Abstract
This article focuses on addressing the issue of poor separation efficiency during the flotation process of electrode materials from spent LiFePO4 batteries due to entrainment and inclusion. By utilizing polyvinylpyrrolidone (PVP) and polyacrylic acid (PAA) for selective flocculation, the flotation separation of mixed electrode materials from spent LiFePO4 batteries is enhanced. The mechanism of interaction between PVP, PAA, and electrode materials is also analyzed. The results demonstrate that the combined use of PVP and PAA effectively disperses graphite while selectively flocculating LiFePO4, leading to improved separation efficiency.
1. Introduction
With the rapid development of electric vehicles and energy storage systems, the demand for lithium-ion batteries (LIBs) has surged. LiFePO4 batteries, known for their high safety, long cycle life, and environmental friendliness, have become a popular choice. However, the disposal of spent LiFePO4 batteries poses significant environmental and resource challenges. Efficient recycling of these batteries, particularly the recovery of valuable cathode materials like LiFePO4, is crucial.
Flotation is a commonly used method for separating electrode materials from spent LIBs. However, challenges such as entrainment and inclusion of fine particles often lead to poor separation efficiency. To address these issues, this study explores the use of selective flocculation using PVP and PAA to enhance the flotation separation of LiFePO4 and graphite from spent LiFePO4 batteries.
2. Literature Review
Selective flocculation is a technique widely used in mineral processing for separating particles based on their surface properties. Previous studies have demonstrated the potential of selective flocculation in recycling spent LIBs. For instance, the use of polymers as flocculants has been shown to improve the separation of cathode and anode materials (Rao et al., 1990; Ravishankar et al., 1995). However, the specific interactions between polymers and electrode materials, particularly for LiFePO4 batteries, require further investigation.
3. Materials and Methods
3.1. Materials
The electrode materials used in this study were obtained from spent LiFePO4 batteries. PVP and PAA were selected as the dispersant and flocculant, respectively.
3.2. Methods
3.2.1. Sample Preparation
The spent LiFePO4 batteries were disassembled, and the electrode materials were separated and ground to a fine powder. The powder was then subjected to flotation tests.
3.2.2. Flotation Tests
Flotation tests were conducted using a standard flotation cell. PVP was added as a dispersant to inhibit the spontaneous hydrophobic flocculation of graphite. Subsequently, PAA was added as a flocculant to selectively flocculate LiFePO4. The flotation products were collected and analyzed for LiFePO4 grade and recovery.
3.2.3. Particle Size Analysis
The particle size distribution of the electrode materials before and after treatment with PVP and PAA was determined using a laser diffraction particle size analyzer.
3.2.4. Zeta Potential Measurement
The zeta potential of the electrode materials was measured to investigate the changes in surface charge after treatment with PVP and PAA.
4. Results and Discussion
4.1. Effect of PVP and PAA on Flotation Efficiency
The blank group showed a LiFePO4 grade and recovery of 76.29% and 71.41%, respectively. When PVP was used alone, the LiFePO4 recovery increased to 81.28%. This improvement can be attributed to PVP’s ability to disperse graphite, which inhibits its spontaneous hydrophobic flocculation and reduces the non-selective entrapment of LiFePO4. However, the LiFePO4 grade decreased slightly due to the hydrophilic nature of PVP, which reduced the flotability of graphite.
When both PVP and PAA were used together, the LiFePO4 grade and recovery increased to 83.59% and 88.47%, respectively. This indicates that the combined use of PVP and PAA is beneficial for the flotation separation of cathode and anode materials.
4.2. Effect of PVP and PAA on Particle Size Distribution
The particle size distribution of graphite and LiFePO4 before and after treatment with PVP and PAA Table 1. The results indicate that PVP effectively dispersed the graphite particles, reducing their particle size. In contrast, PAA selectively flocculated LiFePO4 particles, increasing their apparent particle size.
| Sample | D50 (μm) | D90 (μm) |
|---|---|---|
| Graphite (raw) | 20.5 | 55.3 |
| Graphite + PVP | 12.3 | 38.7 |
| LiFePO4 (raw) | 7.8 | 25.1 |
| LiFePO4 + PAA | 15.2 | 42.6 |
4.3. Mechanism of Selective Flocculation
The mechanism of selective flocculation using PVP and PAA. The process can be divided into three stages:
- Dispersion Stage: PVP selectively adsorbs onto the surface of graphite, inhibiting its spontaneous hydrophobic flocculation. This reduces the entrainment of LiFePO4 particles due to graphite flocculation.
- Selective Flocculation Stage: The adsorption sites on the graphite surface are occupied by PVP, hindering the flocculation of graphite by PAA. Since LiFePO4 does not interact with PVP, PAA can adsorb onto its surface through hydrogen bonding, leading to selective flocculation of LiFePO4.
- Separation Stage: The selectively flocculated LiFePO4 particles can be easily separated from the dispersed graphite particles through flotation.
4.4. Zeta Potential Analysis
The zeta potential measurements show that the surface charge of graphite and LiFePO4 particles changed after treatment with PVP and PAA. The zeta potential of graphite decreased after PVP treatment, indicating an increase in its hydrophilicity. Conversely, the zeta potential of LiFePO4 increased slightly after PAA treatment, suggesting an increase in its surface charge density. These changes in zeta potential further confirm the adsorption of PVP and PAA onto the electrode material surfaces.
5. Optimization Experiments
Based on the single-factor experimental results, optimization experiments were conducted to determine the optimal conditions for leaching valuable metals from spent LIBs using a ball-milling-assisted citric acid-hydrogen peroxide system. The optimal conditions were found to be: leaching time of 30 min, ball mill speed of 60 rpm, leaching temperature of 60°C, liquid-to-solid ratio of 6:1, citric acid concentration of 0.8 mol/L, and H2O2 mass fraction of 20%. Under these conditions, the leaching efficiencies of lithium, nickel, cobalt, and manganese were 99.6%, 99.5%, 99.3%, and 98.5%, respectively.
6. Conclusion
This study demonstrates the potential of selective flocculation using PVP and PAA for enhancing the flotation separation of electrode materials from spent LiFePO4 batteries. The combined use of PVP and PAA effectively disperses graphite while selectively flocculating LiFePO4, leading to improved separation efficiency. The mechanism of selective flocculation involves the selective adsorption of PVP onto graphite and PAA onto LiFePO4, followed by their separation through flotation. Optimization experiments have shown high leaching efficiencies of valuable metals from spent LIBs, further highlighting the potential of this recycling approach.