Study On Washing Distribution Laws And Roasting Leaching Of Coal-Based Lithium,Gallium And Rare Earth Elements

Lithium,gallium and rare earths are strategic critical metals,and with the rapid development of science and technology,their demand is increasing and the recovery of critical metals from secondary sources has become a hot research topic.Coal is considered as one of the potential alternative sources of critical metals in the future,and lithium,gallium or rare earths associated with coal in some areas of China are close to the recommended minimum industrial grade and have potential for exploitation.This thesis focused on coal-based critical metals lithium,gallium and rare earth,and studied the enrichment distribution law of lithium,gallium and rare earths in each product after washing of raw coal,and explored the method of enriching and recovering lithium,gallium and rare earths from coal gangue to provide reference for the resource utilization of coal gangue.In this thesis,the raw coals and washing products of a coal preparation plant in Zhunger area of Inner Mongolia were taken as the research object.The raw coals of the plant were from different coal seams of the Haidaigou mine,all of which were enriched or slightly enriched in lithium,gallium and rare earths,with kaolinite and bomite as the main mineral components.Both jig separation and heavy medium shallow tank separation are conventional gravity separation processes,which have the same effect on the migration and enrichment of lithium,gallium and rare earths in coal.The lithium migrates to coal gangue,the gallium tends to enrich in fine-grained coal slime,and rare earths have no obvious enrichment pattern.However,the relative enrichment rates of gallium and rare earths in coal slime after heavy medium shallow tank separation are significantly higher than those after jig separation.Based on the study of migration laws,the concentration and extraction of lithium,gallium and rare earths from coal gangue with high content of lithium,gallium and rare earths were studied.The screening tests showed that the lithium and gallium in coal gangue were mainly enriched in the+0.125 mm particle size fraction,with an enrichment factor of 1.06 and 1.03 respectively.Rare earths tended to be enriched in the-0.075 mm particle size fraction,with an enrichment factor of 1.17.The float-sink tests showed that lithium in coal gangue was enriched in the+2.4 g/cm~3 density fraction with an enrichment factor of 1.16.Gallium was enriched in the+2.2 g/cm~3 density fraction with an enrichment factor of 1.04.Rare earths were mainly enriched in the-2.4g/cm~3 density fraction with an enrichment factor of 1.21.Particle size and density classification had little effect on the leaching of lithium,gallium and rare earths from coal gangue,and the leaching rate of each element was lower than 25%.In order to improve the leaching rate of lithium,gallium and rare earths from coal gangue,roasting activation method was used.The experimental results showed that the leaching rate of lithium,gallium and rare earths was greatly improved after the coal gangue was roasted at 400℃for 20 min.XRD and FTIR analysis showed that some kaolinite had been converted into active metakaolinite and some organic matter had been removed under this condition.The leaching test was optimised using the orthogonal method and the leaching rates of 94.32%,56.08%and 72.86%were achieved for lithium,gallium and rare earths respectively at a leaching temperature of60℃,a hydrochloric acid concentration of 2 mol/L and a leaching time of 4 h.The kinetic analysis of leaching reactions was carried out in the investigation of leaching patterns of lithium,gallium and rare earths from roasted coal gangue.It was found that the leaching of lithium was controlled by chemical reaction at surface,and its apparent activation energy was 67.99 k J/mol.The leaching of rare earth elements was controlled by diffusion of across solid product layer,and its apparent activation energy was 16.24 k J/mol.The leaching of gallium was controlled by both chemical reaction at surface and diffusion of across solid product layer,and its apparent activation energy was 20.14 k J/mol.Finally,on the basis of the above study,a combined“gravity separation-roasting-leaching”scheme was proposed for the recovery of lithium and gallium from coal gangue.There are 31 figures,15 tables and 118 references in this thesis.