The overall decrease in the quality of mineral raw materials, combined with the use of arsenic-containing ores, results in large amounts of various intermediate products containing this highly toxic element. The use of hydrometallurgical technologies for these materials is complicated by the formation of multicomponent solutions and the difficulty of separating copper from arsenic. Previously, for the selective separation of As from copper–arsenic intermediates a leaching method in the presence of Cu(II) ions was proposed. This paper describes the investigation of the kinetics of arsenic sulfide-containing materials leaching by copper sulfate solution. The cakes after leaching of arsenic trisulfide with a solution of copper sulfate were described using methods such as X-ray diffraction spectrometry (XRD), X-ray fluorescence spectrometry (XRF), scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy analysis (EDS). The effect of temperature (70–90 °C), the initial concentration of CuSO₄ (0.23–0.28 M) and the time on the As recovery into the solution was studied. The process temperature has the greatest effect on the kinetics, while an increase in copper concentration from 0.23 to 0.28 M effects an increase in As transfer into solution from 93.2% to 97.8% for 120 min of leaching. However, the shrinking core model that best fits the kinetic data suggests that the process occurs by the intra-diffusion mode with the average activation energy of 44.9 kJ/mol. Using the time-to-a-given-fraction kinetics analysis, it was determined that the leaching mechanism does not change during the reaction. The semi-empirical expression describing the reaction rate under the studied conditions can be written as follows: 1/3ln(1 − X) + [(1 − X) − 1/3 − 1] = 4560000Cu^3.61e^−44900/RT t.

Ammonia leaching is a promising method for processing low-grade copper ores, especially those containing large amounts of oxidized copper. In this paper, we study the effect of Si-containing minerals on the kinetics of Cu and Ag leaching from low-grade copper concentrates. The results of experiments on the pressure leaching of the initial copper concentrate in an ammonium/ammonium-carbonate solution with oxygen as an oxidizing agent are in good agreement with the shrinking core model in the intra-diffusion mode: in this case, the activation energies were 53.50 kJ/mol for Cu and 90.35 kJ/mol for Ag. Energy-dispersive X-ray spectroscopy analysis (EDX) analysis showed that reagent diffusion to Cu-bearing minerals can be limited by aluminosilicate minerals of the gangue. The recovery rate for copper and silver increases significantly after a preliminary alkaline desilication of the concentrate, and the new shrinking core model is the most adequate, showing that the process is limited by diffusion through the product layer and interfacial diffusion. The activation energy of the process increases to 86.76 kJ/mol for Cu and 92.15 kJ/mol for Ag. Using the time-to-a-given-fraction method, it has been shown that a high activation energy is required in the later stages of the process, when the most resistant sulfide minerals of copper and silver apparently remain.

At present, the processing of refractory gold–arsenic sulphide concentrates is becoming more relevant due to the depletion of rich crude ore reserves. In the process of the nitric acid leaching of arsenic sulphide minerals, solutions are formed containing 20–30 g/L of arsenic (III). Since market demand for arsenic compounds is limited, such solutions are traditionally converted into poorly soluble compounds. This paper describes the investigation of precipitating arsenic sulphide from nitric acid leaching solutions of refractory sulphide raw materials of nonferrous metals containing iron (III) ions using sodium hydrosulphide with a molar ratio of NaHS/As = 2.4–2.6, which is typical for pure model solutions without oxidants. The work studied the effect of temperature, the pH of the solution and the consumption of NaHS and seed crystal on this process. The highest degree of precipitation of arsenic (III) sulphide (95–99%) from nitric acid leaching solutions containing iron (III) ions without seed occurs with a pH from 1.8 to 2.0 and a NaHS/As molar ratio of 2.8. The introduction of seed crystal significantly improves the precipitation of arsenic (III) sulphide. An increase in seed crystal consumption from 0 to 34 g/L in solution promotes an increase in the degree of transition of arsenic to sediment from 36.2 to 98.1% at pH = 1. According to SEM/EDS and XRF sediment data, from the results of experiments on the effect of As₂S₃ seed crystal consumption, acidity and molar ratio of NaHS/As on the precipitation of arsenic (III) sulphide and the Fe_total/Fe²⁺ ratio in the final solution, it can be concluded that the addition of a seed accelerates the crystallisation of arsenic (III) sulphide by increasing the number of crystallisation centres; as a result, the deposition rate of As₂S₃ becomes higher. Since the oxidation rate of sulphide ions to elemental sulphur by iron (III) ions does not change significantly, the molar ratio of NaHS/As can be reduced to 2.25 to obtain a precipitate having a lower amount of elemental sulphur and a high arsenic content similar to that precipitated from pure model solutions.

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.

Iron collector is a type of middlings produced in spent automotive catalyst recycling. Platinum group metals are encapsulated in the ferrosilicium matrix, ferrosilicium being the main component of the collector. Application of conventional hydrometallurgical processes (such as leaching in hydrochloric or sulphuric acids) for ferrosilicium liberation does not appear to be effective. So, it is proposed to use a mixture of hydrochloric and hydrofluoric acids for leaching of the collector in order to intensify the hydrometallurgical process. The said process ensures a high degree of liberation of the ferrosilicium matrix resulting in the production of cakes suitable for further refining. Using the shrinking core model, the authors of this research study examined the kinetics of leaching an iron collector containing ferrosilicium phases in a mixture of hydrochloric and hydrofluoric acids. Some generic kinetic equations were obtained as a result, which adequately describe the process of iron recovery in solution (R2 = 0.96) and that of silicon recovery in gas phase (R2 = 0.93) at the concentration of hydrochloric acid of 2.74 to 6.86 mol/l, that of hydrofluoric acid of 1.50 to 7.50 mol/l, at the temperature of 323 to 363 K and the iron collector leaching duration of 0 to 110 min. The concentration of hydrochloric acid and the temperature were found to produce the strongest effect on iron recovery in the case of iron recovery in solution, whereas in the case of silicon recovery in gas phase it was the concentration of hydrofluoric acid. Apparent activation energy values were calculated: 38.7 kJ/mol for iron and 4.3 kJ/mol for silicon. These values are typical of processes developing in transition and diffusion modes, respectively. Diffusion of reagents through the layer of products present at the ferrosilicium surface adsorbed (SiF4) and in the form of conglomerates (FeF2) was found to be the limiting stage of the iron collector leaching process. The authors defined certain iron collector leaching parameters that enable to liberate at least 95% of ferrosilicium avoiding precipitation of secondary phases.This research was funded by the Ministry of Science and Higher Education of the Russian Federation as part of the Development Programme of the Ural Federal University named after the First President of Russia B. N. Yeltsin, in line with the Strategic Academic Leadership Programme Prioritet-2030.Contributors to this research study include D. I. Golovkin, a Research Engineer at the Laboratory of Advanced Technologies in Non-ferrous and Ferrous Metals Raw Materials Processing, Institute of Novel Materials and Technology, Ural Federal University named after the First President of Russia B. N. Yeltsin, Yekaterinburg, Russia.

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.