[Ecological Effects of Species Diversity on Plant Growth and Physico-Chemical Properties in a Pb-Zn Mine Tailings].

The remediation of metalliferous mine tailings remains a challenge in many regions of the world. A field experiment was conducted on representative Pb-Zn mine tailings with different species richness (1-, 4-, 8-, and 16-species) to evaluate the potential roles of species diversity in the phytoremediation of metalliferous mine tailings. The main results were ① high species diversity greatly enhanced vegetation cover and biomass. For example, the average vegetation cover and biomass were 33.4% and 66.7 g ·m-2 in 1-species plots and reached 78.4% and 183.8 g ·m-2 in 16-species plots, respectively. ② Plant species diversity had significant effects on nutrient accumulation. Total organic carbon (TOC), water organic carbon (SOC), total nitrogen (TN) and total phosphorus (TP) significantly increased with the species diversity (TOC:r=0.30,P<0.001; SOC:r=0.20,P<0.05; TN:r=0.24,P<0.05; TP:r=0.20,P<0.05). ③ Species diversity not only reduced the concentration of diethylenetriamine pentaacetate (DTPA)-extracted metals in the mine tailings, but also decreased heavy metal transfer and accumulation in the soil-plant system. With enhanced species diversity, DTPA-extracted Cd, Cu, Pb, and Zn decreased significantly (DTPA-Cd:r=0.20,P<0.05; DTPA-Cu:r=0.19, P<0.05; DTPA-Pb:r=0.23, P<0.05; DTPA-Zn:r=0.23, P<0.05). With increasing species diversity, a slightly decreasing trend was observed for Cd, Cu, Pb, and Zn concentrations in the aboveground parts of plants (Cd:r=-0.16, P<0.01; Cu:r=-0.23, P<0.001; Pb:r=-0.15, P<0.05; Zn:r=-0.18, P<0.001). In conclusion, plant diversity can play an important role in mine reclamation.

[Effects of Amendments with Different C/N/P Ratios on Plant and Soil Properties of a Pb-Zn Mine Tailings].

A field trial was conducted with abandoned Pb-Zn mine tailings to evaluate the effectiveness of amendments with different C/N/P ratios on plant growth, soil nutrients and enzyme activities, and heavy metal concentrations in plant tissues and the mine tailings. The following results were noted. ①The application of amendments with different C/N/P ratios promoted plant growth and development. The vegetation cover and biomass increased from 2.0%-20.0% and 9.4-115 g·m-2 at 6 months to 62.5%-98.5% and 389-2358.3 g·m-2 at 30 months, respectively. ②When compared with the control tailings, the mean values of organic carbon, water organic carbon, nitrate nitrogen, and available phosphorus in the treatments with different C/N/P ratios increased 6.0%-93.3%, 1.3%-49.3%, 12.3%-214.7%, and 2.7%-81.3%, respectively. Similarly, the addition of amendments with different C/N/P ratios enhanced the soil enzyme activities of dehydrogenase, ß-glucosidase, urease, and phosphatase 0.3-2.8, 0.1-1.4, 0.1-0.6, and 0.1-0.5 times those in the tailings. ③The addition of amendments with different C/N/P ratios decreased the concentrations of diethylenetriamine pentaacetate (DTPA)-extracted Cd, Cu, Pb, and Zn in the mine tailings and the accumulation of Cd, Cu, Pb, and Zn in plant tissues in different degrees. DTPA-Cd, DTPA-Cu, DTPA-Pb, and DTPA-Zn decreased 2.5%-40.2%, 1.4%-25.6%, 1.4%-15.2%, and 0.4%-24.9%, respectively, compared with the control tailings. ④Pearson's correlation coefficients showed that the vegetation cover and biomass were correlated positively with the soil nutrient elements and enzyme activities and negatively with DTPA-extractable metal concentrations. No correlations were observed between the plant metal concentrations and soil DTPA-extractable metal concentrations, nutrient elements, and enzyme activities. Generally, amendments with different C/N/P ratios aided phytostabilization of some types of mine tailings is the preferred option for full remediation of these mine wastelands.

[Effects of Three Industrial Organic Wastes as Amendments on Plant Growth and the Biochemical Properties of a Pb/Zn Mine Tailings].

A field trial was conducted in an abandoned Pb/Zn mine tailings to evaluate the effectiveness of three industrial wastes [sweet sorghum vinasse (SSV), medicinal herb residues (MHR) and spent mushroom compost (SMC)] as organic amendments on plant growth, soil nutrients and enzyme activities, and heavy metal concentrations in plant tissues and the mine tailings. (1) The main findings were as follows: (1) The mean concentrations of diethylene-triamine-pentaacetic acid (DTPA)-extractable Cd, Cu, Pb and Zn in SSV, MHR and SMC treatments decreased by 24.2%-27.3%, 45.7%-48.3%, 18.0%-20.9% and 10.1%-14.2% as compared to the control tailings. When compared to the control tailings, the mean values of organic matter, ammonium-N and available P in SSV, MHR and SMC treatments increased by 2.27-2.32, 12.4-12.8 and 4.04-4.74 times, respectively. Similarly, the addition of SSV, MHR and SMC significantly enhanced soil enzyme activities (dehydrogenase, beta-glucosidase, urease and phosphatase), being 5.51-6.37, 1.72-1.96, 6.32-6.62 and 2.35-2.62 times higher than those in the control tailings. (2) The application of these wastes promoted seed germination and seedling growth. The vegetation cover reached 84%, 79% and 86% at SSV, MHR and SMC subplots. For Lolium perenne and Cynodon dactylon, the addition of SSV, MHR and SMC led to significant increases in the shoot biomass yields with 4.2-5.6 and 15.7-17.3 times greater than those in the tailings. Moreover, the addition of SSV, MHR and SMC significantly reduced the concentrations of Cd, Cu, Pb and Zn in the shoots of L. perenne and C. dactylon in comparison with the control tailings. (3) Pearson's correlation coefficients showed that the vegetation cover and biomass were positively correlated with soil nutrient elements and enzyme activities. Significant negative correlations were observed between DTPA-extractable metal concentrations and vegetation cover and biomass. The metal concentrations in plants were positively correlated with soil DTPA-extractable metal concentrations and negatively correlated with soil nutrient elements and enzyme activities. The results obtained in this field study confirmed that the three organic-rich industrial wastes could be used as amendments for aided phytostabilization of some types of mine tailings.

Manganese-electrolysed slag treatment: bioleaching of manganese by Fusarium sp.

A fungi strain named Fusarium sp. was isolated from manganese-electrolysed slag by using a gradient dilution spread plate method, identified by 26S RNA sequence analysis and phylogenetic tree analysis, and explored for the bioleaching capacity to manganese (II) from manganese-electrolysed slag in liquid mineral medium under different environmental conditions, including system temperature, incubator rotation speed and initial pH value. DNA sequence and phylogenetic analysis indicated the name of this fungi strain, that is, Fusarium sp., and higher bioleaching efficiencies (71.6%) of manganese by this fungi were observed when the bioleaching was carried out under the optimized conditions as follows: contact time: 72 h; system temperature: 28 degrees C; inoculums concentration: 2% (v/v); incubator rotation speed: 150 rpm; pH 4.0. Because of its low cost, environment friendliness and better efficiency, the bioleaching technique will have a significant impact on manganese-electrolysed slag pollution mitigation.

[Study on the bioleaching mechanism of manganse (II) from manganese-electrolytic residue by manganese-resistant strain Fusarium sp].

The manganse bioleaching mechanism by a manganese-resistant strain Fusarium sp. was investigated, through analyzing the bioleaching rate and manganese-electrolytic residue characterizations with the presence of Fusarium sp. and with the addition of organic acids. Special attention was paid to explore the relationship among the manganese's leaching rate, pH, and organic acid concentration during Fusarium sp. bioleaching process. The research results showed that, with the addition of Fusarium sp., some looser and more porous manganese-electrolytic residues could be obtained. And after 47 hours, the leaching rate reached to 84% which was 2.30 times higher than that leached by individual organic acid even after 130 hours; the leaching rate of manganese and the concentrations of organic acids increased at the initial stage and then decreased, while pH was the reversed. Additionally, the concentration of Succinic acid and L-Malic acid reached their crest value (11.12 g/L and 10.23 g/L) at 57 and 62 hours respectively. Yet the pH reached the lowest (4.09) at 29 h, which implied that, Fusarium sp. and organic acid produced played an important role in the leaching of manganese, leading to a high-efficiency and time-saving process. However, due to the high density of manganese-electrolytic residue and the concurrence of the produce and consumption of organic acid together with the adsorption and complexation, the relationship among the extraction rate for manganese ion, pH, and the concentration of organic acid produced could not be described by simple linear correlation and the leaching rate decreased significantly in the later stage.

Manganese waste water treatment by fungi derived from manganese slag.

The aim of this study was to isolate a mould from the surface of manganese slag which had strong resistance and high adsorption of Mn(2 + ), and to determine the effects of initial Mn(2 + ) concentration, incubation temperature, rotation speed and inoculation amount on adsorption of Mn(2 + ) from manganese waste water solution. The result showed that a mould (A5) which was isolated from manganese slag had the adsorption rate of Mn(2 + ) to 97.5% at the initial pH value 6, inoculation amount 2%, rotation speed 150 r/min, a concentration of Mn(2 + ) 500 mg/L, and a temperature of 28 degrees C cultivated for 50 h. As there is no research on adsorption of Mn(2 + ) from manganese waste water by fungi before, this research showed a theoretical guidance on this field.