Phytoremediation potential of indigenous plants growing in soils affected by mine activities in Gejiu City, Yunnan Province.

Indigenous plants growing in mining spoils for phytoremediation have attracted great interest. To search the suitable plants, six plant species popular in the mine slag heaps of Gejiu City were collected and metal concentrations in plants and rhizosphere soils were analyzed. Results showed that the soils were greatly influenced by mine activities and heavy metal contents in plants were dependent upon those in the rhizosphere soils. However, the adaptation strategies varied among them. Bothriochloa ischcemum (Linn.) Keng and Equisetum ramosissimum Desf. had the Cr bioaccumulation factor (BAF) of 1.48 and 1.34, respectively, even though the rhizosphere soils were not contaminated by Cr. However, B. ischaemum and Agave americana Linn. showed the BAF for Pb, Zn Cu and Sn < 1.0, and Cyperus rotundus Linn. showed the similarly low BAF for Zn and Cu. Therefore, the three species had a great tolerance to phytostabilize these metals. Gymnema sylvestre (Retz.) Schult showed the translocation factor (TF) > 1.0 for Pb, Cu and Sn, so translocating these metals to the aboveground parts would be a feasible option. Similarly, Euphorbia cyathophora Murr. demonstrated the high phytotranslocate capacity for Cd and Sn, so it could be employed to remedy Cd and Sn-contaminated soils.

This study investigated the phytoremediation potential of six indigenous plants widely growing on mine slag heaps in Gejiu, Yunnan. Bothriochloa ischcemum (Linn.) Keng and Equisetum ramosissimum Desf. were found to own a remarkable capacity to phytoaccumulate Cr. Bothriochloa ischaemum and Agave americana Linn. showed a great capacity to phytostabilize Pb, Zn Cu and Sn. Gymnema sylvestre (Retz.) Schult demonstrated the phytotransfer capacity for Pb, Cu and Sn, and Euphorbia cyathophora Murr. demonstrated the high phytotranslocate capacity for Cd and Sn. These findings will be useful to select suitable indigenous plants for the phytoremediation of local soils contaminated by mining activities.

Metal immobilization by sludge-derived biochar: roles of mineral oxides and carbonized organic compartment.

Pyrolyzing sludge into biochar is a potentially promising recycling/disposal solution for municipal wastewater sludge, and the sludge-derived biochar (SDBC) presents an excellent sorbent for metal immobilization. As SDBC is composed of both mineral oxides and carbonized organic compartment, this study therefore compared the sorption behaviour of Pb and Zn on SDBC to those of individual and mixture of activated carbon (AC) and amorphous aluminium oxide (Al2O3). Batch experiments were conducted at 25 and 45 °C, and the metal-loaded sorbents were artificially aged in the atmosphere for 1-60 days followed by additional sorption experiments. The Pb sorption was generally higher than Zn sorption, and the co-presence of Pb reduced Zn sorption on each studied sorbent. Higher sorption capacities were observed at 45 °C than 25 °C for SDBC and AC, while the opposite was shown for Al2O3, indicating the significance of temperature-dependent diffusion processes in SDBC and AC. Nevertheless, metal sorption was more selective on Al2O3 that showed a greater affinity towards Pb over Zn under competition, correlating with the reducible fraction of sequential extraction. Furthermore, significant amounts of Pb and Zn were additionally sorbed on SDBC following 30-day ageing. The X-ray diffraction revealed the formation of metal-phosphate precipitates, while the X-ray photoelectron spectroscopy showed a larger quantity of metal-oxygen bonding after 30-day ageing of metal-loaded SDBC. The results may imply favourable long-term transformation and additional sorption capacity of SDBC. In conclusion, SDBC resembles the sorption characteristics of both organic and mineral sorbents in different aspects, presenting an appropriate material for metal immobilization during soil amendment.

Synthesis, characterization, and catalytic application of hierarchical nano-ZSM-5 zeolite.

Hierarchical nano-ZSM-5 zeolites (Z5-X) with different grain sizes were synthesized by varying amounts of 3-glycidoxypropyltrimethoxysilane (KH-560) in the hydrothermal synthesis strategy. Moreover, the conventional ZSM-5zeolite(Z5), which was prepared without KH-560, was used as the reference sample. The crystalline phases, morphologies, porous characteristics, Si/Al molar ratios and acidic properties of all fresh catalysts were characterized using the X-ray diffraction (XRD), Fourier transform infrared spectra (FT-IR), scanning electron microscopy (SEM), N2 adsorption-desorption, inductively coupled plasma atomic emission spectroscopy (ICP) and temperature programmed desorption of ammonia (NH3-TPD) techniques. Results show that the grain size and strong acid amount of zeolite decreased with the increasing amount of KH-560. The micropore surface areas and the corresponding volume of Z5-X changed less compared with Z5. Consequently, the high shape-selectivity of zeolite was preserved well under the addition of KH-560. However, the mesopore surface areas and the corresponding volume increased significantly with the increasing amount of KH-560. Benefiting from the abundant hierarchical structure, the Z5-X catalysts exhibited a larger coke capacity than the Z5 catalyst. The coke depositions of all the deactivated catalysts were characterized by the thermogravimetric technique (TG), and the results are indicative of the decreased average rate of coke deposition with an increasing amount of KH-560, which could result from the gradually reduced strong acid amount and the nano-sized crystallites. The catalytic performance of methanol-to-aromatics (MTA) indicates that the Z5-0.12 catalyst exhibited higher catalytic activity and selectivity of BTX as the reaction was prolonged, which could result from the synergistic effect among the proper strong acid amount, the smaller zeolite grain size, and the abundant hierarchical structure.

Effects of light irradiation on the complexes of cadmium and humic acids: The role of thiol groups.

In natural environments, humic substances (HS) play a key role in the control of Cd stability by forming Cd-HS complexes. In this study, we investigated the influence of the photo-irradiation on the Cd levels remaining in Leonardite humic acid (HA) standard solution after chemical precipitation. The kinetic experiment showed that after the irradiation of ultraviolet light, especially UVC, Cd-HA complexes become more stable. The coexisting Cd in the HA solution under light irradiation seemed to enhance the stability of Cd-HA complexes. Both Fourier transform infrared and X-ray photoelectron spectrometric spectra indicated an increase in the thiol amounts in the HA samples treated by light irradiation. Therefore, we developed a fluorescent method to quantify thiol groups in HA with N-(1-pyrenyl) maleimide (NPM). The HA samples were initially spiked with known amounts of glutathione, the reference containing thiol groups, and then was titrated with various amounts of NPM. The measured thiol amounts in the HA treated by UV were found to significantly increase, and the increment was almost equivalent to those of Cd level in HA solution after chemical precipitation. Therefore, it was concluded that the increased thiol groups in HA induced by ultraviolet irradiation resulted in the formation of more stable Cd-HA complexes in solution.

Continuous leaching modifies the surface properties and metal(loid) sorption of sludge-derived biochar.

After the application of sludge derived biochar (SDBC) for soil stabilization, it is subjected to continuous leaching that may change its surface properties and metal(loid) immobilization performance. This study simulated the continuous leaching through the fresh SDBC sample in columns with unsaturated and saturated zones under flushing with 0.01M NaNO3 solution (pH5.5) and acidic solution (pH adjusted to 3.2 by HNO3:H2SO4=1:2), respectively. The resultant changes were assessed in terms of the SDBC surface characteristics and metal(loid) sorption capacities. Continuous leaching was found to gradually decrease the density of basic functional groups and increase the density of carboxyl groups as well as cation exchange capacity on the SDBC surface. It was attributed to the surface acidification and oxidation process by the leaching process, yet it occurred to a lesser extent than the atmospheric exposure. Continuous leaching increased Pb(II), Cr(VI), and As(III) sorption capacity of the SDBC, probably because the increase in carboxyl groups promoted inner-sphere complexation and Fe oxidation as revealed by spectroscopic analysis. It was noteworthy that the SDBC in the unsaturated and saturated zones under continuous leaching displayed distinctive effects on metal(loid) sorption capacity than the atmospheric exposure. Future investigations are needed for understanding the fate and interactions of the SDBC under varying redox conditions and intermittent leaching process.