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

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 NO_x, (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)_0.94K_0.04Ca_0.01Mg_0.01]_Σ1.00(Al_0.90Fe_0.09Ti_0.01)_Σ1.00[(SO₄)_1.99 (n=24); it thus bears 8 mol% sabieite and 3% steklite end-members. The local sabieite's formula is [(NH₄)_0.96K_0.03Mg_0.01]_Σ1.00(Fe_0.58Al_0.40Ti_0.02)_Σ1.00(SO₄)_2.00. Chemistry of millosevichite from sulfate crust of Radlin is expressed as  (Al_1.73Fe_0.19Ca_0.07K_0.02Na_0.01Mg_0.01Ti_0.01)_Σ2.04[(SO₄)_2.97(PO₄)_0.01]_Σ2.98 (n=16), while that for its minor Fe-analogue mikasaite is (Fe_1.38Al_0.51K_0.04Ca_0.03Ti_0.02Na_0.02)_Σ2.00[(SO₄)_2.90(PO₄)_0.02]_Σ2.92 (n=3). The local dolerophanite is likely stabilized by iron: (Cu_1.96Fe_0.03)_Σ1.99O_1.03(SO₄)_0.98 (n=15). Locally, a Fe-rich variety is observed, its chemistry being, possibly, (Cu_1.26Fe_0.65Na_0.04K_0.03Al_0.02)_Σ2.00[(SO₄)_0.95(SiO₄)_0.01]_Σ0.96(O_0.99Cl_0.01)_Σ1.00 (n=5). Dolerophanite is associated with honey-yellow crystals with the (Cu_3.85Fe_0.15)_Σ3.00O_1.33(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 Rydułtowy), the forming abundant inclusions in extremely (Br,I)-enriched salammoniac. The wealth of the heap's exhalative zones is "completed" by (NH₄)₃XCl₅ (X = Zn, Fe, Mg, Mn, Cu), a sodium thiosulfate pentahydrate, a potassium sodium dithionate chloride, an ammonium sulfate nitrate, and a phosphimate (tetra-μ-imidocyclotetraphosphate). Both the above halogen-bearing gaseous species and minerals result from transformation of the pore-contained post-mining brines.

Kruszewski, Ł., 2021. Burning Coal-Mining Heaps as an Organochemical Laboratory: Interesting Trace Compounds and Their Potential Sources.  Chapter 3, in: Organic Compounds, Las Vegas, Nevada, USA, ISBN: 978-93-87500-41-9, 38 pp., openaccessebooks.com/organic-compounds.html