Coal and coal ash characteristics to understand mineral transformation : A case study from Senakin coal field Indonesia

Coal ash is a material from coal combustion and recently is an economical source for the extraction of valuable elements such as rare earth elements and Yttrium (REY) and base metals. Eight coal samples from Senakin coal field were collected to identify their mineralogy composition in raw coal and coal ash. The ashing was carried out on coal samples at temperature 1000°C for 1 hour. The coal and coal ash samples were made polish section to identify the organic and inorganic constituents. In addition, the minerals in coal sampel were identified by X-ray diffraction analysis. From this study, organic constituent consist of vitrinite (60 – 71%), liptinite (22 – 33%) and inertinite (5 – 9%). Minerals found in coal are kaolinite (25,78 – 46,90), pyrite (24,16 – 38,38%), quartz (6,07 – 12,80%), gypsum (4,81 – 10,34%), chlorite (2,56 – 8,40%), jarosite (0,72 – 4,63%), hematite (0,96 – 3,81%), calcite (0,37 – 5,07%), Mg-calcite (0,11 – 3,20%), dolomite (1,35 – 3,55%), and siderite (1,22%). Coal ash is composed of organic and inorganic components. Organic components found is unburned coal (3,09 – 8,55%) derived from maceral which does not burn out, mainly inertinite group. While inorganic components found are fe-oxide mineral (40,36 – 54,55%), quartz (24,55 – 33,64%), mullite (5,09 – 7,82%), cenosphere (7,45 – 10,91%), pleiosphere (1,64 – 2,36%), pyrite (0,18 – 1,27%), and spinel (0,18 – 1,09%). Fe-oxide minerals are interpreted derived from Fe-bearing minerals in coal samples such as pyrite, hematite, and siderite. Kaolinite which is the dominant mineral in coal is transformed to cenosphere, pleiosphere, and mullite. Quartz in coal ash derived from quartz in the coal sample because ashing temperature does not exceed the melting temperature of quartz. Characterization of the coal ash component can be used as a reference for the extraction method of valuable elements.