As the global demand for renewable energy and electric vehicles surges, the proliferation of energy storage lithium battery systems has led to a rapid accumulation of spent batteries, posing significant environmental and resource challenges. In my research, I focus on developing sustainable hydrometallurgical processes to recover valuable metals from these spent energy storage lithium batteries, particularly from ternary lithium-ion types, which contain high concentrations of nickel, cobalt, manganese, and lithium. Traditional methods like pyrometallurgy are energy-intensive and polluting, whereas hydrometallurgy offers a greener alternative with higher metal recovery rates. Among hydrometallurgical techniques, solvent extraction stands out for its selectivity and efficiency, but conventional sodium-soap systems introduce sodium impurities that compromise product purity. To address this, I explored a nickel-saponification approach using extractants like P204 and P507, which minimizes sodium introduction while enabling high-purity separation of manganese and cobalt. This study systematically investigates the factors influencing extraction and stripping performance, providing a foundation for industrial applications in recycling energy storage lithium battery materials.
The core principle of solvent extraction in this context involves ion-exchange reactions. For extractants like P204 (di-2-ethylhexyl phosphoric acid) and P507 (2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester), the general reaction for metal extraction can be represented as:
$$ n\text{HR}_{(org)} + \text{M}^{n+}_{(aq)} \rightleftharpoons \text{MR}_{n(org)} + n\text{H}^+_{(aq)} $$
where HR denotes the organic extractant and M represents a metal ion. This reaction releases H+ ions, lowering the pH and potentially reducing extraction efficiency. To stabilize the process, saponification is employed, where the extractant is pre-treated with a base. In sodium-soap systems, NaOH is used, but it introduces Na+ ions. Instead, I utilized nickel saponification, where NiSO4 reacts with sodium-soaped extractant to form nickel-soaped organic phases, as shown below:
$$ \text{NiSO}_4 + 2\text{NaR}_{(org)} \rightarrow \text{NiR}_{2(org)} + \text{Na}_2\text{SO}_4 $$
Subsequently, the nickel-soaped extractant exchanges Ni2+ for target metal ions during extraction:
$$ \frac{n}{2} \text{NiR}_{2(org)} + \text{M}^{n+}_{(aq)} \rightleftharpoons \text{MR}_{n(org)} + \frac{n}{2} \text{Ni}^{2+}_{(aq)} $$
This approach significantly reduces sodium impurity levels, which is critical for producing high-purity products from spent energy storage lithium battery components. The selectivity of extraction depends on the pH and the extractant’s affinity for specific metals. For P204, the extraction order is Ca2+ > Al3+ > Cu2+ > Mn2+ > Co2+ > Ni2+, while for P507, it is Cu2+ > Co2+ > Ni2+ > Li+. By controlling pH and other parameters, I achieved selective separation of manganese and cobalt, leaving nickel and lithium in the aqueous phase for subsequent recovery.
In my experiments, the leaching solution from spent ternary energy storage lithium batteries was provided by an industrial partner, with its composition detailed in Table 1. The solution was pre-treated with Ni(OH)2 to remove impurities like Fe, Al, and Cu by adjusting the pH to 4.8, which minimized sodium introduction compared to conventional NaOH treatment. After pre-treatment, the solution was subjected to a two-stage cross-flow extraction process: first using nickel-saponified P204 for manganese extraction, followed by nickel-saponified P507 for cobalt extraction. Each stage involved optimization of key parameters, including extractant concentration, pH, phase ratio (VO/VA), saponification rate, and extraction time. The performance was evaluated based on extraction efficiency, co-extraction rates, and separation factors, calculated as follows:
$$ E = \frac{\rho_{0(a)} V_{0(a)} – \rho_{(a)} V_{(a)}}{\rho_{0(a)} V_{0(a)}} \times 100\% $$
where E is the extraction rate, ρ0(a) and ρ(a) are the metal concentrations in the aqueous phase before and after extraction, and V0(a) and V(a) are the corresponding volumes. The distribution ratio D and separation factor β are given by:
$$ D_M = \frac{\rho_{(o)}}{\rho_{(a)}} $$
$$ \beta_{M1/M2} = \frac{D_{M1}}{D_{M2}} $$
After extraction, loaded organic phases were washed with low-acidity sulfuric acid to remove co-extracted impurities, followed by stripping with higher-concentration sulfuric acid to recover the target metals. The entire process was conducted at room temperature (approximately 25°C) to simulate energy-efficient conditions, aligning with the sustainability goals of recycling energy storage lithium battery materials.
| Metal Ion | Concentration (g/L) |
|---|---|
| Mn2+ | 13.19 |
| Co2+ | 7.46 |
| Ni2+ | 27.04 |
| Li+ | 6.13 |
| Fe3+ | 1.03 |
| Al3+ | 0.41 |
| Cu2+ | 0.11 |
| Ca2+ | 0.10 |
The pre-treatment with Ni(OH)2 at 60°C for 80 minutes effectively reduced impurity levels, as shown in Table 2. This step is crucial for preparing the solution for efficient extraction, as high concentrations of Fe, Al, and Cu can interfere with the selectivity of the process. By using Ni(OH)2, I maintained low sodium levels (<0.005 g/L), which is a significant advantage over traditional methods when handling spent energy storage lithium battery waste.
| Metal Ion | Concentration (g/L) |
|---|---|
| Li+ | 6.03 |
| Mn2+ | 12.54 |
| Ni2+ | 33.23 |
| Co2+ | 7.06 |
| Al3+ | 0.058 |
| Cu2+ | 0.026 |
| Fe3+ | <0.005 |
| Ca2+ | 0.10 |
| Na+ | <0.005 |
For manganese extraction, I optimized the P204 system through a series of single-stage experiments. The extractant concentration was varied from 15% to 35% (v/v) in sulfonated kerosene, and the results indicated that 25% P204 provided the best balance, achieving over 93% manganese extraction while controlling co-extraction of cobalt and lithium below 17% and 9%, respectively. Similarly, pH was critical; at pH 3.5, manganese extraction peaked without excessive co-extraction. The phase ratio (VO/VA) of 2.5 and saponification rate of 30% were optimal, as higher values increased impurity uptake. Extraction time had minimal impact beyond 5 minutes, indicating rapid kinetics. The single-stage conditions are summarized in Table 3, based on data from parametric studies.
| Parameter | Optimal Value | Mn Extraction Rate (%) | Co Co-extraction Rate (%) | Li Co-extraction Rate (%) |
|---|---|---|---|---|
| P204 Concentration | 25% | 93.36 | 16.98 | 8.96 |
| pH | 3.5 | 93.36 | 16.98 | 8.96 |
| Phase Ratio (VO/VA) | 2.5 | 93.36 | 16.98 | 8.96 |
| Saponification Rate | 30% | 93.36 | 16.98 | 8.96 |
| Extraction Time | 5 min | 93.36 | 16.98 | 8.96 |
To enhance manganese recovery and impurity removal, I implemented a two-stage cross-flow extraction. The first stage used the optimal single-stage conditions, while the second stage employed a lower phase ratio (VO/VA = 0.5) to minimize co-extraction. This approach achieved a manganese extraction rate exceeding 99.96%, with co-extraction rates for cobalt and lithium at 18.67% and 9.89%, respectively. Importantly, impurities like Al, Cu, and Ca were reduced to below 0.01 g/L in the raffinate, as shown in Table 4. The sodium concentration remained low (<0.05 g/L), underscoring the benefit of nickel saponification for spent energy storage lithium battery recycling.
| Metal Ion | Concentration (g/L) |
|---|---|
| Ni2+ | 44.61 |
| Co2+ | 5.60 |
| Li+ | 5.01 |
| Mn2+ | <0.01 |
| Al3+ | <0.01 |
| Cu2+ | <0.01 |
| Ca2+ | <0.01 |
| Na+ | <0.05 |
The loaded organic phase from manganese extraction contained residual impurities and co-extracted metals, which I addressed through washing with 0.03 mol/L H2SO4 at a phase ratio of 1:1 for 10 minutes per stage. Three washing stages effectively removed over 99% of cobalt, lithium, and impurities, with only 5.98% manganese loss, as detailed in Table 5. This selective washing ensured that valuable metals like cobalt and lithium could be recycled back into the process, minimizing waste in the energy storage lithium battery recovery system.
| Metal Ion | Elution Rate (%) |
|---|---|
| Co | 99.98 |
| Li | 99.99 |
| Al | 99.75 |
| Cu | 99.86 |
| Ca | 99.99 |
| Mn | 5.98 |
Stripping of manganese was performed with sulfuric acid, and the concentration was optimized to achieve high recovery. As shown in the data, 0.5 mol/L H2SO4 resulted in a stripping efficiency of 99.96%, based on the equation:
$$ \text{MR}_{n(org)} + n\text{H}^+_{(aq)} \rightleftharpoons n\text{HR}_{(org)} + \text{M}^{n+}_{(aq)} $$
This step yielded a pure manganese solution, suitable for further processing in energy storage lithium battery material regeneration.
For cobalt extraction, I turned to nickel-saponified P507, leveraging its selectivity for Co2+ over Ni2+ and Li+. The optimization process mirrored that of P204, with extractant concentration, pH, phase ratio, saponification rate, and extraction time being key variables. A P507 concentration of 25% in sulfonated kerosene yielded a cobalt extraction rate of 95.65% in single-stage tests, with a lithium co-extraction rate of 6.90%. The optimal pH was 4.0, where the separation factor β(Co/Li) reached a maximum of 312, indicating excellent selectivity. A phase ratio (VO/VA) of 1.0 and saponification rate of 70% were ideal, as higher values increased lithium co-extraction without significantly improving cobalt recovery. Extraction time plateaued at 5 minutes, confirming fast equilibrium. The single-stage results are summarized in Table 6.
| Parameter | Optimal Value | Co Extraction Rate (%) | Li Co-extraction Rate (%) |
|---|---|---|---|
| P507 Concentration | 25% | 95.65 | 6.90 |
| pH | 4.0 | 95.65 | 6.90 |
| Phase Ratio (VO/VA) | 1.0 | 95.65 | 6.90 |
| Saponification Rate | 70% | 95.65 | 6.90 |
| Extraction Time | 5 min | 95.65 | 6.90 |
To achieve near-complete cobalt recovery, I employed a two-stage cross-flow extraction. The first stage used the optimal single-stage conditions, and the second stage with a phase ratio of 0.5 boosted the cobalt extraction rate to 99.92%, while lithium co-extraction was limited to 13.68%. The raffinate after this process contained less than 0.01 g/L Co2+, with nickel and lithium concentrations of 46.85 g/L and 4.56 g/L, respectively, and sodium below 0.1 g/L (Table 7). This demonstrates the effectiveness of nickel saponification in maintaining low impurity levels throughout the recovery of energy storage lithium battery materials.
| Metal Ion | Concentration (g/L) |
|---|---|
| Li+ | 4.56 |
| Ni2+ | 46.85 |
| Na+ | <0.1 |
| Co2+ | <0.01 |
The loaded P507 organic phase was washed with 0.02 mol/L H2SO4 in three stages to remove co-extracted lithium. This achieved a lithium elution rate of 99.87% with only 1.98% cobalt loss (Table 8), ensuring high-purity cobalt recovery. Stripping with 0.5 mol/L H2SO4 then recovered 99.87% of cobalt, following the same ion-exchange principle as manganese stripping. The washed solutions rich in lithium and cobalt were recycled back to the process, creating a closed-loop system that minimizes waste in energy storage lithium battery recycling.
| Metal Ion | Elution Rate (%) |
|---|---|
| Li | 99.87 |
| Co | 1.98 |
In conclusion, my research on nickel-saponification extraction presents a robust and sustainable method for separating manganese and cobalt from spent energy storage lithium batteries. By using nickel-based saponification with P204 and P507, I achieved extraction and stripping efficiencies exceeding 99.8% for both metals, while keeping sodium concentrations below 0.1 g/L. This approach addresses the purity issues associated with traditional sodium-soap systems and offers a viable pathway for industrial application. The process not only recovers valuable metals but also aligns with circular economy principles by enabling the reuse of nickel and lithium from the raffinate. Future work should focus on scaling up this technology and integrating it with other separation techniques for nickel and lithium, to fully realize the potential of recycling energy storage lithium battery materials. Overall, this study contributes to the advancement of green hydrometallurgical processes, supporting the global transition to sustainable energy systems.