Zinc recovery from metallurgical slag and dust by coordination leaching in NH ₃–CH ₃COONH ₄–H ₂O system

Abstract

Metallurgical slag and dust (MSD) from lead and zinc smelting, steel dust and galvanized steel scrap are important secondary sources of zinc and other valuable metals. This paper describes the production feasibility and rationality of a cleaner zinc recovery process using MSD and a hydrometallurgical method. It was found that the addition of CH ₃COONH ₄ to a NH ₃–H ₂O system promotes zinc extraction, and 83.76% of zinc could be dissolved and recovered from the MSD under the following conditions: total ammonia concentration of 5 mol l ⁻¹, stirring speed of 300 r.p.m., ammonia/ammonium ratio of 1 : 1, solid/liquid ratio of 1 : 5, leaching temperature of 25°C and a leaching time of 60 min. A leaching kinetic study indicates that the leaching process is controlled by the diffusion and interface transfer and that the reaction apparent activation energy is 22.66 kJ mol ⁻¹. Fourier transform infrared spectroscopy and electrospray ionization mass spectrometry analysis showed that zinc can combine with the carboxylate anion to form Zn complexes such as [Zn ₂(Ac) ₃(NH ₃) ₂] ⁺. Zn ₂SiO ₄, ZnS and ZnFe ₂O ₄ in NH ₃–CH ₃COONH ₄–H ₂O system did not disappear according to X-ray diffraction analysis for leaching residue.