Zhi Dang

Soil Heavy Metal Pollution Around the Dabaoshan Mine, Guangdong Province, China

Soil contamination in the vicinity of the Dabaoshan Mine, Guangdong Province, China, was studied through determination of total concentrations and chemical speciation of the toxic metals, Cu, Zn, Cd, and Pb, using inductively coupled plasma mass spectrometry. The results showed that over the past decades, the environmental pollution was caused by a combination of Cu, Zn, Cd, and Pb, with tailings and acid mine drainage being the main pollution sources affecting soils. Significantly higher levels (P ≤ 0.05) of Cu, Zn, Cd, and Pb were found in the tailings as compared with paddy, garden, and control soils, with averages of 1 486, 2 516, 6.42, and 429 mg kg−1, respectively. These metals were continuously dispersed downstream from the tailings and waste waters, and therefore their concentrations in the paddy soils were as high as 567, 1 140, 2.48, and 191 mg kg−1, respectively, being significantly higher (P ≤ 0.05) as compared with those in the garden soils. The results of sequential extraction of the above metals from all the soil types showed that the residual fraction was the dominant form. However, the amounts of metals that were bound to Fe-Mn oxides and organic matter were relatively higher than those bound to carbonates or those that existed in exchangeable forms. As metals could be transformed from an inert state to an active state, the potential environmental risk due to these metals would increase with time.

Heterogeneous photo-Fenton photodegradation of reactive brilliant orange X-GN over iron-pillared montmorillonite under visible irradiation.

Decolorization and mineralization of reactive brilliant orange X-GN was investigated under visible light irradiation (lambda>or=420 nm) by using Fe-Mt/H(2)O(2) as the heterogeneous photo-Fenton reagent. The characterization results (XRD, FTIR, XRF, BET, XPS, UV-vis diffuse spectra) of Fe-Mt suggested that small-sized hydrolyzed iron successfully intercalated into the interlayer spaces of the clay via pillaring. The stability of the Fe-Mt catalyst was evaluated according to the decolorization efficiency for X-GN with used catalyst from previous runs and the concentration of iron ions leached from the solid structure into the reaction solution. The catalytic results showed that at a reaction temperature of 30 degrees C, pH 3.0, 4.9 mmol/L H(2)O(2) and 0.6g/L catalyst dosage, 98.6% discoloration and 52.9% TOC removal of X-GN were achieved under visible irradiation after 140 min treatment. Furthermore, the maximum concentration of dissolved iron ions was 1.26% of the total iron content in the Fe-Mt catalyst after photocatalysis. A halogen lamp as light source has demonstrated that visible radiation can be successfully used for a heterogeneous photo-Fenton process.

Bioleaching of metal concentrates of waste printed circuit boards by mixed culture of acidophilic bacteria.

Metal concentrates of printed circuit boards (PCBs) are the residue valuable metals from which non-metallic components are removed. The non-metallic components show bacterial toxicity in bioleaching process and can be recycled as well. In this study, the effects of initial pH, initial Fe(II) concentration, metal concentrate dosage, particle size, and inoculation quantity on the bioleaching were investigated so as to determine the optimum conditions and evaluate the feasibility of bioleaching of metal concentrates of PCBs by mixed culture of acidophilic bacteria (MCAB). The results showed that the initial pH and Fe(II) concentration played an important role in copper extraction and precipitate formation. Under the optimized conditions of initial pH 2.00, 12g/L initial Fe(II), 12g/L metal concentrate dosage, 10% inoculation quantity, and 60-80 mesh particle size, 96.8% the copper leaching efficiency was achieved in 45h, and aluminum and zinc 88.2% and 91.6% in 98h, respectively. All findings demonstrated that metals could be efficiently leached from metal concentrates of waste PCBs by using the MCAB, and the leaching period was shorten from about 8 days to 45h.

Removal of Cd2+ from aqueous solution by adsorption using Fe-montmorillonite

Fe-montmorillonite (Fe-Mont.) is obtained by exchanging the original interlayer cations of montmorillonite by poly-hydroxyl ferric. In this paper, Fe-Mont. was synthesized by using Ca-montmorillonite (Ca-Mont.) directly under ultrasonic treatment with the aim to enhance the ability of removal of heavy metal ions from wastewater. The modified materials were characterized by X-ray diffraction (XRD) and Fourier transform infrared (FT-IR). Batch equilibrium experiments of Cd(II) ions (Cd(2+)) adsorption on the Fe-Mont. were performed. Effects of the initial pH of the solution and contact time on the adsorption of Cd(2+) were studied. Four types of adsorption isotherms were applied to describe the adsorption isotherms of Cd(2+) by Fe-Mont. The relationship between adsorbing capacity (q(e)) and equilibrium mass concentration (C(e)) is in accordance with the isothermal adsorption equation of Langmuir. Three kinetic models, including pseudo-first-order, pseudo-second-order and the Elovich equation model, were used to analyze the Cd(2+) adsorption process. The pseudo-second-order chemical reaction kinetics provide the best correlation of the experimental data, therefore the adsorption dynamics follows the laws of pseudo-second-order kinetics.

Equilibrium and kinetic studies of adsorption of Cd(II) from aqueous solution using modified corn stalk.

This paper describes the adsorption of cadmium ions from aqueous solution using acrylonitrile (AN)-modified corn stalk (AMCS). AMCS was characterized by elemental analysis, scanning electron microscopy, surface area and porosity analyzer, Fourier transform infrared and solid-state CP/MAS (13)C NMR spectra, and then used to evaluate the adsorption capacity in different pH values, adsorption isotherm, kinetics and thermodynamics in batch experiments. The results showed that AMCS is found to be an effective adsorbent because of its pore size and functional groups (-CN). The pH of 7.0 was an optimal pH for removal of Cd(II) ion and the Langmuir model provides a better fit to the equilibrium data than the Freundlich model, showing a maximum uptake of 12.73 mg g(-1), compared to raw corn stalk (RCS) (3.39 mg g(-1)). Analysis indicated that pseudo-second-order kinetics controlled the adsorption rate. The activation energy (E(a)) was 9.43 kJ mol(-1). Thermodynamic parameters such as DeltaG, DeltaH and DeltaS were also evaluated to predict the nature of adsorption process.

Chemical speciation of fine particle bound trace metals

This study reported quantifications of fine particle bound trace metals and their potential health risks for residents in Guangzhou, a rapidly developing and most populated city in South China. The fine particle samples were collected from October 29th. to November 8th. of 2006 at two different elevations in a mainly residential area and analyzed for the total concentration of aluminum, iron, zinc, lead, manganese, copper, arsenic, chromium, nickel, cadmium, molybdenum and cobalt. Results showed that the fine particle concentrations ranged from 95.8μg/m3to 194.7 μg/m3 at the ground and 83.3-190.0 μg/m3 on the roof, which were much higher than the 24 h fine particle standard (35 μg/m3) recommended by USEPA. The total concentrations of zinc, lead, arsenic, chromium and cadmium in fine particle were 504.8, 201.6, 24.3, 7.7 and 4.4 ng/m3, respectively, which were comparable to other major cities of China, but much higher than major cities outside of China. A sequential extraction procedure was used to fractionate these fine particle bound metals into four different fractions. Results indicated that most toxic metals were mainly distributed in bioavailable fractions. For instance, about 91 % of cadmium, 85 % of lead and 74 % of arsenic were in bioavailable forms. Risk calculations with a simple exposure assessment model showed that the cancer risks of the bioavailable fractions of arsenic, chromium and cadmium were 3 to 33 times greater than usual goal, indicating serious health risks to the residents in this urban area.

Remediation of soil co-contaminated with pyrene and cadmium by growing maize (Zea mays L.)

Sites co-contaminated with organic and metal pollutants are common and considered to be a more complex problem as the two components often causes a synergistic effect on cytotoxicity. Phytoremediation has been proposed as a cost-effective technology for treating heavy metal or organic contamination and may be suitable for remediation of co-contaminated soil. This study investigated the concurrent removal of pyrene and cadmium in co-contaminated soil by growing maize in a pot experiment. At the end of 60 day culture, pyrene in spiked soil diminished significantly, accounting for 21–31 % of the initial extractable concentration in unplanted soil and 12–27 % in planted soil. With the increment of cadmium level, the residual pyrene both in unplanted and planted soil tended to increase. Although the presence of cadmium increased the accumulation of pyrene in maize, plant accumulation only account for less than 0.30 % of the total amount of the dissipated pyrene in vegetated soils. It implied that plant-promoted microbial biodegradation was the predominant contribution to the plant-enhanced dissipation of pyrene in co-contaminated soil. Unlike pyrene, heavy metal cadmium cannot be degraded. It was observed that maize can concurrently removed about on the average 0.70 % of the total cadmium amount in soil by plant uptake, but cadmium phytoextraction would be inhibited under contamination of pyrene. Maize CT38 can normally grow in the co-contaminated soil with high level cadmium and pyrene and can effectively remedy the sites co-contaminated with these two types of contamination, which suggest the possibility of simultaneous phytoremediation of two different contaminant types.

Nickel oxide and carbon nanotube composite (NiO/CNT) as a novel cathode non-precious metal catalyst in microbial fuel cells.

Comparing with the precious metal catalysts, non-precious metal catalysts were preferred to use in microbial fuel cells (MFCs) due to the low cost and high oxygen reduction reaction (ORR) efficiency. In this study, the transmission electron microscope and X-ray diffraction as well as Raman investigation revealed that the prepared nanoscale NiO was attached on the surface of CNT. Cyclic voltammogram and rotating ring-disk electrode tests showed that the NiO/CNT composite catalyst had an apparent oxygen reduction peak and 3.5 electron transfer pathway was acquired under oxygen atmosphere. The catalyst performance was highly dependent on the percentage of NiO in the CNT nanocomposites. When 77% NiO/CNT nano-sized composite was applied as cathode catalyst in membrane free single-chamber air cathode MFC, a maximum power density of 670 mW/m(2) and 0.772 V of OCV was obtained. Moreover, the MFC with pure NiO (control) could not achieve more than 0.1 V. All findings suggested that NiO/CNT could be a potential cathode catalyst for ORR in MFCs.

Enhancement of photocatalytic degradation of dimethyl phthalate with nano-TiO2 immobilized onto hydrophobic layered double hydroxides: A mechanism study

The organic layered double hydroxides (LHDs)/TiO(2) composites with various mass ratios were prepared by the reconstruction of mixed metal oxides to photodegrade dimethyl phthalate (DMP). The physicochemical properties of the obtained products were analyzed by X-ray diffraction (XRD) spectra, X-ray photoelectron spectra (XPS), UV-vis diffuse reflectance spectroscope and scanning electron microscope (SEM). The results showed that the TiO(2) particles and the organic LDHs were combined together through chemical bonds, and TiO(2) particles were well distributed on the surface of the interconnecting organic LDHs nano-flakes. According to the experimental results of adsorptive and photodegradation of DMP, the organic LDHs with flaky structure could effectively adsorb the DMP molecules and the adsorption isotherm by the composites modeled well with the Langmuir equation. The enrichment of DMP onto the composites and the external hydroxyl groups of the composites produce a synergistic effect leading to greatly enhance the rate of DMP photocatalytic degradation by the obtained composites.

Biosorption of Cd(II) by live and dead cells of Bacillus cereus RC-1 isolated from cadmium-contaminated soil

The present study investigated the biosorption capacity of live and dead cells of Bacillus cereus RC-1 for Cd(II). The biosorption characteristics were investigated as a function of initial pH, contact time, and initial cadmium concentration. Equilibrium biosorption was modeled using Langmuir, Freundlich and Redlich-Peterson isotherm equations. It was found that the maximum biosorption capacities calculated from Langmuir isotherm were 31.95 mg/g and 24.01 mg/g for dead cells and live cells, respectively. The kinetics of the biosorption was better described by pseudo-second order kinetic model. Desorption efficiency of biosorbents was investigated at various pH values. These results indicated that dead cells have higher Cd(II) biosorption capacity than live cells. Furthermore, zeta potential, transmission electron microscopy (TEM), scanning electron microscopy (SEM) coupled with energy dispersive X-ray (EDX), and Fourier transform infrared spectroscopy (FTIR) studies were carried out to understand the differences in the Cd(II) biosorption behavior for the both biosorbents. The bioaccumulation of Cd(II) by B. cereus RC-1 was found to depend largely on extracellular biosorption rather than intracellular accumulation. Based on the above studies, dead biomass appears to be a more efficient biosorbent for the removal of Cd(II) from aqueous solution.