Yingying Xie

Mineralogical characteristics of sediments and heavy metal mobilization along a river watershed affected by acid mine drainage

Trace-element concentrations in acid mine drainage (AMD) are primarily controlled by the mineralogy at the sediment-water interface. Results are presented for a combined geochemical and mineralogical survey of Dabaoshan Mine, South China. Developed sequential extraction experiments with the analysis of the main mineralogical phases by semi-quantitative XRD, differential X-ray diffraction (DXRD) and scanning electron microscopy (SEM) were conducted to identify the quantitative relationship between iron minerals and heavy metals. Results showed that schwertmannite, jarosite, goethite and ferrihydrite were the dominant Fe-oxyhydroxide minerals which were detected alternately in the surface sediment with the increasing pH from 2.50 to 6.93 along the Hengshi River. Decreasing contents of schwertmannite ranging from 35 wt % to 6.5 wt % were detected along the Hengshi River, which was corresponding to the decreasing metal contents. The easily reducible fractions exert higher affinity of metals while compared with reducible and relatively stable minerals. A qualitative analysis of heavy metals extracted from the sediments indicated that the retention ability varied: Pb > Mn > Zn > As ≈ Cu > Cr > Cd ≈ Ni. Results in this study are avail for understanding the fate and transport of heavy metals associated with iron minerals and establishing the remediation strategies of AMD systems.

Effects of eggshell addition on calcium-deficient acid soils contaminated with heavy metals

In this study, effects of water conditions (flooded, wet, or dry) and eggshell dosages (0, 0.1, 1.0, and 10.0 g/kg soil, respectively) on pH variation, content of unavailable state of heavy metals, form of heavy metals, and available nutritious element calcium (Ca) in acid soils contaminated with heavy metals were investigated, respectively. The soil samples were continuously cultivated indoors and analyzed by toxicity characteristic leaching procedure and community bureau of reference (BCR) sequential extraction procedure. The results showed that the addition of eggshell could effectively improve the pH of acid soil and increase it to neutral level. Moreover, the contents of unavailable state of heavy metals Cu, Zn, and Cd increased significantly. Furthermore, when the soil was cultivated under the flooded condition with 1.0 g/kg eggshell, the unavailable state of Cu, Zn, and Cd increased the most, and these heavy metals were transformed into residual state. On the other hand, the amount of available state of Ca increased to 432.19 from 73.34 mg/kg with the addition of 1.0 g/kg eggshell, which indicated that the addition of eggshell dramatically improved the available state of Ca. Therefore, eggshell could ameliorate the soil environment as it led to the decrease of available heavy metals and improvement of fertilization effectively. In a word, this study indicates that the addition of eggshell would be a new potential method for remediation of acid field soils contaminated with heavy metals.

Role of Dissolved Organic Matter in the Release of Chromium from Schwertmannite: Kinetics, Repartition, and Mechanisms

Dissolved organic matter (DOM) is an important factor influencing mineral biogeochemistry, although the role of labile DOM in the release of chromium (Cr) from schwertmannite, a mineral with high surface area, is unclear. In this study, the interaction of DOM with synthetic CrO-schwertmannite was investigated to better understand the potential fate of Cr in high-DOM environments. Minerals and their products were analyzed using Fourier transform infrared spectroscopy, X-ray diffraction, transmission electron microscopy, scanning electron microscopy, and X-ray photoelectron spectroscopy. Experiments were conducted at pH 3.2 or 6.5 for different lengths of time, with a shrinking core model developed to describe kinetic processes. The concentration of total Cr in solution reached a maximum when the pH was 6.5 and the concentration of L-tryptophan was 5 mM. The newly formed minerals were confirmed to be mixtures involving residual schwertmannite, goethite, ferrihydrite, and jarosite. A possible mechanism is proposed to be a ligand-controlled binary system, accompanied by possible reduction at acidic pH conditions (3.2), including mass transfer and charge transfer processes. This study gives a new perspective for understanding the reactivity and stability of schwertmannite in the environment; it also provides some predictions on the mobility and fate of Cr. These findings will help design remediation strategies for Cr contamination.

Isotope geochemistry, hydrochemistry, and mineralogy of a river affected by acid mine drainage in a mining area, South China

The Hengshi River is a classic example of an acid mine drainage (AMD)-affected river located in the Dabaoshan mining area in southern China. This work utilized stable isotopes (δ34S and δ18O) and hydrochemical data of surface water samples as well as the mineralogical composition of sediment samples to evaluate the processes that affect the sulfate content in water of the Hengshi River. High concentrations of heavy metals (e.g. Fe: >347.78 mg L−1; Zn: >96.48 mg L−1) in the mud impoundment and relatively stable S isotope values (δ34S: −1.53‰ ∼ −0.88‰) in the upper stream suggested that most of the sulfates were derived from sulfide oxidation. Dilution and mineralization could decrease SO42− concentration, but had no significant influence on the isotope composition of SO42−. However, δ34S and δ18O increased with the decrease of SO42− concentration, accompanied by the elevation of pH and adequate organic matter being available, suggesting that bacterial (dissimilatory) sulfate reduction played an important role in the transformation of sulfate downstream. The methods used in this study can also be used in other natural systems. Furthermore, it is important to understand the causes of environmental pollution and to help environmental remediation.

Biosurfactant rhamnolipid enhanced modification of corn stalk and its application for sorption of phenanthrene

The application of modified agricultural wastes for removing polycyclic aromatic hydrocarbons (PAHs) from water is gaining a growing interest. However, most modified methods using synthetic chemicals may cause secondary pollution. To overcome this limitation, in this study, a rhamnolipid modified corn stalk (RL-CS) for the removal of phenanthrene (PHE) from aqueous solution was prepared using a rhamnolipid-enhanced acid modification method. RL-CS with higher surface area and lower polarity exhibited higher PHE removal efficiency than that of raw corn stalk (RCS). The adsorption kinetics of RL-CS fitted well with pseudo-second-order kinetics (R2 > 0.999). Sorption coefficients and carbon-normalized sorption coefficient of RL-CS were 4.68 and 2.86 times higher than that of RCS. Sorption process of RL-CS was nonlinear. Meanwhile, the sorption was an exothermic process and could occur spontaneously. The present study demonstrated that biosurfactant-modified biosorbent RL-CS may be of great potential for the removal of low concentrations of PAHs from the contaminated waters.