Experimental formation of Pb, Sn, Ge and Sb sulfides, selenides and chlorides in the presence of sal ammoniac: A contribution to the understanding of the mineral formation processes in coal wastes self-ignition

The formation of sulfides, selenides and chlorides was experimentally studied at 800 or 900 °C in the presence of sal ammoniac in sealed silica glass tubes. Synthetic PbS, PbSe, SnS, GeS, SnGeS2, PbSnS3, SnS, Sb2S3, and natural uraninite were used as substrates. Depending on the chemical composition of the sulfide/selenide charge, compounds corresponding to cotunnite, galena, herzenbergite, berndtite, ottemannite, stibnite, panichiite, and unnamed SnGeS3, SnSb2S4 and Sn2Sb3S6 phases were identified in sublimates. When natural uraninite in a mixture with sal ammoniac was used as a charge, the reaction produced abundant cotunnite and minor challacolloite due to volatilization of radiogenic lead. When sulfur was introduced to the charge with uraninite and sal ammoniac, galena was found in reaction products. Results of the experiments revealed that an addition of chlorine may contribute to the mobility of metals and metalloids in coal wastes self-burning processes.