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.

This paper describes the results of a laboratory study that looked at the conditioning of POX slurries produced by pressure oxidation (225 oC) of refractory gold flotation concentrates. The authors used a case study of sulphide concentrates produced as a result of flotation of refractory gold ores of the Malomyr and Pioner deposits to define the conditioning parameters applicable to POX slurries: i.e. temperature — 95 oC, duration — 2 to 4 hours. The above conditions help improve the quality of POX cakes before cyanidation so that the POX residue contained less sulphate sulphur and the cake weight could be lowered by 40–70%. The authors looked at the relationship between the conditioning parameters (60–95 oC with the duration of up to 7 hours) and the solids yield. They also examined how the above parameters influenced the transfer of the key components (i.e. iron, sulphur and arsenic) into liquid phase. In particular, the authors examined the process of conditioning POX cakes obtained from concentrates with the minimum (up to 2%) and high (8–10%) concentration of arsenic. The paper examines how the material composition of POX products tends to change after conditioning when dealing with sulphide concentrates. Conditioning was found to benefit the recovery of gold from POX cakes when dealing with high-arsenic concentrates. The gold particles in cakes can be encapsulated by mixed arsenate/sulphates of iron(III), which get dissolved during atmospheric conditioning, and the gold surface becomes available for cyanide solution. After conditioning, the share of cyanidable gold in POX cakes increases by 3.0 to 5.5%.

This paper shows the results of laboratory tests of autoclave oxidation of double-refractory flotation concentrates. The presence of organic carbon (0,7–2,6%), which has a high sorption activity in relation to gold complexes is the main processing problem. Gold recovery from the autoclave oxidation cakes of such materials at a temperature of 200–225 oC does not exceed 80–90%. High temperatures (225–250 oC) and the duration of the material's residence time in the autoclave can influence the indicators of the process. Gold recovery from carbonaceous concentrates depends on the amount of organic carbon oxidized and removed to the vent gas in the form of carbon dioxide. Carbon oxidation process goes simultaneously at a low rate with the destruction of sulfides. The active phase of organic carbon oxidation occurs after the oxidation of sulfides when redox potential in a solution reaches about 530–540 mV. It is shown that organic carbon oxidation requires several hours of slurry residence time in the autoclave at operating parameters after the oxidation of sulfides (>99%). The optimal duration of overoxidation depends on the content and sorption activity of carbon in the material and the operating temperature. The almost full elimination of organic carbon is required to increase the gold recovery up to 96–98% from the tested concentrates. Concentrates with carbon content up to 1,5% must be overoxidized for 30–60 minutes, with content of 1,5–3,0% – for about 120 minutes at a temperature of 250 oC. Reducing the operating temperature in the autoclave by 10–25 oC leads to increase in overoxidation period by 1,5–2 times. The authors would like to thank the leadership of the Petropavlovsk Group for the possibility to carry out this research study and publish the findings.

Pokrovskiy pressure oxidation hub (POX hub) JSC “Pokrovskiy rudnik” is part of the Petropavlovsk, which is one of the largest gold mining companies in Russia. Pokrovskiy POX hub was designed to extract gold from sulfide concentrates by resin in pulp cyanidation after pre-oxidation in the autoclave. This article briefly describes the main stages of the Pokrovskiy POX hub project, the features of commissioning and rump-up of the technology of pressure oxidation of gold-bearing double refractory materials. The design capacity by the processed concentrate of one autoclave was achieved during first month of operation. Main indicators of autoclave technology are presented and discussed in this paper. The paper also contains: characteristics of the operation of the main equipment, discussion of technical and technological difficulties of the start-up period, and their influence on the main technological indicators. The problems were quickly resolved by local stuff with support of other subdivision of Petropavlovsk.

This paper describes the key results of research carried out with the aim of developing hydrometallurgical technology for the processing of substandard copper-zinc concentrates and middling products. The proposed technology allows to remove low-grade concentrates with a high content of impurities (zinc, lead, arsenic) from the pyrometallurgical plant, which helps to increase copper recovery in the pyrometallurgical processing. Also, the problem of processing of a lead dust from the Balkhash and the Zhezkazgan smelters was solved. The addition of atmospheric lead dust leaching into the hydrometallurgical flowsheet does not lead to its complication. The flowsheet already assumed the separation of copper and zinc into individual commodity concentrates and the transfer of harmful impurities to the tailings. The developed flowsheet for processing substandard concentrates is 80% provided with the equipment of the reconstructed Zinc Plant, Balkhash, Kazakhstan. At the moment, the development of working documentation for the reconstruction of the hydrometallurgical plant is underway. The establishment of a metallurgical hub in Balkhash will increase the efficiency of existing Kazakhmys corporation facilities. Also, it will reduce the manufacturing cost and ramp up the amount of processed raw materials and output products.

Autoclave leaching of sulfide concentrates may produce various ferric secondary phases, depending on the arsenic content and temperature. Silver is converted to argentojarosite, from which it is not recoverable by standard cyanidation methods. To increase silver recovery, it is necessary to reduce the argentojarosite formation during autoclave leaching. This study was devoted to the influence of gypsum on the formation of secondary phases of ferric arsenate and the subsequent recovery of gold and silver by cyanidation. The addition of gypsum at a consumption of 0.1 g/g(concentrate) helped to increase silver extraction from 13.4 to 98% at cyanidation. Gold recovery was 99%. An increase in gypsum consumption contributed to the ferric arsenate sulfate formation with an increased sulfate sulfur content, and a decrease in the As/S_(sulfate) molar ratio in the cake from 3.7 to 0.88 contributed to an increase in silver extraction at cyanidation of up to 98%. Basic ferric sulfate is not formed in this case, since according to EDS mapping, the distribution of arsenic and sulfur over ferric-containing particles is uniform. According to TCLP, stable, sparingly soluble ferric arsenate phases are formed and the cake obtained after cyanidation is stable and suitable for disposal, since the final arsenic concentration in the solution was 0.45 mg/dm³.