Direct extraction of lithium from ores by electrochemical leaching

Lithium demand has surged due to widespread electric vehicle adoption, driving up prices of lithium chemicals such as lithium carbonate. Presently, most lithium is produced from brines using solar evaporation, which suffers from large land footprint, long extraction times, environmental issues, and geographical limitations. Lithium-bearing ores (e.g., spodumene, lepidolite, petalite, Li-rich clays) are globally distributed, with spodumene (LiAlSi₂O₆) being the primary ore owing to its high Li₂O content. Conventional extraction typically requires converting natural α-spodumene to β-spodumene via high-temperature calcination (>1100 °C) to enable efficient acid leaching, or uses alkaline leaching that necessitates downstream impurity removal. These approaches entail high energy consumption, process complexity, and environmental burdens. Electrochemical leaching offers a potentially more sustainable route by using an electric field to facilitate metal ion dissolution, but it is often limited by heterogeneous kinetics, large overpotentials, side reactions, and low Faradaic efficiency. This work aims to directly extract Li from α-spodumene at room temperature by electrochemical leaching with H₂O₂ as a homogeneous promoter to lower reaction barriers, elucidate the mechanism, and develop high-throughput current collectors for scalable processing.

Prior lithium extraction is dominated by brines due to low cost, yet suffers from slow solar evaporation, large land use, and regional constraints. Ore-based routes, especially from spodumene, typically require thermal conversion of α to β phase (700–1100 °C) to reduce density and enhance reactivity, followed by strong acid leaching (Li⁺/H⁺ exchange) or base leaching (Si–O bond breaking). Acid leaching entails significant energy use for calcination; base leaching introduces impurities (Al³⁺, SiO₃²⁻, Na⁺) that complicate separation. Electrochemical leaching has been explored for e-waste and spent lithium-ion batteries, with soluble promoters such as H₂O₂, FeCl₃, and SO₂ used to improve electron-transfer kinetics. H₂O₂ is attractive because it avoids ion separation but poses stability/safety issues due to decomposition during storage and transport. Traditional 2D current collectors suffer from mass transport limitations that cap throughput. These gaps motivate promoter-assisted electrochemical leaching coupled with improved electron and mass transport designs to enable direct α-spodumene extraction at mild conditions.

Electrochemical leaching of α-spodumene was performed in 0.5 M H₂SO₄ at room temperature with H₂O₂ promoter. Small-scale tests used a three-electrode cell: spodumene powders (α or β) mixed with conductive carbon and binder (6:3:1 wt.%) coated on a graphite rod as the working electrode; graphite rod or carbon paper as counter; saturated calomel electrode (SCE) as reference. Linear sweep voltammetry (LSV) and cyclic voltammetry (CV) were conducted at 0.5 mV s⁻¹. Electrochemical leaching was performed by potential holds between 0.8–1.1 V vs. SCE. H₂O₂ concentrations were varied between 0–1 wt.% to determine activation thresholds and optimal levels. Faradaic efficiency was determined by comparing charge passed with lithium content measured in the leachant; Li concentration was quantified by inductively coupled plasma atomic emission spectroscopy (ICP-AES). In-situ Raman spectroscopy (785 nm) with a home-built three-electrode cell (Ag wire reference and counter; Au-coated stainless steel working disk coated with α-spodumene/Nafion 9:1) probed intermediates during voltage steps (0.4–1.0 V vs. SCE). Structural evolution was assessed by X-ray diffraction (XRD) (Cu Kα), scanning electron microscopy (SEM), transmission electron microscopy (TEM/HRTEM), and X-ray photoelectron spectroscopy (XPS) with depth profiling. Cryo-STEM/EELS was used to probe oxygen states while minimizing beam damage. For scale-up and throughput, a 3D current collector was fabricated by infiltrating carbon felt (CF) with graphene oxide (GO) solution and a binder (Nafion, PVDF, or CMC/SBR), followed by freeze-drying to form GO-CF. Gold nanoparticles (~<5 nm) were electrodeposited in 0.5 mM HAuCl₄/0.5 M H₂SO₄ at −1 V vs. SCE for 10 s and freeze-dried, yielding Au-GO-CF. Suspended-electrode leaching used slurries of α-spodumene (1 g in 50 mL 0.5 M H₂SO₄ with H₂O₂) stirred at 500 rpm; air/O₂ was purged to enable in-situ H₂O₂ generation on Au catalysts. H₂O₂ near-electrode concentration was monitored with a 34 µm glassy carbon microelectrode placed 5 mm from the current collector; calibration via diffusion-limited currents at −0.65 V vs. SCE established concentration-current relationships. Chronoamperometry (CA) quantified leaching currents and stability. Techno-economic and CO₂ emission assessments compared traditional chemical leaching and the proposed electrochemical process.

• H₂O₂ promoter lowers the thermodynamic barrier and leaching potential: calculated ΔG for α- and β-spodumene leaching without H₂O₂ are 405.81 and 365.55 kJ mol⁻¹ at 298 K, respectively; with H₂O₂, ΔG drops to 53.52 kJ mol⁻¹ (α) and 6.08 kJ mol⁻¹ (β).
• Electrochemical activation of α-spodumene requires ≥0.1 wt.% H₂O₂; above this, leaching is initiated, but higher concentrations can enhance side reactions (H₂O₂ decomposition, O₂ evolution).
• With 0.5 wt.% H₂O₂, leaching current for α-spodumene increases from ~0.10 mA to ~1.96 mA at 0.95 V vs. SCE; the optimized leaching potential is 0.95 V vs. SCE.
• Structural evolution: α-spodumene retains the monoclinic phase with ~2.1% shrinkage of the (110) interplanar spacing (6.09 Å → 5.96–5.97 Å) after leaching; β-spodumene exhibits Li⁺/H⁺ exchange, forming HAISi₂O₆ with peak splitting in XRD.
• XPS reveals Al 2p shifts consistent with AlOOH formation on leached β-phase (to ~75.1 eV), while α-phase shows modest Al 2p and O 1s positive shifts indicative of higher-valence oxygen species; EDS/ICP confirm Al:Si ~1:2 in residue, supporting selective Li removal.
• Reaction intermediate: in-situ Raman detects Li₂O₂ feature at 258 cm⁻¹ emerging at ≥0.8 V vs. SCE during leaching, evidencing O₂²⁻-related intermediates; signals diminish above ~1.0 V due to OER.
• 3D current collector performance: at 1.0 V vs. SCE, Au-GO-CF and GO-CF achieve ~32 mA, CF ~7.9 mA. Under 0.95 V hold (20 h), current retention: Au-GO-CF 65.26%, GO-CF 22.84%, CF 47.25%.
• Faradaic efficiency (FE) peaks in region II (0.9–1.0 V vs. SCE); maximum FE 71.5% at 0.95 V for Au-GO-CF; GO-CF and CF peak FEs 64.9% and 43.2% (at ~1.0 V).
• Leaching efficiency: up to 92.2% Li extraction at 0.95 V vs. SCE after 12 h using Au-GO-CF; at 0.9 V only 24.3% after 20 h; at 1.0 V full leaching achieved but slower due to side reactions.
• Scale-up demonstration with suspended α-spodumene and catalyst-modified current collector achieved 18 mA leaching current and 92.2% efficiency.
• Techno-economics and sustainability: compared to traditional leaching, electrochemical leaching lowers process cost by 35.6% and CO₂ emissions by 75.3%; overall energy consumption reduced by ~90% (room-temperature operation).

The study demonstrates that promoter-assisted electrochemical leaching can directly extract lithium from α-spodumene at room temperature, addressing the long-standing need to avoid high-temperature phase conversion to β-spodumene. H₂O₂ shifts the reaction pathway by facilitating oxygen redox (formation of O₂²⁻/Li₂O₂ intermediate), lowering the leaching potential and suppressing competing oxygen evolution when operated near the optimal potential (0.95 V vs. SCE). Structural and spectroscopic analyses corroborate distinct mechanisms: β-phase follows Li⁺/H⁺ exchange to HAISi₂O₆, whereas α-phase undergoes direct Li deintercalation with lattice contraction but no new bulk phase formation. The designed 3D current collector (GO-CF with Nafion and Au nanoparticles) enables higher currents, improved mass/electron/proton transport, and in-situ H₂O₂ generation to stabilize promoter concentration, thereby increasing Faradaic efficiency and throughput. These advances collectively enhance extraction efficiency (92.2%), reduce energy and chemical inputs, and lower cost and emissions relative to traditional routes. The findings suggest electrochemical leaching can be a scalable and sustainable alternative for lithium extraction from ores, with potential integration into continuous flow systems and renewable-powered operations.

This work introduces a promoter-assisted electrochemical leaching process that directly extracts Li from α-spodumene at room temperature using dilute sulfuric acid, avoiding high-temperature calcination. Mechanistic studies show that H₂O₂ promotes oxygen redox and O₂²⁻ intermediates, enabling Li removal from α-spodumene with lattice shrinkage and without phase transformation, while β-spodumene follows a Li⁺/H⁺ exchange to HAISi₂O₆. A high-surface-area 3D current collector with proton-conducting Nafion and Au catalysts delivers high currents, elevated Faradaic efficiency (up to 71.5%), and high leaching efficiency (92.2% after 12 h). Techno-economic assessment indicates 35.6% cost reduction and 75.3% CO₂ emission reduction compared with traditional methods. Future work can focus on continuous flow implementations, optimizing catalyst and promoter management for closed-loop H₂O₂ generation, expanding to other lithium ores and mixed feedstocks, and further improving Faradaic efficiency by mitigating side reactions.

• Side reactions at higher potentials (>1.0 V vs. SCE), such as oxygen evolution and H₂O₂ decomposition, reduce Faradaic efficiency and slow leaching at later stages.
• Promoter (H₂O₂) stability and concentration management are critical; although in-situ generation mitigates supply and safety issues, precise control is required to avoid decomposition and ensure consistent performance.
• Detection of transient O₂²⁻ intermediates is challenging; ex-situ methods showed limited sensitivity, requiring in-situ Raman and cryo-STEM/EELS with careful interpretation.
• Faradaic efficiency, while improved (max 71.5%), indicates remaining electron losses to side processes; further catalyst and reactor optimization are needed.
• Scale-up demonstrations processed grams of material; industrial-scale validation, long-term durability of current collectors, and impurity tolerance in real ores remain to be established.