Immobilization mechanism of antimony by applying zirconium-manganese oxide in soil

Cellulose nanocrystal-infused polymer hydrogel imbued with ferric-manganese oxide nanoparticles for efficient antinomy removal

Antimony is a highly poisonous pollutant that needs to be removed from water to ensured safety. In this work, we have fabricated a novel adsorbent, the ferric-manganese oxide (FeMnOx) nanoparticles embedded cellulose nanocrystal-based polymer hydrogel (FeMnOx @CNC-g-PAA/qP4VP, denoted as FMO@CPqP), specifically engineered for the remediation of antimony-laden water. Comprehensive evaluations have been conducted to investigate the efficacy of the FMO@CPqP hydrogel in removal of antimony from water. The hydrogel exhibits superior affinity for antimony, with maximum adsorption capacities of 276.1 mg/g for Sb(III) and 286.8 mg/g for Sb(V). The adsorptive dynamics, governed by the kinetics and isotherm analyses, elucidate that the immobilization of both Sb(III) and Sb(V) is facilitated through a homogeneous and monolayer chemisorption mechanism. The hydrogel has a three-dimensional interconnected porous structure and exhibits good swelling behavior, which facilitates the rapid absorption of antimony ions by this high surface area hydrogel into the channels. Furthermore, various effects, including the oxidation and inner-sphere coordination mediated by FeMnOx NPs and the electrostatic attractions of the quaternized P4VP chains, promote the immobilization of antimony species. Owing to its high removal efficiency, stability and reusability, the FMO@CPqP hydrogel emerges as an exemplary candidate for the removal of antimony contaminants in water treatment processes.

Incorporation of Shewanella oneidensis MR-1 and goethite stimulates anaerobic Sb(III) oxidation by the generation of labile Fe(III) intermediate

Dissimilatory iron-reducing bacteria (DIRB) affect the geochemical cycling of redox-sensitive pollutants in anaerobic environments by controlling the transformation of Fe morphology. The anaerobic oxidation of antimonite (Sb(III)) driven by DIRB and Fe(III) oxyhydroxides interactions has been previously reported. However, the oxidative species and mechanisms involved remain unclear. In this study, both biotic phenomenon and abiotic verification experiments were conducted to explore the formed oxidative intermediates and related processes that lead to anaerobic Sb(III) oxidation accompanied during dissimilatory iron reduction. Sb(V) up to 2.59 μmol L-1 combined with total Fe(II) increased to 188.79 μmol L-1 when both Shewanella oneidensis MR-1 and goethite were present. In contrast, no Sb(III) oxidation or Fe(III) reduction occurred in the presence of MR-1 or goethite alone. Negative open circuit potential (OCP) shifts further demonstrated the generation of interfacial electron transfer (ET) between biogenic Fe(II) and goethite. Based on spectrophotometry, electron spin resonance (ESR) test and quenching experiments, the active ET production labile Fe(III) was confirmed to oxidize 94.12% of the Sb(III), while the contribution of other radicals was elucidated. Accordingly, we proposed that labile Fe(III) was the main oxidative species during anaerobic Sb(III) oxidation in the presence of DIRB and that the toxicity of antimony (Sb) in the environment was reduced. Considering the prevalence of DIRB and Fe(III) oxyhydroxides in natural environments, our findings provide a new perspective on the transformation of redox sensitive substances and build an eco-friendly bioremediation strategy for treating toxic metalloid pollution.

Mechanism of efficient adsorption for arsenic in aqueous solution by zeolitic imidazolate framework‑8

Arsenic (As) is one extremely hazardous and carcinogenic metalloid element. Due to mining, metal smelting, and other human activities, the pollution of water (especially groundwater) and soil caused by As is increasingly serious, which badly threatens the environment and human health. In this study, a zeolite imidazolate framework (ZIF-8) was synthesized at room temperature and employed as an adsorbent to facilitate the adsorption of As(III) and As(V) from the solution. The successful synthesis of ZIF-8 was demonstrated by X-ray diffraction (XRD), and scanning electron microscopy (SEM) revealed that its particle size was approximately 80 nm. The adsorption kinetics, adsorption isotherm, solution pH, dose, coexisting ions, and the synonymous elements antimony (Sb) were conducted to study the adsorption of As by ZIF-8 nanoparticles. The maximum saturation adsorption capacity was determined to be 101.47 mg/g and 81.40 mg/g for As(III), and As(V) at initial pH = 7.0, respectively. Apparently, ZIF-8 had a good removal effect on As, and it still maintained a good performance after four cycles. The coexisting ions PO43- and CO32- inhibited the adsorption of both As(III) and As(V). ZIF-8 performed well in removing both As and Sb simultaneously, although the presence of Sb hindered the adsorption of both As(III) and As(V). Both FTIR and XPS indicated the adsorption mechanism of As on ZIF-8: ZIF-8 generates a large amount of Zn-OH on the surface through hydrolysis and partial fracture of Zn-N, both of which form surface complexes with As.

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.

Superior capacity and easy separation of zirconium functionalized chitosan melamine foam for antimony(III/V) removal

Nowadays, highly toxic antimony has severely posed threat to water sources and jeopardized human health. Fabricating adsorbents with the capability of easy separation, high efficiency and large adsorption capacity remains a major challenge. In this paper, zirconium functionalized chitosan melamine foam (ZCMF) was fabricated with zirconium and chitosan crosslinked onto melamine foam, then utilized for the removal of antimony(III/V) in water. The characterization of SEM and EDS collectively showed that ZCMF has a porous structure which could boost the mass transfer rate and zirconium ions on the surface could provide plentiful active adsorption sites. Systematic adsorption experiments demonstrated that the experimental data of Sb(III) and Sb(V) were consistent with the pseudo-second-order and Elovich kinetic models, respectively, and the Langmuir maximum adsorption capacities were separately 255.35 mg g-1 (Sb(III)) and 414.41 mg g-1 (Sb(V)), which displayed prominent performance among adsorbents derived from biomass. Combining the XPS and FTIR characterization with experimental data, it is rational to speculate that ZCMF could remove Sb from aqueous solution through ligand exchange, electrostatic attraction, and surface complexation mechanisms. ZCMF exhibited excellent performance, including large adsorption capacity, easy separation, facile preparation and eco-friendliness. It could be a promising new adsorbent for the treatment of antimony-containing wastewater.

Induced transformation of antimony trioxide by Mn(II) oxidation and their co-transformed mechanism

Antimony (Sb) is a toxic and carcinogenic element that often enters soil in the form of antimony trioxide (Sb₂O₃) and coexists with manganese (Mn) in weakly alkaline conditions. Mn oxides such as birnessite have been found to promote the oxidative dissolution of Sb₂O₃, but few researches concerned the co-transformations of Sb₂O₃ and Mn(II) in environment. This study investigated the mutual effect of abiotic oxidation of Mn(II) and the coupled oxidative dissolution of Sb₂O₃. The influencing factors, such as Mn(II) concentrations, pH and oxygen were also discussed. Furthermore, their co-transformed mechanism was also explored based on the analysis of Mn(II) oxidation products with or without Sb₂O₃ using XRD, SEM and XPS. The results showed that the oxidative dissolution of Sb₂O₃ was enhanced under higher pH and higher Mn(II) loadings. With a lower Mn(II) concentration such as 0.01 mmol/L Mn(II) at pH 9.0, the improved dissolution of Sb₂O₃ was attributed to the generation of dissolved intermediate Mn(III) species with strong oxidation capacity. However, under higher Mn(II) concentrations, both amorphous Mn(III) oxides and intermediate Mn(III) species were responsible for promoting the oxidative dissolution of Sb₂O₃. Most released Sb (∼72%) was immobilized by Mn oxides and Sb(V) was dominant in the adsorbed and dissolved total Sb. Meanwhile, the presence of Sb₂O₃ not only inhibited the removal of Mn(II) by reducing Mn(III) to Mn(II) but also affected the final products of Mn oxides. For example, amorphous Mn oxides were formed instead of crystalline Mn(III) oxides, such as MnOOH. Furthermore, rhodochrosite (MnCO₃) was formed with the high Mn(II)/Sb₂O₃ ratio_, but without being observed in the low Mn(II)/Sb₂O₃ ratio. The results of study could help provide more understanding about the fate of Sb in the environment and the redox transformation of Mn.

Speciation, in vitro bioaccessibility and health risk of antimony in soils near an old industrial area

Antimony (Sb) contamination in soil has become a major environmental issue due to its adverse effects on ecosystems and human health. In this paper, 1255 soil samples were analyzed to investigate the distribution, speciation, in vitro oral bioaccessibility (8 soil samples) and human health risk of Sb in contaminated soils and its impacts on groundwater. The results showed that 4.38 % of the soil samples within the depth of 0-31 m exceeded the Risk Screening Values (RSV). Sb mainly existed in the residual fraction (38.05 % ∼ 94.22 %), Fe/Mn oxides (0.01 % ∼ 31.80 %) and the organic fraction (0.32 % ∼ 21.55 %) with poor mobility. The bioaccessibility of Sb was approximately <31 %. The total concentration of Sb (TSb) in soil was the dominant factor influencing the bioaccessible concentration of Sb (SbBio). Soil physiochemical properties such as Fe, Mn, and organic matter content (OM) also affected the magnitude of SbBio. Health risk assessment based on in vitro bioaccessibility suggested that the hazard quotient (HQ) of adults was within the acceptable level (HQ < 1) for industrial scenario, while the HQ of children and adults was greater than the acceptable level (HQ ≥ 1) for residential scenario, with a higher risk to children than adults. The results of the leaching experiment involving Dilution-Attenuation Factor (DAF) model suggested that the predicted maximum concentration of Sb in groundwater was 2.40 μg/L that is lower than the acceptable standard value (5 μg/L), implying that groundwater was not contaminated by Sb in soil. The findings of this study provide some insights into the speciation, in vitro bioaccessibility and health risk of toxic trace metals in contaminated soils and the potential environmental impacts.

Insight into the Adsorption Behaviors of Antimony onto Soils Using Multidisciplinary Characterization

Antimony (Sb) pollution in soils is an important environmental problem, and it is imperative to investigate the migration and transformation behavior of Sb in soils. The adsorption behaviors and interaction mechanisms of Sb in soils were studied using integrated characterization techniques and the batch equilibrium method. The results indicated that the adsorption kinetics and isotherms of Sb onto soils were well fitted by the first-order kinetic, Langmuir, and Freundlich models, respectively, while the maximum adsorbed amounts of Sb (III) in soil 1 and soil 2 were 1314.46 mg/kg and 1359.25 mg/kg, respectively, and those of Sb (V) in soil 1 and soil 2 were 415.65 mg/kg and 535.97 mg/kg, respectively. In addition, pH ranging from 4 to 10 had little effect on the adsorption behavior of Sb. Moreover, it was found that Sb was mainly present in the residue fractions, indicating that Sb had high geochemical stability in soils. SEM analysis indicated that the distribution positions of Sb were highly coincident with Ca, which was mainly due to the existence of calcium oxides, such as calcium carbonate and calcium hydroxide, that affected Sb adsorption, and further resulted in Sb and Ca bearing co-precipitation. XPS analysis revealed the valence state transformation of Sb (III) and Sb (V), suggesting that Fe/Mn oxides and reactive oxygen species (ROS) served as oxidant or reductant to promote the occurrence of the Sb redox reaction. Sb was mobile and leachable in soils and posed a significant threat to surface soils, organisms, and groundwater. This work provides a fundamental understanding of Sb adsorption onto soils, as well as a theoretical guide for studies on the adsorption and migration behavior of Sb in soils.