Aluminum adsorption and antimonite oxidation dominantly regulate antimony solubility in soils.

Soil antimony (Sb) contamination occurs globally due to natural processes and human activities. Total Sb concentration in soils fails to assess its ecological risk, while determined by the concentration of available Sb, which is readily for biological uptake. Available Sb in different soils varied significantly according to soil properties. However, so far it is unknown how soil properties regulate Sb availability, and no model has been established to predict it through soil properties. In this study, 19 soils spiked with antimonite [Sb(III)] were used to identify the major factors controlling Sb availability and establish its predicting models. The results showed that available Sb in different soils varied largely depending on the contents of free aluminum (fAl), free iron (fFe) and electric conductivity (EC), which explained 33%, 27% and 24.9% of the total variation, respectively. During the first 42 days of soil aging, fAl and EC effectively predicted the concentrations of available Sb with R2 = 0.64, while during the later stages (70-150 d) of soil aging, fAl content was the unique parameter employed into the predicting model (R2 = 0.53). These results firstly demonstrate that the content of free aluminum (fAl) is the most important factor regulating Sb availability in soils, although the content of fAl is much lower than that of fFe. This finding can help to develop new remediation materials for Sb-contaminated soils. The prediction models can provide promising tools of assessing the ecological risk. In addition, Sb availability was also affected by the oxidation of Sb(III). After 150 days aging, 1-61% of Sb(III) was oxidized to pentavalent Sb [Sb(V)], which was significantly positively correlated with available Sb, suggesting that Sb(III) oxidization mobilizes Sb in soils. All these findings would help to understand Sb migration and transformation in soils, and to develop new strategies for remediating Sb-contaminated soils.

[Mechanism of groundwater As(V) removal with ferric flocculation and direct filtration].

The As removal process and mechanism from groundwater using ferric flocculation-direct filtration system was investigated using batch, field pilot tests, extended X-ray absorption fine structure ( EXAFS) spectroscopy, and charge-distribution multisite complexation (CD-MUSIC) model. The results showed that arsenate [As(V)] was the dominant As species in the groundwater with a concentration of 40 µg x L(-1). The treatment system could supply 64 984 L As-safe drinking water (< 10 µg L(-1)) using Fe 1.5 mg x L(-1). Toxicity characteristic leaching procedure (TCLP) demonstrated that the leachate As was 3.4 µg x L(-1), much lower than the EPA regulatory concentration (5 mg x L(-1)). EXAFS and CD-MUSIC model indicated that As(V) was adsorbed onto ferric hydroxide via bidentate binuclear complexes in the pH range of 3 to 9.5, while formation of precipitate with Ca or Mg dominated the As removal at pH > 9.5.

Colorimetric Au nanoparticle probe for speciation test of arsenite and arsenate inspired by selective interaction between phosphonium ionic liquid and arsenite.

The exposure of millions of people to unsafe levels of arsenite (AsIII) and arsenate (AsV) in drinking waters calls for the development of low-cost methods for on-site monitoring these two arsenic species in waters. Herein, for the first time, tetradecyl (trihexyl) phosphonium chloride ionic liquid was found to selectively bind with AsIII via extended X-ray absorption fine structure (EXAFS) analysis. Based on the finding, an AsIII-specific probe was developed by modifying gold nanoparticles with the ionic liquid. Futhermore, Hofmeister effect was primarily observed to significantly affect the sensitivity of gold nanoparticle probe. With the colorimetric probe, we developed a protocol for naked eye speciation test of AsIII and AsV at levels below the World Health Organization (WHO) guideline of 10 µg L(-1). This method featured with high tolerance to common coexisting ions such as 10 mM PO4(3-), and was validated by assaying certified reference and environmental water samples.

[Treatment of Cr( VI) in deoxygenated simulated groundwater using nanoscale zero-valent iron].

Laboratory experiments and theoretical modeling studies were performed to investigate the mechanisms of Cr( VI) removal from deoxygenated simulated groundwater using nanoscale zero-valent iron, and to evaluate influencing factors and kinetics based on zeta potential, redox potential, ferrous concentrations, and the pe-pH diagram of Fe-Cr-H2O system. Experimental results demonstrate that the removal efficiency of Cr(VI) decreases with the increasing Cr( VI)/Fe mass ratio. When the Cr(VI)/Fe mass ratios are 0.025, 0.050, 0.075, and 0.100, the corresponding Cr(VI) removal rates are 100.0%, 85.6%, 72.7% and 39.6%, respectively. The Cr( VI) removal is favorable at acidic pH with fixed Cr(VI)/Fe mass ratio of 0.100. When pH are 3.0, 5.0, 7.0, 9.0 and 11.0, the Cr(VI) removal rates are 73.4%, 57.6%, 39.6%, 44.1%, and 41.2%, accordingly. The Cr(VI) removal follows the pseudo second-order kinetics. When pH is 7.0 and Cr(VI)/nZVI mass ratio is 0.025, the rate of Cr(VI) removal is the highest with rate constant at 9.76 x 10(-3) g x (mg x min)(-1). The conversion from Cr2O7(2-) to Cr3+ should be instantaneous when Cr2O7(2-) is absorbed on the surface of Fe. The Cr(VI) was reduced to Cr(III), which was subsequently incorporated into the FeOOH shell and formed a Cr-Fe film. The film once formed could further inhibit the electron transfer between Cr2O7(2-) and Fe. Then Cr(V) removal was primary controlled by the adsorption process.