The Influence Of Vegetation On Coal Gangue’s Supergenic Geochemical Processes

Coal and metallic ore resources are the primary pillar energy in the development of economy;they brought huge economic benefits, followed by environmental pollution and ecological damage.It’s worth noting that these processes certainly would produce vast tailings and waste residue,which would take up a lot of land and produce raise dust, poisonous gas, waste water, especially the oxidation of sulphidic minerals. The oxidation of pyritic mining waste is a self-perpetuating corrosive process which generates acid mine drainage(AMD) effluent for centuries or longer.Acid mine drainage is one of the typical environmental problems. It attracted the attention of the international scientific community due to its obvious acidity, salinity, Fe, Mn and heavy metals.Nowadays, the series of ecological environment problems of coal fields have become important problems restricting sustainable development and ecological security.Natural vegetation affected the evolution process of the surficial material as the key biology,and had important effect on the biogeochemical process of elements. While rare natural vegetation survived due to the toxic effect of acid, salt and heavy metals ion. But the acidophilic microorganisms presented higher biological activity promoting the weathering of coal gangue, and the mechanism had been studied deep and roundly. While the studies involved vegetation recovery lacked obviously. What’s the effect of restore vegetation on the weathering process of coal gangue?Did it promote or inhibit the process? The impact of restore vegetation on characteristic weathering components, particle size and mechanisms were still unclear. Hence, it was important and necessary to study the the influence of vegetation on coal gangue’s supergenic geochemical processes. The results would provide supports to the processes, replenishing the knowledge of the processes. It would have important theoretical significance for the control and ecological remediation of sulfide tailings.In this paper, we summarized the researches basis of supergene geochemical process by acidophilic microorganisms, and selected high sulfur coal gangue dumps in Maiping of Guiyang as the object of study(sulphur content>5%). Under warm wet climate, we studied the effect of the natural recovery vegetation such as Dryopteridacea, Neyraudia reynaudiana, Masson pine and the artificial restoration vegetation on weathered coal gangue, including the effect on Eh, p H,salinity(EC), gangue particle size, elementary composition, primary/secondary mineral composition; H+, SO42-, total iron, ferrous, Mn, Cu, Zn ion, etc.. We also studied the abundance and biocatalysis activity of acidophilic microorganisms, the abundance of invading microorganisms(bacteria, fungi and actinomycetes), phytoextraction and phytostabilization of typical elements, formulating the law of biogeochemical process with plant. Further, we would studied the vegetation as bermuda grass, ryegrass and clover and their effect on coal gangue’s geochemical process. At the same time, analyzing the change of the original and secondary mineral to understand the effects of vegetation on the weathering processes of coal gangue.Component analysis and correlation analysis were carried to the main impact factors and the interaction. The results as follows:1. The weathered coal gangue dumps had unique physical characteristics, chemicalcharacteristics and biological features: which presented lower p H, higher conductivity and strong oxidation; there were also rich in soluble metal ions(Fe, Mn, Cu, Zn) and acidity, SO42-; The clay,silt content were high but sand content was low and larger specific surface area, thiner D50, area of mean diameter and volume mean diameter upper dump, but in the bottom, the coal gangue was coarser, showing the typical unweathered characteristics. The whole gangue yard was rich in jarosite, and quartz accumulated in mid-upper layer, but gypsum, plagioclase presented the characteristics of leaching in mid-upper and accumulating respectively mid-under layer. Pyrite was almost not found in mid-upper layer, but was abound in 60-70 cm. The abundance and activity of acidophilic microorganisms, total microbial biomass was high. But quantity of natural bacteria, fungi, actinomycetes microorganisms were extremely rare, and which distributed mainly on the surface, presenting the typical characteristic of tailings weathering with produce-acid microbial.2. Restore vegetation could obviously change the yard p H, Eh, EC and moisture content.Recovering Dryopteridacea, Neyraudia reynaudiana, Masson pine and the artificial restoration vegetation on weathered coal gangue dumps could improve the dumps p H, reduce soluble salt content, especially in the upper layer; and reduce upper oxidation, but increase mid-lower oxidation. In addition, restore of the vegetation reduced the moisture content of surface layer, but increased the moisture content of mid-low layer.3. The restore of the vegetation could change the particle size of gangue effectively. On the whole, these vegetation could reduce the clay, silt content and specific surface area of gangue, but increase the sand content, D50, area mean diameter, volume mean diameter, which promoted aggregate structure of mid-upper layer presenting the characteristic of loam texture evolution,while the mid-low layer wasn’t the same, there increase the clay, silt content, but reduce the sand content, promoting coal gangue crushing collapse.4. Restore vegetation could change coal gangue mineralogical characteristics significantly. In the artificial herbage recovery dumps, restoring vegetation could reduce the jarosite content in mid-upper layer effectively, its level from mid-low to bottom layer was quite(even higher) with the blank. The gypsum and plagioclase content also increased especially in mid-upper layer, but the accumulation of quartz reduced obviously. But we didn’t observe the obvious characteristic peak of Fe S2 on the whole yard.5. The recovery vegetation could The recovery vegetation could inhibit the weathering components leaching significantly, especially the upper layer was more obvious. The recovery vegetation could lower the content and ratio of exchangeable Fe, Mn, Cu and Zn, but increase oxidible and residual forms. The reductive Fe dropped in a certain extent, but the reductive and oxydic Mn, Cu, Zn increased.6. Restore vegetation could markedly alter dumps microbiological characteristics. These restore vegetation could increase the abundance of Bacteria, fungi and actinomycetes obviously, but the abundance and activity of original acidophilic microorganisms reduced significantly. The total microbial biomass reduced especially in mid-low layer.7. Acid producing microorganisms, weathering compositions and particle size of the coal gangue were the main factors affecting the coal gangue weathering process. The correlation analysis results showed: there were obvious correlation between acidophilic microorganisms,particle size characteristics and weathering components. The analysis of principal component showed: the variation of produce-acid microbial and main weathering components(acidity, SO42-,Fe, Mn, Cu, Zn) and The particle size characteristics, as clay, particle, and sand, specific surfacearea, intermediate diameter and so on,were the most important factor effecting gangue weathering process, Nevertheless, the bacteria, fungi and actinomycetes being brought in and p H, Eh,moisture content and the total microbial biomass had quite little effect on the weathering process.8. The secretory or metabolic component from vegetation could effect the abundance and activity of the acidophilic microorganisms. The analysis indicated that litter and root exudate of vegetation had significant effect, low concentration of the metabolic component(humic acid and fulvic acid) had no obvious effect, but high concentration could inhibit the growth and activity of acidophilic microorganisms significantly. The low concentration of secretory component(acetic acid, malic acid, citric acid) could promote the growth and activity of aacidophilic microorganisms,but it was inhibited in high concentration.According to the above results, recovery vegetation changed the original process of supergene geochemical obviously. Restore vegetation changed the gangue dumps p H and oxidation-deoxidation environment, affected the particle size and granular structure of gangue; It inhibited the abundance and activity of the acidophilic microorganisms and the fixation and extraction of vegetation. Finally, the content and leaching amount of the characteristic weathering components of coal gangue reduced making the original environmental characteristics no longer exist.