Experimental Study On Ecological Restoration Of Copper Tailings By Composite Amendments Combined With Herbaceous Plants

Copper sulfide is an important strategic mineral resource in the world at present.The current mining technology inevitably leads to many copper tailings discharge and storage,which not only occupies a large amount of precious land but also covers the original vegetation and destroys the ecosystem.After the large copper sulfide tailings pond is closed,ecological restoration must occur.The ecological restoration method that directly replaces the guest soil with the tailings as the planting substrate is a new method that saves the restoration cost and avoids the environmental damage caused by the guest soil.The key lies in the selection of plant varieties and soil amendments.Herbaceous plants have the characteristics of rapid greening and convenient management and are generally considered the preferred species for vegetation restoration in abandoned mines.Adding amendments can improve the substrate environment for plant growth and restoration efficiency.Therefore,in this study,the copper tailings from the Liujiagou tailings pond of Chengmenshan Copper Mine were taken as the research object.Through the pot experiment,the effects of four kinds of amendments,including conditioner,straw,EM bacterial solution and HDS sludge,on plant growth were studied,and the best compound amendment was selected for promoting plant growth and development.Furthermore,as discovered from the gray correlation analysis results,the effects of composite amendments combined with ryegrass（Lolium perenne L.）,vetiver（Chrysopogon zizanioides L.）and tall fescue（Festuca arundinacea Schreb）on physicochemical properties and heavy metal adsorption of copper tailings were investigated.The results of the study are as follows:（1）The copper tailings showed weak alkalinity（pH=8.05）,a conductivity of 134.63μS/cm,poor water and fertilizer retention ability,and showed non-saline phenomenon.The contents of organic matter,available potassium,total nitrogen and available phosphorus were10.20 g/kg,8.28 mg/kg,0.06 g/kg and 5.15 mg/kg,respectively,which were far lower than the standard required for normal growth and development of plants.The copper,zinc,lead and cadmium contents in copper tailings are 674.48 mg/kg,409.26 mg/kg,27.13 mg/kg and 2.71mg/kg,respectively,polymetallic composite pollution of copper,cadmium,lead and zinc.（2）Compared with the control group and other treatment groups,the combined application of conditioners,straws and EM bacterial solution significantly affected the biomass and plant height of tall fescue.Physiological indicators such as chlorophyll content and catalase activity have significant effects.They can effectively reduce the toxic effect of Cu²⁺in copper tailings on tall fescue,while copper tailings added with conditioner and EM bacterial solution can significantly improve tall fescue.The ability of tall fescue to transport Cu²⁺can more effectively reduce the content of heavy metal copper in copper tailings.（3）In the pot experiment of a single application and combined application of conditioner and straw,a single application of conditioner or straw had the best effect,a single application of conditioner or straw had the best effect,and the length and fresh weight of stem（root）of tall fescue were 2.21（1.78）and 1.81（2.05）times of original tailings（CK）,respectively.The effect of conditioner and straw was better than that of single conditioner or single straw.The plant height,root length,aboveground fresh weight and below-ground fresh weight of tall fescue were the best in C₂S₂ treatment（5%conditioner and 0.5%straw）.The average plant height was20.23 cm,root length was 34.37 cm,fresh aboveground weight was 14.83 g,and fresh underground weight was 3.80 g,237.17%,244.73%,248.37%and 224.79%of the original tailings（CK）.Then,C₃S₃（10%conditioner and 1%straw）and C₁S₁（1%conditioner and 0.1%straw）were successively treated.（4）By grey correlation analysis,it was found that the comprehensive physicochemical properties of copper tailings improved by adding composite amendments were the best,followed by tall fescue and ryegrass.When the total amount of heavy metals increased,the available content of heavy metals decreased significantly,which was beneficial for plant roots to absorb metals.Compared with untreated,BCFroot of Pb and Zn increased by 57.4%and23.4%,respectively,and ryegrass had the most obvious removal effect on heavy metals.