Antimony release from contaminated mine soils and its migration in four typical soils using lysimeter experiments

Evaluation of the effectiveness of ex-situ stabilization for arsenic and antimony contaminated soil: Short-term and long-term leaching characteristics

Ex-situ stabilization for As and Sb co-contaminated soil was conducted through an iron-based stabilizer, PFSC (a mixture of polymerized ferric sulfate (PFS) and hydrated lime (Ca(OH₂)) with a dry mass ratio of 2:1). After field aging for one week, the stabilized contaminated soil was subjected to a horizontal vibration leaching test (HJ 557), Wenzel's sequential extraction, and a semi-dynamic leaching test (ANS 16.1). By assessing the cumulative fractions of As and Sb, the observed diffusion coefficients (D^obs) and leachability indices (LX) of metalloids released from the soil specimens were calculated. The PFSC ex-situ stabilization was effective to immobilize metalloids, and the As and Sb leached concentrations of stabilized contaminated soil samples were lower than remediation targets. Nonspecifically bound As and Sb in the stabilized contaminated soil samples decreased from 4.5 - 9.2 % to 1.5-2.5 % and from 2.2 - 5.8 % to 1.1-1.5 %, respectively. The mechanisms controlling the leaching behaviors of As and Sb included wash-off and diffusion and they were changed with the leaching interval. The mean D^obs of As and Sb released from stabilized contaminated soil specimen were 3.46 × 10^-12 and 2.99 × 10^-13 cm² s^-1, in the which were two orders of magnitude lower than that of untreated contaminated soil specimen. The mean LX of stabilized contaminated soil specimen for As and Sb releases were 11.40 and 12.83, respectively, indicating that the stabilized contaminated soil was acceptable for "controlled utilization".

Kinetics of antimony biogeochemical processes under pre-definite anaerobic and aerobic conditions in a paddy soil

While the transformation of antimony (Sb) in paddy soil has been previously investigated, the biogeochemical processes of highly chemical active Sb in the soil remain poorly understood. In addition, there is a lack of quantitative understanding of Sb transformation in soil. Therefore, in this study, the kinetics of exogenous Sb in paddy soils were investigated under anaerobic and aerobic incubation conditions. The dissolved Sb(V) and the Sb(V) extracted by diffusive gradient technique decreased under anaerobic conditions and then increased under aerobic conditions. The redox reaction of Sb occurred, and Sb bioavailability significantly decreased after 55 days of incubation. The kinetics of Fe and the scanning transmission electron microscopy analysis revealed that the Fe oxides were reduced and became dispersed under anaerobic conditions, whereas they were oxidized and re-aggregated during the aerobic stage. In addition, the redox processes of sulfur and nitrogen were detected under both anaerobic and aerobic conditions. Based on these observations, a simplified kinetic model was established to distinguish the relative contributions of the transformation processes. The bioavailability of Sb was controlled by immobilization as a result of S reduction and by mobilization as a result of Fe reductive dissolution and S oxidation, rather than the pH. These processes coupled with the redox reaction of Sb jointly resulted in the complex behavior of Sb transformation under anaerobic and aerobic conditions. The model-based method and findings of this study provide a comprehensive understanding of the Sb transformation in a complex soil biogeochemical system under changing redox conditions.

Reduction of Sb(V) by coupled biotic-abiotic processes under sulfidogenic conditions

Increasing use and mining of antimony (Sb) has resulted in greater concern involving its fate and transport in the environment. Antimony(V) and (III) are the two most environmentally relevant oxidation states, but little is known about the redox transitions between the two in natural systems. To better understand the behavior of antimony in anoxic environments, the redox transformations of Sb(V) were studied in biotic and abiotic reactors. The biotic reactors contained Sb(V) (2 mM as KSb(OH)₆), ferrihydrite (50 mM Fe(III)), sulfate (10 mM), and lactate (10 mM), that were inoculated with sediment from a wetland. In the abiotic reactors, The interaction of Sb(V) with green rust, magnetite, siderite, vivianite or mackinawite was examined under abiotic conditions. Changes in the concentrations of Sb, Fe(II), sulfate, and lactate, as well as the microbial community composition were monitored over time. Lactate was rapidly fermented to acetate and propionate in the bioreactors, with the latter serving as the primary electron donor for dissimilatory sulfate reduction (DSR). The reduction of ferrihydrite was primarily abiotic, being driven by biogenic sulfide. Sb and Fe K-edge X-ray absorption near edge structure (XANES) analysis showed reduction of Sb(V) to Sb(III) within 4 weeks, concurrent with DSR and the formation of FeS. Sb K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy analysis indicated that the reduced phase was a mixture of S- and O-coordinated Sb(III). Reduction of Sb(V) was not observed in the presence of magnetite, siderite, or green rust, and limited reduction occurred with vivianite. However, reduction of Sb(V) to amorphous Sb(III) sulfide occurred with mackinawite. These results are consistent with abiotic reduction of Sb(V) by biogenic sulfide and reveal a substantial influence of Fe oxides on the speciation of Sb(III), which illustrates the tight coupling of Sb speciation with the biogeochemical cycling of S and Fe.

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.

Soil migration of antimony and arsenic facilitated by colloids in lysimeter studies

The migration behaviors of antimony (Sb) and arsenic (As) and its influence factors have not been well understood among the different soils. In this study, we used lysimeter experiments to investigate the migration behavior of Sb compared with that of As in four representative soil materials from China. All the experiments processes and management measures were conducted to simulate the actual natural environmental conditions. Results indicated that after two years of leaching, the concentrations of Sb and As at the soil surface had decreased, whereas they increased in the deep soil profiles. In the polluted soil materials, 28.5%-39.2% of Sb and 0.4%-1.3% of As existed in the stable fraction, respectively. As and Sb levels were higher in the surface soil layer, and decreased with the soil depth in the different soil profiles. In soil leachate, Sb was mainly found in particle sizes smaller than 0.45 μm with the organic colloids, which had a peak in the spring and summer. On contrast, As was found in particle sizes larger than 0.45 μm with the inorganic colloids such as iron (Fe) and aluminum (Al) oxides. Pearson correlation results showed that the concentrations of Sb in the soil leaching solution and 0.45-μm-filltered solution were all positively correlated with Fe and Al. The results confirmed that Sb was combined with Fe and Al in the solution, and As posed a greater environmental risk than Sb during the leaching process. This study will help us to describe and predict As and Sb pollution in the soil environment, providing a basis for managing soil contaminated by these pollutants.

Influence of Soil Properties and Aging on Antimony Toxicity for Barley Root Elongation

The study explored the Sb toxicity by investigating the impacts of 10% and 20% effective concentrations (EC10 and EC20, respectively) of Sb on the inhibition of barley root elongation in 21 Chinese soils with a wide range of physicochemical properties after aging for 3 months. The results demonstrated that various soil properties profoundly influenced the Sb toxicity which was ranged from 201-2506 mg Sb kg^-1 to 323-2973 mg Sb kg^-1 under EC10 and EC20, respectively. Soil sand fraction was a significant soil factor responsible for elevating Sb bioavailability. The bioavailable Sb concentration accounted for 2.08%-11.94% of total Sb content in all 21 soil samples and the decreased Sb bioavailability in this study was attributed to soil properties including soil clay fraction, amorphous and crystalloid iron, and oxides of manganese and aluminum. The findings would contribute in developing Sb toxicity threshold for establishing standard for Sb regulation in crop production.

The source apportionment, pollution characteristic and mobility of Sb in roadside soils affected by traffic and industrial activities

Antimony (Sb), as an emerging pollutant, has aroused people's concerns for its wide usage in industrial production. In this study, we identify and quantify the traffic-derived Sb and investigate its mobility in roadside soils affected by traffic and industrial activities. 73 surface roadside soils and 5 transects in three areas nearby different industries (smelting, power and refining, and waste incineration) were collected and analyzed. Results showed that the Sb concentration ranged between 0.54 and 9.32 mg/kg, and the mean EF_s value was 4.63, which indicated moderate to significant Sb enrichment. Significantly high concentrations of Sb occurred at locations with heavy traffic and frequent braking process, with an average concentration of 4.13 mg/kg, compared to the control sites (2.01 mg/kg). Moreover, Sb diffused exponentially with increasing distance from road edges. These results suggested that traffic activities were the main source of Sb in roadside soils. According to the quantitative calculation, the average contributions from traffic, industrial activities and soil parent material to Sb accumulation in roadside soils were 50.73%, 21.38% and 27.88%, respectively. Even though Sb was slightly mobile, roadside soils was a persistent source of potentially mobile Sb which may release into water and cause long-term environmental risk.

Mobility, distribution, and potential risk assessment of selected trace elements in soils of the Nile Delta, Egypt

Environmental pollution has received considerable attention over the last 50 years. Recently, there has been an increasing interest in pollution of the Nile Delta, Egypt, which is one of the longest settled deltaic systems in the world. Pollution in the delta is increasingly recognized as a serious health concern that requires proper management of ecosystems. Therefore, this project aimed to study the distribution and assess the risk associated with selected trace elements (TEs) in different soils (i.e., marine, fluvial, and lacustrine parent materials) in the northern Nile Delta. Mehlich-3 extraction was used to determine the availability of antimony, vanadium, strontium, and molybdenum in agro-ecosystems in this area and their spatial distributions were investigated. Five indices were used to assess ecological risk. Results showed that TEs were higher in the southern part of the study area because it is affected by multiple pollution sources. The available concentrations of TEs were Sr < V < Sb < Mo. The bioavailability of Sr was highest among the studied TEs. The studied indices suggested the study area was moderately polluted by Sr and Sb. Furthermore, the results showed that marine soils had higher TE levels then lacustrine and fluvial soils. The ecological risk assessment indicated that V and Mo were of natural origin, while Sr and Sb were anthropogenically linked. Therefore, the situation calls for planning to reduce pollution sources, especially in the protected north Nile Delta, so these productive soils do not threaten human and ecological health.

Leaching behaviors and chemical fraction distribution of exogenous selenium in three agricultural soils through simulated rainfall

To clarify the leaching risk of selenium (Se) in agricultural soils, a laboratory column experiment was conducted to study the characteristics of leaching and chemical fractions of Se in three different soils treated with different levels of exogenous selenate under simulated local rainfall. Results demonstrated that the Se concentration in leachates of all tested soils decreased rapidly at the beginning of leaching and slowly decreased thereafter. After leaching, Se concentrations in leachates of all tested soils at 1, 3, and 6 mg/kg exogenous Se concentrations were 0.06-0.24, 0.25-0.84, and 0.60-1.65 mg/L, respectively, which exceeded the standard limit of the Chinese Environmental Quality Standards for Groundwater (<0.01 mg/L) (GB/T 14848-2017). The cumulative leached Se amount accounted for 51.27-86.22% of the total Se. Those results indicated the high risk of Se leaching in the tested soils. The Elovich model could better describe Se leaching processes in krasnozem, while the leaching processes of Se in black soil and loess soil accorded with the power function model. Se mainly existed in soluble fraction (61.33-81.05%) before leaching and residual fraction (48.91-68.04%) after leaching. The soluble and exchangeable Se fractions were the main contributors of Se in leachates. In addition, the parameters of the U_ts and I_R values could well describe the distribution of Se fractions in soil during leaching. In general, more attention should be placed on the assessment of Se leaching in soil.

Antimony mobility during prolonged waterlogging and reoxidation of shooting range soil: A field experiment

Due to its increasing anthropogenic use, antimony (Sb) soil pollution is of growing concern. Many soils experience fluctuating hydrological conditions, yet very little is known about how this affects the mobility of this toxic element under field conditions. In this study, we performed an outdoor lysimeter experiment to compare Sb leaching from a calcareous shooting range soil under drained and prolonged waterlogged conditions (1.5-2.75years), followed by a 1.5-year period of soil reoxidation. Waterlogging reduced Sb leachate concentrations significantly compared to drained conditions and soil solution concentrations decreased with depth due to the increased reducing conditions. This was attributed to the reduction of Sb(V) to Sb(III) and the more effective sorption of the latter to metal (hydr)oxides. However, reductive dissolution of iron (hydr)oxides released Sb into solution, although Sb concentrations never exceeded those in the drained lysimeters. On reoxidation of the soil, Sb was remobilized, but even after 1.5years under reoxidised conditions, Sb leachate and soil solution concentrations still remained below those of the drained lysimeters. Our results demonstrate that prolonged waterlogging may have an irreversible effect on Sb leachate and soil solution concentrations.