应用能谱-扫描电镜和X射线衍射技术研究原煤伴生矿物中稀土和放射性元素赋存形式

The Occurrence of Rare Earth and Radioactive Elements in the Associated Minerals with Raw Coal by EDX-SEM and XRD

研究原煤中稀土及放射性元素的赋存形式,对原煤是集中还是分散利用、燃煤过程中粉煤灰的排放截留、从原煤或粉煤灰中提取稀土及放射性元素等方面都具有指导意义。由前人研究可知不同矿区原煤中稀土及放射性元素的赋存形式有差异。本文研究了山西省霍西煤田两个矿区175个煤样中稀土及放射性元素的赋存形式,应用背散射电子图像(BSEI)定位分析区域,应用BSEI、能谱-扫描电镜法(EDX-SEM)中的面分析(EDS-mapping)和粉晶X射线衍射法确定了主要伴生矿物,应用BSEI和EDX-SEM中的点分析(EDS-point)确定了微量伴生矿物。在煤样中发现了铈镧钕钇镝钪六种稀土元素及一种放射性元素钍,其中铈、镧和钕主要以磷酸盐形式伴生于高岭石类矿物中,部分伴生在含氧化铝或氧化硅较多的矿物中,少量存在于碳中;钇、镝以磷酸盐或氧化物形式独立存在于碳中;在部分锆石、独居石中分别发现了钪和钍。研究表明,该矿区煤样中稀土元素主要以细粒自生矿物的形式伴生在其他矿物中,少数以独立矿物的形式存在于碳中,放射性元素钍伴生在独居石中。

BACKGROUND: The study on the occurrences of rare earth and radioactive elements in raw coal is of great significance in terms of whether the raw coal is concentrated or dispersed,the emission of fly ash is intercepted,and the rare earth elements( REEs) and radioactive elements are extracted from raw coal or fly ash. Previous studies showed that the occurrences of rare earth and radioactive elements in raw coal of various mining areas are different.OBJECTIVES: To study the occurrences of rare earth and radioactive elements in 175 coal samples from two mining areas in the Huoxi coalfield of Shanxi Province.METHODS: The analysis region was located by back scattered electron imaging( BSEI),and the main associated minerals were determined by EDS-mapping and powder X-ray diffraction. The trace associated minerals were determined by BSEI and EDS-point methods.RESULTS: Six rare earth elements and a radioactive element were determined in the coal samples. Cerium,lanthanum and neodymium were associated with kaolinite minerals in the form of phosphate,partly occuring in minerals containing alumina or silicon oxide,and in carbon to a small degree. Yttrium and dysprosium existed independently in carbon in the form of phosphate or oxide,whereas scandium was found in zircon,and thorium is found in monazite.CONCLUSIONS: The REE in the coal samples of the mining area were associated with other minerals in the form of fine-grained authigenic minerals,and a few occurred as independent minerals in carbon. The radioactive element thorium was associated with monazite.