Zheng-ji Yi

Uranium biosorption from aqueous solution onto Eichhornia crassipes.

Batch experiments were conducted to investigate the biosorption of U(VI) from aqueous solutions onto the nonliving biomass of an aquatic macrophyte Eichhornia crassipes. The results showed that the adsorption of U(VI) onto E. crassipes was highly pH-dependent and the best pH for U(VI) removal was 5.5. U(VI) adsorption proceeded rapidly with an equilibrium time of 30 min and conformed to pseudo-second-order kinetics. The Langmuir isotherm model was determined to best describe U(VI) biosorption with a maximum monolayer adsorption capacity of 142.85 mg/g. Thermodynamic calculation results indicated that the U(VI) biosorption process was spontaneous and endothermic. Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy analysis implied that the functional groups (amino, hydroxyl, and carboxyl) may be responsible for the U(VI) adsorption process, in which the coordination and ion exchange mechanisms could be involved. We conclude that E. crassipes biomass is a promising biosorbent for the removal of uranium pollutants.

Cu and Cr enhanced the effect of various carbon nanotubes on microbial communities in an aquatic environment.

Environmental impacts of carbon nanotubes (CNTs) arise both from the characteristics of CNTs as well as from their sorbed contaminants from aquatic environments. In this work, we employed pristine, carboxyl-, hydroxyl- and amino-functionalized multi-walled CNTs and pristine single-walled CNTs to quantify and compare their impacts on aquatic microbial communities in the absence and presence of Cu or Cr. Aliquots of samples were set up to 10 and 40 days for culture-dependent analyses, namely, quantitative real-time polymerase chain reaction and denaturing gradient gel electrophoresis. Results revealed that the presence of CNTs or the mixture of CNTs and metals transiently affected microbial communities, and toxicity of CNTs was enhanced with the addition of metals. Meanwhile, functionalized CNTs exhibited stronger toxicity. The major impacts were observed after 10 days of exposure, but the microbial community could recover at 40 days to some extent. Though microbial communities recovered, total microbial numbers continued to decrease with contact time. Analysis of sequence cloned 16S rDNA indicated that Bacillus sp. and Acidithiobacillus sp. were the dominant taxa. Overall, CNTs would have more serious risk to an ecosystem in the presence of metals.

Removal of Pb(II) by adsorption onto Chinese walnut shell activated carbon

The excessive discharge of Pb(II) into the environment has increasingly aroused great concern. Adsorption is considered as the most effective method for heavy metal removal. Chinese walnut shell activated carbon (CWSAC) was used as an adsorbent for the removal of Pb(II) from aqueous solution. Batch experiments were conducted by varying contact time, temperature, pH, adsorbent dose and initial Pb(II) concentration. Adsorption equilibrium was established within 150 min. Although temperature effect was insignificant, the Pb(II) adsorption was strongly pH dependent and the maximum removal was observed at pH 5.5. The Pb(II) removal efficiency increased with increasing CWSAC dosage up to 2.0 g/L and reached a maximum of 94.12%. Langmuir and Freundlich adsorption isotherms were employed to fit the adsorption data. The results suggested that the equilibrium data could be well described by the Langmuir isotherm model, with a maximum adsorption capacity of 81.96 mg/g. Adsorption kinetics data were fitted by pseudo-first- and pseudo-second-order models. The result indicated that the pseudo-first-order model best describes the adsorption kinetic data. In summary, CWSAC could be a promising material for the removal of Pb(II) from wastewater.

Uranium biosorption from aqueous solution by the submerged aquatic plant Hydrilla verticillata

The biosorption characteristics of U(VI) from aqueous solution onto a nonliving aquatic macrophyte, Hydrilla verticillata (dry powder), were investigated under various experimental conditions by using batch methods. Results showed that the adsorption reached equilibrium within 60 min and the experimental data were well fitted by the pseudo-first-order kinetic model. U(VI) adsorption was strongly pH dependent, and the optimum pH for U(VI) removal was 5.5. Isotherm adsorption data displayed good correlation with the Langmuir model, with a maximum monolayer adsorption capacity of 171.52 mg/g. Thermodynamic studies suggested that U(VI) adsorption onto H. verticillata was an exothermic and spontaneous process in nature. Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy indicated that the amino and hydroxyl groups on the algal surface played an important role in U(VI) adsorption. The mechanisms responsible for U(VI) adsorption could involve electrostatic attraction and ion exchange. In conclusion, H. verticillata biomass showed good potential as an adsorption material for the removal of uranium contaminants in aqueous solution.