The Effect And Mechanism Of Coal Gangue Combined With Plants On The Improvement Of Copper Mine Tailings

Copper mine tailings is a typical industrial solid waste.Due to the low level of comprehensive utilization,plenty of copper tailings was dumped on the ground.The deposit of copper mine tailings always leaded to heavy metal pollution and safety problems.Therefore,it is meaningful to advocate the ecological restoration of copper mine tailings to reduce the ecological risk.Vegetation restoration is a popular technique in the ecological restoration of tailings,the key point of which is the improvement of substrate and selection of tolerant species.At present,it is a useful method to adopt waste as amendment to remediate the tailings.Coal gangue is a solid waste which is produced in the process of coal mining.It can be used as soil ameliorant in arid and saline-alkali land,and has the potential to be used as heavy metal adsorption material.Therefore,this research added the coal gangue in the copper mine tailings,combined with planting perennial ryegrass(Lolium perenne)and vetiver(Vetiveria zizanioides),by using the pot experiment,leaching experiment,adsorption experiment and particle size experiment,through the variation of physical and chemical properties of amended copper mine tailings,heavy metals behavior in the tailings and the ecological response of repair plants grown in the copper mine tailings,to explore the mechanism and probability of the combination of coal gangue and plant on the ecological restoration of copper mine tailings.This study would supply the comprehensive utilization of copper mine tailings with new ideas and new methods.The main conclusions of the study were as follows:(1)Coal gangue has the material basis and can be recognized as a kind of amendment for remediation of coal gangue.Low nutritional level was found in the copper mine tailings and Cu and Cd concentrations were high in tailings.The comprehensive potential ecological risk index for copper mine tailings reached the level of moderate pollution,which would pose the risk to the environment.Coal gangue belongs to clay mineral,nutritional level in gangue were higher than those in tailings.The total and available heavy metals concentrations of Cd,Cu,Pb and Zn in coal gangue were lower in coal gangue compared with those in copper mine tailings.Therefore,coal gangue has the potential of improvement for the barren environment and heavy metal pollution caused by copper mine tailings;(2)Coal gangue combined with repair plants(ryegrass and vetiver)can cooperate to improve the copper mine tailings.Under three different repair modes of coal gangue+ryegrass,coal gangue+vetiver grass and coal gangue alone,addition of 1%?20%(w/w)coal gangue to tailings,increased the pH and nutritional level in tailings,shifted Cd,Cu,Pb,Zn bound with F1(exchange form)and F2(carbonate form)to F3(iron and manganese form),F4(organic form)or F5(residue form)in the tailings,thus,decreased the bio-availability of Cd,Cu,Pb,Zn in tailings.Therefore,the application of coal gangue could stabilize and repair the Cd,Cu,Pb,Zn in the copper mine tailings.The stabilization and reparation effects were successively listed as follows:coal gangue+ryegrass>coal gangue+vetiver grass>coal gangue.Application the coal gangue to tailings increased the OM(organic matter)content in copper tailings,which is the key factor for changing the behavior of heavy metals and decreasing the metals bioavailability in the copper mine tailings;(3)The remediation plants showed certain response of physiological and ecological characteristics to the copper tailings improved by coal gangue.With the increase of coal gangue addition ratio(1%?20%),the enrichment ability and accumulation level of heavy metals Cd,Cu,Pb and Zn in ryegrass and vetiver grass both decreased,the transport ability was also changed,and heavy metals were mainly enriched at the root of the plant.Meanwhile,chlorophyll a,chlorophyll b and carotenoid,soluble protein and proline contents increased,MDA decreased,and coal gangue could selectively adjust the activities of SOD,POD and CAT to enhance the plant resistance to the stressed environment of the copper mine tailings.The F2 form of heavy metals were the key factor affected the transfer of Cu,Pb and Zn from tailings to the plant root.OM was the key factor affected the uptake of Cd,Cu and Zn from the root to shoot.EC was the key factor affected Pb mobility in the root;(4)Particle size of coal gangue can affect the improvement effect of copper tailings.Within the particle size of 100?1000 um,adding ratio of 1%?20%coal gangue,the smaller the particle size and the higher the addition rate,the lower mobility of Cu in the copper mine tailings.As the gangue size increased,the germination rate,photosynthetic pigment contents and SP content decreased,MDA contents and SOD,POD and CAT enzyme activities increased in the plant.In general,P100+T5(particle size 100um and addition rate 5%)for ryegrass and P100+T1 for vetiver grass would enhance physiological and ecological activities of the plants when they growing in the amended tailings.Therefore,it is concluded that coal gangue has the potential ability for ecological improvement of copper mine tailings and can be regarded as a candidate solid waste amendment.Adding gangue into copper tailings can not only improve the barren environment of copper tailings,but also stabilize the heavy metals in copper mine tailings.Coal gangue combined with plants(ryegrass or vetiver)can produce better stabilization effect of heavy metals in copper mine tailings than coal gangue alone.Figures[24]Tables[31]References[314]...