the serpentine and brucite assemblage. Antimony reduction appears linked to water reduction accompanying the bulk iron oxidation, as half the initial Fe(II) is oxidized into Fe(III) and incorporated into the serpentine products once the reaction is over. The reduction of Sb implies a decrease of its solubility, but the type of secondary Sb-rich phases identified here might not be representative of natural systems where Sb concentrations are lower. These results bring new insights into the uptake of FME by sorption on serpentine products that may form in hydrothermal environments at low temperatures. FME sequestration here appears to be sensitive to various physicochemical parameters and more particularly to redox conditions that appear to play a preponderant role in the concentrations and mechanism of sequestration of redox-sensitive elements.

Adsorption of antimony on kaolinite as a function of time, pH, HA and competitive anions

This study was to understand the sorption behavior of Sb(III) on kaolinite as a function of various solution properties such as pH, initial Sb concentration, temperature and humic acid (HA). Kinetic studies suggested that the adsorption equilibrium was achieved within 24 h and the order of reaction with regard to the Sb(III) concentration is two. The adsorption of Sb(III) is strongly dependent on pH and decreases with increasing pH. The Langmuir and Freundlich models were used to fit the adsorption data obtained at three different temperatures. The thermodynamic parameters (ΔG, ΔH and ΔS) were calculated from the dependence of the adsorption process on the reaction temperature, and the calculated parameters suggested that the adsorption of Sb(III) on kaolinite is spontaneously exothermic. The presence of competitive anions have no obvious effect on the adsorption of Sb(III) on kaolinite.