Search Results (22)

This study aims to develop an environmentally friendly hydrometallurgical process for the recovery of zinc from zinc oxide ores. The process includes monosodium glutamate (MSG) leaching, followed by zinc recovery from the pregnant leach solution via electrowinning, and the recirculation of the spent solution to the leaching stage. The study investigated the effects of key leaching parameters and identified the optimal conditions as a pH of 9.5, temperature of 70 °C, 5 h leaching time, solid-to-liquid ratio of 50 g/L, particle size of d₈₀ = 115 µm, and initial MSG concentration of 1.0 M. Under these conditions, 82.3 ± 0.05% of the zinc was extracted with minimal co-dissolution of impurities. Subsequent electrowinning at 100 A/m² for 150 min yielded 74.97 ± 2.43% zinc recovery with 96.4 ± 0.76% purity. The process achieved a current efficiency of 87.08%, while the specific energy consumption was calculated to be 3.98 kWh per kilogram of zinc recovered. The reusability of MSG was examined by recirculating spent electrowinning solution back to the leaching stage. Zinc extraction decreased from 82.2% to 28.5% over three electrowinning–leaching cycles, due to MSG degradation during electrowinning. The results of this study demonstrated that MSG is a selective and effective lixiviant for zinc recovery, while underlining the limitations of its reuse. Full article

Ammonia zinc refining has the benefits of low energy consumption, high zinc recovery, and good environmental protection compared with traditional acid and alkaline zinc refining. However, in the production process of refining zinc with ammonia, the anode undergoes chlorine precipitation, and then the oxidation of the ammonia precipitation of some nitrogen occurs. Ammonia replenishment is a cumbersome process that results in large amounts of ammonia volatilization and environmental pollution. In ammonia zinc refining, it is important to ensure the concentration of ammonia and chlorine, as the graphite anodes used in conventional ammonia zinc refining do not retain chlorine and ammonia and dissolve slowly due to oxidation. Therefore, this paper proposes a new measure to conserve chlorine and ammonia to reduce anode chlorine generation by adding an anionic barrier layer and selecting manganese anode materials with selective oxygen precipitation. Under the conditions of 50 × 100 mm sized electrodes, a current density of 350 A/m², and a temperature of 60 °C, a graphite anode and manganese anode were used for electrowinning and for the collection of anode gas under different additive conditions. For the first time, we present a comparative analysis of gas composition, using gas chromatography to demonstrate the feasibility of the different measures used to preserve chlorine, ammonia, and oxygen for industrial applications, as well as the advantages of using these methods in reducing costs. And the experiments show that, by adding the anionic barrier layer, adding urea, and using manganese anode materials with selective oxygen precipitation, the nitrogen precipitation in the anode gas can be reduced to 40–50%, and oxygen precipitation reaches 48.76%. Full article

Bi³⁺ doped Ti/Sb-SnO₂/PbO₂ electrode materials were fabricated by electrodeposition to improve their electrochemical performance in zinc electrowinning. The surface morphology, chemical composition, and hydrophilicity of the as-prepared electrodes were characterized using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and contact angle. An electrochemical measurement and an accelerated lifetime experiment were also conducted to investigate the electrocatalytic performance and stability of the electrodes. The results show that the Bi³⁺ modification electrode has an important effect on the coating morphology, the crystal structure, the surface hydrophilicity, the electrocatalytic activity, and the stability. The electrode prepared from the solution containing 2 mmol·L⁻¹ Bi(NO₃)₃ (marked as the Ti/Sb-SnO₂/2Bi-PbO₂ electrode) exhibits the best hydrophilicity performance (θ = 21.6°) and the longest service life (1196 h). During the electrochemical characterization analysis, the Ti/Sb-SnO₂/2Bi-PbO₂ electrode showed the highest oxygen evolution activity, which can be attributed to it having the highest electroactive surface (q_T* = 21.20 C·cm⁻²) and the best charge-transfer efficiency. The DFT calculation demonstrated that the doping of Bi³⁺ leads to a decrease in the OER reaction barrier and an increase in the DOS of the electrode, which further enhances the catalytic activity and the conductivity of the electrode. Moreover, the simulated zinc electrowinning experiment demonstrated that the Ti/Sb-SnO₂/2Bi-PbO₂ electrode consumes less energy than other electrodes. Therefore, it is expected that the Bi³⁺ modified electrode will become a very promising electrode material for zinc electrowinning in the future. Full article

This study outlines findings from an investigation into the development of a hydrometallurgical process for manufacturing various forms of zinc perrhenate, entirely from waste from recycling and from the Zn–Pb industry. Scraps of Re-bearing Ni-based superalloys and acidic waste, circulating zinc solutions generated during the production of Zn by the electrolytic method and which contain >45 g/dm³ of Zn, Na, Mn, and Mg, were used in the research. In the publication, the conditions for the production of three types of zinc perrhenate, i.e., Zn(ReO₄)₂·4H₂O, Zn(ReO₄)_2, and Zn(ReO₄)₂·2H₂O, are presented. As a result of the analysis of the obtained results, it was concluded that to obtain the above-mentioned forms of zinc perrhenate, zinc carbonate can be used, precipitated from acidic, waste, and multi-component solutions after their prior neutralization to pH 4.0 and partial purification from Mn, Mg, and Na using metallurgical zinc oxide. Zinc carbonate should be precipitated using Na₂CO₃ at pH 6.3 and subsequently purified from other impurities, i.e., Mg, Na, and Mn, using aqueous ammonia solutions. As a result, zinc carbonate was obtained, which was used in a reaction with an aqueous solution of HReO₄ to produce zinc perrhenate. The precipitated forms of Zn(ReO₄)₂ were obtained by appropriately drying the crude and hydrated Zn(ReO₄)₂ to obtain its tetrahydrate, dihydrate, and anhydrous forms, respectively, using drying temperatures of 55, 135, and 185 °C. The developed technology has been submitted for a patent and is an example of a technology founded on the principles of sustainable development, with a particular emphasis on the minimalization of loss of rhenium and zinc at all stages of its realization. Full article

Removing manganese from zinc electrolytes is necessary to pave the way for replacing lead-based anodes with mixed metal oxide (MMO) anodes. MMO anodes offer significantly lower overpotential towards oxygen evolution reactions, thus are attractive from an energy consumption viewpoint. Previous studies had shown that, thanks to the catalytic effect of cobalt, manganese can be removed successfully from the zinc purification solution through the oxidative precipitation method using a simulated roasting off-gas plant. This study focuses on understanding the primary mechanism behind manganese oxidation precipitation and investigating the influence of various operating parameters such as temperature, dissolved oxygen (DO), and solution potential on the reaction kinetics. The results revealed that the kinetics of the reaction was highly dependent on the temperature and catalyst activity rather than on the reactant concentration. Additives, with radical scavenging effects, were added to identify the radicals responsible for the oxidation of Mn. The manganese oxidation reaction was dramatically suppressed when methanol was added. However, in the presence of tert-butyl alcohol (TBA), a sensible reduction in manganese removal was not observed, suggesting sulfate radical as the predominant species for oxidizing manganese. The physical and chemical characteristics of the sediments were also presented. Full article

During hot-dip galvanization, wastes such as bottom dross, zinc ash, spent pre-treatment solutions, and galvanizing flue dust (GFD) are generated. In scientific publications, research devoted to GFD waste recycling is absent, and companies generating this waste require a solution to this complex problem. GFD is often landfilled in hazardous waste landfills. However, it is possible to process this waste hydrometallurgically, where GFD is first leached, the solution is refined, and finally, zinc metal is obtained by electrowinning. During specific environmentally friendly leaching, not all solid GFD is dissolved, and the aim of this study is to process the remaining solid GFD residue. The analysis shows that the GFD residue material mainly contains zinc (42.46%) in the form of oxides, but there is also a small amount of polluting elements such as Al, Fe, and Pb. This study examines the leaching of the samples in HCl and H₂SO₄ under different conditions with the aim of obtaining a solution with a high concentration and high leaching efficiency of zinc. The L/S ratio of 3, 4 M H₂SO_4, and ambient temperature proved to be optimal for the leaching of the GFD residue, where 96.24% of zinc was leached out, which represents a zinc concentration of 136.532 g/L. Full article

Super-hot acid leach residue is generated during zinc production in the roasting–leaching–electrowinning route, where both primary and secondary resources are used as feed material. This residue may contain valuable metals, such as lead, zinc, and iron, as well as precious metals, such as gold and silver. Four materials, namely super-hot acid leach residue, a residue formed when super-hot acid leach residue is selectively leached for lead with triethylenetetramine, as well as flotation concentrate, and flotation tailings formed in a selective silver flotation process with super-hot acid leach residue as the feed material were characterized to obtain a deeper understanding of possible further metal extraction. These four materials were characterized for chemical composition, mineralogy, and mineral distribution via chemical analyses, X-ray diffraction, and energy-dispersive scanning electron microscopy, respectively. The scanning electron microscope images showed that the materials have large variations in particle size distribution and composition. The results showed that the main lead phase in super-hot acid leach residue is lead sulfate, whereas it is mostly converted to lead sulfide during the selective lead leaching of the super-hot acid leach residue. The remaining lead sulfate is found in a solid solution with barium sulfate. Extracting lead from super-hot acid leach residue via triethylenetetramine leaching resulted in increased concentrations of gold and silver by 41% and 42%, respectively. The identified silver phases in super-hot acid leach residue may correspond to silver sulfide, silver chloride, and elementary silver, where silver sulfide was the most commonly occurring silver phase. After leaching this selectively for lead with triethylenetetramine, similar silver phases were identified, but silver sulfide and silver chloride occurred to a similar extent. Additionally, silver copper sulfide was detected. The presence of different silver phases might pose a challenge to reaching high silver recovery during leaching as the optimum leaching conditions differ somewhat. Furthermore, elemental sulfur, with a tendency to coat gold and silver particle surfaces, which is indicated to be present in all materials except the silver flotation tailings, may hinder metal extraction. Full article

Implementing mixed metal oxide (MMO) anodes in zinc electrowinning is highly desired due to the considerable reduction in electrical energy consumption. However, the presence of manganese in the electrolyte is a major obstacle for implementing MMO anodes in the zinc cell houses. In this work, we explore the possibility of using plant off-gas, containing SO₂, to remove manganese. A SO₂/air gas mixture with different SO₂ and O₂ concentrations was therefore used for the oxidative precipitation of manganese. It was shown that the manganese oxidation reaction is highly pH-dependent. Calcium hydroxide was used to control the pH during the process. Different operating parameters, i.e., pH, SO₂/air ratio, reaction time, and effect of cobalt as a reaction catalyst, were investigated. Optimal conditions for manganese removal were reported. Under the optimal conditions, the manganese concentration decreased from 1 g L⁻¹ to less than 1 mg L⁻¹ within 30 min. Precipitates were characterized using EDS, XRF, and XPS techniques and showed coprecipitation of manganese, zinc, gypsum, and cobalt. Full article

Nickel–iron-layered double hydroxide (NiFeLDH) is one of the promising catalysts for the oxygen evolution reaction (OER) in alkaline electrolytes, but its conductivity limits its large-scale application. The focus of current work is to explore low-cost, conductive substrates for large-scale production and combine them with NiFeLDH to improve its conductivity. In this work, purified and activated pyrolytic carbon black (CBp) is combined with NiFeLDH to form an NiFeLDH/A–CBp catalyst for OER. CBp not only improves the conductivity of the catalyst but also greatly reduces the size of NiFeLDH nanosheets to increase the activated surface area. In addition, ascorbic acid (AA) is introduced to enhance the coupling between NiFeLDH and A–CBp, which can be evidenced by the increase of Fe-O-Ni peak intensity in FTIR measurement. Thus, a lower overvoltage of 227 mV and larger active surface area of 43.26 mF·cm⁻² are achieved in 1 M KOH solution for NiFeLDH/A–CBp. In addition, NiFeLDH/A–CBp shows good catalytic performance and stability as the anode catalyst for water splitting and Zn electrowinning in alkaline electrolytes. In Zn electrowinning with NiFeLDH/A–CBp, the low cell voltage of 2.08 V at 1000 A·m⁻² results in lower energy consumption of 1.78 kW h/Kg_Zn, which is nearly half of the 3.40 kW h/Kg_Zn of industrial electrowinning. This work demonstrates the new application of high-value-added CBp in hydrogen production from electrolytic water and zinc hydrometallurgy to realize the recycling of waste carbon resources and reduce the consumption of fossil resources. Full article

This article presents the history of zinc, its production and demand. The quantity of zinc production, both primary zinc from ores and concentrates, and secondary zinc from scrap and zinc-rich waste, was discussed. A comprehensive economic analysis covers zinc prices in the years 1960–2021. The basic methods of obtaining zinc from ores, including pyrometallurgical (Imperial Smelting Process ISP, Kivcet, Ausmelt) and hydrometallurgical (roasting–leaching–electrowinning RLE, atmospheric direct leaching ADL, Engitec Zinc Extraction EZINEX, zinc pressure leach) and their short characteristics, are presented. The global zinc market and the main areas of its application were analyzed. Technologies used for the recovery of zinc from scrap are discussed along with their characteristics. Galvanized steel is the main source of secondary zinc, both in the galvanizing process and in the remelting of galvanized steel. It can be easily recycled with other scrap steel in the electric arc furnace (EAF) for steel production. Currently, with high volatility in the price of zinc, as well as its natural resources in the earth’s crust, recycling is an important activity, despite the fact that zinc concentrates have a relatively constant chemical composition, while the resulting zinc waste contains zinc in varying amounts. Full article

Autoclave leaching of zinc concentrate (Sphalerite) is an environmentally friendly process compared to roasting, which discharges pollutants into the atmosphere. Due to the amount of iron in the final product, a study is proposed to evaluate different reagents for eliminating iron from the autoclave outcome, minimizing Zn losses. The colloid formation, zinc losses, iron removal, phase separation stage characteristics (sedimentation and filtering), and reagent costs were used to evaluate six-iron precipitating reagents: CaO, Na₂CO₃, CaCO₃, NaOH, MgO, and Ca(OH)₂. CaO shows 99.5% iron removal and 87% zinc recovery. Although CaO was one of the reagents with significant zinc recovery, it presented operational difficulties in the filtration stage due to the high viscosity of the mixtures. Finally, Ca(OH)₂ is the reagent recommended due to its ease of use, zinc yield recovery, electrowinning efficiency, and iron precipitate filtration rate. Zinc recovery was above 80%, while the iron concentration in the solution was below 50 ppm. Full article

The current study presents an effort to develop a sustainable hydrometallurgical process for the recovery of copper from waste printed circuit boards (PCBs) to be applied at local small to medium industrial units. The process aims to separate and recover copper from filter dust produced during the crushing of PCBs using a hammer mill in a recycling facility. Due to the high plastic content in the dust (approximately 30% w/w), the metal fraction was separated gravimetrically, and the material originated consisted mainly of Cu (23.8%), Fe (17.8%), Sn (12.7%), Pb (6.3%), Zn (3.4%), Al (3.3%), Mn (1.6%), and Ni (1.5%). Prior to copper recovery, the dust was leached with HCl as a pretreatment step. During this step, more than 80% of iron, zinc, and tin were leached out. The resulting solid consisted mainly of Cu (37.6%) and Fe (10.7%), leading to a copper enrichment of around 60% in the powder. The leaching of copper was conducted in a two-step process using H₂SO₄ as a leaching agent with the addition of H₂O₂ as an oxidizing agent. The experimental conditions had low energy requirements (no heating or agitation needed). The leaching of Cu reached 98%. Despite the pretreatment step, the concentration of other metals (Fe, Zn, Ni) in the pregnant solution was too high to proceed to electrowining. Therefore, the organic solvent ACORGA M5640 was selected for the extraction of copper from the pregnant solution. The extraction was conducted in two stages at pH equilibrium 1.5, and the loaded organic phase was stripped with HCl in two steps. The strip liquor was suitable for electrowinning. Full article

Zinc electrowinning is an energy-intensive step of hydrometallurgical zinc production in which ohmic drop contributes the second highest overpotential in the process. As the ohmic drop is a result of electrolyte conductivity, three conductivity models (Aalto-I, Aalto-II and Aalto-III) were formulated in this study based on the synthetic industrial electrolyte conditions of Zn (50–70 g/dm³), H₂SO₄ (150–200 g/dm³), Mn (0–8 g/dm³), Mg (0–4 g/dm³), and temperature, T (30–40 °C). These studies indicate that electrolyte conductivity increases with temperature and H₂SO₄ concentration, whereas metal ions have negative effects on conductivity. In addition, the interaction effects of temperature and the concentrations of metal ions on solution conductivity were tested by comparing the performance of the linear model (Aalto-I) and interrelated models (Aalto-II and Aalto-III) to determine their significance in the electrowinning process. Statistical analysis shows that Aalto-I has the highest accuracy of all the models developed and investigated in this study. From the industrial validation, Aalto-I also demonstrates a high level of correlation in comparison to the other models presented in this study. Further comparison of model Aalto-I with the existing published models from previous studies shows that model Aalto-I substantially improves the accuracy of the zinc conductivity empirical model. Full article

Lead composites have been used as anodes in the electrowinning process to produce metals such as copper and zinc. Manufacturing stable lead anodes with appropriate mechanical and chemical properties is required to improve the performance of the electrowinning process. In this study, an accumulative roll bonding (ARB) method was used to fabricate a Co/Pb nanocomposite. Utilizing the ARB method can help us to achieve a uniform structure with enhanced mechanical properties via severe plastic deformation. The results showed that suitable tensile properties were obtained in Pb–0.5%Co–10pass samples. The tensile strength and strain of these samples were 2.51 times higher and 83.7% lower than that of as-cast pure Pb. They also showed creep resistance and hardness up to 1.8 and 2.5 times more than that of as-cast pure Pb. The ARB technique uniformly distributed Co particles in the Pb matrix. The enhanced strength of Pb samples was observed in the composite including grain sizes of less than 50 nm as a result of hindering the recovery phenomenon. The particle size of the Co distributed in the Pb matrix was 353 ± 259 nm. Compared to conventional methods, the ARB process improved the mechanical properties of Co/Pb composites and can open a new horizon to fabricating this composite in metal industries. Full article

Zinc recovery from spent pickling acids (SPAs) can play an important role in achieving a circular economy in the galvanizing industry. This work evaluates the scale-up of membrane-based solvent extraction technology aimed at the selective separation of zinc from industrial SPAs as a purification step prior to zinc electrowinning (EW). The experiments were carried out at a pilot scale treating SPAs batches of 57 to 91 L in a non-dispersive solvent extraction (NDSX) configuration that simultaneously performed the extraction and backextraction steps. The pilot plant was equipped with four hollow fiber contactors and 80 m² of total membrane area, which was approximately 30 times higher than previous bench-scale studies. Tributylphosphate diluted in Shellsol D70 and tap water were used as organic and stripping agents, respectively. Starting with SPAs with high Zn (71.7 ± 4.3 g·L⁻¹) and Fe (82.9 ± 5.0 g·L⁻¹) content, the NDSX process achieved a stripping phase with 55.7 g Zn·L⁻¹ and only 3.2 g Fe·L⁻¹. Other minor metals were not transferred, providing the purified zinc stripping with better quality for the next EW step. A series of five consecutive pilot-scale experiments showed the reproducibility of results, which is an indicator of the stability of the organic extractant and its adequate regeneration in the NDSX operation. Zinc mass transfer fluxes were successfully correlated to zinc concentration in the feed SPA phase, together with data extracted from previous laboratory-scale experiments, allowing us to obtain the design parameter that will enable the leap to the industrial scale. Therefore, the results herein presented demonstrate the NDSX technology in an industrially relevant environment equivalent to TRL 6, which is an essential progress to increase zinc metal resources in the galvanizing sector. Full article