The origin of the sulfur and trace elements of the Saray (Tekirdağ) and Pinarhisar (Kirklareli) coals and evaluation of environmental effects on hydrogeochemistry

This study, which is presented as a doctoral dissertation at Istanbul Technical University Institute of Science, includes coal fields in Saray (Tekirdağ) and Pınarhisar (Kırklareli) districts in Thrace Basin. Within the framework of the increasing energy demand of our country and planning the use of domestic energy resources, coal drilling works in the Thrace Basin have increased and the current coal reserve has been revised as about 1.5 billion tons. The detection of high coal reserves in the basin has brought projects of thermal power plants in the region to the agenda. The newly discovered coal veins which are important in terms of economy in the Thrace Basin are also within the Oligo-Miocene Danişmen Formation. There are many coal production finished areas in the basin where coal production is still going on, and large and small mine ponds have been occurred in these areas. The main purpose of this study is to determine the origin of the sulfur and trace elements in the coal within the Danişmen Formation in the Saray and Pınarhisar regions of the north-western part of the Thrace Basin and to investigate the possible effects of the coal on the surface and groundwater. The actively operated coal field in the Saray region is Edirköy; in the Pınarhisar region the actively operated coal fields are Tozaklı and Akören. There are twelve large and small ponds formed by the waters accumulated in the abandoned coal field have been identified in these regions. Within the scope of the study, to investigate the mineralogical and geochemical characteristics of the coal, to determine the types and ratios of sulfur in the coal, to define the origins of the sulfur and try to remove the sulfur from the coal, to evaluate the usability of the coal ash and to reveal the effect of abandoned coal fields on the surface and ground waters, was aimed. In line with the determined targets, coal samples were taken from active coal fields by channel sampling method. In addition, pyritic coal and pyrite veins were sampled for determine the origin of sulfur. The soil samples and the underclays and overclay samples which are associated with coal were also taken from the study area. Coal ash was obtained at 525 ° C, 750 ° C and 1000 ° C ashing temperatures from the coal to evaluate the potential of coal ash to be used in the industry. In order to investigate the possible effect of coal on surface and groundwaters, surface waters from the abandoned coal fields were sampled. In addition the groundwaters near and far away from the coal fields were also sampled. The water samples were taken in two periods which are rainy and dry periods. Additionaly, the in-situ parameters of the waters which are temperature (T), hydrogen ion concentration (pH), redox potential (Eh), electrical conductivity (EC), salinity (NaCl), dissolved oxygen (DO) and alkalinity were measured at the field. Coal samples' mineralogical and petrographic investigations were carried out by ore microscopy. The coals quantitative maceral and mineralogical composition of were identified by point counting method. In addition, the X-Ray Diffraction (XRD) method was used to identify the mineralogical composition of the coals, coal ashes, underclays and overclays. Aforementioned whole samples' major and trace element compositions were determined by Inductively Coupled Plasma – Mass Spectrometer (ICP-MS). Physical and physicochemical methods have been tried to separate sulfur and sulfur minerals from the coal. Sulfur isotope (δ34S) studies were carried out on pyrite, native sulfur (S) and rozenite specimens extracted from the desulfurization of coal. Also, sulfur isotope (δ34S) and Oxygen-18 isotope (δ18O) analysis were carried out in BaSO4 samples which were precipitated from coal. The major anion and cation values of surface and groundwater samples were determined by ion chromatography (IC) method and trace element concentrations were determined by ICP-MS method. Sulfur isotope (δ34S) and δ18O analyzes were also performed to determine the sulfate (SO4) source in the abandoned coal fields waters. All the obtained data have been evaluated together and the origin of sulfur and trace elements in coal is revealed and hydrogeochemical risk assessment of coal and abandoned coal fields was carried out. The coals in the study area are located within the Danişmen Formation of the Oligo-Miocene age. The formation was deposited of lacustrine, swamp, flood plain and fluvial environments. The coal in the formation was developed in the delta plain swamp. The coal formation was partially affected by the paralic environment towards the north of the basin. Coals in the study area are with high sulfur content (> 3%) and are classified as lignite by volatile matter, calorific value and carbon (C) content. Pyritic sulfur, organic sulfur and sulfate sulfur species were detected in the coal. It has been revealed that organic sulfur is predominant in the Pınarhisar region, which is dominated by pyritic and organic sulfur in the Saray region. In the microscopic study of the coals, the main maseral group has been identified as huminite. The inertinite and liptinite contents of the coals are lower than those of the huminite maceral group. Pyrite, clay minerals, quartz and muscovite are inorganic components of the coal and accompanied with these macerals. The mineralogical composition obtained by XRD analysis of the coals was determined as pyrite, barite, gypsum, butlerite, rozenite, muscovite, kaolinite, smectite, tamarugite, quartz and chlorite. Correlations between the major and trace element contents of the coals indicated that the coal formation was fed from three sediment source regions: these are the oldest basement rocks of the Thrace region, the Strandja Massif and the remnant oceanic crust of the Tethys Oceans. In addition, the volcanism starting from Middle Eocene to Pliocene and the volcanic rocks of this volcanism affect the trace element contents of the coals. Beside the correlations, the enrichment factors of the trace elements indicated that the Strandja Massif was the prevailing sediment source for Pınarhisar region, the Tethys Oceans remnant rocks dominant sediment source for the Saray region. The mineralogical composition of the ash obtained by burning the coals is composed mainly of hematite, anhydrite, quartz and muscovite and these minerals are accompanied by thenardite, tridymite, calcite, wollastonite, anorthite, cristobalite, gibbsite, ternesite, mullite, nahcolite and nacrite. It has been revealed that the ashes have highly prone to being slagging. According to major oxide content, loss on ignition value and the available alkalies, it has been found that the ashes use as an additive in industrial use is partially appropriate. The coal ashes are enriched in V, Cr, Co and Ni which are indicating a basic ultrabasic source in the Saray region. As for the Pınarhisar region, Mo, Pb, Th and U elements indicating acidic-intermediate magmatic / volcanic source were enriched. A total of 12 mine ponds were identified in abandoned coal fields in the regions. The in-situ measurements of mine ponds showed that the pH values did not change on a regional basis and the values ranged 7.75 to 8.82. Neutral and/or alkaline pH values of the mine pond waters indicate that coal mined drainage (CMD) not occur even though the coal has high pyrite content. The nonformation of CMD in the region, it has emerged as a consequence of the realization of natural acid neutralization with lithology control. The EC values of mine pond water were measured between 5090 and 2390 μS / cm in the Saray region and 245 to 2980 μS / cm in the Pınarhisar region. Saray region EC values are higher than Pinarhisar region. The obtained results of EC values coincide to the anion and cation values of the mine ponds. In the Saray mine ponds, the dominant cation is Mg2+, dominant anion emerged as SO42-. In the Pınarhisar mine ponds, there is not a single sequence in the cation and anion trends, the multiple anion-cation sequences are monitored. The trace element content of the mine ponds in the region, is quite low from the World and Turkey CMD areas. The pH values of groundwaters were measured as neutral and/or alkaline and the EC values show an increase locally in the groundwater. The dominant cation Ca2+ in groundwater was identified as predominant anion HCO3-. In the diagrams of Ca2+, HCO3- and Na+ ions corresponding to the total ion (TI) of waters, in the study area wide-ranging nutrition has dominating in general and the periodic changes of the water originated from the local litholocigal properties of the region. The maximum values of Mn, Ni, As and U elements of groundwater in both dry and rainy periods have exceeded the recommended/suggested limits by WHO, US EPA and TS266 for drinking water. High concentrations of these elements have been determined on a sample basis, and values have not constitute anomalies on a regional basis. In addition to lithological properties of the region, the lower trace elements concentrations of mine pond and groundwater, it has been evaluated as a function of the mineralogical composition of the underclay and overclay units to which is associated with coal. The underclay and overclay units consist of claystones in the Edirköy and Tozaklı areas, and sandstones in the Akören area. The mineralogical composition of claystones consists of kaolinite-chlorite, illite-mica, smectite, quartz, calcite and feldspar, and the sandstone mineralogical composition consists of quartz, kaolinite and muscovite. Pollution load index (PLI) was calculated from the enrichment factors in the underclay and overclay and Edirköy soil samples which were taken from study areas. According to PLI results, all of these samples were contaminated in terms of Cr, Ni, As, Sn, Cs, La, Tm, W, Pb and Bi elements (PLI>1). In addition to these elements, underclays and overclays were contaminated by Al, V, Zn, Rb, Th and U and soil samples were contaminated by Mn, Zr and Cd. Therefore, the absence of pollution in terms of these elements in groundwater was explained by the presence of clay minerals (illite and smectite) which have ion absorbing properties. Sulfur isotope (δ34S) results have shown that the high sulfur in the coals occurred from bacterial reduction of trapped seawater sulfate in general. In addition, these results shown that the volcanism accompanying the sedimentation of the region also constitutes a source of sulfur. The δ34S and δ18O values of SO42- in mine pond waters show that the SO42- ions source in the mine ponds were lithologically controlled and that atmospheric precipitation was also effective in SO42- ions content in the mine ponds. The δ18O, δ2H and T values of groundwater have shown that groundwaters in the study area has been meteoric origin, shallow-deep cycled and young waters. Taking all the points mentioned into account, it is revealed that there is no pollution originating from coal in terms of hydrogeochemistry in the North Thrace Basin, the high element concentrations locally detected in the waters are completely controlled by lithology and they do not constitute a regional anomaly and therefore there is no risk of water pollution originating from coal in the study areas.