Pyrolysis Characteristics Of Typical Plants Around Tailings Area And The Migration Rules Of Metal Elements

Most of the raw material tailings produced by Baotou Iron and Steel Group in the process of metal smelting and mining are piled up in the open air for a long time,resulting in the surrounding soil and plants suffering from different degrees of compound pollution of heavy metals and rare earth elements,and a large number of plants in the tailings area enriched with heavy metals and rare earth elements,which will cause secondary pollution if not treated properly.In this thesis,three plants,Artemisia carvifolia,Artemisia argyi and Phragmites australis,which are typical representative plants in the tailing area of Baosteel,were studied by biomass pyrolysis,microwave digestion and oxygen-enriched combustion ashing,respectively,to investigate the distribution and migration rules of heavy metal elements and rare earth elements,and to compare the enrichment of each metal in the solid phase products of biomass pyrolysis and oxygen-enriched ashing products.The organic composition of the three pyrolysis tar products was analyzed using FTIR and GC-MS,and the following conclusions were drawn.(1)Three typical plants from the tailings area were pyrolyzed at 650°C using a self-built reaction platform to obtain gas-liquid-solid three-phase products.analysis of the IR spectra of the pyrolysis tar of the three plants revealed the presence of aromatic rings C=C and various oxygen-containing functional groups such as-OH,-COOR,C=O,-O-,etc.GC-MS results showed that the pyrolysis tar of the three plants contained the highest content of aromatic compounds,and most of them were benzene and its congeners,and the aromatic compounds in Artemisia carvifolia tar were as high as 69.96%,followed by Artemisia carvifolia tar with 52.08%,and finally,the Phragmites australis tar content was46.99%.(2)According to the results of ICP-OES,AFS and AAS,it was found that different plants were selective in the absorption of different heavy metal elements and rare earth elements.Artemisia carvifolia showed preferential selective absorption of heavy metal element Cu and rare earth element La;Artemisia carvifolia showed stronger selective absorption of Zn and Er;Phragmites australis showed significant enrichment of Cu and Er.In the detection of rare earth elements in biomass pyrolysis tar,it was found that all three plants contained large amounts of rare earth elements Ce and Er.Gd and La,which were detected in the original samples of the three plants,were not detected in the tar,which opened up new ideas for the subsequent exploration of the selective capture of rare earth elements by typical plant pyrolysis products in tailings areas.(3)In the pyrolysis biochar and oxygen-enriched combustion ash of the three plants,the enrichment trend of each metal element in the two solid-phase products was approximately the same,and the enrichment ability of heavy metal element Zn and rare earth element Er was the most significant,indicating that Zn and Er were more easily converted in solid phase.Comparing the recovery efficiency of the two solid-phase products Zn and Er,it was found that the pyrolysis biochar was more efficient in recovering the two metals,and the highest recovery efficiencies of 97.53% and 59.29% for Zn and Er,respectively,were achieved by Artemisia biochar,which can be used as the focus of subsequent research on the solid-state recovery of heavy metals and rare earth elements.The traditional oxygen-enriched combustion ash return to the field or humus return to the field did not play a role in heavy metal and rare earth removal,and the choice of pyrolysis biomass to recover biomass energy(biomass char,biotar,biomass pyrolysis gas)while recovering and reusing heavy metals and rare earth elements in the soil can gradually restore the mine soil.In summary,this thesis establishes a method for the subsequent resourceful treatment of typical plants around Baogang tailings dams,Artemisia carvifolia,Artemisia argyi and Phragmites australis,analyses the organic composition of the biomass pyrolysis products of the three plants,and summarises the migration patterns of heavy metals and rare earth elements during the pyrolytic combustion process of the three plants,providing a basis for the solidification and recovery of plants around Baogang tailings dams,as well as theoretical support for the effective remediation of tailings areas.