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The effects of sulfur on the weathering extent of carbon. A companson of two mines in Hato de la Virgin, State of Tachira, Venezuela

Abstract:

Ten bituminous coal samples, showing several weathering levels, were collected at different depths into two subsurface galleries: G-11, where coalbed 20 is mining, with a sulfur-content > 5%; and G-24, where coalbed 24 is present, with a sulfur content less than 1.5%). Both mines are located in Hato de la Virgen, State of Táchira, Venezuela. The aim of this work is to evaluate the effect of sulfur on the weathering extent in coal. For comparative purposes, fresh samples were collected from cored intervals of four different wells near of the galleries. The following analysis were done: proximate (moisture, volatile matter, fixed carbon, ash, calorific power), free swelling index (FSI) elemental analysis (C, H, N, O) total and different sulfur species (pyritic, sulfate and organic sulfur), FT-IR infrared spectroscopy, and major composition of ash (Si, Al, Ca, Mg, Mn, Fe, K, Na, Cl, P). Only coal samples from core wells are absolutely fresh: those collected within galleries show evidence of low or remarkable oxidation, detected by several parameters (moisture, calorific power, elemental and ash composition) and by infrared spectroscopy (appearance of carbonyl signal, decrease in C-H strength absorption). Sulfur content in a high proportion does not modify the style or extension of the oxidation in the organic matrix of coal. However, sulfur is responsible of an important variation in the alteration style of the inorganic matrix of coal, modifying the scheme of leaching in some elements (mainly Fe, and in lesser extent, Si, K, P). These elements are preferentially removed from coal, immobilizing other species (Ca, Mg, Mn) by precipitation as insoluble sulfates.