Browsing by Author "Haapalainen, Mika"
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Item Effect of biological pretreatment on metal extraction from flotation tailings for chloride leaching(2018-12-01) Altinkaya, Pelin; Mäkinen, Jarno; Kinnunen, Päivi; Kolehmainen, Eero; Haapalainen, Mika; Lundström, Mari; Department of Chemical and Metallurgical Engineering; Hydrometallurgy and Corrosion; VTT Technical Research Centre of Finland; Outotec Research CenterThis study focuses on investigating the extraction of gold, copper, iron, nickel, cobalt, and zinc present in the flotation tailings. The studied sample contained iron (3.56%), copper (0.09%), and gold (0.2 ppm) as major target elements, whereas cobalt (0.04%), nickel (0.03%) and zinc (0.04%) were trace elements of interest. Primarily, bioleaching with mixed acidophilic culture was applied as a pretreatment process for the recovery of nickel, cobalt, and zinc, as well as for iron removal. The effect of solid concentration (5–12.5%) in bioleaching was investigated at pH 1.8 and the temperature was kept at 32 °C. The highest extractions of nickel, cobalt, zinc, and iron at 5% and 7.5% solid concentrations in the bioleaching experiments were 90%, 60%, 86% and 67%, respectively. Dissolution of gold and copper was not observed. The residues from bioleaching pretreatment were applied for chemical chloride leaching to extract gold and copper into the solution. In chloride leaching, the highest extractions of copper and gold were 98% and 63%, respectively. In addition, residual nickel, cobalt, and zinc were dissolved into the solution with the extraction of 99%, 80%, and 90%, respectively. In all chloride leaching experiments, the highest extractions of iron, copper, gold, nickel, cobalt, and zinc were observed with biologically pretreated feed. Alternatively, residues from bioleaching were also subjected to conventional cyanide leaching. Dissolutions of copper, nickel, cobalt and zinc were shown to be higher in chloride solution, however, 7%-unit more of gold could be extracted by cyanidation. With these findings, it appears that the combination of biological pretreatment and chloride leaching can provide a non-toxic process for improved valuable metals extraction from low-grade tailings.Item Electro-hydrometallurgical chloride process for selective gold recovery from refractory telluride gold ores: A mini-pilot study(Elsevier Science, 2022-02-01) Korolev, Ivan; Altinkaya, Pelin; Haapalainen, Mika; Kolehmainen, Eero; Yliniemi, Kirsi; Lundström, Mari; Department of Chemical and Metallurgical Engineering; School services, CHEM; Department of Chemistry and Materials Science; Hydrometallurgy and Corrosion; Outotec Research CenterThe 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.Item Ferric and Cupric Chloride Leaching of Valuable Metals from Process Residues(2019-06) Altinkaya, Pelin; Korolev, Ivan; Kolehmainen, Eero; Haapalainen, Mika; Lundström, Mari; Hydrometallurgy and Corrosion; Outotec Research Center; Department of Chemical and Metallurgical Engineering; Waschki, UlrichThe 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 byferric 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.Item Gold Recovery from Chloride Leaching Solutions by Electrodeposition-Redox Replacement Method(2019-06) Korolev, Ivan; Kolehmainen, Eero; Haapalainen, Mika; Yliniemi, Kirsi; Lundström, Mari; School services, CHEM; Outotec Research Center; Department of Chemistry and Materials Science; Hydrometallurgy and Corrosion; Department of Chemical and Metallurgical Engineering; Waschki, UlrichCurrently, 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 as30 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.Item Leaching and recovery of gold from ore in cyanide-free glycine media(PERGAMON-ELSEVIER SCIENCE LTD, 2020-11-01) Altinkaya, Pelin; Wang, Zulin; Korolev, Ivan; Hamuyuni, Joseph; Haapalainen, Mika; Kolehmainen, Eero; Yliniemi, Kirsi; Lundström, Mari; School services, CHEM; Department of Chemical and Metallurgical Engineering; Department of Chemistry and Materials Science; Hydrometallurgy and Corrosion; Outotec Research CenterGlycine 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.Item Leaching of Trace Amounts of Metals from Flotation Tailings in Cupric Chloride Solutions(SPRINGER, 2019-04) Altinkaya, Pelin; Liipo, Jussi; Kolehmainen, Eero; Haapalainen, Mika; Leikola, Maria; Lundström, Mari; Department of Chemical and Metallurgical Engineering; Outotec Research Center; Hydrometallurgy and CorrosionWith decreasing ore grades, the tailings of mining operations are becoming of increasing interest as metal-containing secondary raw materials. The objective of the current work was to investigate chloride leaching of gold, copper, cobalt, nickel, and zinc present in the flotation tailings. In the current study, the effect of cupric ion as an oxidant (0–50 g/L) and NaCl (150–250 g/L) on metals extraction was investigated. The other parameters, such as pH (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. Gold dissolution rate was shown to increase with increase in cupric ion concentrations up to 50 g/L. Also, increase in NaCl concentration up to 250 g/L increased gold extraction. Majority of the copper present in the flotation tailings could be dissolved with all the all solutions investigated. The other base metals, cobalt, nickel, and zinc extractions were also shown to increase with increase in the cupric ion and sodium chloride concentration. However, even in the absence of cupric ion addition (t = 72 h, 250 g/L NaCl), the final extraction of Cu, Ni, Zn, Co, and Fe increased up to 98, 93, 83, 76, and 80%, respectively. This shows the power of inherently originating oxidants present in the tailings. Furthermore, the solid analysis of the leach residue indicated that leaching the flotation tailings in pure NaCl may result in partial gold dissolution. The results demonstrate that significant amount of metals present in the tailings could be extracted even with only NaCl as added chemical in the presence of oxygen feed, oxidizing agents originating directly from the raw material. This can provide an advantageous cyanide-free method for extraction of metals from very low-grade tailings with low chemical consumption.Item Optimization of a settler with the computational fluid dynamics(2004) Hirsi, Tuomas; Kankaanpää, Timo; Ekman, Eero; Haapalainen, Mika; Materiaali- ja kalliotekniikan osasto; Teknillinen korkeakoulu; Helsinki University of Technology; Gasik, MikhailIn this master's thesis the development of the liquid-liquid extraction equipment for manufacturing of copper has been covered. In the computational part of this thesis the flows in the settler were studied by using computational fluid dynamics software. In the beginning of the literature part the liquid-liquid extraction process in hydrometallurgical industry and specifically the manufacturing of copper have been examined. The copper extraction equipment has also been discussed. The literature part of this thesis is mainly concentrated on development of extraction equipment. The development process has been discussed stage by stage. First the laboratory equipment has been discussed and then the pilot equipment. Specific attention has been laid on obtaining data about the flow patterns inside development equipment, because one of the main problems in research of copper extraction equipment due to the non-transparent nature of the liquids used in copper extraction. The functioning of Outokumpu's settler has been studied with the CFX software package in the computational part of this thesis. The subject of the research in the settler was the effect of altering the height of the cap between the bottom of the settler and the second fences in the picket fence pairs. Especially possible eddies created by the altering were observed, because these eddies can disturb the functioning of settler. The results from the fluid dynamics software predicted that the lower version of cap increased the eddies in the settler and raised the flow rate in the settler notably. The flow rate of the flow going downwards in the central part of settler increased, which can in the real life system make the separation of the phases more difficult particularly in the water continuous system. At the end of the settler the alteration on cap changed the flow pattern substantially. Based on calculations the wider cap between picket fence and the bottom of the settler is more optimum for the functioning of the settler. In that case the flow was smoother and the flow rate was lower in the settler.Item Recovery of Gold From Industrial Solutions via Electrodeposition-Redox Replacement(2019-04-03) Korolev, Ivan; Haapalainen, Mika; Kolehmainen, Eero; Yliniemi, Kirsi; Lundström, Mari; School services, CHEM; Outotec Research Center; Department of Chemistry and Materials Science; Hydrometallurgy and Corrosion; Department of Chemical and Metallurgical EngineeringCurrently, 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.Item Sulfuric acid leaching for capturing value from copper rich converter slag(ELSEVIER SCI LTD, 2019-04-01) Khalid, Muhammad; Hamuyuni, Joseph; Agarwal, Vivek; Pihlasalo, Jouni; Haapalainen, Mika; Lundström, Mari; Department of Chemical and Metallurgical Engineering; Hydrometallurgy and Corrosion; Outotec Research CenterIn this research, a hydrometallurgical method for recovery of copper from copper rich converter slag is investigated. The main copper containing phases of the slag are cuprite (Cu2O), delafossite (CuFeO2) and metallic copper (Cu). The study investigates the effect of particle size, temperature, acid concentration, agitation and leaching time under oxidizing conditions. The results showed that at optimized conditions (40 °C, 2 M H2SO4, 60 min leaching time, 0.26 kW/m3 mixing power, and 2000 mL/min oxygen flow rate), ca. 100% extraction of copper from slag into the solution was obtained. X-ray diffraction (XRD) analysis consolidated the experimental results by confirming that no Cu containing phases were present in the leach residue. Results also showed that temperature ≤40 °C had the larger influence on Cu and Fe yield, whereas higher temperature (>40 °C) favored Ni and Zn dissolution. The acid consumption of the optimized leaching process was found to be 23.7 mol of H2SO4 per kg of copper.
