Research ArticleENGINEERING

Toward a more sustainable mining future with electrokinetic in situ leaching

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Science Advances  30 Apr 2021:
Vol. 7, no. 18, eabf9971
DOI: 10.1126/sciadv.abf9971
  • Fig. 1 Schematic illustration of metal extraction from a subsurface ore body via EK-ISL.

    (A) 3D isometric view of an industrial-scale EK-ISL operation, including potential electrode configuration, above-ground energy source, lixiviant supply and recovery reservoirs, and metal recovery treatment facility. (B) Cross-sectional view of the ore interface between an individual anode and cathode. (C) Conceptual illustration of principal hydrogeochemical reactions between the lixiviant and the ore material when subjected to EK-driven electromigration.

  • Fig. 2 Experimental setup and key results.

    (A) Illustration of experimental setup for EK-ISL of both synthetic and intact ore samples. CEM and AEM refer to cation and anion exchange membrane, respectively. The distance between anode and cathode was 0.57 m (synthetic ore) and 0.48 m (intact ore), respectively. Results of the laboratory-scale leaching experiments using (B to D) 0.5 M FeCl3 and synthetic ore (quartz and chalcopyrite powder mixture, containing 9.15 mmol chalcopyrite) and (E to G) an intact ore sample composed of 75, 21, and 4 wt % of total Cu content present as chalcopyrite, covellite, and chalcocite, respectively. Symbols represent the measured experimental data taken from the target reservoir and the solid lines represent the results of the process-based model. Chalcocite was not considered in the model simulations because of its comparably small initial Cu mass fraction.

  • Fig. 3 Numerical model setup and key results.

    (A) Schematic illustration of the EK-ISL design for the field-scale model. (B) Reactive transport simulation results for field-scale Cu recovery via EK-ISL assuming a 500 V difference between electrodes, a 5 m spacing between electrodes, and an 11 kg m−3 average Cu concentration within the ore. (C) Model simulation results for the cumulative Cu recovery during EK-ISL. (D) Chalcopyrite mass within the defined control domain [black rectangles indicated in (B)].

  • Fig. 4 Four-centimeter-long copper ore sample (3.8 cm in diameter) before the start of the experiment.

    Source-facing side (left) and target-facing side (right). The ore sample was molded in epoxy resin to a thickness of ~1 cm to fit in the experimental apparatus.

  • Table 1 QXRD analysis of the chalcopyrite powder.

    Cu minerals are highlighted in blue.

    MineralIdeal formulaContent (wt %)
    KaoliniteAl2Si2O5(OH)41.2
    TalcMg3(Si2O5)2(OH)20.5
    Jarosite(Na, K, H3O+)(Fe,Al)3(OH)6(SO4)20.7
    IlliteK0.6(H3O)0.4Al1.3Mg0.3Fe2+0.1Si3.5O10(OH)2 · (H2O)0.8
    VermiculiteAl10Fe2H80Mg22O124Si220.3
    Melanterite(Fe, Cu, Zn)SO4 · 7H2O1.7
    ApatiteCa10(PO4)6(OH)28.1
    QuartzSiO21.7
    PyriteFeS20.3
    ChalcopyriteCuFeS284.6
  • Table 2 Total element concentrations in the pure copper mineral powder (chalcopyrite) used in the synthetic ore experiments analyzed using ICP-OES following borate fusion method (lithium borate flux).

    ElementAlCaFeMgSiCuSKNiCrMnTiZnAsBaCoPNaCCl
    %0.123.226.80.251.1129.130.100.040000.0100.00500.0211.3800.010.03
  • Table 3 QXRD analysis of the copper ore offcuts (not affected by EK-ISL treatment) and the ore sample after EK-ISL treatment.

    *Cu minerals. The determined values after EK-ISL have been corrected for the mass loss due to the leaching process.

    MineralIdeal formulaMass (wt %)#
    Offcuts (untreated)Sample after EK-ISL
    K-aluniteK(Al, Fe)3+3(OH)6(SO4)23.55.1
    SiderotilFeSO4.5H2O1.10.5
    Na-jarositeNa(Al, Fe)3+3(OH)6(SO4)21.10.7
    PyrophylliteH2Al2O12Si410.14.4
    QuartzSiO255.360.4
    PyriteFeS25.52.5
    Chalcopyrite*CuFeS218.27.6
    Chalcocite*Cu2S0.81.3
    Covellite*CuS2.60.0
    MolybdeniteMoS20.30.4
    IlliteK0.6(H3O)0.4Al1.3Mg0.3Fe2+0.1Si3.5O10(OH)2 · (H2O)1.61.0
    Elemental sulfurS0.01.9
  • Table 4 Total element concentrations of crushed and milled offcuts (no EK-ISL treatment) and the ore sample after EK-ISL treatment using ICP-OES following borate fusion method (lithium borate flux).

    The mass balance for Cu indicates Cu leached + residual Cu retained in the ore, as determined by total acid digestion = 9.26 g; initial Cu mass estimated by QXRD analysis for offcuts of the same drill core sample = 10.85 g. The values determined after EK-ISL have been corrected for the mass loss due to the leaching process.

    SampleConcentration (%)
    AlCaFeMgAuMoSiCuKS
    Sample offcuts
    (untreated)
    5.450.059.480.030.010.0726.208.240.7213.40
    Sample after
    EK-ISL
    5.120.054.600.010.010.1126.202.970.6810.28
  • Table 5 ICP-OES data for selected solution samples in the EK-ISL test on the rock sample.

    T6 = target after 6.9 days, T10 and S10 = target and source after 20.9 days, T20 and S20 = target and source after 49.1 days.

    SampleConcentration (mg/liter)
    AlCaFeMgAuMoSiCuKSTC
    T68.2515719965.370.3856.191.3521262.047158.08
    T1013.890.926204.910.33014.92.0827484.125078.68
    T203.6053.05127<0.20.3693.881.6922410.67517.15.60
    S101.4442.121,6180.3800.539<0.23.791912.7840513.4
    S208.499.5722,544<0.20.7660.5161.165682.373288.28

Supplementary Materials

  • Supplementary Materials

    Toward a more sustainable mining future with electrokinetic in situ leaching

    Evelien Martens, Henning Prommer, Riccardo Sprocati, Jing Sun, Xianwen Dai, Rich Crane, James Jamieson, Pablo Ortega Tong, Massimo Rolle, Andy Fourie

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    • Tables S1 to S7
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