Partitioning of minerals and elements during preparation of Taixi coal, China

Abstract

Mineralogy, sulfur and 40 other element contents were determined on eight samples of the Taixi coal and its preparation products from the Rujigou mining district, China. INAA, ICP-AES, CV-AAS, GAAS, XRD, SEM/EDX, conventional chemical and maceral analysis were carried out on the samples. This study is focused on the partitioning behavior of the minerals and elements during the coal cleaning, and the main factors influencing the partitioning behavior of elements were also discussed. The clay minerals (kaolinite, illite, montmorillonite and chlorite), quartz and, to a lesser extent, carbonate minerals (calcite, dolomite and siderite) dominate the mineralogy of Taixi coal. There is also minor amounts of pyrite and trace amounts of gypsum and feldspar. The quartz is dominantly epigenetic in origin, and clay minerals were modified by the thermal metamorphism. They are easily liberated from the coal by cleaning. However, although the majority of carbonate minerals are also mainly epigenetic in origin, its degree of removal is relatively low, especially with respect to dolomite and siderite, which are often finely dispersed in coal macerals, so that they are mostly retained in cleaned coal. Most of the elements studied could be removed effectively during the cleaning processes, especially for the elements predominantly hosted in coarse, epigenetic minerals. Compared with other sized cleaned coals, the coarse-grained cleaned coal is cleanest and has a relatively low potential of environmental risk. The majority of the potentially hazardous elements are notably enriched in the coal waste so that the waste is not feasible to be used as fuel. The partitioning of elements during the coal cleaning processes is essentially controlled by some factors such as the modes of occurrence of elements, maceral type, grain size and textural relation of minerals, and types of cleaning technique used.