UBC Theses and Dissertations
Development of energy storage systems capable of Cu extraction from CuFeS₂ Deen, Kashif Mairaj
Two hybrid energy storage systems, i.e., a fixed bed flow cell (FBFC) and a tri-functional battery (TFB) are introduced, which use either synthetic CuFeS₂ or a mineral concentrate (MC) as electrode materials and a source of Cu. In the FBFC, the composite negative electrode is CuFeS₂ or MC sandwiched in graphite felt (GF). The Fe^II^/Fe^III^ redox reaction (in the presence of Cu^II^) occurs on a GF positive electrode. Under optimized conditions, the presence of CuFeS₂ resulted in a continuous increase in the specific capacity of the FBFC from 9 to 48 mAh g-¹ and in the specific energy from 2 to 6.3 Wh kg-¹ in 500 galvanostatic charge/discharge (GCD) cycles. However, in the same setup, the MC had an increase in the specific energy from 3.5 to 8.5 Wh kg-¹ in 400 GCD cycles. Advantageously, 10.3 and 12.7% Cu is extracted from the synthetic CuFeS₂ and MC, respectively. In the TFB, two energy intensive processes, Cu extraction from CuFeS₂ and Zn electrowinning, are integrated for energy storage. In this setup, the positive slurry electrode (PSE) composed of CuFeS₂ or MC mixed with activated carbon (AC) in H₂SO₄ was separated by a membrane from the circulating Zn²⁺ solution in the negative compartment. The Zn deposition/re–dissolution and commencement of reversible reactions in the PSE during GCD cycles are responsible for energy storage akin to a battery. The maximum 388 Wh kg-¹ specific energy (1.13 Wh l-¹) during the 1st discharge cycle decreased to ≈50 Wh kg-¹ over the subsequent 14 GCD cycles. The low coulombic (≈50%) and energy (~40%) efficiencies are offset by ~23% Cu extraction from CuFeS₂ in 100 GCD cycles. The cell potential of ~0.95 V and potential efficiency (>70%) imply that the TFB can be used as a hybrid energy storage device. Using MC in the TFB-M, a monotonic increase in energy density from 2.6 to 36.2 mWh l-¹ at low energy efficiency (between 14–43%) was obtained for the initial 14 GCD cycles. On the other hand, in 100 GCD cycles, ~16.1% Cu was also extracted from the MC.
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