Geochemical and Geophysical Investigations of Coal Deposits Belonging to the Hangu Formation, Western Khyber Pakhtunkhwa, Pakistan

Abstract

This research work has been carried out in Akkakhel, Akhorwal and Shiekhan areas of Khyber agency, Kohat subdivision and at Lower Orakzai agency of Khyber Pakhtunkhwa, Pakistan. It involved the investigation of geochemical features of existing coal deposits of the studied area in terms of their upgradation using froth flotation technique and also to find out new prospects of coal through geophysical surveys to assess the potential zones of coal seams and their lithological variations. Thirteen coal mines were sampled for the determination of major and trace elements and identification of mineral phases in coal. The geochemical data of the studied coal deposits indicate that majority of the coal samples have higher concentration of major and trace elements such as Fe, K, Na, Mg, Ca, Mn, Ag, Co, Ni, Cd, Cr, Cu, Zn, Pb and S relative to the other known coal deposits elsewhere in the world. This could be attributed to the higher concentration of spinel group, sulfides, carbonates and clay minerals in the studied coal which has severely affected its quality. The ash and sulfur contents of the studied coal deposits are also above the permissible limit which has drastically limited their supply and use. The studied coal samples were tried to upgrade by using froth flotation technique wherby the ash and sulfur contents were tried to reduce to greater extent. The optimum process parameters established were -140 mesh (105 μm) particle size, 20 % solids in floation pulp and pH value of 9. Under these conditions ash was reduced from 40.6% to 13.8% (60 % reduction) and sulfur from 3.97 to 1.57% (60.45 % reduction) while the calorific value was enhanced from 7070 kcal/kg to 7963 kcal/ kg (13% enhancement) in the coal samples of Akkakhel area. In the coal samples of Akhorwal area, ash was reduced from 35% to 18.16% (48.11 % reduction) and sulfur from 6.31 to 3.51% (44.37 % reduction) while the calrific value was enhanced from 5500 kcal/kg to 6308 kcal/ kg (14.69% enhancement). Similarly, in the coal samples of Shiekhan area, ash was reduced from 41.6% to 20.1% (51.68% reduction) and sulfur from 3.1% to 1.5% (51.61% reduction) while the calorific value was enhanced from 3795 kcal/kg to 4941 kcal/ kg (30.19% enhancement). The geophysical methods such as Vertical Electrical Soundings (VES) and Ground Penetrating Radar (GPR) techniques were used in the study areas in order to account for thickness, depth of coal bed seams and lithology of the surrounding rocks. The geoelectric sections were categorized into several lithological sections. Very low modeled resistivity values (20 to 55 Ohm m) were interpreted to be dry silty clay and clayey shale, the slightly high modeled resistivity values (120-380 Ohm m) were interpreted to be medium-grained sandstone incorporated with coal beds. The high resistivity values (500 to 1000 Ohm m) were structurally modeled to be massive sandstone. While the higher resistivity values (>1000 Ohm m) were structurally modelled into dolomite and limestone respectively. It is concluded that the processing techniques applied to the coal samples during the current sudy have prmoising results for up-gradation of the coals of Akkakhel, Akhorwal and Shiekhan areas. The data obtainded during this study will be very useful for the industries such as energy, power and cement manufacturing. Moreover, upgradation of coal will result in reduction of sulfur to considerable level that will contribute in reduction of SOX emission to environment and a significant reduction in ash as combustion residue. Both VES and GPR data complemented each other and together provided a broad understanding of the subsurface geology. The integration of geochemical and geophysical techniques with field and laboratory data provided new insights into exploration of coal in unknown areas.