| The vanadium/titanium magnetite is mostly ultra-lean ore,and a large number of tailings will be produced in the exploitation process.The current technology can’t achieve the comprehensive utilization of all tailings,and most tailings can only be stored in a way that has a certain impact on the ecological environment.The tailings are characterized by loose structure,poor nutrient,complex composition and high heavy metal content.Therefore,in order to protect tailings resources and minimize the impact on the environment,it is of great significance to seek effective ecological remediation technology to solve the problem of vanadium/titanium magnetite tailings stockpiling.In order to improve the environmental quality of vanadium/titanium magnetite tailings,solidified heavy metals,and reduced the ecological environmental damage caused by the migration and transformation of heavy metal ions to the surrounding environment,it is necessary to adopt ecological remediation technology to improve the tailings.The microorganism-plant combined remediation technology is an effective means to improve the tailings environment sustainably.Arbuscular mycorrhizal fungi(AMF)can form symbiotic relationship with most plants,which is one of the effective strategies to adapt to stress environment in nature.Based on the selection of alfalfa varieties suitable for vanadium/titanium magnetite tailings and the remediation of the ameliorant,the remediation mechanism of AMF-Alfalfa symbiotic system on vanadium/titanium magnetite tailings was studied.The main research contents and results were as follows.1)In order to explore the indigenous AMF community structure composition in vanadium/titanium magnetite tailings,the methods of applying sewage sludge compost,planting and in-situ returning green manure(alfalfa,tall fescues and ryegrass,which were screened out earlier and had strong tolerance to vanadium/titanium magnetite tailings)were used to promote plant colonization.The improvement effect of three cycles of green manure returning on the environment of vanadium/titanium magnetite tailings and the community composition of AMF in vanadium/titanium magnetite tailings were analyzed.The results showed that the application of sewage sludge compost,planting and in-suit returning green manure,effectively increased the contents of the carbon,nitrogen and phosphorus and passivated the heavy metals Cd and Zn in vanadium/titanium magnetite tailings.The concentrations of available Cd and Zn in the returning treatment were reduced by 7.72%～23.79% and 8.02%～24.37%,respectively,compared with those in the non-returning treatment.Meanwhile,the AMF in vanadium/titanium magnetite tailings all belonged to the Glomeromycete class analyzed by high-throughput sequencing.The dominant genera were Glomus,Paraglomus and unclassified＿c＿＿Glomeromycetes.Moreover,the AMF richness was increased with the alfalfa green manure returning to the vanadium/titanium magnetite tailings,and the Sobs index was 1.28 to 1.73 times of that in the non-returning treatment.2)The alfalfa cultivar dryland and Xinjiang big leaf selected with strong tolerance through pot experiment and affiliated with the strains Funneliformis mosseae and Claroideoglomus etunicatum belonging to Glomus were selected to establish four different symbiotic systems.The results showed that the primary remediation effect of the symbiosis system between Claroideoglomus etunicatum-alfalfa(dryland)was the best.The nutrient concentration was significantly increased and the growth and nutrient absorption of alfalfa were effectively promoted by the symbiotic system in the barren tailings environment.Compared with the control treatment,the dry weight,root length,root volume,root surface area and the proportion of root diameter greater than 1 mm of alfalfa were increased effectively.The concentrations of available nitrogen,available phosphorus and organic carbon in tailings could reach 3.96 times,1.52 times and 1.07 times of the control treatment,respectively.3)Furthermore,the symbiosis system of Claroideoglomus etunicatum-alfalfa(dryland)was established in vanadium/titanium magnetite tailings,and the composition,structural characteristics and content changes of glomalin-related soil protein(GRSP)in vanadium/titanium magnetite tailings were analyzed by SEM-EDS and FTIR.It was found that the content of GRSP in the vanadium/titanium magnetite tailings was only2.35%-12.19% of that in the normal farmland soil,and it contained a variety of metal elements such as Fe,Cr,Cu,Zn,and a variety of functional groups such as polysaccharide,amides and carboxylic acids,among which the functional groups of polysaccharides were significantly lower than those in the normal farmland soil.Additionally,the content of easily extracted GRSP and total extracted GRSP in vanadium-titanium magnet tailings were 1.71 times and 1.67 times of that in the control treatment,respectively,after the remediation of the Claroideoglomus etunicatum-alfalfa(dryland)symbiosis system.The accumulation of GRSP could be effectively increased by the symbiosis system in barren environment.Moreover,it was proved that the increase of GRSP content was conducive to the accumulation of organic carbon and the formation of large aggregates,so as to effectively improve the tailings environment.4)The effect of the Claroideoglomus etunicatum-alfalfa(dryland)symbiosis system on the heavy metal morphologies,activities in vanadium/titanium magnetite tailings and their accumulation in alfalfa were studied.The results indicated that the Claroideoglomus etunicatum-alfalfa(dryland)symbiosis system could effectively passivate Cu,Zn and Pb in vanadium/titanium magnetite tailings and promote the transformation of heavy metals to residual state.The contents of bioavailable Cu and Pb in tailings could be reduced by21.60%and 40.65%,respectively,compared with the control treatment.In addition,the absorption of Cu,Zn and Pb in alfalfa was reduced under the effect of the symbiosis system.Furthermore,the structural characteristics of GRSP-heavy metal complex were further explored through the adsorption and analytical experiments of GRSP for heavy metals.The experiments showed that GRSP reduced the activity of heavy metals in vanadium/titanium magnetite tailings by binding with heavy metals through C=O and-OH ligands,and the content of heavy metals in GRSP was 1.18 to 2.67 times that of the control treatment.In conclusion,it was revealed that the Claroideoglomus etunicatum-alfalfa(dryland)symbiosis system could effectively remediate the vanadium/titanium magnetite tailings by increasing nutrient content,reducing heavy metals bioavailability,improving aggregate structure and promoting alfalfa growth,which provided theoretical support for the application of AMF-Alfalfa symbiotic system in tailings ecological remediation.Figure 83;Table 15;Reference 291... |
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