Evaluation Of Heavy Metal Contaminated Soil And The Effect Of Dominant Plants Remediation In Mining Wasteland In Gui Zhou Mountain District

With the development of social economy, environmental pollution and ecological damage was becoming increasingly prominent, adjust the energy structure was imperative. In recent:years, coal mine closed consolidation efforts were increased in Guizhou province. However, due to the lack of necessary environmental restoration measures to abandoned coal mine, about the results that lead to a large number of farmland area was contaminated by acid wastewater and heavy metal and then becoming abandoning farmland area.This caused serious impact on food security and agricultural foundation stability. Therefore, carry out evaluation of heavy metal contaminated soil and the measures of ecological remediation in mining wasteland had important application value and practical significance.In this paper, with the healthy development of the mining area ecological environment as the premise, with the ecological restoration theory as the guide, combined with the actual situation of ecological restoration of coal mine in Guizhou province, Feng xiang shu, Jin tian, Yin dong, Gui’an coal mine wastelands in Huaxi district of Guiyang, Guizhou were selected as objects of the research. in search of suitable materials for soil remediation in coal mine wastelands, the study of the affection of Pteris vittata on soil remediation by heavy mental pollution, the physiological property of Boehmeria nivea treated by different concentration of Tea saponin and enrichment effect on heavy mental Cd contaminated soil were conducted based on outdoor survey, lab analysis and pot experiment methods. The approaches of ecological remediation were studied to provide basic data and technical references. The main research findings were as follows:(1) The soil essential physiochemical properties in coal reclamation area, coal gangue hill reclamation area of Feng xiang shu and Jin tian coal mine wastelands were measured. The results showed that the value of pH in coal mine wastelands was generally low, and even it was extreme acidic in some areas. It was because the acidic substances produced by the acidic waste water form mine outfall and the pyrite associated coal gangue with the oxygen in the air occurring oxidation reactions. The soil pH value was generally low in mining wasteland in function of rainfall and surface runoff, even some regional soil was strongly acidic condition. The capacity of maintenance fertilizer showed larger differences in different coal mine wastelands. It was in middle level in the reclamation area of farmland which cation exchange was10～20cmol/kg. However, it was weak in coal gangue hill reclamation area with cation exchange was below10cmol/kg in the most areas. Soil organic content in the reclamation area of farmland was higher than in coal gangue hill reclamation area. It was indicated that the utilization status and degree of maturation in the former was better than that in the latter. The total amount of N, P, K in coal mine wastelands soils was in lower-middle level. The effective amount of them was generally low due to the acidic soil, especially the effective amount of P which was mainly insoluble aluminum P and iron P-based.(2) The analysis of heavy metal content and morphology was conducted under Feng xiang shu coal mine wastelands, the reclamation area of farmland, coal gangue hill reclamation area, Jin tian coal mine wastelands, wastelands and farmland. It was shown that the heavy metal content Cu, Zn, Pb and Cd was exceeded soil background values in Gui zhou province. Among them, the Cu content of heavy metal was in excess of the 《National soil environmental quality standards》(GB15618-1995) secondary standard, that was50mg/kg. In the reclamation area of farmland, the Cd content was twice much than the primary standard that was0.20mg/kg, even more than in the secondary standard prescribed0.30mg/kg. In the coal mine wastelands, the accumulation of Pb was exceeded the background values of Guizhou provice. The Pb content in some areas was more than the primary standard prescribed35mg/kg, but far below the secondary standard prescribed250mg/kg. Meanwhile, the Zn and Cr content was in a clean level which was lower than the secondary standard.(3) The results of the heavy metal pollution index of Feng xiang shu coal mine wastelands showed that, in farmland reclamation area, the single factor pollution index (Pi) was arranged as:Cd>Cu>Pb>Zn>Cr. It suggested that Cd accumulation was the most serious in farmland reclamation area that the Pi was3.38. The evaluation of N·L·Nemerow pollution index showed that, integrated pollution index was2.15-2.81in five plots of farmland reclamation area. The pollution degree was IV grade that was at moderate level. In coal gangue hill reclamation area, Pi was ranked as:Cd>Cu>Pb> Zn>Cr. It suggested that Cd accumulation was the most serious in coal gangue hill reclamation area that the Pi was3.75. Integrated pollution index was2.41-3.07in five plots. It was shown that overall was in moderate pollution level. In Jin tian coal mine wastelands, wastelands and farmland, the Pi was ranked as Cd>Pb>Cu>Zn>Cr, that was at the moderate and light levels of pollution. The results of evaluation of nemerow pollution showed that:tying area> farmland> wasteland. That was2.13,1.83and1.58, respectively. Cd accumulation of heavy metals in the study area was more obvious. The single factor pollution index was higher. It was proved that there was a potential ecological risk. As a result, Cd should be as a control object in cola mine wastelands in the view of environmental risk and food safety.(4) The patience to extreme acidic soil and the ability of repair soil heavy metal pollution of pteris vittata was studied. The results showed that the soils in these wastelands were acidic, biodiversity was poor, and vegetation was single. Pteris vittata as dominant plant had s strong acid resistance at higher levels of the study area such acidic soils. It still was growing normally. The coverage of pteris vittata was changed along with the value of pH. The smaller the soil pH, the biodiversity in the region was reducing, and the coverage of pteris vittata was smaller. In Jin tian, Yin dong, Gui’an coal mine wastelands, Cd、Pb、Cr、Cu、Zn was varying degrees of overweight. Compared with the soil background value of Gui zhou province, Cd was the most serious excessive heavy metals, up to three times. Effective removal of heavy metal pollution in coal mine was prerequisite in ecological restoration and rehabilitation work. There was a big risk to food safety when planted crops blindly in wastelands.There was a big difference in the capacities of enrichment different heavy metals about pteris vittata. Enrichment factor was Cd>Pb>Cr>Cu>Zn. It was greater than one for Cd and Pb, in which the highest coefficient of Cd concentration reached4.3. So pteris vittata could be considered as a preferred species in restoration and rehabilitation work. The trend of heavy metal transfer coefficient about pteris vittata was roughly Cu>Zn>Pb>Cd>Cr. Heavy metal transfer coefficient of Cu was less than one in Jin tian coal mine because of its extreme Ph. The other two areas was greater than one, which was3.3in Gui’an coal mine wastelands. It was instructive in soil remediation.(5) The effect of ramie growth in different tea saponin solution and the capacity of enrichment and transport of Cd on ramie was measured by pot experimental studies. There was dose effect in the impact of tea saponin of ramie paint height and stem diameter. When the concentration of tea saponin was in0.1and0.5mmol/L, it would exacerbate the toxic effects of heavy metals on ramie. When the concentration was in 1.0～5.0mmol/L, the heavy metal Cd toxic effect on ramie was reduced. The stem diameter reached its maximum if the concentration was2.5mmol/L. Above this threshold, higher concentration did not further reduce the toxic effects of Cd on plant. The dry weight of ramie leaves, seeds and raw jute was significantly decreased when the concentration of tea saponin was in low level (0.1mmol/L) and high level (5.0mmol/L). The dry weight of ramie leaves, seeds and raw jute was upward trend with the increase of the concentration when it was in0.5～2.5mmol/L. The dry weight was significantly increased at2.5mmol/L, indicating that this concentration had effective in leaching Cd heavy metals in soil. The soil toxicity of Cd was exacerbated, ramie root growth was inhibited when the concentration was0.1mmol/L. In some extent, it undermined the ability of upward transport of heavy metals into ramie plant body, causing the Cd content was low in stems and leaves. The Cd content was gradually increased in ramie roots, stems and leaves when then concentration was0.5-2.5mmol/L. However, it was opposite when then concentration was2.5-5.0mmol/L. So, the best choice of tea saponin concentration was2.5mmol/L in the actual mining wasteland Cd contamination governance.The synthesis of chlorophyll a was inhibited when the concentration was in low level(0.1mmol/L). The content of chlorophyll a and chlorophyll b was rise with the increase of the concentration when it was in0.5～2.5mmol/L, reached their maximum at2.5mmol/L. As a result, adding an appropriate amount of concentration of tea saponin in Cd contaminated soil, the content of chlorophyll in ramie was significantly increased.The enrichment factor of Cd in ramie roots, stems and leaves was first increased and then decreased with then concentration of tea saponin. It reached the highest when then concentration was2.5mmlo/L. It was indicated that tea saponin could effectively improve the ability of the enrichment of Cd at the2.5mmol/L.The transfer coefficient was generally upward trend but the increase rate was not obvious when the concentration in0.1～2.5mmol/L. It was0.75that was slightly higher than the other concentration tea saponin treatments when then concentration was in2.5mmol/L. The result showed that there was little impact to Cd transfer coefficient on ramie through different concentrations of tea saponin in Cd contaminated soil.