Efficient removal of Sb(â ¤) from water using sulphidated ferrihydrite via tripuhyite (FeSbO4) precipitation and complexation.

Elevated concentrations of antimony (Sb) in the ecological environment have received considerable attention due to the harmful consequence involved. This study synthesized sulphidated ferrihydrite with different S:Fe molar ratios to efficiently remove Sb(V) from water. As the S:Fe molar ratio ranged from 0.00 to 1.48, the removal efficiency of Sb(V) by sulphidated ferrihydrite first decreased before increasing considerably. Sulphidated ferrihydrite with an S:Fe molar ratio of 0.74 exhibited a strong affinity towards Sb(V) with an optimal removal capacity of 963.74 mg Sb/g, which was 3.2-fold higher than that of ferrihydrite. In the kinetic experiments, the removal behavior of Sb(V) was well described by the pseudo-second-order model, suggesting that the removal process was controlled via chemisorption. Moreover, Sb(V) was efficiently removed over a wide pH range of 3.00-11.00, and coexisting anions (NO3-, Cl-, SO42-, SiO32-, CO32- and PO43-) exhibited marginal impact on the Sb(V) removal by sulphidated ferrihydrite (S:Fe ≥ 0.44). The characterization results of XRD, SEM, TEM mapping and etched XPS revealed goethite to be the dominant phase of sulphidated ferrihydrite with an S:Fe molar ratio of 0.15, while a mixed constitution of mixed-valent iron (hydro)oxides and iron sulphide was formed when the S:Fe molar ratio exceeded 0.44. Moreover, sulphidated ferrihydrite acted as a donor for Fe and S for the effective retention of Sb(V) by two main pathways: precipitation (tripuhyite, FeSbO4) and complexation (≡S-H and ≡Fe-OH). Therefore, sulphidated ferrihydrite is a promising material for eliminating Sb(V) contamination from water.

Distribution and speciation of Sb and toxic metal(loid)s near an antimony refinery and their effects on indigenous microorganisms.

Although several studies have investigated the effects of Sb contamination on surrounding environments and indigenous microorganisms, little is known about the effect of co-contamination of Sb and toxic metal(loid)s. In this study, the occurrence of Sb and other toxic metal(loid)s near an operating Sb refinery and near-field landfill site were investigated. Topsoil samples near the refinery had high Sb levels (∼3250 mg kg-1) but relatively low concentrations of other toxic metal(loid)s. However, several soil samples taken at greater depth from the near-field landfill site contained high concentrations of As and Pb, as well as extremely high Sb contents (∼21,400 mg kg-1). X-ray absorption fine structure analysis showed that Sb in the soils from both sites was present as Sb(V) in the form of tripuhyite (FeSbO4), a stable mineral. Three-dimensional principal coordinate analysis showed that microbial community compositions in samples with high toxic metal(loid)s concentrations were significantly different from other samples and had lower microbial populations (∼104 MPN g-1). Sequential extraction results revealed that Sb is present primarily in the stable residual fraction (∼99 %), suggesting low Sb bioavailability. However, microbial redundancy analysis suggested that the more easily extractable Pb might be the major factor controlling microbial community compositions at the site.

Antimony speciation and mobility during Fe(II)-induced transformation of humic acid-antimony(V)-iron(III) coprecipitates.

Antimony, as the Sb(V) species, often occurs in oxic soils and sediments as coprecipitates with poorly-crystalline Fe(III)-bearing minerals. It is common for these Sb(V)-Fe(III) coprecipitates to also contain varying quantities of co-occurring humic acid (HA). When exposed to reducing conditions, the production of Fe(II) may cause the initial metastable HA-Sb(V)-Fe(III) phases to undergo rapid transformations to more stable phases, thereby potentially influencing the geochemical behavior of coprecipitated Sb(V). However, little is known about the impacts of this transformation on the mobility and speciation of Sb. In this study, we reacted synthetic HA-Sb(V)-Fe(III) coprecipitates (Fe:Sb ratio = 4, and C:Fe molar ratios = 0, 0.3, 0.8 and 1.3) with 0, 1 or 10 mM Fe(II) under O2-free conditions at pH 7.0 for 15 days. Fe K-edge EXAFS spectroscopy revealed that solid-phase Fe(III) in the initial coprecipitates contained a mixture of ∼4/5 ferrihydrite (Fe10O14(OH)2) and ∼1/5 tripuhyite (FeSbO4), regardless of the corresponding amount of coprecipitated HA. Tripuhyite persisted throughout the full experiment duration, while ferrihydrite was partially replaced by goethite (FeOOH) when either 1 or 10 mM Fe(II)aq was added to the coprecipitates. The greatest level of goethite formation (∼55% of solid-phase Fe) was observed in the HA-free/10 mM Fe(II)aq treatment, with ferrihydrite transformation being partially attenuated at higher levels of HA. Mobilisation of aqueous Sb was the greatest for 1 mM Fe(II) treatments at high HA:Fe ratios. Sb K-edge XANES spectroscopy showed that the largest reduction of Sb(V) to Sb(III) (∼37%) and the greatest repartitioning of Sb to the mineral surface (∼7.9-9.8%) occurred in the coprecipitates with the highest HA contents in the presence of 10 mM Fe(II). The results indicate that the amount of HA in HA-Sb(V)-Fe(III) coprecipitates can greatly influence mobility and speciation of Sb in Fe(II)-rich conditions. The results of this study provide new insights into alterations in Sb mobility and retention in response to Fe cycling under organic matter-rich reducing conditions.