煤中铀的赋存分布及其在利用过程中的迁移特征

煤炭与铀两种资源在空间配置和成矿上有关联性，其合理开发利用及污染控制是我国国民经济和社会持续发展的重大需求。基于大量文献调研及前期研究成果，探讨了铀在煤中赋存分布及其在洗选、燃烧、淋滤过程中的迁移特征，取得一些认识：①煤中铀的富集成矿与成煤大地构造演化相关联，西南富铀煤主要与峨眉山玄武岩及断裂构造有关；西北富铀煤一般分布在拗陷和断拗陷盆地开阔地带一侧并与上覆砂岩型铀矿有关。②煤中铀主要与煤中有机质（主要是腐殖酸）结合，富铀煤中铀可以微细粒含铀矿物形式存在，并与有机硫、硫化物紧密共生，故在选煤过程中，无论重选还是浮选，其洗选脱除率均不高（最高为68.3%），部分煤浮选时铀甚至富集到精煤中；在煤燃烧过程中，铀或多或少都会以气相形式挥发到大气中。③富铀煤一般也同时富集V、Mo、Se、Re、Cr等高价态变价元素，这与有机体深埋分解造成的强还原环境有关，对于那些不变价元素如Sc、Y、La等的沉淀富集主要与腐殖酸形成的酸化条件有关；这些共生组合元素，在富铀煤的分选及煤矸石的淋滤过程中表现出一致的迁移行为。④电厂燃煤过程中铀主要富集（呈数量级的增加）到飞灰和底灰中，粉煤灰中铀淋出浓度一般随淋滤液pH的增加呈降低趋势，其萃取率随灰化温度的升高呈现降低趋势。研究结果为铀资源利用和环境污染控制提供参考和依据。

Distribution and occurrence of uranium in coal and its migration behavior during the coal utilization

Coal and uranium resources are closely related in spatial disposition as well as mineralization,and the reasonable development,utilization and pollution control of them play an essential role in the sustainable development of our national economy and society.Based on a large number of literature research and the previous results of our research group,some conclusions were drawn with regard to the distribution and occurrence of uranium in coal`and its migration in the process of coal preparation,combustion and leaching:(1)The enrichment and mineralization of uranium in coal has reflected the evolution of coal-forming tectonics:The U-rich coal in Southwest China is mainly related to Emei Mountain basalt and fault structure;the U-rich coal in Northwest China is generally located in depression and open area of fault-depression basin,and is connected with overlying sandstone-type uranium deposit.(2)Uranium is mainly combined with organic matter(mainly humic acid)in coal.It can occur in the form of micro-fine uranium bearing minerals,and is closely associated with organic sulfur and sulfide in U-rich coal.Therefore,in the process of coal preparation,whether gravity separation or flotation,the removal rate of uranium is not high(the highest is 68.3%),and uranium of some coal even enriched in clean coal during flotation;uranium will volatilize to the atmosphere more or less in the form of gas phase during coal combustion.(3)Generally,U-rich coal is also enriched with V,Mo,Se,Re,Cr and other variable valence elements in high valence,which is related to the strong reduction environment caused by the burial depth and decomposition of organisms;the precipitation enrichment of those constant-valence elements,such as Sc,Y,La,is mainly connected with the acidification conditions of humic acid formation.These paragenetic assemblage elements show consistent migration behavior during U-rich coal separation and the leaching process of coal gangue.(4)Uranium is mainly enriched(increase in the form of magnitude)in fly ash and bottom ash during coal combustion in power plant.Generally,with the increase of pH value of leaching solution,the leaching concentration of uranium in fly ash decreases;the extraction rate of it decreases with the increase of ashing temperature.The results provide reference and basis for uranium resource utilization and environmental pollution control.