Gas Vent Mineralization and Coal Combustion - Coal and Peat Fires: A Global Perspective - page 141

Figure 9.1.5. GLP process observed in an SEM image of elongate GeS 2 crystals capped by a bulb of amorphous
sulfur. Note the smaller rods of GeS 2 capped by the small sulfur bulbs. From Mineral Resources Report 78,
Lapham et al., 1980 with modifications, permission of the Pennsylvania Geological Survey.

1
2 n 1 S 2 g

Condenses

ðÞ ! n ðÞ

1 Sl

Solution

Ge ð Absorbed Þþn 1 S ð l Þ ! X ð l Þ

ð 9 : 1 : 6 Þ

In Solution
X

Ge þ 2S ð l Þþn 2 S ð l Þ ! GeS 2 ð Precipitate Þþn 2 S ð l Þ

ð l Þ

= 2 S ð l Þ→ = 2 S ð s Þð Amorphous Þ

where X(l) designates the liquid phase containing n 1 moles of S(l) and absorbed Ge and the total number of moles
of S(l) in X(l) is n 2 with 2 being the number of moles of S(l) that react with each mole of absorbed Ge to

form GeS 2 and n 2 designating the

n 1 =2+

remaining number of moles of S(l) from X(l) that condense to amorphous S(s).

Gas Reaction Liquid-Solidification (GRLS) is a hypothetical mineral-forming process initiated by gas reac-

tions during or after exhalation at the vent. Such reactions, however, are undocumented in the literature. GRLS
consists of one or more of the steps in reactions (9.1.1) through (9.1.5). Many gas-vent assemblages attributed to
sublimation may have actually formed by GRLS. For example, salammoniac (NH 4 Cl) occurs globally in associa-
tion with coal fires as well as volcanic vents and burning oil shale. It is often cited in the literature as a sublimate
(Cole, 1975; Gaines et al., 1997; Lapham et al., 1980; West, 2001). Textural evidence offered in support of this
includes euhedral crystals that do not share faces (Stracher et al., 2005a). Although salammoniac contains elements
commonly found in the components of coal-fire gas, the salammoniac molecule is absent from gas analyses.
Consequently, salammoniac may be the solid reaction product of N-, H-, and Cl-bearing gas components. In
general, the exothermic reaction for such mineralization processes is

+

React

∑ SGC ! X ð s Þþ Y ð g Þ↑ ð 9 : 1 : 7 Þ

where SGC denotes select gas components that react to produce an element or compound X(s), like salammoniac.
This is not sublimation in the strictest sense of the definition; note that the process is not isochemical. Additional
plausible, although also undocumented GRLS processes include

React Solidifies

∑ SGC ! X ð l Þ ! X ð s Þ ð 9 : 1 : 8 Þ