| Non-ferrous metal beneficiation tailings pond is a heavily polluted site,tailings are often hazardous waste,after the closure should be timely reclamation treatment,high-risk,heavy pollution characteristics make its reclamation treatment measures different from the usual land reclamation,tailings pond reclamation treatment measures and its planning and design is particularly important.Due to the complexity of the reclamation and governance of non-ferrous metal tailings ponds,involving the content considerations of multiple professional fields,there is no complete technical standard so far,and its reclamation governance often borrows the standards and specifications of related professional fields.From a comprehensive multidisciplinary perspective,aiming at the problems of pollutant leaching and diffusion,sewage treatment and land ecological restoration and utilization existing in the existing models,the way of pollutant diffusion on the impact of land ecological environment is comprehensively analyzed,and the ecological closure model of"ecological closure"land reclamation and environmental governance of heavily polluted sites was previously proposed from the concept of source restoration and treatment of tailings ponds.This model includes soil layer structure,isolation layer setting,vegetation establishment,runoff regulation and surrounding slope interception in the tailings ponds area,etc.,which realizes the three-dimensional spatial closure of the closed tailings pond,which not only completely blocks the wind erosion and water erosion diffusion pathways of tailings pollutants in the tailings pond,realizes the source control of heavy metal pollution and the ecological use of land,but also contributes to the safety and stability of the tailings dam body,thus providing a theoretical basis for the systematic improvement of relevant technical standards and specifications of the tailings pond.In this paper,combined with the existing measures of the Chaihe lead-zinc mine tailings pond,the relevant literature and technical standards at home and abroad were searched and searched in various aspects,the existing measures and their effects in the study area were analyzed,the parameters such as soil heavy metal elements,soil moisture infiltration rate,maximum water holding capacity and soil bulk density were measured under different measures,and remote sensing images of the tailings pond were obtained and related parameters were measured in the field,and the methods and measures of soil structure and vegetation establishment in the tailings pond area under the mode of ecological closure restoration for the tailings pond were studied.As well as the design of methods and measures of the drainage system and the determination of its key technical parameters.The main findings are as follows:(1)For the soil layer structure in the tailings pond area,two soil structure methods can be selected considering the source conditions of regional soil cover.(a)In arid and semi-arid regions with abundant soil sources,thick layer soil covering measures can be used to determine the soil cover thickness according to the parameters such as soil bulk density,soil field water holding capacity and annual precipitation,and the corresponding calculation formula of soil cover thickness is given.(b)In the sareas where soil sources are lacking or precipitation is large,soil structure measures of thin layer cover+isolation layer are adopted.The thickness of the mulch should be more than 30 cm to ensure good growth of shrub grass.The thin-layer soil covering in the tailings pond area has high requirements for the isolation layer,and the impermeable high-density polyethylene(HDPE)composite geomembrane is additionally covered with a 5 cm lime layer or crushed limestone layer,which can effectively prevent rainwater infiltration and block the upward migration of heavy metal elements in tailings for a long time.(2)The ecological closure and reclamation management model of tailings ponds requires the establishment of effective vegetation cover in tailings ponds,and the primary goal of tailings pond vegetation is to prevent wind and water erosion in the tailings pond area,and avoid the diffusion of heavy metals and other pollutants or erosion of the overburden layer.Consider the differences in soil cover,regional climatic conditions and suitable tree species in the tailings pond,a large number of literature retrieval and data search analysis were carried out,and corresponding vegetation modes were selected according to the soil cover measures:the thickness of the soil layer≥100 cm,and the mixed vegetation method of Jo-shrub-grass multilayer could be adopted.When the thickness of the soil cover is 30-50 cm,the shrub-grass mixed planting is adopted,and mixed planting is the way to quickly establish the stable structure of vegetation.(3)Planning,analysis and calculation and measure design of tailings pond drainage system.The runoff sources of the tailings pond include heavy rainfall water in the tailings pond area and slope convergence around the tailings pond area,and ArcGIS was used to determine the watershed extent,the area of the catchment area and the average slope of each zone.According to the size of the tailings pond area,two types of calculation methods are selected for the design of storm runoff:for large and medium-sized tailings ponds,it is suitable to use the reasoning formula method of the Academy of Water Sciences for the analysis and calculation of storm runoff;For small tailings ponds with large quantities and wide areas of several square kilometers,the proposed appropriate analytical calculation method is used for calculation.According to the ecological closure mode of the tailings pond,the layout and design of the drainage system of the tailings pond are more systematic,and the comprehensive consideration of the tailings pond area and the surrounding slope convergence is more conducive to the safety of the tailings dam.The calculation method of the total flow and peak flow of production flow in the tailings pond area and its surrounding areas is proposed,according to which drainage analysis and engineering measures can be designed,which can not only effectively discharge storm runoff,but also reduce the construction cost and drainage system floor space compared with the previous drainage design.Analysis and design of reclamation treatment measures under the ecological closed treatment mode of Chaihe lead-zinc tailings pond:(a)soil structure measures:30 cm soil cover+composite geomembrane+5 cm lime layer,which can effectively prevent water infiltration,hinder the upward migration of heavy metals,and have good ecological restoration effect;(b)vegetation restoration measures:shrubs are mainly purple locust,herbaceous sowing ryegrass,alfalfa,mugwort,cold artemisia,dogtail,dandelion,etc.,in the tailings pond area to establish a shrub-grass combined ecosystem,reasonable planting density can play a good role in wind protection and sand fixation;(c)combined with the actual situation of the tailings pond,the designed rainstorm frequency is once in 100 years,and the drainage channel with a bottom width of 1 m and a design water depth of 1.5 m can pass the maximum flow of 5.050 m~3/s,which can effectively discharge floodwater,save floor space and construction costs,and prevent the risk of dam failure. |
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