Gas-phase element transfer, rare mineral deposition, and other exhalative phenomena associated with coal fires in heaps: the state of art based on the data from the Upper Silesian Coal Basin
Authors: Kruszewski Łukasz 
Published: February 2023

The coal-fire gases are the main actors in terms of element and heat transfer within burning post-mining waste heaps (BPWHs). Although they mainly comprise CO2 and water, they can locally be enriched in dimethyl (di)sulfide (as much as 15000 ppm, Bytom site), thiophene, SO2, H2S; 1,1- and 1,2-dichloroethane, dichloromethane and other halocarbons; chlorobenzene, ammonia, pyridine, HCN, numerous NOx, (iso)cyanogen halides, and triazine-based and imine-type compounds, AsH3, PH3, SiF4, and SF6, to mention some. Metals are most likely transported as neutral hydroxides, and/or carbonyl, nitrosyl, and hydride complexes, while iodine - as I2, iodosomethane, iodocyanoacetylene, and - alongside with Br and Cl - as halocarbons. Occurrence of exotic gases is possible considering their transient nature. The most recent proposal compounds include HNC, formaldoxime isocyanate, peroxyethyl nitrate; tetrafluoro-p-xylylene, perfluorinated p-benzyne, CHClF, HCFBr, 1,2,4-trixolane, thioacetaldehyde, thiocarbonyl fluoride, bromomethane, dithio-p-benzoquinone, monomethylsilane, and titanacyclopropene (e.g., Kruszewski, 2021). Still, the image of the coal-fire exhalative processes is not full. Here, crystal chemistry of some major minerals deposited within exhalative vents of the Upper Silesian Coal Basin heaps is presented. Chemistry of godovikovite - the major component of the Czerwionka-Leszczyny sulfate crust - is [(NH4)0.94K0.04Ca0.01Mg0.01]&#931;1.00(Al0.90Fe0.09Ti0.01)&#931;1.00[(SO4)1.99 (n=24); it thus bears 8 mol% sabieite and 3% steklite end-members. The local sabieite's formula is [(NH4)0.96K0.03Mg0.01]&#931;1.00(Fe0.58Al0.40Ti0.02)&#931;1.00(SO4)2.00. Chemistry of millosevichite from sulfate crust of Radlin is expressed as &#160;(Al1.73Fe0.19Ca0.07K0.02Na0.01Mg0.01Ti0.01)&#931;2.04[(SO4)2.97(PO4)0.01]&#931;2.98 (n=16), while that for its minor Fe-analogue mikasaite is (Fe1.38Al0.51K0.04Ca0.03Ti0.02Na0.02)&#931;2.00[(SO4)2.90(PO4)0.02]&#931;2.92 (n=3). The local dolerophanite is likely stabilized by iron: (Cu1.96Fe0.03)&#931;1.99O1.03(SO4)0.98 (n=15). Locally, a Fe-rich variety is observed, its chemistry being, possibly, (Cu1.26Fe0.65Na0.04K0.03Al0.02)&#931;2.00[(SO4)0.95(SiO4)0.01]&#931;0.96(O0.99Cl0.01)&#931;1.00 (n=5). Dolerophanite is associated with honey-yellow crystals with the (Cu3.85Fe0.15)&#931;3.00O1.33(SeO3)0.96(SO4)1.93 (n=6) formula, likely representing a new mineral species. So is true for a Cu-I-S species and a iodobismuthate (known both at Radlin and Rydu&#322;towy), the forming abundant inclusions in extremely (Br,I)-enriched salammoniac. The wealth of the heap's exhalative zones is "completed" by (NH4)3XCl5&#160;(X = Zn, Fe, Mg, Mn, Cu), a sodium thiosulfate pentahydrate, a potassium sodium dithionate chloride, an ammonium sulfate nitrate, and a phosphimate (tetra-&#956;-imidocyclotetraphosphate). Both the above halogen-bearing gaseous species and minerals result from transformation of the pore-contained post-mining brines.Kruszewski, &#321;., 2021. Burning Coal-Mining Heaps as an Organochemical Laboratory: Interesting Trace Compounds and Their Potential Sources. &#160;Chapter 3, in: Organic Compounds, Las Vegas, Nevada, USA, ISBN: 978-93-87500-41-9, 38 pp., openaccessebooks.com/organic-compounds.html