Washing antimony and arsenic from agricultural soil with eco-friendly organic acids and the relevant bioavailability assessment.

Antimony (Sb) and arsenic (As) contamination in agricultural soil poses human health risks through agricultural products. Soil washing with degradable low molecular weight organic acids (LMWOAs) is an eco-friendly strategy to remediate agricultural soils. In this study, three eco-friendly LMWOAs, oxalic acid (OA), tartaric acid (TA), and citric acid (CA), were used to treat Sb and As co-contaminated agricultural soil from Xikuangshan mine area. The OA, TA, and CA washed out 18.4, 16.8, and 26.6% of Sb and 15.3, 19.9, and 23.8% of As from the agricultural soil, with CA being the most efficient reagent for the soil washing. These organic acids also led to pH decline and macronutrients losses. Fraction analysis using a sequential extraction procedure showed that the three organic acids targeted and decreased the specifically sorbed (F2) (by 19.3-37.6% and 2.41-23.5%), amorphous iron oxide associated (F3) (by 49.1-61.2% and 51.2-70.2%), and crystallized iron oxide associated (F4) (by 12.3-26.0% and 26.1-29.1%) Sb and As. The leachability of Sb and As, as well as their concentrations and bioconcentration factor (BCF) in vegetables reduced due to the soil washing. It demonstrated that the bioavailability of both the elements was decreased by the organic acids washing. The concentrations of Sb and As in typical vegetable species cultivated in CA washed soil were less than the threshold value for consumption safety, while those in OA and TA washed soils were still higher than the value, suggesting that only CA is a potential washing reagent in soil washing for Sb- and As-contaminated agricultural soil.

Repeated inoculation of antimony resistant bacterium reduces antimony accumulation in rice plants.

Applying beneficial bacteria in rice rhizosphere to manage heavy metal behaviour in soil-plant system is a promising strategy. However, colonization/domination of exogenous bacteria in rhizosphere soils remains a challenge. In this study, a bacterium Ochrobactrum anthropi, which showed the potential of transforming soluble SbIII into Sb2O3 mineral, was repeatedly inoculated into the rice rhizosphere weekly throughout the rice growth period, and the colonization of this bacterium in rice rhizosphere soils and its effect on Sb accumulation in rice plants were investigated. Results showed that repeated inoculants changed the native bacterial community in rhizosphere soils in comparison with the control, but the inoculated O. anthropi was not identified as an abundant species. With weekly inoculation, the decrease in Sb in rice roots and straws was maintained throughout the rice growth period, with decrease percentages ranging from 36 to 49% and 33-35%. In addition, decrease percentages of Sb in husks and grains at the maturing stage obtained 34 and 37%, respectively. Furthermore, the XRD identified the formation of valentinite (Sb2O3) on rice root in inoculation treatment, and the decrease percentages in aqueous SbIII in rhizosphere were 53-100% through the growth period. It demonstrated that weekly inoculants performed their temporary activity of valentinite formation, and reduced Sb accumulation in rice plants efficiently. This study suggests that regardless of successful colonization, repeated inoculation of beneficial bacteria is an option to facilitate the positive effects of inoculated bacteria in the management of heavy metal behaviour.

Removal of uranium(VI) from aqueous solution by Camellia oleifera shell-based activated carbon: adsorption equilibrium, kinetics, and thermodynamics.

Camellia oleifera shell-based activated carbon (COSAC) was prepared by H3PO4 activation method and further used to remove U(VI) from the aqueous solution in a batch system. This research examined the influence of various factors affecting U(VI) removal, including contact time, pH, initial U(VI) concentration, and temperature. The results showed that the U(VI) adsorption capacity and removal efficiency reached 71.28 mg/g and 89.1% at the initial U(VI) concentration of 160 mg/L, temperature of 298 K, pH 5.5, contact time of 60 min, and COSAC dosage of 2.0 g/L. The pseudo-first-order, pseudo-second-order, and intraparticle diffusion equations were used to identify the optimum model that can describe the U(VI) adsorption kinetics. The pseudo-second-order kinetics model performed better in characterizing the adsorption system compared with the pseudo-first-order and intraparticle diffusion models. Isotherm data were also discussed with regard to the appropriacy of Langmuir, Freundlich, Temkin, and Dubinin-Radushkevich models. The Langmuir model described the U(VI) adsorption process the best with a maximum adsorption capacity of 78.93 mg/g. Thermodynamic analysis (ΔG0 < 0, ΔH0 > 0, and ΔS0 > 0) indicated that the U(VI) adsorption process is endothermic and spontaneous. All the results imply that COSAC has a promising application in the removal or recovery of U(VI) from aqueous solutions.

Adsorption mechanism of polyethyleneimine modified magnetic core-shell Fe3O4@SiO2 nanoparticles for anionic dye removal.

In this paper, polyethyleneimine modified magnetic core-shell Fe3O4@SiO2 nanoparticles (Fe3O4@SiO2/PEI) were innovatively synthesized and investigated using various techniques such as TEM, TGA, FT-IR, XRD, VSM and XPS. The adsorption performance based on the removal of the anionic dyes Methyl orange and Congo red from aqueous solution was studied systematically. The results showed that the adsorption rate of anionic dyes MO and CR increased rapidly then decreased gradually as the pH increased, the adsorption capacity of Fe3O4@SiO2/PEI for MO was better than that for CR, and the maximum adsorption capacity for MO and CR was 231.0 mg g-1 at pH 4 and 134.6 mg g-1 at pH 6, respectively. The equilibrium adsorption capacities for MO and CR increased rapidly in the initial 40 min, and reached equilibrium in approximately 180 min, while the adsorption capacity for MB was relative low even negligible, demonstrating the strong adsorptive affinity of Fe3O4@SiO2/PEI toward anionic compounds. Both of the adsorption processes followed the pseudo-second-order kinetics model and the Freundlich isotherm model. The mechanism of adsorption was mainly related to electrostatic attraction and the number of active sites occupied by anionic dyes. This study provides valuable guidance and is an effective method for the removal of anionic dyes from aquatic environments.

Competitive adsorption of Pb(II), Cd(II) and Cu(II) onto chitosan-pyromellitic dianhydride modified biochar.

In this work, a novel engineered biochar prepared through modification with chitosan and pyromellitic dianhydride (PMDA) was investigated as an adsorbent for the removal of heavy metal ions from single metal and mixed-metal solutions (Cd, Cu and Pb). Characterization experiments with FTIR and XPS suggested that the novel modified biochar had more surface functional groups compare to the pristine biochar. Adsorption experiments indicated that the initial pH of the solution influenced the ability of biochars to adsorb heavy metals in single- and multi-metal systems. Moreover, the chitosan-PMDA modified biochar had strong selective adsorption of Cu(II). Mechanism studies showed that chemisorption was the major mechanism for heavy metal removal by the chitosan-PMDA modified biochar. Furthermore, the types of effective functional group for these heavy metal removal were different. The NCO group played a dominant role in the process of Pb(II) removal, while several N-containing functional groups and CC groups participated in the adsorption of Cd(II). The novel engineered biochar had selective adsorption capacity for copper due to the N-containing functional groups, meanwhile abundant carbonyl groups also participated in the removal of copper, and may reduce Cu(II) to Cu(I).

Effect of Cu(II) ions on the enhancement of tetracycline adsorption by Fe3O4@SiO2-Chitosan/graphene oxide nanocomposite.

Fe3O4@SiO2-Chitosan/GO (MSCG) nanocomposite was investigated by various techniques (SEM, TEM, XRD, VSM, FT-IR, XPS) for the removal of tetracycline (TC). Effects of pH, zeta potential and initial contaminant concentration were studied in detail. Four background cations (Na+, K+, Ca2+ and Mg2+) with a concentration of 0.01M showed little influence on the TC adsorption at the studied pH range while the divalent heavy metal cation Cu(II) could significantly enhance the adsorption. The results indicated that the highest adsorption capacity of TC were 183.47mmol/kg and 67.57mmol/kg on MSCG with and without Cu(II), respectively. According to mechanism investigation for the adsorption of TC by pH impact study and XPS analysis, besides electrostatic interaction and π-π interactions, the Cu(II) also acts as a bridge between TC and MSCG, which significantly improve the adsorption of TC. This study provided valuable guidance and effective method for the removal of TC from aquatic environments.

The use of microbial-earthworm ecofilters for wastewater treatment with special attention to influencing factors in performance: A review.

With the unique advantages of lower operational and maintenance cost, the use of microbial-earthworm ecofilters (MEEs) for the wastewater treatment has been increasing rapidly in the recent years. This paper provided an overview of the research activities on the use of MEEs for removing pollutants from various wastewater throughout the world. However, the long-term effective treatment performance and sustainable operation of this system still remain a challenge since the treatment performance would be affected by design parameters, operational conditions, and environmental factors. In order to promote the treatment performance, therefore, this paper also provided and summarized the influencing factors of pollutants removal in MEEs. The design parameters and operational conditions of MEEs include earthworm species and load, filter media type, hydraulic loading rate, nutrient load, packing bed height, chemical factors and temperature. Lastly, this review highlighted the further research on these issues to improve performance and sustainability of MEEs.