Material composition of sulfuric acid leaching products of copper smelting slag flotation tailings

Research subject. The flotation tailings of the dump cast slag of the Sredneuralsk Copper Smelter (“SUMZ”) were leached with sulfuric acid at a concentration of 300 g/dm³ at 90°C for at least 15 hours.

Aim. To study the material composition of leaching products of copper smelting slag flotation tailings. Based on the data obtained, we will describe the processes that occurred during the leaching of this type of waste. Material and methods. The methods used were X-ray fluorescence and spectral analysis (EDX-8000 and CPM-35), mass spectrometry with inductively coupled plasma (NexION 300S), powder X-ray diffraction (DRON-3 and D8 ADVANCE), scanning electron microscopy (TESCAN MIRA LMS (S6123) with INCA Energy 450 X-MaxEDS spectrometer).

Results. It has been established that sulfuric acid leaching of copper smelting slag flotation tailings is accompanied by a decrease in the content of zinc, copper, manganese, arsenic and an increase in the sulfur content in the cake, mainly consisting of SiO₂ (32.5 wt %) and Fe₂O₃ (18.0 wt %). X-ray phase analysis of the leaching product revealed the following mineral phases: minerals of the pyroxene group, amorphous silica, gypsum, barite, minerals of the spinel group, sulfides, sulfate forms of ferrous iron, represented by melanterite and ssomolnokite, ferric sulfate – kokimbit, which oxidizes and dehydrates over time, turning into jarosite. According to scanning electron microscopy, the phase composition of cakes is represented by an association of silica, crystalline sulfur, oxygen-containing compounds of iron, lead, zinc, copper and their sulfides. It has been established that zinc is present in all newly formed ferruginous phases. Arsenic is associated with silica. Copper is found in sulfur secretions. Crystalline sulfur is usually found in combination with sulfides. We identified rare earth mineralization represented by cerium, neodymium, lanthanum phosphate, as well as neodymium phosphate in association with niobium and bismuth. The phase composition of cakes is a reflection of the chemical processes occurring during leaching – electrochemical oxidation of sulfides, acid hydrolysis of silicates, ion exchange reactions.

Conclusion. The obtained data on the chemical and mineralogical composition of the products of sulfuric acid leaching of copper smelting slag flotation tailings are of interest for the development of effective methods for their use and disposal, taking into account the ecological consequences for the environment.

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