Bituminous coal seams from underground mines in the Zonguldak Basin (NW Turkey): Insights from mineralogy, coal petrography, Rock-Eval pyrolysis, and meso-and microporosity

The Zonguldak Basin contains the main bituminous coal reserves of Turkey (ca 1.4 Gt), and several coal seams are mined in underground coal mines within the basin. This study focuses on coal petrography, mineralogy, Rock-Eval pyrolysis, and the meso-and microporosity characteristics of the coal samples collected from several Late Carboniferous (Pennsylvanian) bituminous coal seams in the basin. Forty channel samples were collected from various coal seams in underground mines at the Armutcuk, Zonguldak, and Amasra coalfields in the Zonguldak Basin. The studied coal samples have low total moisture contents (avg. 2.3%, on as-received basis), low total S contents (avg. 0.5%, on dry basis), and relatively high ash yields (avg. 21.2%, on dry basis). The random vitrinite reflectance values (0.69-1.21%) and gross calorific values (avg. 33.0 MJ/kg, on dry, ash-free basis) indicate that the coal samples are of high-volatile C bituminous to medium-volatile bituminous coal. Minerals identified by XRD in bulk coal samples are clay minerals (mainly kaolinite and rarely illite and chlorite), quartz, and carbonates (calcite, dolomite, and siderite). In a few samples, pyrite and feldspar were also identified. The SEM-EDX analyses performed on the carbon-coated polished blocks imply that the carbonate minerals are mainly epigenetic, whereas the silicate minerals are generally syngenetic in origin. The results of low-pressure N-2 adsorption analysis indicate that the BET surface areas (1.1-5.5 m(2)/g) and mesopore volumes (0.003-0.011 cm(3)/g) vary within a wide range. The results of the low-pressure CO2 adsorption analyses show that micropores are abundant in the coal samples; however, the BET surface areas (10.41-78.11 m(2)/g) and micropore volumes (0.010-0.049 cm(3)/g) vary widely among the three coal mines and different coal seams. Our results suggest that variations in the mesopore characteristics are mainly controlled by mineral matter, while microporosity is controlled by a combination of organic matter (maceral compositions) and coal rank of the studied coal seams.