Browsing by Author "Liipo, Jussi"

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    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 Corrosion
    With 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.
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    Preg-robbing verification and prevention in gold chloride-bromide leaching
    (2018-11-01) Ahtiainen, Riina; Lundström, Mari; Liipo, Jussi; School services, CHEM; Department of Chemical and Metallurgical Engineering; Outotec Oyj
    The use of cyanide is becoming more challenging due to the related environmental risks, increasing the interest in cyanide-free gold leaching. Chloride-bromide leaching is one of the widely investigated alternative lixiviants for gold recovery. However, gold is known to adsorb or precipitate readily on the carbonaceous matter present in the ore, being one of the challenges in chloride process development. The current study presents an equation indicating gold loss due to preg-robbing into solids in chloride-bromide media. The equation was verified using a naturally preg-robbing gold concentrate. It was shown that the graphite naturally present in gold ore can be an equally active preg-robbing agent for gold chloride complex as industrially manufactured and commercially available activated carbon. In order to study preg-robbing prevention during gold leaching in chloride-bromide media, carbon blinding, and Cl2-pretreatment were applied. Blinding with ShellSol D70 was shown to improve gold recovery only slightly whereas Cl2-pretreatment was shown to increase gold recovery from 2% to 45% for a naturally preg-robbing gold concentrate.
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    Simultaneous sulfide oxidation and gold dissolution by cyanide-free leaching from refractory and double refractory gold concentrates
    (PERGAMON-ELSEVIER SCIENCE LTD, 2021-08-15) Ahtiainen, Riina; Liipo, Jussi; Lundström, Mari; Department of Chemical and Metallurgical Engineering; Hydrometallurgy and Corrosion; Outotec Oyj
    Pyrite and arsenopyrite are known to be the most common gold-bearing sulfide minerals in refractory gold ores. Traditionally, these minerals have been first oxidized by roasting, acidic pressure oxidation or bio-oxidation to release gold, after which the gold is dissolved in the subsequent cyanide leaching step. The chloride (chloride-bromide) solution presents an alternative cyanide-free media, which is able not only to leach gold-bearing sulfide minerals, but also gold, in a single unit process. Therefore, the current study presents an investigation of simultaneous sulfide oxidation and gold leaching from refractory (sulfidic) and double refractory (sulfidic and preg-robbing) gold concentrates. The results show that gold extraction from the investigated refractory concentrate was linearly dependent on the sulfide oxidation: 97% sulfide oxidation resulting in 99% gold extraction, 67% sulfide oxidation resulting in 81% gold extraction, and 46% sulfide oxidation resulting in 67% gold extraction. However, with double refractory concentrate, gold extraction was as low as 18% despite 97% sulfide oxidation ([Cl-]aq,0 = 6.3 mol/L, [Br-]aq,0 = 1.0 mol/L, and [Cu2+]aq,0 = 1.6 mol/L). In order to mitigate the challenges related to gold losses due to preg-robbing, active carbon in chloride leach (CICl) as well as the addition of lead nitrate were investigated. With CICl, the gold recovery could be increased significantly (67%). Further, addition of lead nitrate to CICl was shown to improve gold recovery substantially (88%). The investigation shows that the presented cyanide-free leaching approach can address the refractory nature of gold concentrates in atmospheric pressure - the simultaneous oxidation of sulfide minerals and gold in a single unit process providing new horizons for the future of the utilization of refractory gold ores.