Leaching Kinetics of Selenium, Tellurium and Silver from Copper Anode Slime by Sulfuric Acid Leaching in the Presence of Manganese(IV) Oxide and Graphite

Sulfuric acid leaching of copper anode slime (CAS) in the presence of manganese(IV) oxide (MnO2) and graphite was investigated for Se, Te and Ag recovery. The study reveals that the leaching of Se, Te and Ag was facilitated by the galvanic interaction with MnO2, and graphite played the role of a catalyst. The leaching process could yield 81.9% Se, 90.8% Te, and 80.7% Ag leaching efficiency when the conditions were maintained as 500 rpm, 2.0 M H2SO4, 0.8/0.8/1 MnO2/graphite/CAS, and 90 °C temperature. The kinetic study showed that Se leaching followed the surface chemical reaction at all the tested temperature range (25–90 °C) with the activation energy of 27.7 kJ/mol. Te and Ag leaching at temperature 25–50 °C followed the mixed and surface chemical reaction models, respectively, and changed to fit the diffusion and mixed control models, respectively, in the temperature range 60–90 °C with the corresponding activation energy of 17.8 and 12.2 kJ/mol.

Study of physical and chemical properties of tellurium-containing middlings

The process experts are concerned in tellurium due to its various physical and chemical properties. The copper anode slime is the main industrial source of tellurium, after processing of that tellurium becomes marketable product and can be sold both in elemental form and tellurium-containing middling. Physical and chemical properties of the tellurium-containing middling of Kazakhmys Smelting LLP produced in 2018 have been studied in this paper. The following methods have been applied during the study: particle size distribution, X-ray phase, X-ray fluorescence and scanning electron probe microscopy. It was found that material is mainly represented by the large pieces of 0.2 mm in size, with moisture content of 15.57 %, bulk density of 0.8 g/cm3 without tapping and 0.88 g/cm3 with tapping, the angle friction - 33°. The elemental composition of the material was determined by X-ray fluorescence method as follows, wt. %: Cu – 33.327; Te – 21.863; Se – 0.766, O – 35.116; S – 5.045. X-ray phase analysis showed that material is mainly in the amorphous state, the following phases had been identified: Cu2.5SO4(OH)3·2H2O, Cu3(SO4)(OH)4, CuSO4(H2O)3. Tellurium-containing phases could not be detected due to strong amorphism. Hydrosulfate forms of copper in the form of flakes have been found on the surface of the middlings by electron probe microscopy. EDS analysis of individual areas showed that patina also contains small amounts of chlorine, selenium and up to 25 % tellurium, in addition to such elements as copper, sulfur and oxygen. Small amounts of sulfur, chromium, selenium and up to 45 % of oxygen has been found in the open area of material, that is specific for its oxidation.