The nature of the hydrothermal reaction between arsenopyrite particles (FeAsS) and copper sulfate solution (CuSO₄) was investigated in this study. The effects of temperature (443–523 K), CuSO₄ (0.08–0.96 mol/L) and H₂SO₄ (0.05–0.6 mol/L) concentrations, reaction time (1–120 min), stirring speed (40–100 rpm) and particle size (10–100 μm) on the FeAsS conversion were studied. The FeAsS conversion was significant at >503 K, and it is suggested that the reaction is characterized by the formation of a thin layer of metallic copper (Cu⁰) and elemental sulfur (S⁰) around the unreacted FeAsS core. The shrinking core model (SCM) was applied for describing the process kinetics, and the rate of the overall reaction was found to be controlled by product layer diffusion, while the overall process was divided into two stages: (Stage 1: mixed chemical reaction/product layer diffusion-controlled) interaction of FeAsS with CuSO₄ on the mineral’s surface with the formation of Cu¹⁺ and Fe²⁺ sulfates, arsenous acid, S⁰, and subsequent diffusion of the reagent (Cu²⁺) and products (As³⁺ and Fe²⁺) through the gradually forming layer of Cu⁰ and molten S⁰; (Stage 2: product layer diffusion-controlled) the subsequent interaction of CuSO₄ with FeAsS resulted in the formation of a denser and less porous Cu⁰ and S⁰ layer, which complicates the countercurrent diffusion of Cu²⁺, Cu¹⁺, and Fe²⁺ across the layer to the unreacted FeAsS core. The reaction orders with respect to CuSO₄ and H₂SO₄ were calculated as 0.41 and −0.45 for Stage 1 and 0.35 and −0.5 for Stage 2. The apparent activation energies of 91.67 and 56.69 kJ/mol were obtained for Stages 1 and 2, respectively.

Automotive catalysts containing Platinum Group Metals (PGMs) are valuable secondary raw materials for refineries. Hydrometallurgical processing of catalysts is ineffective due to the low PGMs content—0.15–0.3%. Therefore, such raw materials are melted into an iron collector containing 1.5–5% PGMs. However, when leaching a collector containing 10–20% Si in both HCl and H₂SO₄, the recovery of PGMs does not exceed 40%. The latter indicates incomplete destroying of the PGM-encapsulating ferrosilicon matrix. To completely destroy the ferrosilicon matrix, it is proposed to carry out the leaching process in a mixture of HCl and HF. In this case, the extraction of Fe into solution and Si into the gas phase (in the form of SiF₄) exceeds 90%. This should be sufficient to completely destroy the ferrosilicon matrix and release PGMs. The current work presents the results of studies of the leaching kinetics of the iron collector containing ferrosilicon in a mixture of HCl and HF using the Shrinking Core Model (SCM). It was found that the greatest positive effect on Fe extraction into solution is exerted by HCl concentration and temperature, while Si release into the gas phase is only influenced by HF concentration. In addition, during the destroying of ferrosilicon, FeF₂ is formed and deposited on the surface of the material in the form of thin-film conglomerates. This leads to diffusion difficulties and a gradual decrease in the intensity of the iron collector leaching 30 min after the start of process. After 120 min, there may be a decrease in Fe recovery into solution.

Autoclave oxidative leaching is one of the most promising hydrometallurgical approaches for copper suplhide materials processing. In previous studies [2–4], the possibility of an efficient autoclave treatment of chalcopyrite concentrate was confirmed. The concentrate has the following chemical composition, %: 21.5 Cu, 0.1 Zn, 26.5 S, 24.5 Fe, 0.05 Pb, 0.04 Ni, 16.2 SiO₂ [1]. At high temperature conditions (190–200 °C; 4–6 bar) in sulfuric-acid media during 100–120 min about 98% Cu was extracted. A leaching residue after POX (POX-cake) contained the following compounds, %: 55 Fe₂O₃, 40 SiO₂, 4 MeS₂/MeS. Current paper presents the results on purification of POX-cakes from iron by autoclave treatment. Futher ways for by-products (SiO₂-cake and FeSO₄-solution) processing are sugested.

The nature of tennantite (Cu₁₂As₄S₁₃), chalcopyrite (CuFeS₂) and sphalerite (ZnS) particles’ mixture dissolution in nitric acid (HNO₃) media was investigated in this study. The effects of temperature (323–368 K), HNO₃ (1–8 mol/L) and Fe³⁺ (0.009–0.036 mol/L) concentrations, reaction time (0–60 min) and pyrite (FeS₂) additive (0.5/1–2/1; FeS₂/sulf.conc.) on the conversion of the minerals were evaluated. It has been experimentally shown that the dissolution of the mixture under optimal conditions (>353 K; 6 mol/L HNO₃; FeS₂/synt. conc = 1/1) allows Cu₁₂As₄S₁₃, CuFeS₂ and ZnS conversion to exceed 90%. The shrinking core model (SCM) was applied for describing the kinetics of the conversion processes. The values of E_a were calculated as 28.8, 33.7 and 53.7 kJ/mol, respectively, for Cu₁₂As₄S₁₃, CuFeS₂ and ZnS. Orders of the reactions with respect to each reactant were calculated and the kinetic equations were derived to describe the dissolution rate of the minerals. It was found that the interaction between HNO₃ solution and Cu₁₂As₄S₁₃, CuFeS₂ and ZnS under the conditions investigated in this are of a diffusion-controlled nature. Additionally, the roles of Fe(III) in the initial solution and FeS₂ in the initial pulp as catalysts were studied. The results indicated that the increase in Fe³⁺ concentration significantly accelerates the dissolution of the mixture, while the addition of FeS₂ forms a galvanic coupling between FeS₂, and Cu₁₂As₄S₁₃ and CuFeS₂, which also accelerates the reaction rate. The results of the study are considered useful in developing a hydrometallurgical process for polymetallic sulfide raw materials treatment.

The leaching kinetics of an industrial iron collector containing PGMs (Pd, Pt, Rh) in HCl and HF solutions were investigated. The effects of the HCl concentration (2.74–6.86 mol/L), the HF concentration (1.46–7.50 mol/L), temperature (323–363 K), and leaching time (0–210 min) on the extraction of Fe into the solution and Si into the gas phase from the iron collector were studied. The HCl concentration had a negative effect on the extraction of Si, which decreased from 78.2% to 58.1% and from 97.4% to 87.2% in the time ranges of 0–30 min and 30–120 min, respectively. This occurred due to the accumulation of Fe²⁺ in the solution and its interaction with HF, which led to a reduction in both the HF concentration and the extraction of Si. In addition, there were diffusion difficulties of the Fe and Si extraction because Fe precipitated on the surface of the cakes in the form of thin-film conglomerates of FeF₂. This was confirmed by the XRF and EDS results, indicating that F was present on the surface of the cakes. The processes of the Fe and Si extraction were diffusion-chemically controlled and diffusion controlled—the apparent activation energies decreased from 26.9 kJ/mol to 7.8 kJ/mol and from 2.2 kJ/mol to 2.0 kJ/mol in the time range of 0–120 min, respectively. Using the shrinking core model and the full factorial experiment model, the kinetic equations, the optimal parameters of iron collector leaching, and the extraction rates of Fe and Si were determined. These optimal parameters ensure the extraction of Fe and Si at the level of 95% with high leaching rates: the HCl concentration of 4.36 mol/L, the HF concentration of 6.93 mol/L, temperature of 363 K, and leaching time of 80 min.