Leaching and recovery of gold from low grade raw materials in cyanide-free media

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School of Chemical Technology | Doctoral thesis (article-based) | Defence date: 2021-04-23
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Date

2021

Department

Kemian tekniikan ja metallurgian laitos
Department of Chemical and Metallurgical Engineering

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Mcode

Degree programme

Language

en

Pages

98 + app. 50

Series

Aalto University publication series DOCTORAL DISSERTATIONS, 34/2021

Abstract

Due to the toxicity and low efficiency of the dominant cyanide technology in the treatment of refractory gold ores, there is a growing demand for environmentally friendly and techno-economically efficient gold extraction methods. At the same time, high grade gold ores are depleting fast, whereas low grade gold ores and residues are currently underutilized. Therefore, there is a need for a cyanide-free leaching process that can be used to extract gold from low grade raw materials. This study investigates gold extraction from flotation tailings and gold ore by chloride and glycine leaching, as it has been suggested that these leaching media are among the most potential leaching methods in the route towards cyanide replacement. Chloride leaching can provide fast dissolution kinetics and has the capability for simultaneous oxidation of sulfides and gold. Additionally, the impact of biological pretreatment on gold recovery in chloride leaching was studied as this can potentially provide a supportive pretreatment process specifically for sulfide minerals. It is environmentally friendly and can be used for oxidation of sulfidic minerals from tailings, with no necessity for high temperature, pressure, or gaseous emissions. Glycine is a more recent non-toxic innovation and has been claimed to provide good leaching efficiency at low reagent cost. Besides the leaching processes, the applicability of the electrodeposition-redox replacement (EDRR) method for gold recovery from chloride and glycine solution was investigated and the results are compared with the conventional carbon adsorption process. The results of this research suggest that biological pretreatment support subsequent chloride leaching, providing improved gold extraction for flotation tailings, with up to 63% extraction. In the direct cupric chloride leaching of flotation tailings, an increase in the cupric and sodium chloride concentration also improved the final gold extraction. However, the increase in ferric ion concentration enhanced gold dissolution only up to 30 g/L. Beyond this concentration, a negative effect was observed. For flotation tailings, ferric chloride leaching was shown to provide the highest gold extraction (67%). For the investigated gold ore too, the highest gold extraction was achieved in ferric chloride leaching (93%), followed by cupric chloride (91%), glycine (90%), and cyanide (80%). The optimal conditions in glycine media were 1.25 M glycine concentration, pH = 12, and T = 60 °C. EDRR was applied for the first time for gold recovery from chloride and glycine solutions. A recovery of 9.3% was achieved from chloride pregnant leach solution (PLS), whereas for glycine solutions, 88% gold could be recovered from synthetic glycine solution, but only 35% from real PLS. This suggests lower gold recovery by the EDRR parameters used compared to state-of-the-art carbon recovery, which resulted in 100% gold recovery from glycine media.

Description

Defence is held on 23.4.2021 10:00 – 13:00 Remote: https://aalto.zoom.us/j/69597217589

Supervising professor

Lundström, Mari, Asst. Prof., Aalto University, Department of Chemical and Metallurgical Engineering, Finland

Thesis advisor

Kolehmainen, Eero, Dr., Metso Outotec, Finland

Keywords

gold ore, flotation tailings, gold leaching, recovery, cyanide-free

Other note

Parts

  • [Publication 1]: Altinkaya, Pelin; Mäkinen, Jarno; Päivi, Kinnunen; Kolehmainen, Eero; Haapalainen, Mika; Lundström, Mari, 2018. Effect of biological pretreatment on metal extraction from flotation tailings for chloride leaching. Minerals Engineering, volume 129, pages 47-53.
    Full text in Acris/Aaltodoc: http://urn.fi/URN:NBN:fi:aalto-201810165363
    DOI: 10.1016/j.mineng.2018.09.012 View at publisher
  • [Publication 2]: Altinkaya, Pelin; Liipo, Jussi; Kolehmainen, Eero; Haapalainen, Mika; Maria, Leikola; Lundström, Mari, 2019. Leaching of trace amounts of metals from flotation tailings in cupric chloride solutions. Mining, Metallurgy & Exploration, volume 36, issue 2, pages 335-342.
    Full text in Acris/Aaltodoc: http://urn.fi/URN:NBN:fi:aalto-201908154719
    DOI: 10.1007/s42461-018-0015-9 View at publisher
  • [Publication 3]: Korolev, Ivan; Altinkaya, Pelin; Halli, Petteri; Hannula, Pyry-Mikko; Yliniemi, Kirsi; Lundström, Mari, 2018. Electrochemical recovery of minor concentrations of gold from cyanide-free cupric chloride leaching solution. Journal of Cleaner Production, volume 186, pages 840-850.
    Full text in Acris/Aaltodoc: http://urn.fi/URN:NBN:fi:aalto-201805222430
    DOI: 10.1016/j.jclepro.2018.03.177 View at publisher
  • [Publication 4]: Altinkaya, Pelin; Wang, Zulin; Korolev, Ivan; Hamuyuni, Joseph; Haapalainen, Mika; Kolehmainen, Eero; Yliniemi, Kirsi; Lundström, Mari, 2020. Leaching and recovery of gold from ore in cyanide-free glycine media. Minerals Engineering, volume 158, 106610.
    Full text in Acris/Aaltodoc: http://urn.fi/URN:NBN:fi:aalto-202009045290
    DOI: 10.1016/j.mineng.2020.106610 View at publisher

Citation

Permanent link to this item

https://urn.fi/URN:ISBN:978-952-64-0301-4

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[diss] Kemian tekniikan korkeakoulu / CHEM