Browsing by Author "Korolev, Ivan"

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Effect of Impurities in Precious Metal Recovery by Electrodeposition-Redox Replacement Method from Industrial Side-Streams and Process Streams
(2018-05) Yliniemi, Kirsi; Wang, Zulin; Korolev, Ivan; Hannula, Pyry-Mikko; Halli, Petteri; Lundström, Mari
A4 Artikkeli konferenssijulkaisussa
The recovery of precious metals (Ag and Au) by electrodeposition-redox replacement (EDRR) method was studied in three different solutions: sulfate based Zn-Fe-Ag solution, chloride based Cu-Fe-Au solution and industrial multi-metal chloride solution. The common factor to these solutions is that the base (Zn or Cu) metal is present in g/L scale while the precious metal is present in ppm or lower level. The results showed that the presence of impurity Fe (in g/L scale) decreases the recovery efficiency of precious metals but at the same time, it may lead to selective dissolution of the base metal, resulting in the higher purity of the precious metal deposit. Moreover, a successful deposition of Au on carbon nanotube (CNT) films from industrial multi-metal solution was demonstrated.
Electro-hydrometallurgical chloride process for selective gold recovery from refractory telluride gold ores: A mini-pilot study
(2022-02-01) Korolev, Ivan; Altinkaya, Pelin; Haapalainen, Mika; Kolehmainen, Eero; Yliniemi, Kirsi; Lundström, Mari
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
The current paper introduces for the very first time recently invented electrodeposition-redox replacement (EDRR) method in continuous leaching-recovery-solution purification process. The mini-pilot study reveals that longer duration of the EDRR process is beneficial as it increases gold recovery per stage and decreases the specific energy consumption of the EDRR. This extraordinary behavior is postulated to be inherent to the EDRR process, as during the EDRR the cathode surface is gradually transformed from stainless steel surface to gold(±copper) surface, thus increasing process performance with time. In addition, gold concentration of 1 mg/L in the PLS was established as the minimum concentration required for efficient operation of the EDRR process. Gold extraction from ore to solution throughout the pilot test reached up to ca. 90%, whereas in reference cyanidation test only 64% of gold was dissolved. Overall, after 150 h of pilot experiment, 83% of dissolved gold was recovered from solution on the cathode, resulting in 68.5% holistic recovery of gold from ore. Furthermore, process simulation model was built, and it suggested that closed-loop operation of cupric chloride leaching – EDRR recovery – copper precipitation process can recover in total over 84% of gold from refractory telluride ore to the cathode product, providing further evidence of true potential of EDRR in sustainable gold extraction.
Electrochemical recovery of minor concentrations of gold from cyanide-free cupric chloride leaching solutions
(2018-02-20) Korolev, Ivan; Altinkaya, Pelin; Halli, Petteri; Hannula, Pyry-Mikko; Yliniemi, Kirsi; Lundström, Mari
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Despite of being the most common hydrometallurgical process for extraction of gold from ores and concentrates, cyanide leaching is blamed for its hazardous impact on environment and human health. These concerns have given a rise for alternative cyanide-free technologies, such as cupric chloride leaching. However, the state-of-art processes for gold recovery from chloride solutions are facing issues of high reagent consumption and poor selectivity. This article describes an innovative method for recovery of minor concentrations of gold from hydrometallurgical solutions by repetitive Electrochemical Deposition-Redox Replacement (EDRR) cycles. In contrast to conventional carbon-in-leach/resin-in-leach technologies or solvent extraction, the proposed electrochemical method does not require addition of any chemicals in the process and remarkably selective gold recovery can be achieved from concentrated cupric solution by tailoring the process parameters. A number of electrochemical experiments was performed in order to identify the process variables affecting the Au recovery. Results indicate that so called cut-off potential and deposition time were the EDRR parameters having the strongest impact on gold recovery at fixed concentration of Cu and Au ions. The Au content in the metal deposit after 250 EDRR cycles exceeded 75% and the Au:Cu ratio has increased by a factor of 1000, from 1:340 in the solution up to 3.3:1 in the final product. X-ray photoelectron spectroscopy analysis of the cathode surface confirmed full replacement of sacrificial copper with gold. Obtained results prove that the EDRR method can be efficiently used for the recovery of trace amounts of gold from cupric chloride solutions used for cyanide-free gold leaching.
Ferric and Cupric Chloride Leaching of Valuable Metals from Process Residues
(2019-06) Altinkaya, Pelin; Korolev, Ivan; Kolehmainen, Eero; Haapalainen, Mika; Lundström, Mari
A4 Artikkeli konferenssijulkaisussa
The object of the current study was to compare the extraction yields of various valuable metals from process residues by ferric and cupric chloride leaching as an alternative to cyanidation. Flotation tailings, with low amount of gold, copper, nickel, cobalt and zinc were used as a raw material. In the chloride leaching experiments, the effect of the oxidant type and concentration ([Fe3+] and [Cu2+] from 10 to 50 g/L), was investigated on the metals extraction. At the same time, pH (1 and 1.8), temperature (95 °C), solid/liquid ratio (25 %), oxygen feed rate (1200 mL/min), leaching time (24 h), and stirring rate (950 rpm) were kept constant. Additionally, the reference leaching experiment with sodium cyanide (NaCN) at 22 °C, pH = 11, solid/liquid ratio of 25 %, air feed rate 500 ml/min, stirring rate 400 rpm and 24 hours of leaching time was run to benchmark leaching efficiencies of cyanide-free processes. The results showed that the maximum gold extraction was observed with cyanidation (78 %) and followed by ferric and cupric chloride leaching. For copper, the extractions were higher in chloride leaching (75 – 100 %) whereas cyanide could dissolve 50 % of copper. Extraction of nickel and zinc were slightly higher in ferric chloride leaching compared to cupric chloride leaching, but cobalt extraction was similar in both chloride leaching methods. However, extraction of these metals was insignificant in cyanide leaching. With these results, it seems that chloride leaching with the presence of cupric and ferric oxidants can be used as an alternative cyanide-free method for extraction of metals from process residues.
Gold Recovery from Chloride Leaching Solutions by Electrodeposition-Redox Replacement Method
(2019-06) Korolev, Ivan; Kolehmainen, Eero; Haapalainen, Mika; Yliniemi, Kirsi; Lundström, Mari
A4 Artikkeli konferenssijulkaisussa
Currently, the adsorption methods (e.g., CIP / CIL) are by far dominating the recovery of gold from leaching solutions, especially in cyanide media. However, gradual shift towards cyanide-free gold processes also requires new developments in the recovery technologies. High concentrations of base metal and impurities cause co-adsorption by activated carbon or ion exchange resins and consequently lower gold recovery. As an alternative solution, the electrodeposition-redox replacement (EDRR) method was recently demonstrated for recovery of gold from synthetic chloride solutions. In contrast to adsorption, EDRR does not require addition of chemicals in the process and is suitable for elemental gold recovery from chloride leaching solution. In this paper, cupric chloride solution from ore leaching was tested for applicability of the EDRR method. Obtained results demonstrate that gold can be recovered from industrial process solutions containing Au at ppm scale while the base metal (Cu) concentration was as high as 30 g/L and other impurities (mainly Fe, also Zn, Co and Ni) present at various levels between ppm and g/L. The final gold deposit was analyzed with scanning electron microscopy, which confirmed the recovery of gold from the solution. Further optimization of the EDRR process parameters could make it a viable alternative to existing best available technologies due to simplicity of the process flowsheet, energy efficiency and ability for selective recovery of elemental gold even from very low concentrations.
Leaching and recovery of gold from ore in cyanide-free glycine media
(2020-11-01) Altinkaya, Pelin; Wang, Zulin; Korolev, Ivan; Hamuyuni, Joseph; Haapalainen, Mika; Kolehmainen, Eero; Yliniemi, Kirsi; Lundström, Mari
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Glycine has recently gained plenty of attention in gold processing as an alternative lixiviant to cyanide due to its non-toxicity, efficiency in metal dissolution as well as selectivity for valuable metals. This paper presents an investigation on the combination of agitated reactor leaching and recovery of gold from mildly refractory ore in cyanide-free alkaline glycine media. Optimal leaching parameters for gold extraction were evaluated using response surface methodology. The investigated parameter range was 0.5–2 M for glycine concentration, pH of 10–12 and temperatures of 23–60 °C, with constant leaching time (24 h) and solid/liquid ratio (100 g/L). Based on the experimental series, a mathematical tool was built to predict gold extraction. It was found that, in the investigated parameter range, glycine concentration did not have a statistically significant effect on gold dissolution. Conversely, both temperature and pH had a substantial role in leaching kinetics. The statistical model suggested that the optimal conditions for gold dissolution were 1.25 M of glycine, pH = 12, and T = 60 °C, corresponding to a predicted 87% gold extraction. The experimental verification showed good reliability of the model with 90% extraction of gold achieved under the predicted optimum conditions. The addition of 15 g/L of activated carbon to the pregnant leach solution (PLS) could provide 100% recovery of gold from solution onto activated carbon, i.e. holistic recovery of 90%. Presence of carbon in leach (CIL) resulted in slightly lower (95%) gold uptake from solution and significantly decreased the holistic gold recovery down to 77%. Additionally, the applicability of direct electrochemical carbon-free recovery method, namely electrodeposition–redox replacement (EDRR), was investigated. In the synthetic solution, a gold recovery as high as 88% was achieved (1247 cycles). However, in the real PLS, only 35% of gold was recovered, which is attributed to different speciation of metals and presence of the other dissolved elements.
Mechanism of selective gold extraction from multi-metal chloride solutions by electrodeposition-redox replacement
(2020-06-07) Korolev, Ivan; Spathariotis, Stylianos; Yliniemi, Kirsi; Wilson, Benjamin P.; Abbott, Andrew; Lundström, Mari
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
The electrodeposition-redox replacement (EDRR) process is a promising method for a selective extraction of minor metals from complex mixtures. When it is performed in a benign medium (such as sodium chloride solution or deep eutectic solvent), the EDRR method provides a non-toxic alternative for a conventional cyanide-based process. The detailed reaction mechanisms of the EDRR in Cu–Au systems, as well as the effect of the reaction medium are elucidated in this article. Electrogravimetric studies show that the EDRR process comprises three distinct stages: (1) deposition of Cu at a constant applied potential; (2) dissolution of deposited Cu at open circuit conditions in reaction with dissolved species in solution; (3) reduction of Au to elemental form in reaction with various Cu species. It is discovered that the recovery of Au takes place surprisingly via both the redox replacement between Cu and Au at the surface and the homogeneous Au reduction by Cu(I) species in solution. Both of these reaction pathways are facilitated by open circuit conditions (redox replacement step) between electrodeposition cycles and the utilization of other sacrificial elements in the solution is crucial. The use of aqueous chloride solution is advantageous over 1 : 2 ChCl : EG for the increased Au recovery (94.4%) and the purity of the product (93.7%), although it consumes slightly more electricity. Therefore, the EDRR enables energy and resource efficient selective extraction of Au from multi-metal industrial solutions even when it is present at low concentrations.
Performance-Based Selection of the Cathode Material for the Electrodeposition-Redox Replacement Process of Gold Recovery from Chloride Solutions
(2021-10) Korolev, Ivan; Yliniemi, Kirsi; Lindgren, Mari; Carpén, Leena; Lundström, Mari
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Recently, an emerging electrodeposition-redox replacement (EDRR) method was demonstrated to provide exceptionally efficient gold recovery from cyanide-free hydrometallurgical solutions. However, the effect of electrode material and its corrosion resistance in this process was overlooked, even though the EDRR process is carried out in extremely corrosive, acidic chloride solution that also contains significant amounts of strong oxidants, i.e., cupric ions. In the current study, nickel alloy C-2000, stainless steels 316L and 654SMO, and grade 2 titanium were for the first time critically evaluated as potential cathode materials for EDRR. The particular emphasis was placed on better understanding of the effect of cathode substrate on the overall efficiency of the gold recovery process. The use of a multiple attribute decision-making method of material selection allowed reaching of a well-founded compromise between the corrosion properties of the electrodes and process efficiency of gold extraction. The 654SMO steel demonstrated outstanding performance among the examined materials, as it enabled gold recovery of 28.1 pct after 3000 EDRR cycles, while its corrosion rate (CR) was only 0.02 mm/year.
Recovery of Gold From Industrial Solutions via Electrodeposition-Redox Replacement
(2019-04-03) Korolev, Ivan; Haapalainen, Mika; Kolehmainen, Eero; Yliniemi, Kirsi; Lundström, Mari
Poster
Currently, the adsorption methods are by far dominating the recovery of gold from leaching solutions. However, the presence of impurities reduces the metal recovery. As an alternative, electrodeposition-redox replacement (EDRR) method was recently introduced to recover pure gold from chloride process streams. This method can be applied directly after leaching without solution purification, thus decreasing the number of process stages and reducing the consumption of chemicals.
Selective gold recovery from complex solutions via electrochemical deposition with redox replacement
(2024) Korolev, Ivan
School of Chemical Engineering | Doctoral dissertation (article-based)
Global transition toward a carbon-neutral economy and broader use of renewable energy increases demand for raw materials and metals in particular, including gold. Despite gold cyanidation being the de facto industrial standard, concerns about its adverse effects on the environment and human health stimulated the search for alternatives. The electrodeposition-redox replacement (EDRR) method provides a unique possibility for selective, additive-free, and fully electrified metal recovery from complex industrial process streams. This dissertation investigates the recovery of gold from multimetal chloride solution by EDRR as a basis for non-cyanide technology for processing refractory gold ores. Initial EDRR experiments aimed to outline the detailed reaction mechanism of EDRR and study the effect of process variables using model gold and copper chloride solutions. Electroanalytical techniques, such as cyclic voltammetry, electrochemical quartz crystal microbalance, and rotating ring-disk electrode, were employed for this purpose. The quantity and quality of the produced gold deposits were analyzed with scanning electron microscopy, X-ray photoelectron spectroscopy and inductively coupled plasma mass spectrometry. The experiments with two-component solutions demonstrated the viability of EDRR: gold recovery of 94.4% was achieved in an 8.5-hour experiment, with the purity of the final product reaching 93.7 wt% Au. As part of the process upscaling effort, four alloys were evaluated as potential cathode materials for a large-scale process. The high corrosion resistance of the cathode material in the chloride leaching solution was found to inversely correlate with gold recovery and energy efficiency of the EDRR process due to electrode surface passivation. In a trade-off between performance and durability under typical EDRR conditions, the highly alloyed superaustenitic stainless steel 654SMO was selected as the optimal cathode material. In order to validate EDRR as a relevant gold recovery process, a continuous mini-pilot test was conducted involving leaching of refractory gold ore, filtration of the leach solution, recovery of metallic gold by EDRR and recycling of spent electrolyte. After 150 h of continuous operation, about 83% of the dissolved gold was recovered from solution onto the cathode. According to the process simulation results obtained using HSC Chemistry 10 software, the recirculation of intermediate streams within the flowsheet would increase the total gold recovery from the ore to the cathode up to 84%, exceeding that of the conventional cyanidation process. With the increasing affordability and availability of renewable energy, electrochemical metal recovery methods such as EDRR will become a feasible option to advance cyanide-free gold extraction technologies and reduce the carbon footprint of the extractive industry.
Sustainable valorisation of industrial residues as an enabler for achieving the goals of the EU Green Deal: European Training Network SOCRATES
(2021-05-04) Korolev, Ivan; Yliniemi, Kirsi; Lundström, Mari
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
The accomplishment of the goals set in the EU Green Deal and the Agenda 2030 for Sustainable Development requires a metallurgical industry that is even more resource-efficient, environmentally friendly and socially responsible than it is today. The European Training Network SOCRATES has taken this up by developing ground-breaking metallurgical processes for the valorisation of industrial intermediate products. This short article summarises the results obtained in the 4-year project and discusses the outcomes in light of the recently adopted EU Green Deal.