Abstract
This work investigated the extraction behavior of Zn, Cu, and Fe during sulfuric acid leaching of metallurgical waste from the Ust-Kamenogorsk zinc production plant. At the same time, the detailed kinetic analysis was restricted to Zn dissolution. This study aimed to determine the structural and morphological characteristics of metallurgical wastes and the extraction efficiencies of Zn, Cu, and Fe, and to evaluate the apparent kinetics of Zn dissolution comparatively. The phase composition of the initial and mechanically treated samples was studied by X-ray diffraction analysis, functional groups by FTIR spectroscopy, and morphological features by scanning electron microscopy. Leaching experiments were conducted to assess the effect of sulfuric acid concentration, temperature, and process duration. The results showed that mechanical treatment produced qualitative morphological and structural changes in the slag and was accompanied by improved extraction of Zn, Cu, and Fe during sulfuric acid leaching. The extraction behavior depended on the experimental variable investigated. In the sulfuric acid concentration series, extraction from the mechanically treated sample reached 70.55 ± 0.88% for Zn, 90.50 ± 0.47% for Cu, and 42.37 ± 0.47% for Fe at 1.0 M H2SO4. In the leaching time series conducted at 1.0 M H2SO4 and 75 °C, Zn extraction reached 78.06 ± 0.92% at 120 min after mechanical treatment, whereas Cu extraction reached its maximum of 90.78 ± 0.55% at 60 min. The time-dependent extraction behavior differed among the investigated metals, and no single leaching time maximized Zn, Cu, and Fe extraction simultaneously. Comparative analysis using Shrinking Core Model expressions indicated that both surface-reaction and product-layer-diffusion expressions provided comparable descriptions of the Zn leaching data; however, the limited number of kinetic data points does not allow definitive identification of a unique rate-controlling mechanism. For Zn dissolution, the apparent activation energies were 8.16 and 10.17 kJ mol−1 for the surface chemical reaction expression and 14.37 and 17.81 kJ mol−1 for the product-layer diffusion expression before and after mechanical treatment, respectively. A conceptual leaching pathway based on the available experimental observations was proposed to relate the observed structural and morphological changes to Zn extraction and the formation of a gypsum-containing solid residue. The results indicate that mechanical treatment is a promising pretreatment approach for improving the hydrometallurgical processing of the investigated metallurgical waste under the tested conditions.