Gallium and germanium in selected Indiana coals

The distribution of gallium (Ga) and germanium (Ge) was studied in two Pennsylvanian high volatile bituminous coals of Indiana: the Springfield Coal Member of the Petersburg Formation and the Danville Coal Member of the Dugger Formation. Gallium in the Springfield and Danville Coals shows similar ranges, from 1.70 to 8.90 ppm (averaging 5.06 ppm) for the Danville Coal and 1.40 to 12.30 ppm, with an average of 3.39 ppm, for the Springfield Coal. For Ge, these ranges are 2.50 to 26.70 ppm (average 14.19 ppm) for the Danville Coal and 1.54 to 38.0 (average 9.40 ppm) for the Springfield Coal. In the vertical section, Ga shows a symmetric distribution with the lowest values in the middle part of the seam in the Springfield Coal and an asymmetric distribution (increasing or decreasing upward) in the Danville Coal. Gallium is dominantly associated with the mineral matter, and clay minerals in particular. Germanium shows a symmetric distribution with the largest enrichment in the topmost and the basal benches of the coal. It appears to be associated with either mineral matter (dominantly clays, occasionally pyrite) or organic matter.

► Springfield and Danville Coals in Indiana are a good source of Ga and Ge.
► Ge shows enrichment in the topmost and the basal part of the coal seams.
► Ga in the coal shows lower values than the surrounding clastic sediments.
► Fly ashes of both coals are predictably concentrated in both Ge and Ga.