Mechanisms of low-temperature vapor-gas streams formation from sulfide mine waste

This paper presents experimental data that revealed the potential for chemical element transport by low-temperature vapor-gas streams. The study was conducted on sulfide waste heap sites located in the Kemerovo region, Russia. Condensates of vapor-gas streams were collected and analyzed in the air above the waste heaps and during laboratory experiments using samplers specially designed for this purpose. The gas streams from a waste heaps are complex mixtures consisting of water vapor, sulfur- and selenium-containing compounds (sulfur dioxide SO₂, dimethyl sulfide C₂H₆S, carbon disulfide CS₂, dimethyl disulfide C₂H₆S₂, dimethyl selenide C₂H₆Se, and dimethyl diselenide C₂H₆Se₂), elemental sulfur (S₆, S₇, and S₈) and various chemical elements, including rock-forming elements (Ca, Mg, Na, K, Si, Fe, Al, and Mn), metals (Cu, Zn, Pb, Ni, and Sn), and metalloids (As, Te, and Sb). The main sources of chemical elements in the gas streams are unstable secondary minerals associated with crystalline hydrates: gypsum CaSO₄ × 0.5H₂O, sideronatrite Na₂Fe(SO₄)₂(OH) × 3H₂O, serpierite CaCu₃Zn(SO₄)₂(OH)₆ × 3H₂O, and copiapite (Mg,Zn,Fe²⁺Fe³⁺)₄(SO₄)₆(OH)₂ × 20H₂O that formed during the oxidation of sulfide minerals. Some of the elements come from pore waters that are acidic, highly mineralized solutions. The mechanism of element migration from the pore waters is as follow: the water vapor phase transports elements in the form of aqueous ions, but complexed species (such as MeSO₄(aq), MeCl(aq), Me(OH)⁺, etc.) remain in the salt residue. A significant contribution to the processes of transformation and transport of elements is made by biochemical methylation reactions, which occur in the presence of bacteria producers of methyl groups and are accompanied by the formation of volatile compounds of arsenic, selenium, sulfur, and tellurium.