Reconstruction Of Amorphous Structure Of Coal Gasification Slag And Leaching Of Lithium And Gallium Based On Alkali Fusion System

Metallics,Li and Ga,are important strategic resources.However,with the development of aerospace,nuclear industry,electronics industry and other scientific and technological fields,the demand for Li and Ga is increasing.While traditional mineral resources are gradually depleted.Recovery of Li and Ga from secondary resources has received widespread attention.Coal gasification slag is a solid waste produced in the process of Coal gasification,and some coal gasification slag is rich in Li and Ga,which has potential utilization value.Therefore,establishing an appropriate method for recovering Li and Ga from coal gasification slag is a critical issue in achieving its high value utilization,and the main work of this thesis is as follows:In this study,X-ray diffractometer（XRD）,X-ray fluorescence spectrometer（XRF）,scanning electron microscope and energy dispersive spectrometer（SEM-EDS）,Fourier transform infrared spectroscopy（FTIR）,and inductively coupled plasma mass spectrometry（ICP-MS）were used to study the physical and chemical properties of coal gasification slag and the occurrence of Li and Ga.The main phase of coal gasification slag are amorphous aluminum silicate and quartz,and the morphology of coal gasification slag is spherical particles with smooth surface.The contents of Li and Ga in coal gasification slag are 36.2 mg/kg and 38.8 mg/kg,respectively.They are mainly occurred in aluminosilicate vitreous structures,accounting for 80.42%and90.60%,respectively.Effects of different alkali fluxes and fusion conditions on the leaching rates of Li and Ga in coal gasification slag were explored.It was found that the structure of coal gasification slag could be destroyed by five different alkali fluxes,including Na OH,KOH,Na₂O₂,Na₂CO₃ and K₂CO₃,which would promote the leaching of Li and Ga.The leaching rate of Li（40.81%）under the action of Na OH is slightly lower than that under the action of KOH（41.19%）,while the leaching rate of Ga（47.89%）under the action of Na OH is higher than that under the action of KOH（35.76%）.The leaching rate of Li under the action of Na OH is higher than that under the action of Na₂O₂（25.32%）,while the leaching rate of Ga under the action of Na OH is slightly lower than that under the action of Na₂O₂（52.40%）.The leaching rate of Li under the action of Na₂CO₃（28.20%）is lower than that under the action of K₂CO₃（34.29%）,while the leaching rate of Ga under the action of Na₂CO₃（48.58%）is higher than that under the action of K₂CO₃（38.61%）.Using Na OH as an alkali flux,the leaching rates of Li and Ga is 36.02%and 69.20%respectively.When the mass ratio of Coal gasification slag to Na OH of 1:1.2,the alkali melting temperature of 300℃,and the alkali melting time of 120 min.However,when the leaching conditions were changed,the leaching rates of Li and Ga was not significantly promoted by the water leaching process.Based on the results of XRD,when leaching rates of Li and Ga were relatively high,it was found that the Si and Al elements in the alkali fusion product mainly existed in the form of Na₂Si O₃,nepheline,and other aluminosilicates under the action of Na OH,Na₂O₂ or Na₂CO₃ alkali flux.In addition,the Si element in the alkali fusion product mainly existed in the form of K₂Mg Si O₄,and the Al element existed in the form of aluminate or aluminum oxide under the action of KOH or K₂CO₃ alkali flux.It was found that,when the anions of alkali flux were the same,the destructive effect of Na OH or Na₂CO₃ alkali flux on the structure of coal gasification slag was stronger than that of KOH or K₂CO₃ alkali flux.And when the cations of alkali flux were the same,the destructive effect of Na OH or KOH alkali flux on the structure of coal gasification slag was stronger than that of Na₂CO₃ or K₂CO₃ alkali flux.Thus,anion and cation have a synergistic effect on destroying the structure of coal gasification slag.As a whole,Na OH has a strong destructive ability on the structure of coal gasification slag.Based on the analysis results of NMR,it was found that the structure of coal gasification slag is mainly composed of Q⁴ structure.The structure of coal gasification slag occurs depolymerization after alkali fusion of coal gasification slag,resulting in the formation of aluminosilicate and silicate materials with a Q² structure.Based on the comparison of phase between leaching slag and alkali fusion product,it was found that aluminosilicate,such as nepheline,can be fully dissolved to form Si O₄ and Al O₄ monomers if Na₂Si O₃ presented in the solution.The dissolution of nepheline and other minerals creates a prerequisite for the leaching of Li and Ga.However,the Si O₄ and Al O₄ monomers dissolved in the alkaline solution will form amorphous aluminum silicate,which would result in a part of Li and Ga into the amorphous aluminosilicate structure in the form of isomorphism,thereby reducing the leaching rates of Li and Ga.Furthermore,it was also found that the Q² structure of alkali fusion product undergoes a polymerization reaction after leaching,resulting in a large number of Q⁴ structures formed.This thesis contains the figures of 36,the tables of 7,and the references of 121.