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  • 1.
    Mulenshi, Jane
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Minerals and Metallurgical Engineering.
    Geometallurgical study of historical tailings from the Yxsjöberg tungsten mine in Sweden: Characterization and reprocessing options2019Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Tungsten (W) is listed among the European Union (EU) critical raw materials (CRMs) for its supply risk and economic importance. Primarily, tungsten is produced from scheelite and wolframite mineral ores with 0.08-1.5% tungsten trioxide (WO3) grade. However, as primary deposits for these resources are becoming less or lower in grade, alternative sources need to be explored. These alternative tungsten sources include scrap from end-of-life products, mine waste and rejects from the ore beneficiation processes (tailings). The latter alternative source is the focus within this thesis.

    Historical tailings repositories often pose environmental risks but may also become secondary sources of CRMs. This is because of relatively high minerals and metals content due to less efficient extraction methods and/or relatively low metal prices at the time of active mining. Therefore, reprocessing of such tailings is not only a supply risk-reducing measure but also an approach to remediation that contributes to the mining industry’s aim of moving towards a circular economy.

    The aim of this thesis has been to develop efficient methods for separating valuable minerals from the tailings in order to leave behind a stable and environmentally safe residue. Geometallurgical studies were conducted by collecting drill core samples from the Smaltjärnen tailings repository in Yxsjöberg, Sweden, for evaluating the potential of this repository for further processing. The tailings were originally produced from the ore that was mined by Yxsjö Mines while it was in operation from 1935 to 1963, with average ore grades of 0.3-0.4 wt.% WO3, 0.2 wt.% Cu and 5-6 wt.% fluorspar. The exploited minerals were scheelite for W, chalcopyrite for Cu and fluorspar. The tailings repository is estimated to have about 2.2 million tons of tailings covering an area of 26 hectares, with elemental concentrations of 1-2 wt.% S, 0.02-0.2 wt.% Cu, 0.02-0.3 wt.% W, 0.02-0.04 wt.% Sn and 0.02-0.03 wt.% Be.

    Sampling and characterization of the historical tailings were conducted based on geometallurgical units (i.e. a distinction between different layers and locations in the repository), followed by metallurgical test work. The tailings were characterized with regard to color and granulometry, particle size distribution, chemical composition, scheelite mineral occurrence, texture and mineral liberation, as well as mineralogical composition. Based on a comprehensive literature survey, tailings characteristics, and assessment of the earlier processes from which the Yxsjöberg tailings were produced, feasible separation methods were pre-selected involving dry low-intensity magnetic separation (LIMS) and high intensity magnetic separation (HIMS), enhanced gravity separation (EGS) using a Knelson concentrator, and batch froth flotation.

    The average WO3 and Cu concentration in these tailings based on the sampled locations was 0.15 % and 0.11 % respectively. Applying them to the estimated 2.2 million tons of tailings in this repository gives approximately 3300 tons of WO3 and 2512 tons of Cu. From the metallurgical test work, several feasible processing routes have been identified that need to be further assessed based on the economic and environmental criteria.

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  • 2.
    Mulenshi, Jane
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Minerals and Metallurgical Engineering.
    Historical tailings as secondary sources of critical raw materials: Feasibility of reprocessing Yxsjöberg historical tungsten ore tailings2019In: In-use stocks and secondary supply of Critical Raw Materials (CRMs): 4th International Round Table on Materials Criticality (IRTC) Round Table, 2019Conference paper (Refereed)
    Abstract [en]

    The research shows the role historical tailings will play in the secondary supply of critical raw materials like tungsten. It also shows how the geometallurgical approach will play a significant role in assessing the feasibility of reprocessing such mine wastes, and developing efficient methods where residues that are inert and environmentally safe will be left behind. This holistic approach to reprocessing such historical mine wastes will contribute to the mining industry moving towards the circular economy. The Yxsjöberg case study is a good example of how the supply risk-reducing measure in material criticality would contribute to a circular economy in the mining industry.

  • 3.
    Mulenshi, Jane
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Minerals and Metallurgical Engineering.
    Khavari, Pourya
    Chehreh Chelgani, Saeed
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Minerals and Metallurgical Engineering.
    Rosenkranz, Jan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Minerals and Metallurgical Engineering.
    Geometallurgical study of historical tungsten tailings for reprocessing: The Yxsjöberg caseManuscript (preprint) (Other academic)
  • 4.
    Mulenshi, Jane
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Minerals and Metallurgical Engineering.
    Khavari, Pourya
    Chelgani, Saeed Chehreh
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Minerals and Metallurgical Engineering.
    Rosenkranz, Jan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Minerals and Metallurgical Engineering.
    Characterization and beneficiation options for tungsten recovery from Yxsjöberg historical ore tailings2019In: Processes, ISSN 2227-9717, Vol. 7, no 12, article id 895Article in journal (Refereed)
    Abstract [en]

    Repositories of historical tungsten mining tailings pose environmental risks, but are also potential resources for valuable metals. They still contain large tonnages of useful minerals and metals, reflecting the inefficient extraction methods and/or low metal prices at the time they were mined. The focus of this study is to evaluate the technical viability of reprocessing the tailings to recover some of the contained valuable minerals and metals, as well as reducing the negative environmental impact associated with the tailings. Geometallurgical studies were conducted on drill core samples taken from the Smaltjärnen tailings repository of the closed Yxsjöberg tungsten mine, Sweden. The collected samples were characterized physically, chemically, and mineralogically. Knelson concentrator dry low- and high-intensity magnetic separation methods were tested as potential beneficiation methods. The tailings are dominated by the −600 to +149 µm particles. The highest concentration of tungsten (W) was 0.22% WO3. Using a Knelson concentrator, scheelite (main W mineral) recovery was enhanced, with 75 wt.% tungsten recovered in the 34 wt.% heavy concentrate. Only 1.0 wt.% sulphur (S) reported to the non-magnetic fraction. Based on the findings, a methodology and a preliminary process flowsheet for reprocessing the tailings is proposed.

  • 5.
    Mulenshi, Jane
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Minerals and Metallurgical Engineering.
    Khavari, Pourya
    Chelgani, Saeed Chehreh
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Minerals and Metallurgical Engineering.
    Rosenkranz, Jan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Minerals and Metallurgical Engineering.
    Feasibility of gravity and magnetic separation for Yxsjöberg historical tungsten ore tailings2019Conference paper (Refereed)
    Abstract [en]

    Repositories of historical tailings (HT) pose environmental risks but could also become new resources for valuable metals. This is because relatively high minerals and metals content characterize them due to less efficient extraction methods and/or relatively low metal prices at the time. In this investigation, geometallurgical studies were conducted by collecting drill core samples (DCS) from the Smaltjärnen tailings repository in Yxsjöberg, Sweden. The collected DCS were from the main layers of the longest drill core, and were characterized physically (color, texture, moisture content and particle size distribution) and chemically (elemental composition and distribution, and mineralogical composition). The characterization of DCS indicated that the tailings mass distribution was high in the coarser particle size fraction of +149 μm. Tungsten (W) and Copper (Cu) were the metals of interest with highest concentrations being 0.22 %WO3 and 0.11 %Cu. Feasible physical separation methods selected were Knelson concentrator, LIMS and HIMS, based on the knowledge from literature, tailings characteristics, and assessment of processes from which the Yxsjöberg HT were produced. Using the Knelson concentrator, the recovery of scheelite, which is the main W mineral, was enhanced, with 75 wt.% tungsten recovered in the 34 wt.% of concentrate produced. In magnetic separation, sulphur (S) was mostly recovered in the ferromagnetic and paramagnetic fractions with only 1.0 wt.% in the non-magnetic fraction, meaning pyrrhotite, the main Fe-sulphide mineral in the HT responsible for AMD, was separated to the desired magnetic fractions of the LIMS and HIMS. These results are fundamental in the development of methods for separation of valuable minerals from these HT in order to produce an inert and environmentally safe residue.

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  • 6.
    Mulenshi, Jane
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Minerals and Metallurgical Engineering.
    Khavari, Pourya
    Rosenkranz, Jan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Minerals and Metallurgical Engineering.
    Characterization and feasible physical separation methods for Yxsjöberg historical tungsten ore tailings2019Conference paper (Other academic)
    Abstract [en]

    Relatively high minerals and metals content characterize historical tailings due to less efficient extraction methods and/or relatively low metal prices at the time. Repositories of such tailings pose environmental risks but could also become metals and minerals resources. An example of such tailings is the Yxsjöberg historical tungsten ore tailings in the Smaltjärnen tailings repository in Sweden.   

    The Smaltjärnen tailings repository was sampled by collecting drill core samples from different locations. The collected drill core samples were characterized physically (colour, texture, moisture content and particle size distribution) and chemically (elemental composition and distribution, and mineralogical composition). Feasible physical separation methods (magnetic and gravity separation) were pre-selected based on the tailings characteristics and the knowledge of processes from which the Yxsjöberg historical tailings were produced.

    In this paper, results from three drill cores each representing a different location on the tailings repository are presented. The tailings mass distribution was high in the coarser particle size fractions of +300 µm and +149 µm.  Tungsten (W) and Copper (Cu) were the metals of interest with one location having higher concentrations than the other two at 0.20 %WO3 and 0.14 %Cu. Sulphur (S) was recovered in the magnetic fractions of the LIMS and HIMS. Using the Knelson concentrator, W recovery was enhanced. These results are fundamental in the development of methods for separation of minerals and extraction of metals of interest from the historical tailings in order to leave behind an inert and environmentally safe residue.

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