# Selective metal recovery: Innovating leaching of LFP-NMC cathode mixtures from spent lithium-ion batteries

Pierric Hubert, Anna Vanderbruggen, Safi Jradi, Alexandre Chagnes

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Pierric Hubert, Anna Vanderbruggen, Safi Jradi, Alexandre Chagnes. Selective metal recovery: Innovating leaching of LFP-NMC cathode mixtures from spent lithium-ion batteries. *Sustainable Materials and Technologies*, 2025, 46, pp.e01658. 10.1016/j.susmat.2025.e01658. hal-05285184

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# Selective metal recovery: Innovating leaching of LFP-NMC cathode mixtures from spent lithium-ion batteries☆

Pierric Hubert<sup>a</sup>, Anna Vanderbruggen<sup>a</sup>, Safi Jradi<sup>b</sup>, Alexandre Chagnes<sup>a,*</sup>

## ARTICLE INFO

**Keywords:**

- Lithium-ion battery
- NMC
- LFP
- Leaching
- Speciation
- Hydrometallurgy

## ABSTRACT

Lithium-ion batteries serve as the cornerstone of the shift towards sustainable energy and electric transportation. While the current emphasis of recycling plants is on electric vehicle batteries, there is a growing demand to expand the recycling industry to encompass smaller batteries, such as those powering electric bicycles—a sector experiencing rapid expansion. The chemical procedures essential for recycling these batteries may differ from those employed for electric vehicle batteries due to variations in material composition. In electric vehicles, the materials primarily originate from either NMC (LiNiₓMnᵧCozO₂) or LFP (LiFePO₄) technologies, resulting in well-established compositions. Conversely, batteries from urban electric mobility comprise a blend of NMC and LFP technologies, leading to feeds with varying compositions. Therefore, the hydrometallurgical processes applied to these materials must successfully recover cobalt, nickel, manganese, and lithium, despite the presence of fluc-tuating and significant concentrations of iron—a common challenge in hydrometallurgy. This study will show-case how leveraging the physicochemistry of transition metals in the presence of phosphate can lead to the design of an efficient leaching process. This process selectively dissolves cobalt, nickel, manganese, and lithium from mixtures of NMC and LFP, yielding a sufficiently pure leachate.

## 1. Introduction

Lithium-ion batteries (LIBs) have become an integral part of our daily lives since their introduction to the market in 1991. They have enabled the mobility of numerous electronic devices, and today, they are at the heart of ecological, energy, and digital transitions [1–3]. However, with the increasing use of LIBs, spent batteries have become both a serious pollution risk and a significant secondary source of metals [4]. Battery recycling plays a crucial role in the reutilization of metals found in batteries, mitigating the pollution associated with end-of-life batteries and, consequently, reducing the overall carbon footprint of battery manufacturing [5]. Furthermore, European regulations now mandate that by 2030, 12 % of cobalt (Co), 4 % of lithium (Li), and 4 % of nickel (Ni) in batteries must be sourced from recycled materials. These percentages will further increase to 20 %, 10 %, and 12 %, respectively, by 2035 [6].

The current battery treatment process relies on a diverse combination of physical, thermal, and chemical processes [7,8]. During typical LIB recycling processes, a comminution stage is used as a first stage to

liberate the components. The output of these mechanical reduction steps is often followed by sieving to separate the coarse steel casing, plastics, and metallic foils from fine liberated active particles. The mechanical sorting allows maximization of recovery and enrichment of different LIB components before the downstream metallurgical processes. The sorting process exploits the physical properties of LIB components such as magnetism, density, or conductivity. The casing and plastics particles can be further separated using an air-classifier [9]. The resulting fine fraction is typically referred to as “black mass” (BM) and contains mixed cathode and anode active materials as well as some impurities such as metallic particles from foils. In the state-of-the-art of recycling technologies, the black mass obtained from pre-treatment, which may involve mechanical or thermo-mechanical processes, serves as the initial point for subsequent chemical processes aimed at recovering metals like Ni, Co, Manganese (Mn), and Li [10]. This step in the process involves, most of the time, hydrometallurgical treatment, including leaching, separation/purification and precipitation/extraction/electrolysis [11,12]. The design of the hydrometallurgical process depends on the specific cathode material present in the battery. These processes will be

<footnote><sup>a</sup> Université de Lorraine, CNRS, GeoRessources, F-54000 Nancy, France</footnote>

<footnote><sup>b</sup> Université Technologique de Troyes, Laboratoire Lumière, nanomatériaux et nanotechnologies, 10004 Troyes, France</footnote>

<footnote>* This article is part of a Special issue entitled: 'Responsible Li Production' published in Sustainable Materials and Technologies.</footnote>

<footnote>* Corresponding author.
E-mail address: alexandre.chagnes@univ-lorraine.fr (A. Chagnes).</footnote>
determined by the origin of the LIB. While recycling processes currently focus on spent batteries from electric vehicles (EVs) which produce an homogeneous flow of BM, there will also be a need to develop the recycling industry for smaller batteries which produce a mix of LFP/NMC BM, those batteries can be found in electric bicycles or electric scouters, a market that is rapidly expanding [13,14]. The chemical processes required to recycle these batteries may not necessarily be the same as those for batteries in EVs due to differences in material composition to be processed.

For EVs, the composition will be well established as the cathode active materials will mainly be either NMC (LiNi₁xMnγCo₂O₂) or LFP (LiFePO₄) technologies. Therefore, it is natural that these cathode materials have been studied first, and numerous studies have been conducted in this context [15–20]. However, for smaller batteries, the materials to be processed will be a mix of NMC and LFP technologies (Fig. 1, stream on the right) and it is important to develop a flexible process for recycling a mixture of different batteries. Furthermore, the trend of combining cathode active particles from various sources is becoming increasingly common (Fig. 1, stream on the left). For instance, LFP particles can be blended with NMC to harness the benefits of higher energy density [21]. Consequently, even during the recycling of one type of end-of-life batteries or cathode scrap from production, the resulting black mass will, in both cases, comprises a blend of cathode active particles.

Only a limited number of studies have explored the leaching of a mixture of LMO, LCO, and NMC111 in the past [22–24]. In the study conducted by Li et al. [24], they investigated a blend of LIBs, including LCO, LMO, and NMC, and subjected it to leaching with a 0.5 mol.L⁻¹ citric acid solution. This resulted in the dissolution of 99.1 %, 99.8 %, 98.7 %, and 95.2 % of Li, Co, Ni and Mn, respectively. However, this study did not include LFP material.

Chen et al. [22] also delved into the leaching of mixed-type batteries and included LFP material in their mix. They managed to have 100 %, 92.86 %, 97.57 % and 98.94 % of Li recovered for LCO, LMO, LFP and NMC, respectively, using 0.8 mol.L⁻¹ phosphoric acid. Nevertheless, this study only examined the recovery of Li, which is insufficient and may not align with current environmental and political considerations [6]. In addition to phosphoric acid, one of the most prevalent approaches for leaching black mass involves the use of sulfuric acid with hydrogen peroxide. This method is versatile for leaching both LFP and NMC black masses. More recently, Song et al. [25] proposed a recycling method for recovering Li, Ni, Co, and Mn from spent lithium-ion batteries

containing a blend of LFP and NMC. The process involves alkali leaching to remove Al, followed by selective leaching with H₂SO₄ and H₂O₂ to dissolve Li, Ni, Co, and Mn. The residue from the leaching operation is then further processed to recover and precipitate iron as iron phosphate. Likewise, Zou et al. [26] investigated the leaching of industrial NMC (Nickel Manganese Cobalt) black mass in the presence of lithium iron phosphate (LFP). LFP was used as a reductant during the hydrometallurgical recycling process. This work focuses on the redox potential effect of LFP in the media and its correlation to Co, Ni, Mn, and Li extraction. This work found that LFP not only enhances the dissolution yield but also increases acid consumption and reduces the redox potential.

Previous studies on the leaching of black mass with sulfuric acid (Table 1) have revealed two distinct approaches.

When leaching NMC black mass, the aim of the studies is to recover as many components as possible, i.e. Ni, Mn, Co, and Li. In the case of LFP black mass, the objective is to perform a selective leaching. For this goal, the approach consists in fully consuming the acid to raise the pH at the end of the leaching process in order to facilitate the precipitation of the abundant iron present in the solution [31].

Lastly, it is crucial to emphasize that a black mass is never exclusively composed of cathode active particles. Achieving complete separation with a reasonable effort is challenging, and as a result, the black mass frequently contains impurities such as aluminum (Al) or copper (Cu) derived from electrode foils. For instance, Pourmohammad et al. [33] showed the presence of valuable metals in lithium-ion battery black mass (Li, Co, Ni, Mn) along with impurities such as Al (4.75 wt%), Cu (2.43 wt%), Fe (0.73 wt%), and others (0.08 wt% Mg, 0.37 % wt% Si, 0.19 wt% Na, 0.02 wt% Zn) originating from current collectors and casing materials. These impurities may have implications for the feasibility of subsequent processes, underscoring the need to study the effects of such impurities on the efficiency of hydrometallurgical processes.

The state-of-the-art shows that only a limited number of studies focus on extracting lithium, cobalt, nickel, and manganese from mixtures of NMC and LFP, despite the critical importance of recycling black mass produced from these blended battery technologies. The goal of this work is to demonstrate that using an appropriate amount of sulfuric acid in the presence of hydrogen peroxide can drastically improve the selective dissolution of lithium, nickel, cobalt, and manganese, while leaving aside aluminum, copper, and iron, which are challenging to manage in hydrometallurgy. This study highlight the importance of pH along with redox potential towards the selectivity. This study also analyzes the

<figure><img src="image_3.png" /><figcaption>**Fig. 1.** Example of the possible origin of mixture containing LFP and NMC: cathode scrap (left) or spent LIBs recycling (right). (Legend: blue: NMC, red: LFP, grey: Al foil, orange: Cu foil, black: graphite).</figcaption></figure>
<caption>**Table 1**</caption>

NMC and LFP leaching by sulfuric acid and hydrogen peroxide (S/L: solid/liquid ratio; T: temperature; t: leaching duration). References: (a) [27]; (b) [28]; (c) [29]; (d) [30]; (e) [31]; (f) [32].

<table><thead><tr><th rowspan="2">Battery type</th><th colspan="2">Leaching media</th><th colspan="3">Experimental conditions</th><th colspan="4">Dissolution yield (%)</th><th rowspan="2">Ref</th></tr><tr><th>H<sub>2</sub>SO<sub>4</sub> conc. (mol.L<sup>-1</sup>)</th><th>H<sub>2</sub>O<sub>2</sub> conc. (v/v)</th><th>S/L (g/L)</th><th>T (°C)</th><th>t (min)</th><th>Ni</th><th>Mn</th><th>Co</th><th>Li</th></tr></thead><tbody><tr><td rowspan="2">NMC+LMO + LCO</td><td>1</td><td>15 %</td><td>50</td><td>Room temp.</td><td>90</td><td>99</td><td>99</td><td>99</td><td>99</td><td>(a)</td></tr><tr><td>18.4</td><td>4.5 %</td><td>800</td><td>70</td><td>70</td><td>99</td><td>99</td><td>99</td><td>100</td><td>(b)</td></tr><tr><td>NMC111</td><td>2</td><td>3 %</td><td>50</td><td>50</td><td>60</td><td>100</td><td>100</td><td>100</td><td>100</td><td>(c)</td></tr><tr><td>NMC811</td><td>1</td><td>10 %</td><td>100</td><td>90</td><td>60</td><td>100</td><td>93</td><td>100</td><td>100</td><td>(d)</td></tr><tr><td rowspan="2">LFP</td><td>0.3</td><td>-</td><td>83</td><td>60</td><td>120</td><td>-</td><td>-</td><td>-</td><td>95.7</td><td>(e)</td></tr><tr><td>0.4</td><td>6 %</td><td>100</td><td>50</td><td>60</td><td>-</td><td>-</td><td>-</td><td>95</td><td>(f)</td></tr></tbody></table>

behavior of elements in the black mass during leaching through speciation calculations.

## 2. Materials and methods

### 2.1. Materials

Leaching experiments were performed on pristine materials of NMC and LFP (Xiamen Tob New technology Co., LTD) which their chemical compositions confirmed elemental analyses determined by means of Agilent MP-AES (Table S1 in Supporting Information). Table S1 also shows the particle size distributions in NMC and LFP determined by laser diffraction using Malvern Mastersizer 3000.

Elemental analysis confirmed that the composition of the cathode material provided by Xiamen Tob New Technology Co corresponds to NMC811 and LFP cathode material even if it appears that Ni and Mn content are slightly lower than expected: $LiNi_{0.76}Mn_{0.07}Co_{0.10}O_{1.79}$ instead of $LiNi_{0.8}Mn_{0.1}Co_{0.1}O_2$. LFP also have slightly less iron and phosphorus than expected, $LiFe_{0.92}P_{0.87}O_{4.03}$ instead of $LiFePO_4$.

LFP and NMC cathode materials were used to prepare model black masses containing different LFP/NMC ratios reported in Table 2 in order to investigate the influence of this ratio on the leaching performances. Typically, industrial black masses contain aluminum and copper from electrode foils beside the different metals from the cathodic materials (Li, Ni, Mn and Co from NMC and Li, Fe and P from LFP). These impurities stems from the battery crushing process, with an observed prevalence of Al impurity from cathode foil and Cu impurity from anode foils [7,34,35]. Therefore, a defined amount of copper powder (particle size <75 µm, purity 99 %) and aluminum powder (particle size 25 µm, purity 99 %), both supplied by Aldrich, was added to the model black masses to achieve the copper and aluminum concentrations reported in Table 2. The model black masses were then mixed to ensure homogeneity.

### 2.2. Leaching

The leaching experiments were performed in 100 mL borosilicate glass flasks shaked in a mechanical stirring apparatus (Gherardt Laboshake) thermostated with a Gherardt Thermoshake (THL 500/1) at 200 rpm and 30 °C. Solutions for leaching experiments were prepared

using deionized water (resistivity = 18 Mohms, VWR Purity TU 6+) and sulfuric acid (95–97 %, Fluka, lot #SZBG3220H). 3 % of hydrogen peroxide (30 % weight, Fisher scientific, lot 223,487) were added. Leaching experiments were conducted at a solid-to-liquid ratio S/L = 50 g/L by mixing 1 g of model black mass with 20 mL of leach solution. Leaching tests were stopped at definite time and the solutions were filtered using a 0.45 µm Teflon Digifilter from SCP Science. Prior to analysis, the filtered samples were diluted in 2 % $HNO_3$ (65 %, Sigma Aldrich, lot #STBK3044) for elemental analyses by means of a Micro-wave Plasma-Atomic Emission Spectrometer (Agilent 4210 MP-AES).

The samples were diluted by a factor 10 for Cu and Al analyses whereas 200-fold dilutions in 2 % nitric acid were performed for Ni, Mn, Co, Li, Fe, and P analyses. Elemental analyses of Li, Ni, Mn, Co, Fe, P, Cu and Al were performed at 610.635, 341.476, 279.482, 350.631, 373.486; 213.618, 510.554, 396.152 nm, respectively. The leaching residue was washed with water to remove any remaining sulfuric acid before being dried at a temperature of 100 °C for 8 h. Then, the residue was weighed before being dissolved in 6 mol.L$^{-1}$ hydrochloric acid (HCl 37 %, Merck) and analyzed by MP-AES.

Analysis results were used to calculate the dissolution yield %D as follows:

$$ \%D = 100 \times \frac{C_{\text{measured}}}{C_{\text{total,calc}}} \quad (1) $$

where $C_{\text{measured}}$ corresponds to the measured concentration and $C_{\text{total,calc}}$ represents the concentration that would be obtained after full leaching.

Solid samples were analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). All samples were ground prior to the XRD analysis. The mineralogy was determined using a D8 Discover Bruker diffractometer equipped with an X-ray tube emitting Cu-Kα1 radiation (λ = 1.5406 Å) at 40 kV and 40 mA. X-ray diffraction patterns were recorded with a LynxEye detector under ambient conditions from 2θ = 2.5° to 65° (step 2θ = 0.035°, recording time = 3 s/step). Analyses were performed using DIFFRAC.EVA Bruker software and diffraction peaks were identified using the powder diffraction file database.

SEM analyses were carried out using the Tescan VEGA3 equipped with a energy-dispersive spectrometer (EDS, Bruker XFlash6 with an area of 15 mm2) for semi-quantitative analyses. The accelerating voltage was set at 20 kV.

<caption>**Table 2**</caption>

Compositions of the model black masses used for leaching experiments (weight percentages). LFP/NMC/Cu/Al a/b/c/d denotes for the model black mass composition containing a wt% LFP, b wt% NMC, c wt% Cu, and d wt% Al (wt refers to weight percentages).

<table><thead><tr><th>Nomenclature</th><th>LFP</th><th>NMC</th><th>Cu</th><th>Al</th><th>Graphite</th></tr></thead><tbody><tr><td>LFP/NMC/Cu/Al 100/0/0/0/0</td><td>100</td><td>0</td><td>0</td><td>0</td><td>0</td></tr><tr><td>LFP/NMC/Cu/Al 75/25/0/0/0</td><td>75</td><td>25</td><td>0</td><td>0</td><td>0</td></tr><tr><td>LFP/NMC/Cu/Al 50/5/0/0/0</td><td>50</td><td>50</td><td>0</td><td>0</td><td>0</td></tr><tr><td>LFP/NMC/Cu/Al 25/75/0/0/0</td><td>25</td><td>75</td><td>0</td><td>0</td><td>0</td></tr><tr><td>LFP/NMC/Cu/Al 100/0/0/0/0</td><td>0</td><td>100</td><td>0</td><td>0</td><td>0</td></tr><tr><td>LFP/NMC/Cu/Al 48.5/48.5/1/2/0</td><td>48.5</td><td>48.5</td><td>1</td><td>2</td><td>0</td></tr><tr><td>LFP/NMC/Cu/Al 24. 25/24.25/0.5/1/50</td><td>24.25</td><td>24.25</td><td>0.5</td><td>1</td><td>50</td></tr></tbody></table>

### 2.3. Speciation calculations

Aqueous speciation calculations were performed using PHREEQC version 3.7 [36]. Speciation diagrams were generated with PhreePlot, a charting and plotting extension of PHREEQC. The MINTEQ.V4 thermodynamic database was used for equilibrium constants, and non-ideality in concentrated electrolyte solutions was accounted for with the Pitzer activity coefficient model implemented in PHREEQC. Model inputs included measured element concentrations, pH, temperature, density, and redox potential of the aqueous phases.

The saturation index (SI) was calculated to predict whether a solution is in thermodynamic equilibrium with a given mineral. This saturation index for each mineral was calculated in PHREEQC as:
$$SI = \log \left( \frac{IAP}{K_{sp}} \right) \qquad (2)$$

where IAP is the ion activity product and Ksp is the solubility product constant at the system temperature. SI values indicate whether the solution is at equilibrium (SI = 0), undersaturated (SI < 0), or supersaturated (SI > 0) with respect to a mineral phase.

### 3. Results and discussion

#### 3.1. Acid deficiency assessment

Leaching experiments can be performed at the solid-to-Liquid ratios (S/L) leading to excess or deficiency in sulfuric acid. Li et al. [31] and Fan et al. [28] reported the two following reactions for LFP and NMC leaching with sulfuric acid in the presence of hydrogen peroxide (H₂O₂):

$$2\text{LiFePO}_4 + \text{H}_2\text{SO}_4 + \text{H}_2\text{O}_2 \rightleftharpoons \text{Li}_2\text{SO}_4 + 2\text{FePO}_4 + 2\text{H}_2\text{O} \qquad (3)$$

$$2\text{LiMO}_2 + 3\text{H}_2\text{SO}_4 + \text{H}_2\text{O}_2 \rightleftharpoons 2\text{MSO}_4 + \text{Li}_2\text{SO}_4 + 4\text{H}_2\text{O} + \text{O}_{2(g)} \qquad (4)$$

where M represents Ni, Mn, or Co in the NMC cathode material LiNi₂Mn₃Co₂O₂.

In the present work, sulfuric acid is consumed by leaching NMC and LFP but also Cu and Al when these elements are present in the black mass. Chernyaev et al. [37] wrote the following reactions for Cu and Al dissolution by sulfuric acid in the presence of H₂O₂:

$$\text{Cu} + \text{H}_2\text{SO}_4 + \text{H}_2\text{O}_2 \rightleftharpoons \text{CuSO}_4 + 2\text{H}_2\text{O} \qquad (5)$$

$$2\text{Al} + 3\text{H}_2\text{SO}_4 \rightleftharpoons \text{Al}_2(\text{SO}_4)_3 + 3\text{H}_2(g) \qquad (6)$$

Hence, the following relationship can be derived to calculate the concentration of sulfuric acid C at the solid-to-liquid ratio (S/L) for the stoichiometric leaching of the black mass containing %LFP of LFP, %NMC of NMC, %Al of Al, and %Cu of Cu (weight percentages):

$$C = \frac{S}{L} \left( 0.5 \times \frac{\%_{LFP}}{M_{LFP}} + 1.5 \times \frac{\%_{NMC}}{M_{NMC}} + 1.5 \times \frac{\%_{Al}}{M_{Al}} + \frac{\%_{Cu}}{M_{Cu}} \right) \qquad (7)$$

where M<sub>LFP</sub> = 157.76 g.mol<sup>-1</sup>, M<sub>NMC</sub> = 97.28 g.mol<sup>-1</sup>, M<sub>Al</sub> = 26.98 g. mol<sup>-1</sup> and M<sub>Cu</sub> = 63.55 g.mol<sup>-1</sup> stand for the molecular weights of LFP, NMC, Al and Cu, respectively.

Fig. 2 shows the sulfuric acid concentration, determined by Eq. (7), as a function of the S/L ratio.

The analysis assumes an ideal system where the theoretical amount of acid is sufficient for complete leaching, based on the stoichiometric ratio of the balanced chemical equation. This model does not account for the real complexities and inefficiencies of leaching, such as incomplete reactant contact, slow diffusion rates, and competing side reactions. In practice, these limitations prevent the ideal reaction from achieving 100 % efficiency with the theoretical acid amount. Therefore, achieving a higher dissolution yield often requires more acid than the stoichiometric minimum to compensate for these kinetic and mass-transfer bottlenecks, effectively driving the reaction forward under non-ideal conditions.

The curves in Fig. 2 depicts for the achievement of stoichiometric balance in the leaching process of the model black masses which the composition are reported in Table 2. Any experimental conditions depicted in Fig. 2 (S/L ratio; acid concentration) for which the points are below the curve indicate a deficit in acid. Conversely, conditions that position the points above the curve mean an excess of acid.

#### 3.2. Effect of black mass composition on leaching performance

Leaching of LFP/NMC mixtures in the absence of Cu and Al by sulfuric with 3 % (v/v) H₂O₂ were conducted under acid deficiency conditions at 30 °C (Fig. 3). In all experiments, Fe and P were not detected in the leachates.

<figure><img src="image_4.png" /><figcaption>Fig. 2. Acid deficiency assessment for leaching model black masses containing various amounts of NMC, LFP, Cu and Al (leaching performed by sulfuric acid in the presence of an excess of hydrogen peroxide at S/L solid/liquid ratio). LFP/ NMC/Cu/Al a/b/c/d denotes for the model black mass composition containing a wt% LFP, b wt% NMC, c wt% Cu, and d wt% Al (wt refers to weight percentages).</figcaption></figure>

<figure><img src="image_5.png" /><figcaption>Fig. 3. Dissolution yields (%D) of Ni, Mn, Co and Li during the leaching of LFP/ NMC mixtures by H₂SO₄ + 3 % (v/v) H₂O₂ in the absence of copper and aluminum under acid deficiency conditions. H₂SO₄ concentrations = 0.71, 0.58, 0.45, 0.32, 0.19 mol.L⁻¹ for leaching LFP/NMC/Cu/Al = 100/0/0/0, 75/ 25/0/0, 50/50/0/0 and 0/100/0/0; temperature = 30 °C; Time = 240 min; S/ L = 50 g/L.</figcaption></figure>

This observation aligns with the findings presented by Li et al., who demonstrated that, under acid deficiency, iron dissolution yielded zero because FePO₄ was not soluble under these conditions, while Li dissolution reached 95.74 %. The dissolution yields of Li for NMC/LFP mixtures are slightly lower than those obtained for pure LFP likely due to slower leaching rate of NMC compared to LFP. It is interesting to point out that the dissolution yields of Co, Ni and Mn are lower for LFP/NMC = 75/25 than for NMC-rich mixtures. The leaching of LFP in LFP/NMC = 75/25 leads to phosphate anion dissolution that can react with Co, Ni and Mn to precipitate them as CoPO₄, NiPO₄ and MnPO₄. As a result, this precipitation reduces the dissolution yields of the transition metals. For NMC-rich mixtures, the dissolution yields of the transition metals are higher than for LFP-rich mixtures because less phosphate anions are released into the solution to precipitate the transition metals.
Considering the negligible impact of LFP content in LFP/NMC mixtures on the dissolution yields, the leaching experiments were performed in LFP/NMC = 50/50 hereafter. The addition of 1 % Cu and 2 % Al in the NMC/LFP mixture (NMC/LFP/Cu/Al = 48.5 %/48.5 %/1 %/2 %, composition reported in Table 2) does not influence significantly the dissolution yields of Li, Mn and Co (See Fig. S1 in SI). The inherent challenge in precisely quantifying the impact of impurities on H₂O₂ consumption is duly acknowledged, as underscored in Chernyaev et al. [37].

The influence of the presence of graphite in the black mass on the dissolution yield has been also studied as graphite particles are often present in black mass at much or less high content depending on efficiency of the pre-treatment [38]. In order to align our experiments with the actual recycling scenario, we conducted leaching in the presence of graphite in LFP/NMC/Cu/Al mixtures (LFP/NMC/Cu/Al/Graphite = 24.25/24.25/0.5/1/50, composition reported in Table 2).

As for the presence of Cu and Al, graphite in the black mass does not influence the dissolution yields of Ni, Mn, Co and Li even at high

<figure><img src="image_6.png" /><figcaption>**Fig. 4.** Variation of (a) pH and redox potential (vs. Standard Hydrogen Electrode, SHE), (b) dissolution yields (%D) for the following systems: LFP leached by 0.19 mol.L⁻¹ H₂SO₄ + 3 % (v/v) H₂O₂ quoted LFP/NMC/Cu/Al = 100/0/0/0; NMC leached by 0.71 mol.L⁻¹ H₂SO₄ + 3 % (v/v) H₂O₂ quoted LFP/NMC/Cu/Al = 0/100/0/0; (c) Speciation calculations of Li, Ni, Mn, Co, Fe and P during leaching of NMC as a function of leaching time. Experimental conditions for leaching both systems: temperature = 30 °C, S/L = 50 g/L.</figcaption></figure>
graphite content (Fig. S2 in SI). It seems that graphite does not signifi-
cantly sorb transition metals and Li on its surface as it could have been
expected since acid leaching is used to remove impurities from graphite
concentrates[39].

After the leaching and filtration steps, it seems that some graphite
particles have been impacted. Specifically, there has been a detachment
of flakes from the surface of the spheroidized graphite particles, as
observed in Fig. S3 in SI. This phenomenon may result from friction with
other particles (graphite, Cu, Al and cathode material) or it could arise
due to the acidic and oxidizing conditions encountered during the
process.

3.3. Leaching rate

Fig. 4a and b show, respectively, the variation of pH and redox po-
tential, as well as the dissolution yields of the metals contained in the
model black masses, as a function of time during leaching. The experi-
ments were performed on LFP (LFP/NMC/Cu/Al = 100/0/0/0) and
NMC (LFP/NMC/Cu/Al = 0/100/0/0) using sulfuric acid and H₂O₂
under acid-deficient conditions.

Regarding LFP leaching, after several minutes of leaching, around
100 % of Li was dissolved. Notably, the present study reveals that the
leaching process employed here is much faster than that reported by Li
et al. Indeed, the present work shows a complete dissolution of LFP
within 5 min whereas full leaching takes place within 80 min in the work
of Li et al. [31]. This work was done at 30 °C whereas it was performed at
60 °C in Li et al.'s work. The fact that the solubility of FePO₄ decreases
with temperature [40], or the preference for the amorphous form of
FePO₄ at low temperatures and the crystalline form at higher tempera-
tures [41], seems to influence the dissolution rate of LFP. The dissolution
is responsible for an increase of pH from 0.83 to 2.03 due to the con-
sumption of proton according to Eq. (3). Also, a slight increase in redox
potential is observed. This increase is most probably due to two
concomitant phenomena: (i) decomposition of H₂O₂ which is respon-
sible for a decrease of the redox potential and (ii) LFP dissolution
resulting in an increase of the redox potential due to oxidation of Fe(II)

into Fe(III).

Globally, these concomitant phenomena lead to an increase of redox
potential as observed in Fig. 4a. No dissolution of iron and phosphate
occurs as they react together to precipitate as FePO₄ whereas Li does not
precipitate as Li₃PO₄ but remains in solution as Li⁺ and Li₂SO₄⁻ at pH 2
according to PHREEQC calculations (Fig. 4c). Indeed, these speciation
calculations showed that the solid phases FePO₄·2H₂O, Hematite and H-
Jarosite may potentially form at the steady state under these experi-
mental conditions (pH and redox potential) as the supersaturation index
expressed in Eq. (2) calculated by PHREEQC are SI(FePO₄·2H₂O) = 3.63,
SI(Hematite) = 1.18 and SI(H-Jarosite) = 0.96, respectively.

The presence of iron phosphate in the leaching residue after a
leaching duration of 240 min has been confirmed by X-ray diffraction
(XRD) as shown in Fig. 5a. The same XRD pattern was also obtained after
5 min leaching (XRD pattern not reported in the paper). The presence of
hematite and H-jarosite (hydronium jarosite, (H₃O)(Fe³⁺)₃(SO₄)₂(OH)₆)
is not confirmed by XRD but these phases might be present as amor-
phous phases and thus not visible in the XRD pattern. The presence of
amorphous phases is confirmed by the broad baseline at low 2θ values.
The SEM image and the EDX mapping in Fig. 5b and c show that the
leaching residue is composed of iron and phosphorus, which is consis-
tent with the XRD pattern confirming the presence of iron phosphate in
the residue.

Fig. 4b shows that NMC leaching is slower than LFP leaching as 60 min is necessary to leach NMC whereas only several minutes are needed to leach LFP. As expected, the pH increases from 0.3 to 6.7 during leaching due to proton consumption according to Eq. (4). It is interesting to highlight that the dissolution yields are consistent with those found by Nadimi and Jalalian Karazmoudeh [27]. However, NMC dissolution obtained by Nadimi and Jalalian Karazmoudeh [27] is slightly slower probably because the leaching temperature was a little bit lower (room temperature in their study instead of 30 °C in the present one). Almost the same dissolution rate is observed for Ni, Co, Mn and Li. Mn can exist at different oxidation states (+II, +III, +IV, +VI) but PHREEQC calculations in Fig. 4c show that Mn exists only as Mn(II) in solution as the redox potential is between 583 and 805 mV vs. SHE during leaching.

<figure><img src="image_7.png" /><figcaption>**Fig. 5.** (a) XRD pattern of LFP leaching residue, (b) SEM image of the LFP leaching residue and (c) corresponding EDX spectrum (Leaching reagent: 0.19 mol L⁻¹ H₂SO₄ + 3 % (v/v) H₂O₂ (temperature = 30 °C; S/L = 50 g/L; leaching duration: 240 min).</figcaption></figure>
Likewise, Co exists only as Co(II) in solution (hydrogen peroxide is used to reduce Co(III) contained in NMC into Co(II)). It is interesting to notice that, unlike during LFP leaching, the concomitant consumption of H₂O₂ and oxidation of Co(II) into Co(III) result in a decrease of the redox potential as observed in Fig. 4a.

According to PHREEQC calculations (Fig. 4c), Li, Mn, and Co exist predominantly as Li⁺, Mn²⁺ and Co²⁺ in solution at the beginning of the leaching process. The other forms in solution are Li₂SO₄, MnSO₄ and CoSO₄. Ni behavior is different as Ni²⁺ is predominant at the beginning of leaching but it becomes minor after 120 min of leaching because Ni²⁺ reacts with sulfate to form NiSO₄ and Ni(SO₄)₂²⁻. The change in speciation stems from the change in pH due to proton consumption during leaching. Indeed, after 120 min, pH is greater than 5.5 and sulfate concentration increases through the time, which favors the formation of metal sulfate complexes. Supersaturation index calculated by PHREEQC shows that no solid is expected to precipitate at the beginning of the leaching process. Conversely, Mn₂O₃, Mn₃O₄ and Co₃O₄ may start to precipitate after 180 min as the supersaturation indexes are equal to 3.36, 2.20 and 9.57, respectively. However, XRD patterns in Fig. 6 shows that these phases are not observed and only undissolved NMC remains in the solid phase. The absence of these solid phases in the XRD patterns may be explained by their low concentration or by the slow kinetic of formation.

Fig. 7a and b show, respectively, the variation of pH and redox potential, and the dissolution yields of the metals contained in the model black masses, as a function of time during leaching. The experiments were performed on LFP/NMC/Cu/Al mixtures with compositions of 50/50/0/0 and 48.5/48.5/1/2 (see Table 2), using sulfuric acid and H₂O₂ under acid-deficient conditions as leaching reagents.

Regarding leaching of LFP/NMC/Cu/Al = 50/50/0/0, the pH increased from 0.5 and 5.7 during leaching (Fig. 7a) as it was observed for pure NMC leaching (Fig. 4a). Co, Ni and Mn dissolution follows the same behavior whereas Li is dissolved slightly faster (Fig. 7b). The maximum dissolution yield for Co is around 80 % whereas it reaches 85 % for Ni and Mn, and over 93% for Li. Speciation calculations in Fig. 7c show that Mn exists as Mn(II) and Co exists as Co(II) since the redox potential is comprised between 645 and 957 mV vs. SHE. It is interesting to point out that iron and phosphate concentrations in solution increase up to 10.9 % and 3.3 % after 30 min, respectively, and then decrease to reach zero. Before 30 min, the solution is too acid (pH < 1) to precipitate iron as iron phosphate. During leaching, the pH increases as NMC and LFP lixiviation consumes proton. When pH is greater than 1 after 30 min, iron phosphate precipitates. As a result, iron and phosphate concentrations in solution decrease. When the pH is greater than 2 after 120

min, iron is fully precipitated as iron phosphate and no iron neither phosphate remain in the leach solution.

No reaction occurs between the transition metals and phosphate under these acidity conditions, which prevents their precipitation as phosphate salts. Supersaturation indexes calculated by PHREEQC confirm that iron precipitate as iron phosphate (SI(FePO₄, 2H₂O) = 1.18) and no Co, Ni and Mn precipitation as phosphate salts occurs since all supersaturation index values are negative (SI(Co₃(PO₄)₂) = -16.2, SI (Ni₃(PO₄)₂) = -15.0, SI(Mn₃(PO₄)₂) = -27.4). No other solid phases are formed according to PHREEQC calculations.

XRD analysis (Fig. 8a) shows that only FePO₄ and non-dissolved NMC are present in the residue at the end of the leaching which matches with PHREEQC supersaturation index. The SEM image and the EDX mapping in Fig. 8b and c show that the leaching residue is composed of iron and phosphorus, which is consistent with the XRD pattern confirming the presence of iron phosphate in the residue. The EDX mapping confirms the presence of punctual zones containing nickel as well. The EDX analysis indicates the presence of 3.22 % nickel, 0.86 % cobalt, 0.22 % manganese, 1.00 % copper, 0.77 % aluminum, 53.88 % iron and 39.94 % phosphorus (atomic percentages). Therefore, the residue is indeed mainly composed of iron phosphate as expected, with a fraction of NMC (which the stoichiometry seems to be different from the pristine NMC material contained in the model black mass) as shown by XRD analysis. (See Fig. 8.)

Fig. 7b shows the impact of impurities during leaching. As said before, dissolution rate of Li, Ni, Mn and Co (84 %, 82 % 77 % and 79 % respectively) are similar to those without impurities (Fig. 5a). The pH values increased from 0.5 to 5.7 and redox potential from 555 to 961 mV. Speciation of these elements are also very similar as pH and redox potential are identical. Iron and phosphate concentrations increase during the first minutes of leaching, and then decrease until reaching zero after 120 min of leaching.

Likewise, copper concentration increases during the first minutes, reaches a plateau during 60 min before decreasing until reaching zero after 120 min. Iron and copper concentrations decrease because the pH values allow their precipitation with phosphate as Cu₃(PO₄)₂ and FePO₄. Conversely, aluminum may precipitate even at low pH as its concentration remains null in solution. PHREEQC calculations for copper species highlight that Cu₃(PO₄)₂ (SI(Cu₃(PO₄)₂ = 3.75), copper-iron oxide (SI(CuFe₂O₄) = 15.78) and iron oxide (SI(FeO₂) = 10.09) may precipitate. EDX analysis of the solid observed by SEM in Fig. S4 (Supporting Information) may confirm the presence of such types of compounds as analysis shows the presence of 38.5 % O, 24.5 % Fe, 14.2 % Cu and 12.7 % P (weight percentages).

## 3.4. Process flow diagram

This work paves the way to the development of the innovative flowsheet depicted in Fig. 9.

This flowsheet combines leaching and solvent extraction to extract metals from LFP-NMC mixtures derived from cathode scraps or black mass from LIBs recycling.

The leaching process starts by introducing the solid feed material into a mechanically agitated reactor. The leaching medium consists of 0.45 mol L⁻¹ sulfuric acid (H₂SO₄) combined with 3 % hydrogen peroxide (H₂O₂). A pulp density of 50 g/L is maintained, with the mixture held at 30 °C under continuous agitation for 4 h. The acidic environment promotes dissolution of the active cathode materials, while H₂O₂ enhances the oxidation of iron and facilitates transition metal dissolution.

Upon completion of the leaching reaction, the slurry is transferred to a solid–liquid separation unit (e.g., filtration or thickening). The clarified leachate contains lithium (Li), manganese (Mn), cobalt (Co), and nickel (Ni) in dissolved form. This solution is subsequently directed to a liquid–liquid extraction stage for selective metal recovery.

The solid residue obtained after separation may contain unreacted

<figure><img src="image_8.png" /><figcaption>Fig. 6. XRD patterns of NMC (LFP/NMC/Cu/Al=100/0/0/0) pure leaching residue after 240 min (Leaching reagent: 0.71 mol L⁻¹ H₂SO₄ + 3 % (v/v) H₂O₂ (temperature = 30 °C; S/L = 50 g/L).</figcaption></figure>
<figure><img src="image_9.png" /><figcaption>**Fig. 7.** Variation of (a) pH and redox potential (vs. Standard Hydrogen Electrode, SHE), (b) dissolution yields (%D) and (c) speciation calculation of Li, Ni, Mn, Co, Fe and P as function of leaching time for the following systems: LFP/NMC/Cu/Al = 50/50/0/0 (composition reported in Table 2) leached by 0.45 mol.L⁻¹ H₂SO₄ + 3 % (v/v) H₂O₂ and LFP/NMC/Cu/Al = 48.5/48.5/1/2 (composition reported in Table 2) leached by 0.45 mol.L⁻¹ H₂SO₄ + 3 % (v/v) H₂O₂. Experimental conditions for leaching both systems: temperature = 30 °C, S/L = 50 g/L.</figcaption></figure>

material or inert components. Depending on its composition, it can be reintroduced into the leaching reactor for additional treatment. This recycle loop maximizes metal recovery and minimizes waste generation.

## 4. Conclusions

This study introduced a novel leaching process for the selective extraction of nickel (Ni), manganese (Mn), cobalt (Co), and lithium (Li) from a mixture of lithium iron phosphate (LFP) and nickel manganese

cobalt (NMC) materials. The following conclusions can be drawn based on the results:

* The proportion of LFP in the LFP/NMC mixtures does not affect significantly the dissolution yields; Ni, Mn, Co, and Li exhibit consistent behavior regardless of the presence of LFP.

* Acid leaching of an LFP/NMC/Cu/Al mixture (50/50/0/0) achieves high dissolution rates, with 93.6 % of Li, 86.3 % of Ni, 84.8 % of Mn,
<figure><img src="image_10.png" /><figcaption>Fig. 7. (continued).</figcaption></figure>

<figure><img src="image_11.png" /><figcaption>Fig. 8. XRD patterns of LFP/NMC = 50/50 leaching residue after 240 min (Leaching reagent: 0.45 mol L⁻¹ H₂SO₄ + 3 % (v/v) H₂O₂ (temperature = 30 °C; S/L = 50 g/L).</figcaption></figure>
<figure><img src="image_12.png" /><figcaption>**Fig. 9.** Possible flowsheet for a leaching process of a mixtures of spent LiBs leading to a liquid-liquid extraction step.</figcaption></figure>

and 79.9 % of Co extracted, while Fe and phosphorus (P) are absent in the leachate due to their precipitation as $FePO_4 \cdot 2H_2O$.

* The introduction of impurities such as Cu, Al, and graphite does not significantly alter the composition of the leachate; both Cu and Al precipitate during leaching, and graphite does not adsorb metals onto its surface.

* The leachate produced under conditions of acid deficiency is sufficiently pure to allow for a subsequent liquid-liquid extraction stage, facilitating the effective separation of Mn, Co, Ni, and Li. Notably, the leach solution remains free of Fe, Cu, and Al, even in instances where the black mass contains a high concentration of LFP.

* The solid residue still containing valuable metals can be recycled in the leaching reactor with the feed material in order to recover them and produce a solid containing essentially iron, phosphate, copper and aluminum, which can be processed to produce pure iron phosphate that can be converted into new LFP cathode materials.

### CRediT authorship contribution statement

**Pierric Hubert:** Writing – review & editing, Writing – original draft, Visualization, Investigation, Formal analysis.
**Anna Vanderbruggen:** Writing – original draft, Investigation.
**Safi Jradi:** Writing – review & editing, Supervision, Investigation.
**Alexandre Chagnes:** Writing – review & editing, Writing – original draft, Visualization, Supervision, Project administration, Funding acquisition, Formal analysis, Conceptualization.

### Declaration of competing interest

None.

### Acknowledgements

This work was supported by the French PIA project "Lorraine Université d'Excellence", reference ANR-15-INDEX-04-LUE and the LabEx RESSOURCES 21 through the national program "Investissements d'avenir" with the reference ANR-10-LABX-21-RESSOURCES21.

The authors want to acknowledge Mrs. Laure Clerget from Artemise Company for funding this work within the framework of the Neolithics project.

## Appendix A. Supplementary data

Supplementary data to this article can be found online at https://doi.org/10.1016/j.susmat.2025.e01658.

### Data availability

Data will be made available on request.

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