Co-associated rare earth elements(lanthanide and yttrium,REY)in coal and its by-products have been considered important potential nontraditional rare earth sources.In this study,a coal gangue sample collected from a coal processing plant in Jinsha County of Guizhou Province,southwest China,was used as the research object.The content,modes of occurrence,and extraction(acid leaching after pretreat-ment of selective grinding,tailings discarding,and alkali roasting)of REY from the sample were analyzed.The result shows that the content of REY(1038.26 μg/g)in pyrite and quartz is low but mainly enriched in kaolinite.Under the following conditions of a filling ratio of 40％(grinding media steel ball)and grinding time of 8 min,selective grinding pretreatment is applied to achieve 176.95 μg/g(yield 24.08％)and 1104.93 μg/g(yield 75.92％)of REY in+2 mm and-2 mm fractions,respectively.Thus,the-2 mm coal gangue fraction is selected,used as the feed,and roasted and leached with HCl.When Na2CO3 and NaCl are separately used as roasting activators,the REY leaching ratios are 91.41％and 68.88％,respec-tively,under the optimum conditions.The contents of REY in the final leachate are 1010.02 and 761.08 μg/g when Na2CO3 and NaCl are used,respectively.The two REY contents are relatively higher than the impurity ions in the leachate,which facilitates further REY separation.The mechanism study reveals that high-temperature roasting increases the pore size and the total pore area of the gangue,which promotes leachate penetration and improves reaction efficiency.In addition,roasting facilitates the reaction between the sodium salt activator and kaolinite and other aluminosilicate minerals in the coal gangue to generate soluble salts,thus releasing REY into the solution.The appropriate roasting temperature transforms the activator into a molten state.Thus,the reaction between coal gangue and activator is a solid-liquid reaction rather than a solid-solid reaction,which improves the efficiency of the chemical reaction.

The occurrence modes of rare earth elements(lanthanide and yttrium,abbreviated as REY)in coal are important both for coal geochemistry studies and the application potential of REY as a by-product of coal-based resources.In this study,the adsorption behaviors of REY on organic matter in coal were investi-gated by leaching tests using REY solution and ultra-low ash coal samples.On this basis,the adsorption mechanism of REY on organic matter in coal was also studied by molecular simulation calculations.The leaching tests show that the organic matter in coal has a relatively strong adsorption capacity for REY,and that the average adsorption rate or the net adsorption amount of heavy rare earth elements(HREY:Gd,Tb,Y,Dy,Ho,Er,Tm,Yb and Lu)is always higher than that of the light rare earth elements(LREY:La,Ce,Pr,Nd,Sm and Eu).A molecular model of humic acid(HA)was constructed and the adsorption amount between REY and HA was calculated.The results show that the theoretical adsorption rate of HREY(84.88％)is higher than that of the LREY(84.00％).The analysis of the adsorption distances between REY atoms and various functional groups on HA molecules shows that the minimum adsorption distance of LREY is 0.372 nm on average,which is larger than that of HREY(0.368 nm),indicating that the adsorption capacity of the latter is stronger.In addition,a coal molecule(C18H22O)was also constructed to investigate the adsorption characteristics of various REY atoms on the molecule.As a result,it is found that the average binding energy and bond length between the hydroxyl functional group and LREY atoms are 0.12469 Ha(Hartree,the unit of energy in the atomic unit system)and 0.1407 nm,respectively,while for HREY,0.12883 Ha and 0.1121 nm,respectively.This confirms that HREY is more stable than LREY in binding on organic matter in coal.To conclude,both leaching tests and molecular simulation calculations reveal that REY has a strong adsorption affinity for organic matter in coal,and in particular,HREY shows a stronger organic adsorption preference in coal than LREY,which is probably due to stronger chemical bonding between the former and the functional groups on the coal molecule.

研究了采用氧化焙烧—盐酸浸出工艺从富含锂的煤矸石中浸出锂,优化了焙烧和浸出工艺条件,并探讨了焙烧活化对锂的浸出影响机制.结果表明:煤矸石在550 ℃下氧化焙烧1.5 h后,再加入1 mol/L盐酸溶液,在液固体积质量比10/1、浸出温度80 ℃条件下浸出2 h,锂浸出率可达98.14％;高温焙烧可破坏煤矸石中高岭石的晶体结构,增强反应活性,并使可燃组分和还原性物质发生氧化反应,在煤矸石表面及内部产生大量孔隙,有利于提高煤矸石中锂的浸出效果.

Rare earth elements (lanthanide and yttrium, abbreviated as REY) provide important support for national security, energy production, environmental protection and economic growth. In recent years, many studies have shown that the content of REY in some coal or coal by-products is close to or even higher than that in traditional REY ore, which makes coal a potential source of REY. This study took the No. 17 coal of Panzhou mining area in Liupanshui coal field as the research object, and the content and occurrence modes of REY in raw coal and 7 density fraction samples were studied. The results show that the content of REY in the raw coal reaches 220.67 μg/g, which is significantly higher than the average REY content in the world coal and Chinese coal as reported in the literature. Gravity separation has a certain pre-enrichment effect on REY and the fraction sample >1.8 g/cm3 has the highest REY of 426.27 μg/g (equal to rare earth oxide 0.1%). Study on correlation between REY and ash yields reveals that the organic affinity of the light rare earth is higher than that of the medium rare earth and the heavy rare earth. As shown by X-ray diffraction (XRD) and X-ray flouresence spectroscopy (XRF), the major minerals in coal are kaolinite, quartz and calcite, and the content of REY in coal is significantly related to Al, Si and kaolinite, which implies that REY occur mainly in kaolinite. Laser ablation inductively coupled plasma mass spectroscopy (LA-ICP-MS) was adopted to determine chemical composition of micro-zone in kaolinite in coal and the results show that there is no obvious correlation between REY and the contents of Al and Si. This indicates that the REY occur probably in the form of adsorption. The research results provide a scientific reference for the potential extraction of the associated REY in the coal.