In-situ Control Of Pollutants Of Coal Gangue And Its Biological Effects

Coal resources in Kaili City,Guizhou Province are mainly enriched in the Yudong River Basin.The acid drainage formed after the weathering and oxidation of the high-sulfur and high-iron coal gangue generated during the coal mining process which has caused serious pollution to the water quality of the Yudong River Basin.Thereby controlling the continuous release of gangue pollutants from the source and improving the ecological environment of the mining area is of great significance for the governance of the Yudong River Basin.Phytoremediation is the main content and goal of ecological restoration in mining areas.However,coal gangue enriched sulfur and iron,and it is strongly acidic and oxidizing,and has poor physical and nutrient conditions,which limit the progress of phytoremediation.From that,the in-situ control of pollutants of coal gangue and its biological effects by amendments-plants remediation were carried out in this study.Basing on leaching column test,this study set up 5 groups:coal gangue?CK group?,coal gangue+passivation materials?passivating group?,coal gangue+passivation materials+plant improvement materials?improver group?,coal gangue+passivation materials+plant improvement materials+Trifolium repens L.?Trifolium group?,coal gangue+passivation materials+plant improvement materials+Lolium perenne L.?Lolium group?.According to the local rainfall,the above five groups were leached regularly?a total of 5 times?.The effects of the amendments-plants?Trifolium repens L.or Lolium perenne L.?remediation on the release of pollutants on coal gangue and the effects of leachate on the germination of Lolium seeds were systematically studied,and the physical and chemical properties,acidification ability,metal distribution characteristics and microbial effects of coal gangue with different vertical profiles were analyzed after leaching,which provide theoretical guidance for in-situ pollutant release control of coal gangue.The main research results showed that:?1?The amendments-plants remediation could reduce pollutants of coal gangue release and reduce its biological toxicity.Different combined remediations reduced the Eh and EC values of coal gangue leachates and the contents of Fe,Mn,Cu,Zn,Cd,Cr,SO₄^2-,F^-and other substances in the leachates,increased the germination rate,germination potential of the leaching seed of Lolium perenne L.,and promoted the elongation of roots and shoots of its seeds.?2?Amendments-plants remediation improved the habitat environment and reduced the number of Thiobacillus ferrooxidans in coal gangue.After remediation,the p H values of coal gangue were raised to neutral or alkaline,the conductivity and redox potential were significantly reduced,the components of gravel and coarse sand particles in coal gangue at all depths were reduced,and the components of fine sand particles,powder particles and clay particles were increased.Bulk density,water content and the distribution difference of water content at various depths were also reduced.Adding plant improvement materials significantly increased the content of nutrients and the number and activity of fungi,bacteria,actinomycetes,sulfate-reducing bacteria,reduced the number of Thiobacillus ferrooxidans in coal gangue.Plants participation further increased the content of available nitrogen and decreased the content of available phosphorus and available potassium.What was more,the number of sulfate-reducing bacteria and Thiobacillus ferrooxidans decreased and increased,respectively,with Lolium perenne L.having the most obvious effect.?3?Amendments-plants remediation significantly reduced the acidification capacity of coal gangue and reduced the migration ability of metal and sulfur in coal gangue,thereby reducing the release potential of pollutants in coal gangue.After the combined remediation,the acid neutralization capacity was significantly improved,and the net acid generation and net acid production potential were significantly reduced,but the improved gangue still had the ability to continue to oxidize acid,which belongs to the moderate or highly acid-producing tailings.After leaching,the total content of Fe,Mn,Cu,Zn,Cd,Cr and S in the coal gangue with remediation were higher than the control group.Each metal in coal gangue mainly existed in the form of oxidizable state and residue state.Compared with the control coal gangue,adding passivating materials increased the proportion of reducible fraction of each metal and the acid soluble Mn,Zn,Cd,and Cr.Adding plant improvement materials had reduced the proportion of reducible Fe,Zn,Cd,and Cr to a certain extent.Participation of plants reduced the acid soluble fraction proportion of metals in a certain extent,increased the residue fraction proportion,and absorbed the metal and S elements in the fixed coal gangue,thereby reducing pollutants migration and re-release.?4?Through correlation and principal component analysis of various habitat improvement indicators,the basic physical and chemical properties,physical status,nutrient status,and microbial characteristics of coal gangue showed a close correlation,and the addition of plant improvement materials had a significant contribution to the improvement of coal gangue habitat,moreover,plants could still maintain good habitat conditions after participation.Correlation analysis was performed among various acidification indicators of coal gangue,as well as related indexes of acidification indicators and pollutant release.The results showed that increasing the sulfate content and reducing the number of Thiobacillus ferrooxidans in coal gangue significantly reduced the oxidation acid production of coal gangue,thereby inhibiting the release of its pollutants in situ.In conclusion,the addition of amendments can inhibit the release of gangue pollutants in situ,and reduce the biological toxicity of leachate.In addition,it improves the physicochemical and microbial characteristics of coal gangue,reduces the acidification capacity of coal gangue and the migration of metals.And the plants growth has little effects to the amendments,furthermore,the acidification of coal gangue and the re-release of metals are further reduced,which not only achieves the ultimate goal of ecological restoration of coal gangue mining area,but also significantly inhibits the release of pollutants in situ.