Basic Research On Thermal Activation And HNO₃ Leaching Of Coal Gangue To Extract Al/Ga/Li

Coal gangue is one of the largest industrial solid wastes in China,which contains Al/Ga/Li/Si resources.Thermal activation and HNO3 leaching of coal gangue to extract Al/Ga/Li is likely to be an effective way to achieve its reduction and efficient utilization.In this thesis,the related basic research was conducted,and a series of results were obtained.Process mineralogy study was performed on coal gangue to determine its mineral composition,output form,grain distribution,and the occurrence mode of target metals.The coal gangue was mainly composed of kaolinite and quartz,which was a typical kaolinite-type coal gangue.Al mainly occurred in kaolinite,boehmite,and mica.The content of clay minerals in coal gangue was high,and most of them were outputted in the forms of monomer,symbiosis with carbon or quartz.During the sieving process,carbon was continuously enriched to the fine fraction,while no significant enrichment was observed for Al/Ga/Li.Based on the mineralogical study,direct acid leaching and mechanical activation-acid leaching experiments were carried out on coal gangue.It was found that the acid medium had very limited ability for decomposing kaolinite,while the mechanical force only partially destroyed kaolinite,and the activation effect was not significant.The thermal behavior and chemical reactivity of coal gangue in different atmospheres were contrastively studied,and the internal mechanism of carbon-loaded combustion promoting kaolinite activation was revealed by means of thermo-kinetics analysis.The thermogravimetric characteristics of coal gangue were determined by its TG-DTG-DSC curves obtained in nitrogen and air atmospheres at variable heating rates.The evolution features of Al-and Fecontaining phases in coal gangue at different activation atmospheres and the leaching behaviors of two activated products in HNO3 medium were comparatively investigated.It was found that air atmosphere achieved both the efficient activation of Al-containing phase and the effective passivation of Fe-containing phase.Thermo-kinetic analysis on the activation processes of coal gangue at different atmospheres was performed by combining the model-free method and model-fitting method.Results showed that carbon-loaded combustion in air atmosphere did not change the activation mechanism of coal gangue,but reduced the apparent activation energy required for thermal activation by nearly 70 kJ/mol.Taking kaolinite and boehmite,the main Al-containing minerals in coal gangue,as the research objects,the internal connection between their thermal evolution and leaching activity was established.By means of TG-DTG-DSC,XRD,FTIR,and MAS NMR analyses,the thermal evolutions of kaolinite and boehmite were clarified.Combined with thermodynamic analysis and leaching experiments at variable temperatures,the leaching activities of kaolinite,boehmite,and their thermal products were explored.It was found that elevated leaching temperature greatly promoted the Al extraction.Accordingly,the optimal temperature ranges for activating kaolinite and boehmite were determined.With this as a guide,the process parameters for thermal activation of coal gangue were optimized and regulated,and the optimal conditions were determined as 550℃ and 0.5 h.Through thermodynamic analysis,systematic HNO3 leaching experiment,and reaction kinetics study,the migration,separation,and enrichment regularities of Al/Ga/Li/Fe/Si components in the HNO3 system were revealed,and the thermodynamic and kinetic regulation mechanisms of HNO3 leaching were clarified.The E-pH diagrams of the metals-H2O system at 150℃ were plotted by using the thermodynamic software FactSage 7.0,which confirmed the scheme of synergistic extraction of valuable components Al/Ga into the leach liquor and synchronous precipitation of Fe into the leach residue was feasible.By parameter optimization,the optimal conditions for HNO3 leaching of activated product were determined.Kinetic analysis revealed that the Al leaching from activated product was insensitive to acidity,but was highly dependent on leaching temperature.The leach residue was subjected to alkaline dissolution,and the result showed that the soluble SiO2 in the leach residue accounted for nearly 70%,which was conducive to the efficient utilization of Si component.The low-temperature pyrolysis experiments of mixed nitrates were carried out to clarify the pyrolysis behavior of each metal nitrate.In view of the extremely similar pyrolysis regularity of Al/Fe/Ga nitrates,a scheme of separating Fe/Ga before pyrolysis and water washing after pyrolysis was proposed to purify the leach liquor.