The Reseach On The Eco-Remediation Of Heavy Metals Contaminated Soils In Huayuan Pb/Zn Mine Area Of Xiangxi

With the development and utilization of lead and zinc mine resouces, Pb/Zn ore mining and melting has caused serious environmental pollution and ecological destruction.It has become a popular topic of environmental ecosystem restoration field how to effectively control the environment pollution in mine area,which promote the coordinated development of mining economy and environment.In this study, the Huayuan Pb/Zn mine area of Xiangxi, the country of nonferrous metals, was considered as the subject of research.On the basis of field investigation, sample collection and laboratory analysis,the contents of heavy metals and the various chemical forms of heavy metals in Huayuan Pb/Zn mine area were analyzed,and the pollution of soil heavy metals was evaluated,and the accumulation and distribution of heavy metals in the eleven dominent plants were analyzed,and then ryegrass was selected as the tolerance plant for eco-remediation of multi-metal contaminated soils.The greenhouse pot experiment was conducted to study the responses and the mechanisms of tolerance to multi-metal pollution stress on ryegrass.And effects of soil matrix amendment on the growth and metal accumulation of ryegrass, chemical forms of heavy metals in soils,and on the improvement of soil physical-chemical proporties, micro-ecosystem of Pb/Zn mine tailing were also studied.Based on the above recognitions,a demonstration project was conducted to systematically study the effects of remediation by ryegrass-amendment combined remediation in Huayuan Pb/Zn mine areas,in orer to provide the theoretical basis and the practical experience for eco-remediation of multi-metal contaminated soils and its demonstration project around Huayuan Pb/Zn mine areas.The main results were as follows:1.The contents of heavy metals were analyzed and the pollution degree of heavy metals in the soil of Huayuan Pb/Zn mine area were evaluated, and chemical forms of heavy metals of Pb/Zn mine tailings were studied.The results showed that there was a wide changing range of concentration of the heavy metals in Huayuan Pb/Zn mine area.The content of Cd,Pb,Zn were far exceeds the background value of soil.The content of Cu was little exceeds the background value of soil.According to China Environment Quality Standard for soils(GB15618-1995),most Pb,Zn and Cd exceeded the threshold values of ClassⅢ. According to single-factor indexes of Nemerow pollution index, the soil in melting area and mine tailing area were severely polluted by Pb,Zn and Cd;and the garden soil in Pb/Zn mine area were severely polluted by Cd, were slightly polluted by Pb and Zn.Comprehensive pollution index indicated the total selected soils of Huayuan Pb/Zn mine area were heavily polluted.BCR sequential extraction procedure was adopted to analyze the chemical forms of heavy metals in Huayuan Pb/Zn mine tailings.The chemical form of Cd, Zn and Pb in bare Pb/Zn mine tailings mainly existed in residual fraction.and the chemical forms of heavy metals in the rhizosphere soils of the pioneer species were different with different plants.By promoting the transformation process from residuals fractions to weakly bound fractions,the growth of plants could alter the distribution of Pb, Zn and Cd,could change residual fraction into availability fraction of Pb, Zn and Cd in rhizosphere soils.2.To investigate the plant species composition and accumulation of heavy metals in those species at Lead-Zinc mine melting area and mine tailings disposal sites of Huayuan Pb/Zn mine area, we sampled55species, belonging to23families,49genera.The concentrations of Pb, Zn, Cd and Cu in55plant species were analyzed.The results showed that gramineae and compositae were dominant species of55plant species.The results showed different species had different ability of accumulation and distribution to the same heavy metal.and the different ecological type of same species had different accumulation and distribution ability to the same heavy metal.The average concentrations of Pb,Zn,Cd and Cu in these plants were158.9,853.0,19.0and33.2mg/kg, respectively. The highest concentration of Cd was124.37mg/kg in the leaves of Siegesbeckia glabrescens,followed by Ficus tikoua,Solanum photeinocarpum,Bidens pilosa and Phytolacca Americana with103.3,90.8,77.5and75.7mg/kg in the above-ground. At the contaminated sites, some dominant species with high transfer factor of heavy metals, such as Ficus tikoua, Polygonum flaccidum and Phytolacca Americana might be suitable for use in the phyto-extraction of heavy metals.The dominant species with low transfer factor of heavy metals, such as Imperata cylindrica and Lolium perenne might be suitable for stabilizing heavy metals. On the basis of accumulation and transfer of heavy metal in dominant species and the results of indoor germination test of dominant indigenous plant, Lolium perenne was selected as the pioneer plant for eco-remediation of heavy metals contaminated soils in Huayuan Pb/Zn mine area of Xiangxi.3.A soil culture experiment was conducted to study the response and tolerance mechanisms of ryegrass to the heavy metals stress caused by multi-heavy metals pollution soil of Huayuan Pb/Zn mine area.The biomass and chlorophyll content of ryegrass were decreased by mine muti-metals pollution of Pb/Zn mine area;the contens of Pb, Zn and Cd in the shoots and roots of ryegrass were raised with the increase of heavy metal contents in soils,and the heavy metal concentrations of Pb, Zn and Cd in roots were clearly higher than in above-ground parts of ryegrass,the antioxidant enzyme activities(SOD,POD and CAT) and soluble protein contents in the leaves of ryegrass were basically increased with the increase of multi heavy metal contents in the leaves,and the heavy metals accumulation factor and transfer factor of ryegrass were basicaly decreased with the increase of multi heavy metal contents in soils.Therefore the muti-heavy metal stress of heavy metals to ryegrass was alleviated and the tolerance was enhanced of ryegrass.4.In the pot experiments,red mud and lime stone addition could significantly decreased Pb,Zn and Cd available contents in soil,and reduced Pb.Zn and Cd contents in shoots and roots of ryegrass.Red mud reduced Pb,Zn,Cd exchangeable fraction,and mainly increased the fraction of form bound to Fe-Mn oxides.Lime reduced Pb, Zn and Cd exchangeable fraction,and mainly increased the fraction of form bound to carbonate.Phosphogypsum reduced the available content and exchangeable fraction of Pb,while increased Zn, Cd available contents and exchangeable fraction.The low dosage (1%) of red mud, phosphogypsum and lime could promoted the growth of ryegrass.When the addition dosage was5%of red mud, phosphogypsum,the addition dosage was3%of lime,the growth of ryegrass was limited.All the things considered,red mud was the reasonable amedment and1%was the suiltable dosage for remediation of heavy metal polluted soils in Xiangxi Huayuan Pb/Zn mine area.5.The pot experiments was conducted to study the characters and biological properties of ryegrass and ryegrass-amendment combined remediation in Pb/Zn mine tailing.The results showed that the concentrations of organic matter,olsen phosphorous and alkaline nitrogen were significantly improved with different treatments in Pb/Zn mine tailing,Compared with no remediation,the concentrations of organic matter,alkaline nitrogen and olsen phosphorous in Pb/Zn mine tailing were increased by51.82%,300.00%and901.92%with treatments named the ryegrass and10%garden soil and1%red mud(CNl), respectively.The biomass of ryegrass were promoted under application amendments conditions.The amount of soil bacteria,fungi, actinomyces,soil microbial biomass carbon and nitrogen after remediation were significantly higher than those of no remediation.The amounts of soil bacteria,fungi, actinomyces,soil microbial biomass carbon and nitrogen in CN1treatment was highest among the treatments,with33.78,5.99,21.8,6.34and6.35times respectively.The activities of soil urease,phosphatese,invertase and cellulose were obviously improved by18.43,12.58,5.00and9.15times, in particular,the CN1treatment was highest compared.Thus,it could concluded that combined remediation (CN1),ryegrass and10%garden soil and1%red mud was performed in improving soil fertility,soil micro-ecosystem and promoting ryegrass growth in Pb/Zn mine tailing.6.In the field experiment,the eco-remediation effect by ryegrass combined red mud, phosphogypsum and vegetable garden soil in Huayuan Pb/Zn mine tailings was analysed.The results showed the biomass of ryegrass were remarkably improved,and the growth promoting effectiveness was more significant with the time.Heavy metal contents in the shoots and roots of ryegrass were basically decreased to different extent and the heavy metal accumulation in ryegrass was enhanced and increased with time.Compared with no remediation,the results also showed that the ryegrass-amendment combined remediation in Pb/Zn mine tailing increased the amount of soil bacteria,fungi, actinomyces,soil microbial biomass carbon and nitrogen in ryegrass combined covering soil with5cm depth and1%red mud treatment with3.25,1.48,1.84,1.99and8.79times, respectively.By comparison,the general improvement of soil microorgranism activities and soil nutrient contents by ryegrass combined covering soil with5cm depth and1%red mud treatment were greater than other treatments.In conclusion, ryegrass combined covering soil with5cm depth and1%red mud treatment in Pb/Zn mine tailing improved the soil micro-eco-environment and soil nutrient significantly. Therefore,ryegrass combined covering soil with5cm depth and1%red mud treatment had great potentiality for eco-remediation in pulluted land of Pb/Zn mine area.