Influence of wet oxidation on the surface area and the porosity of some lignites

Abstract

Vertically continuous increment samples of the Fire Clay coal bed (mid-Middle Pennsylvanian, late Westphalian B), collected from a portion of the Central Appalachian Basin, were studied palynologically, petrographically and geochemically in order to partially reconstruct the paleoecology and processes associated with peat formation in the ancient Fire Clay paleomire. Results indicate that four compositional groups can be identified. They are: (1) a Lycospora—vitrinite dominant group, characterized by high percentages of Lycospora and vitrinite macerals and generally low, but variable ash yields and sulfur contents; (2) a mixed palynoflora-high vitrinite group that petrographically is similar to group 1 except that it contains a more diverse palynoflora; (3) a mixed palynoflora-moderate/low vitrinite group characterized by various admixtures of lycopsid, fern and calamite miospores, increased percentages of liptinite and inertinite macerals, and low ash yields and sulfur contents; and (4) a mixed palynoflora-high ash yield group characterized by high percentages of small lycopsid, fern, and occasionally calamite and cordaite miospores, high liptinite and inertinite contents, high ash yields, and moderate to high sulfur contents.The Fire Clay coal bed contains a distinctive flint clay parting of probable volcanic origin that naturally divides the bed into two benches. These two benches, (upper and lower), are highly disparte in occurrence, appearance and composition. In the study area the lower bench generally is thin (< 0.5 m), laterally discontinuous and mainly composed of dull (mainly durain) coal lithotypes. Ash yields typically are high; sulfur contents generally are moderate to high. Compositional group 4, the mixed palynoflora—high ash yield group defines all of the increments examined from the lower bench.In contrast, the upper bench is thick (> 0.75 m), laterally continous and mainly comprised of bright (mainly clarain) coal lithotypes. Overall ash yields and sulfur contents for this bench are generally low, although vertical variation is apparent. All of the compositional groups occur in the upper bench; in some columns, notably those that are thick and uninterrupted by clastic partings, groups 1 and 4 often occupy basal coal layers and groups 2 and 3 occur in higher layers. Other columns, especially those taken in areas of thin (< 0.5 m) Fire Clay coal, are dominated by groups 1 and 4.