| The remaining issues of mine construction are important factors that cause soil and water pollution,ecosystem degradation,and topographical damage.The poor physical and chemical properties of tailings in the abandoned site and the stress of metal or non-metal pollution are the main reasons that limit the ecological restoration of mine.The traditional tailings soil improvement technology is to cover the surface of the waste with a certain thickness of clean soil,and then carry out phytoremediation.This method requires a large amount of engineering,high cost and difficulty in borrowing soil,which can easily cause secondary ecological damage.This paper takes the disposal of huge-scale tailing slag produced in the construction of a fluorite leadzinc mine in Yizhang county,Chenzhou,Hunan province and the greening of the dump as the research object.The comprehensive utilization of tailings and the research on ecological restoration of mines should be strengthened in combination with the relevant knowledge of geotechnical,environmental,and agriculture and forestry disciplines.Firstly,the defects of physical and chemical properties of tailings were determined by toxic leaching method and soil barrier factor identification.Then,biochemical fulvic acid(BFA),ammonium dihydrogen phosphate,zeolite and organic fertilizer were used to modify the corresponding properties.After that,modified tailings matrix was used as planting soil.Furthermore,pot experiment in artificial climate incubator combined with pilot-scale experiment in mine was used to evaluate the remediation effect of modifier and plant on tailing slag,and an ecological restoration method based on insitu matrix improvement and direct vegetation of tailings was proposed eventually.The main work and research results are as follows:(1)The key defect characteristics on the physical and chemical properties of tailings slag in contrasting healthy soils were clarified.Toxicity leaching method and soil barrier factor identification method were used to determine the excess amount of characteristic pollutants in tailings slag,as well as related barrier factors such as fertility,conventional pollutant content,salinity and physical properties.The results show that the tailings have high p H value and salt content,and belong to severe salinealkali soil;Nutrients such as nitrogen,phosphorus and organic matter are lacking,and fertility is seriously insufficient;The dry density is too high,the pore distribution is very poor,and the solidification phenomenon is very serious;The content of lead and zinc is seriously exceeding the standard.The physical and chemical properties of tailing slag are difficult to meet the requirements of planting soil and have serious defects,which need to be modified before they can be applied.(2)A tailings matrix improvement scheme with good effect,simple process and low cost was put forward.The improvement tests of single modifier and orthogonal modifier were carried out to comprehensively analyze the improvement effects of the modifier on various physical and chemical characteristics of tailing slag.The results show that when the dosage of BFA,ammonium dihydrogen phosphate,zeolite and organic fertilizer were 0.5%,0.4%,2% and 15%,respectively,the p H value and dry density of tailing slag used in the pot experiment of artificial climate incubator could be reduced by 26% and 43.6%,respectively.And non-capillary porosity(NCP),noncapillary porosity(NCP): capillary porosity(CP),organic matter content,hydrolytic nitrogen content and available phosphorus content increased by 1.49 times,1.07 times,26.7 times,9.3 times and 20.9 times,respectively,all meeting the requirements of normal planting soil.(3)The effect mechanism of the improvement scheme on the growth of different plants was elucidated.A pot experiment was carried out in an artificial climate incubator to comprehensively analyze the influence of the optimal improvement scheme on the growth of different plants in their whole life cycle,and to measure the enrichment of pollutants by different plants.The results show that pioneer plants grew faster in the modified tailings substrate,with larger plant sizes and higher survival rates.The plants in pot experiment planted for 180 days could grow 0.5m at most,lower than the maximum of 1.5m sown 60 days in the pilot test.The enrichment of lead and fluoride was the highest in Alcea rosea Linnaeus,which was 114 mg/kg and 504mg/kg,respectively.And Cosmos bipinnata Cav.had the highest zinc enrichment,which was 199 mg/kg.The optimal ratio improvement scheme has a good promotion effect on the growth and development of plants,and the selected plants have the potential to become the pioneer plants of fluorite lead-zinc mine.(4)The effect of the best modified formula combined with pioneer plants on tailings remediation was verified.Field pilot tests were carried out to comprehensively analyze the improvement effect of pioneer plants combined with improver on physical and chemical characteristics defects of tailing slag.The results show that amendments combined with pioneer plants reduced the dry density,fluoride content,lead content,zinc content,p H value and salt content of tailing slag by 21.3%,53.6%,11.0%,22.1%,6.8% and 29.6%,respectively.And the NCP,NCP:CP,available phosphorus content,hydrolytic nitrogen content and organic matter content increased by 1.0,1.1,3.8,4.1%and 1.9 times,respectively.After restoration,most of the indexes can meet the standard requirements of planting soil.(5)The dominant pioneer plants which can be used for ecological restoration of fluorite lead-zinc mine were screened.The in-situ pilot study was carried out to comprehensively analyze the enrichment and transport capacity of lead,zinc and fluoride in tailings of different pioneer plants.The results show that among the pioneer plants with good growth,Alcea rosea Linnaeus had the largest lead enrichment,which was 325.3 mg/kg.The enrichment of fluoride was the highest in Cosmos bipinnata Cav.,which was 513.2 mg/kg.And the highest concentration of zinc was found in the Eleusine indica(L.)Gaertn.,which was 439.1 mg/kg.Furthermore,Amaranthus spinosus L.had the best transport capacity for lead and zinc,and Sesamum indicum L.had the best transport capacity for fluoride,with transport coefficients of 3.825,2.385 and 2.433,respectively.The comprehensive transport capacity of Amaranthus spinosus L.was the best,and the transport coefficient of fluoride was 1.158.Therefore,the plants that can be used for reclamation of fluorite lead-zinc mine were selected as follows: Cosmos bipinnata Cav.,Calendula officinalis L.,Alcea rosea Linnaeus,Amaranthus hybridus L.,Sonchus oleraceus L.,Eleusine indica(L.)Gaertn.,Sesamum indicum L.and Amaranthus spinosus L.They can enrich lead,zinc and nonmetal fluoride at the same time,which has a good guiding significance for the study of composite tailings contaminated by both metal and nonmetal. |
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