Occurrence,Enrichment Mechanism And Leaching Of Lithium In The Upper Permian Coal Measures In Guangxi

The Upper Permian coal-bearing rock series in Guangxi Province are abnormally rich in lithium,but the studies on the occurrence state,controlled factors and metallogenic mechanism of lithium are relatively weak and controversial,which limits the research and development of lithium metal in coal measures in this area to a certain extent.In this paper,the lithologic composition,mineral characteristics and geochemical characteristics of the upper Permian Uniheishan Formation coal bearing rock series in Xianxian coalfield,Guangxi are identified,the distribution and occurrence of lithium are revealed,the material source and geological control factors of lithium are discussed,and the lithium rich samples are preliminarily extracted.The main insights are as follows:In the coal bearing rock series of Heshan Formation in the study area,there are four lithium enriched strata,which are Strata 1,2,3 and 4 successively from bottom to top.Strata 1 is deposited at the top of the Middle Permian Maokou Formation and belongs to the bottom coal bearing section of the Upper Permian integrated Shan Formation.The member is composed of ferro-aluminite,clay rock,coal/carbonaceous mudstone from the bottom up.Strata 2,3 and 4 are located in the middle and upper part of Heshan Formation,sandwiched in the limestone of Heshan Formation.The lithology is claystone-coal/carbonaceous mudstone from bottom to top.The mineral association of Strata 1 is illite-chlorite-pyrite-anatase association.The mineral association of Strata 2 includes kaolinite-pyrite-anatase association.The mineral association of Strata 3 is kaolinite-chlorite,pyrite,quartz and anatase.The mineral association of Strata 4 is kaolinite-pyrite quartz-anatase.The distribution of the major elements is consistent with the mineral assemblage of each layer,in which sulfur and Fe₂O₃ mainly exist in pyrite,Al₂O₃ mainly exists in the form of clay minerals and bauxite minerals,calcite is the main contributor to Ca O,Si O₂mainly exists in quartz and clay minerals,and Ti O₂ mainly exists in anatase.The trace elements Be,Ga,Pb,Th,Zr,Hf occur mainly in clay minerals,Tl in pyrite,and Nb and Ta in anatase.In Strata 1 and 3,V,Cr,Ni and U are enriched.V,Cr and Ni mainly occur in titanium minerals,while U exists in an organically bonded state.The rare earth elements in Strata 1 and 3 are mainly in phosphate.Strata 1,2 and 3 are highly enriched,while Strata 4 is mildly enriched.In Strata 1,lithium occurs mainly in lithium chlorite,and the presence of lithium chlorite in Strata 1has been verified in various ways,and lithium occurs mainly in other clay minerals in other stratas.The source of detrital material in the interval is mainly from the Maokou Formation limestone and the volcanic ash erupted during the formation stage of the weathering residue.These original parent materials formed the weathered residue rich in lithium under the action of long-term weathering and leaching.The abnormal enrichment of lithium is the result of the interactions between detritus and volcanic ash inputs,chemical weathering processes,high-temperature hydrothermal fluids,and seawater inputs.Most of lithium（over 90%）can be leached from the lithium rich samples in the interval after the synergistic activation of roasting and acid leaching.No mineral dissolution or transformation occurs in the process of acid leaching.Suitable water bath heating temperature and sulfuric acid concentration can promote the leaching process.Compared with acid leaching process,roasting has more influence on lithium leaching.The best leaching conditions were roasting at 600℃,heating in water bath at 80℃and20%sulfuric acid,and the sample containing lithium chlorite had better leaching effect.