Dry Grinding & Ultrasound Leaching for Lithium Recovery

Resources, Conservation & Recycling 174 (2021) 105784
0921-3449/© 2021 Elsevier B.V. All rights reserved.
Full length article
Dry Grinding - Carbonated Ultrasound-Assisted Water Leaching of
Carbothermally Reduced Lithium-Ion Battery Black Mass Towards
Enhanced Selective Extraction of Lithium and Recovery of
High-Value Metals
Brian Makuza a,b
, Dawei Yu a,b,*
, Zhu Huang a,b
, Qinghua Tian a,b
, Xueyi Guo a,b
a
School of Metallurgy and Environment, Central South University, Changsha 410083, China
b
National and Regional Joint Engineering Research Center of Nonferrous Metal Resource Recycling, Changsha 410083, China
A R T I C L E I N F O
Keywords:
Spent Li-ion batteries
Cathode material
Carbothermic reduction
Grinding
Selective lithium recovery
A B S T R A C T
This paper presents a dry grinding and carbonated ultrasound-assisted water leaching (CUAWL) process for
recycling the black mass of spent lithium-ion batteries constituting anode material (graphite) and different
cathode material combinations (LiCoO2, LiMn2O4, and LiNiO2). The inspiration of the method is to enhance
selective Li2CO3 recovery and reduce energy requirements for evaporative crystallization while achieving
maximum recovery of all the high-value metals. The influence of several factors, including roasting temperature,
roasting time, grinding time, water leaching time, water leaching temperature, sonication, and CO2 flow rate, on
the leaching efficiency of metals are investigated. The SEM-EDS and XRD results depict that the mixture of anode
and cathode material after reduction roasting under optimum conditions of 600 ◦
C for 30 min was primarily
transformed into Li2CO3, Ni, CoO, Co, and MnO. However, the selective recovery of Li with water leaching was
low, and dry grinding followed by CUAWL was adopted to enhance the recovery rate. The optimized experi
mental results achieved improved results for selective recovery of Li of up to 92.25% for the mixture of multiple
cathode materials (LiCoO2, LiMn2O4, and LiNiO2). The recovered leach solution (LiHCO3) is subjected to
evaporative crystallization to attain high-purity Li2CO3 (≥99.2%). Subsequently, over 99% of the high-value
metals Ni, Mn, and Co could be leached out using 4 M H2SO4 without the addition of a reductant.
1. Introduction
Lithium-ion battery (LIB) is considered the leapfrog technology for
powering portable electrical devices and robust utilities such as drive
train (Guo et al., 2021; Makuza et al., 2021), and the ongoing transition
towards a new energy system has caused an ever-growing demand for
LIBs. From statistics released by the European Union (EU) (Tsiropoulos
et al., 2018), electric vehicle growth is to be around 50–200 million units
in 2028 from 4 million units in 2018. The escalating demand is attrib
uted to the high energy density, high voltage, and high theoretical ca
pacity (Yuehua Wang et al., 2019; Zhang et al., 2019) offered by LIBs,
making them the best electrical energy storage option for high-energy
applications such as transportation and stationary storage. The LIBs
comprise five principal components: the anode, cathode, electrolyte,
separators, and current collectors (Velázquez-Martínez et al., 2019), and
differentiation emanates from the type of lithiated metal oxide used for
the cathode material, which is constantly changing to reconfigure bat
tery storage sustainability (Velázquez-Martínez et al., 2019; Yang et al.,
2021).
LIB recycling has been a global research hotspot since its advent
because of the complex nature of battery chemistry (Assefi et al., 2020).
Recycling valuable metals back into circulation promotes environmental
sustainability (Chandra et al., 2021). Besides, the LIBs contain many
toxic chemicals, which, when discharged, percolate into the ground
leading to environmental toxicity (Ji et al., 2021; Tang et al., 2019)
(Golmohammadzadeh et al., 2020).
LIB recycling is conducted using pyrometallurgy, hydrometallurgy,
or a combination of the processes (Mayyas et al., 2019; Pindar and
Dhawan, 2020). Hydrometallurgy encompasses pretreatment to recover
the cathode materials followed by leaching and subsequent purification
* Corresponding author.
E-mail address: dawei.yu@csu.edu.cn (D. Yu).
Contents lists available at ScienceDirect
Resources, Conservation & Recycling
journal homepage: www.elsevier.com/locate/resconrec
https://doi.org/10.1016/j.resconrec.2021.105784
Received 9 April 2021; Received in revised form 30 May 2021; Accepted 30 June 2021

2
and recovery techniques such as selective precipitation, ion exchange,
and solvent extraction to extract the valuable metals (Meshram et al.,
2020; Shi et al., 2019). Some hydrometallurgical processes have draw
backs of relatively long leaching time and low leaching efficiency
because of the high valence state of the active cathode material and the
strong binding force of the organic binders (Makuza et al., 2021).
Moreover, the vast consumption of concentrated acid and reductants
(Di et al., 2020; Shi et al., 2019; Zheng et al., 2018) and the multiple
process steps generate significant effluent, which can exacerbate sec
ondary pollution from the discharge of acidic wastewater and gas during
the leaching processes (Makuza et al., 2021). Li is also dispersed
amongst these separation and refining stages, leading to a low lithium
recovery (Di et al., 2020; Lv et al., 2018; Peng et al., 2019). Alterna
tively, pyrometallurgical treatments can be used to extract and purify
metals (Lv et al., 2018). The pyrometallurgical recycling options possess
the advantages of a high rate of chemical reactions, allowing large
treatment capacity (Jie et al., 2020; Ren et al., 2017), being relatively
flexible in the feed material, simple operation, and the dross has negli
gible environmental impacts (Zheng et al., 2018).
It is noteworthy that much emphasis, especially on the industrial
scale, has been placed on the extraction of heavy metals: cobalt and
nickel, because of the high economic value associated with these metals
(Makuza et al., 2021). Dwelling only on the recovery of these heavy
metals has a couple of drawbacks. Firstly, lithium constitutes a signifi
cant proportion of the LIB. The lithium mineral reserves are gradually
depleting; hence there is a need to recover Li from spent LIBs, which is a
meaningful way to secure its availability. Secondly, battery manufac
turers’ transition to less costly cathode material combinations has
adverse impacts on recycling methods that are material-specific, as it
will deem those processes not economically favorable (Sonoc et al.,
2015). Moreover, Li concentration from spent LIBs is also much higher
than that from primary natural ores and brines, and the separation is
much easier to attain than that from the primary resources (Xiao et al.,
2019). The overall Li demand is skyrocketing, and a plausible way to
increase Li production is by enhancing its recovery from recycling spent
LIBs (Chen and Shen, 2017; Di et al., 2020; Kwon and Sohn, 2020)
(Kamran et al., 2021), which is still low using current processing tech
nologies requiring further improvement.
Past researchers have developed novel combined pyro-
hydrometallurgy recycling processes to extract high-value metals from
the spent LIBs and reduce Li loss. Georgi-Maschler et al. (2012) used a
reduction smelting method to recover valuable metals from spent LIBs.
These valuable metals, including Co, Ni, and Mn, were converted to
alloys. Lithium entered the slag or dust fraction during the process
(Georgi-Maschler et al., 2012). Träger et al. (2015) also proposed a
high-temperature process that entailed vacuum and selective carrier gas
evaporation to evaporate Li from the spent LIBs. However, the temper
ature applied during the process was higher than 1400 ◦
C, which inev
itably led to increased energy consumption (Träger et al., 2015).
Considering the shortcoming of the processes mentioned above, Shi
et al. (2019) used sulfation roasting on LiCoO2 cathode material to
produce water-soluble LiSO4 and CoSO4. However, a maximum con
version rate of 44% was achieved even after 240 min of roasting time.
The implication was that CoO was produced during the reaction; hence
it did not serve the purpose (Shi et al., 2019). NaHSO4•H2O has been
used for sulfation roasting; however, this method requires a sizeable
amount of NaHSO4•H2O, leading to high reagent cost and the recovery
effect of Li in the spent LIBs is not clear (Di et al., 2020).
Lately, carbothermic reduction (CTR) roasting has found application
as a pyrometallurgical option for recycling spent LIBs to curb the
excessive high-temperature requirements and loss of Li in the slag dur
ing pyrometallurgical recycling (Makuza et al., 2021). For instance, Li
et al. (2016) and co-workers roasted LiCoO2 and graphite at 1000 ◦
C for
30 min under nitrogen purge gas. The roasting products underwent
water leaching to recover lithium carbonate (Li2CO3), and subsequent
magnetic separation recovered cobalt (Co), and the filter residue was
entirely carbon (C). However, the concentration of the Li-rich solution
was only 337.4 mg/L, making it challenging to recover Li2CO3 and
exacerbate the evaporative crystallization cost, which restricts industrial
application (W. Wang et al., 2019).
In this study, the effect of CTR roasting on the selective extraction of
Li2CO3 using dry grinding followed by carbonated ultrasound-assisted
water leaching (CUAWL) is investigated. Recycling LIBs active cathode
materials using the proposed method can potentially shorten the recy
cling process steps as it eliminates the need to separate the anode and
cathode material in the pretreatment process. The anode and cathode
separation process after automated crushing, which has significantly
dominated the LIB pretreatment process because of its high throughput
(Zhang et al., 2013), has significant technical hurdles due to the great
variation and complexity of the LIB packs, which makes it time-intensive
and intricate (Gaines, 2018; Zhang et al., 2019). The similarity of the
active cathode material and anode material (graphite) in terms of
morphology complicates the separation process further (Kepler et al.,
2015). The proposed method aims to treat a combination of various
types of active cathode material, which represents the actual situation in
industrial LIB recycling plants. Furthermore, the selective recovery of
Li2CO3 results in decreased process steps in separating the roasted
products for regeneration and minimizes the Li losses (Peng et al., 2019).
Direct acid leaching methods have been associated with a low Li2CO3
recovery attributed to the fact that Li losses occur at numerous points
within the complicated LIBs recycling flowsheet from acid leaching
followed by Co, Ni extraction to evaporation and Li2CO3 precipitation
(Peng et al., 2019).
The solubility of Li2CO3 and the recovery of the high-value metals in
the proposed method can be enhanced by grinding, sonication, and
carbonation. Intensive grinding improves the leaching reaction because
of an increased specific surface area, enhanced surface reactivity, and
crystalline structure changes. Since the calcine comprises a significant
amount of graphite, it is susceptible to absorb the lithium ions, inhib
iting the selective recovery of Li2CO3 from the water leaching solution
(Lombardo et al., 2020; Makuza et al., 2021). Yue et al. (2018) also
reported the difficulty of completely separating Co from Li2CO3 and
graphite from sintered agglomeration products using physical methods.
Sonication is adopted to cause ultrasonic cavitation effects in the
leaching solution, which leads to chemical impacts and mechanical ac
tion between solid and liquid interfaces, thereby facilitating desorption
(Jiang et al., 2018; Zhou et al., 2021). The carbonation process involves
injecting CO2(g) into the leaching solution to transform the lowly soluble
Li2CO3 (13.3 g/L at 20 ◦
C (Hu et al., 2017) into more soluble LiHCO3
(55.0 g/L at 20 ◦
C (Yi et al., 2011).
2. Materials and methods
2.1. Materials
This work was conducted on a black mass (mixture of cathode and
anode material) made up of different cathode material combinations
and anode (graphite) of spent lithium-ion batteries provided by a Chi
nese LIB recycling facility. The X-ray diffractogram of the black mass
before roasting is illustrated in Fig. 1, and Figure S1 shows the SEM and
elemental mapping images. The spatial distribution of the metals Ni, Co,
and Mn in the raw material shows that they are positioned in different
particles. Considering these conspicuous features and using XRD con
firmations (Fig. 1), the principal cathode materials in the black mass are
LiCoO2 (LCO), LiMn2O4 (LMO), and LiNiO2 (LNO). Particle size analysis
shows 90% below 34.026 μm, with a major portion in the 9–40 μm range
(Figure S2). The chemical composition of the black mass used in the
experiment is represented in Table 1.
2.2. Experimental
The recycling of the mixture of the anode and various cathode
B. Makuza et al.

3
materials (LiCoO2, LiMn2O4, and LiNiO2) by carbothermic reduction
roasting and the method of enhanced selective recovery of Li2CO3 was
studied as follows (as depicted in Fig. 2), and the material balance is
illustrated in Table S1.
The black mass of spent lithium-ion batteries was dried at 110 ◦
C for
6 h in an oven (WGL-125, Taisite). The dried powder was mixed using a
roller mixer (RM100 Miulab, Hangzhou, China) at 80 rpm for 30 min to
obtain a homogeneously mixed powder. After which, a sample of 5 ±
0.005 g was placed in an alumina crucible for each roasting experiment,
as illustrated in Fig. 3.
The alumina crucible with the sample was adjacently attached to the
tip of a K-type thermocouple and placed into a horizontal tube furnace
(OTF-1200X-VF, HF-Kejing, China) on the cool zone. A vacuum pump
(RS-2, Haoyu, China) was then used to remove air from the quartz tube
before purging with Ar gas. Ar gas flow rate was maintained at 300 mL/
min using a mass flow controller (Omega, FMA-A2404), and the heating
rate was 30 ◦
C/min. The temperature was recorded by an HH806W
wireless multi-logger (accuracy of ± 0.05%, Omega, Inc., Norwalk,
USA). After attaining the target temperature, the alumina crucible
containing the sample was slowly pushed into the hot zone using the
thermocouple to prevent air ingress and also minimize the reactions
taking place during heating up. During heating, the cathode powder was
Fig. 1. X-ray diffractogram of an untreated sample containing black mass
(mixture of cathodes and anode materials).
Table 1
Elemental composition of the black mass of spent Li-ion batteries used in this study (wt.%).
Composition C Li Ni Co Mn Al Cu Fe O
Content wt.% 40.90 3.61 2.38 19.80 5.98 1.82 0.95 0.09 Balance
Fig. 2. Flowsheet of carbothermic reduction process of the spent lithium-ion battery black mass and the proposed dry grinding – CUAWL process for selective
extraction of lithium and maximized recovery of the high-value metals by acid leaching. (For interpretation of the references to colour in this figure legend, the reader
is referred to the web version of this article.)
B. Makuza et al.

4
reduced by the graphitic anode powder present in the mixture. Once the
pre-determined roasting time elapsed, the sample was slowly pulled
back to the cool zone using the thermocouple to allow fast cooling.
Some factors that may influence the reduction roasting experiment
were investigated, such as roasting temperature (500–1000 ◦
C) and
roasting time (15–120 min).
The roasted product was weighed to determine the relative weight
loss, and a sample of 1 ± 0.005 g was leached with ultra-pure water
(UPW) in a water bath (leaching temperature 50 ◦
C, liquid-solid ratio 50
mL/g, magnetic stirring speed 100 rpm, leaching time 3 h). The effect of
grinding (grinding speed 3000 rpm, grinding time 1–10 min), sonication
(ultrasound frequency 40 kHz), and carbonation (CO2 flow rate 25–100
mL/min) on the leaching efficiency of Li were also studied. After water
leaching, the solid residue from water leaching was digested using a
sulphuric acid solution (leaching temperature 80 ◦
C, liquid-solid ratio
20 mL/g, acid concentration 4 M, magnetic stirring speed 100 rpm,
leaching time 3 h). The residue from sulphuric acid leaching was further
digested completely using aqua regia to determine the percentage of
undissolved high-value metals (leaching temperature 95 ◦
C, acid volume
20 mL, magnetic stirring speed 100 rpm, leaching time 4 h).
The leaching efficiency of metals was mainly used to evaluate the
efficiency/performance of the roasting process, and the leaching effi
ciency is calculated as follows;
ηw =
[
Cw Vw
CwVw + CsVs + CaVa
]
× 100% (1)
ηs =
[
Cs Vs
CwVw + CsVs + CaVa
]
× 100% (2)
ηa =
[
CaVa
CwVw + CsVs + CaVa
]
× 100% (3)
where ηw (%), ηs (%) and ηa (%) represents the water, sulphuric acid, and
aqua regia leaching efficiency respectively of element “i”; Cw (g/L), Cs
(g/L), and Ca (g/L) represents the concentration of element “i” in water,
sulphuric acid, and aqua regia leaching solution, respectively, and Vw
(L), Vs (L), and Va (L) represent the volume of leaching solution of
element “i” in water, sulphuric acid, and aqua regia leaching solution,
respectively.
2.3. Measurement and characterization
Simultaneous thermogravimetric analysis and differential thermal
analysis (TG-DTA, HCT-4, Henven, China) were used to investigate the
thermal decomposition behaviors of the black mass at a heating rate of
10 ◦
C/min under an argon atmosphere. For the TG-DTA measurements,
the temperature range was from room temperature to 1500 ◦
C. The
concentrations of the gaseous reduction product CO and CO2 were
continuously measured using a gas analyzer (Gasboard-3000Plus, Cubic-
Ruiyi, China). The concentrations of all metals in the leachate were
determined by inductively coupled plasma-optical emission spectrom
etry (ICP-OES, PerkinElmer’s-Avio 500). The particle size distribution of
powders was performed using a laser diffraction particle size analyzer
(Malvern Mastersizer MS2000) with the Hydro S dispersion unit (ca
pacity 800–900 mL). Reduced products from the experiments were
mounted into epoxy, ground, and polished to observe their elemental
distribution and morphology using a scanning electron microscope
(SEM; TESCAN–Mira3 h, Czech Republic), complemented by an EDS
detector (Oxford X MAX20, UK). Phase identification in the reduced
samples was conducted using an X-ray powder diffractometer (XRD, D/
Max-2500/PC, Rigaku, Japan) using Cu-Kα radiation for their qualita
tive mineralogical composition. X-ray photoelectron spectroscopy (XPS)
analysis was performed using a Thermo Scientific K-Alpha instrument
equipped with Al Kα monochromatized radiation at constant analysis
energy (CAE) of 50 eV to determine the distribution density and binding
energy of the elements in the materials.
3. Results and discussion
3.1. Theoretical feasibility and thermal analysis of carbothermic
reduction
As reported by Mao et al. (2018) and other numerous researchers,
the active cathode material (LiCoO2, LiMn2O4, and LiNiO2) is not
reduced directly by the graphite (Liu et al., 2019; Mao et al., 2018;
Massarotti et al., 2002; Vieceli et al., 2021). Instead, the active cathode
material decomposes first, as depicted by the elementary reactions
(4–6).
(i) Thermal decomposition
4LiCoO2 = 2Li2O + 4CoO + O2(g) (4)
2.4LiMn2O4 = 1.6Mn3O4 + 1.2Li2O + O2(g) (5)
4LiNiO2 = 2Li2O + 4NiO + O2(g) (6)
After thermal decomposition, the resultant metal oxides are reduced by
graphite (anode material), and the possible chemical reactions corre
sponding to the reaction between the thermally decomposed cathode
material and graphite are depicted by reactions (7–14). The standard
Gibbs free energy change (ΔG) of the carbothermic reduction of the
decomposed cathode materials calculated using HSC 6.2 (Roine, 2018)
and the TG-DTA analysis on the decomposition and carbothermic
reduction of the black mass along with the off-gas CO and CO2 analysis is
illustrated in Fig. 4a,b. Thermodynamic computations were only
considered for the CTR reactions of the decomposed cathode material.
The active cathode material decomposition temperatures were taken
from reference works (Massarotti et al., 2002; Toma et al., 2020; Yue
et al., 2018).
(ii) Carbothermic reduction of decomposed cathode material
Fig. 3. Experimental setup for carbothermic
reduction of the black mass. 1. Pressure gauge;
2. Mass flow controller; 3. Valve; 4. Crucible
with the sample; 5. Thermocouple tip attached
to crucible; 6. Thermal insulation block; 7.
Thermocouple handle for pushing and pulling
the sample in the quartz tube; 8. Temperature
data logger; 9. Vacuum inlet; 10. Off gas outlet
to gas analyzer; 11. Gas analyzer off-gas outlet;
12. Off-gas readings; 13. Temperature readings.
(For interpretation of the references to colour in
this figure legend, the reader is referred to the
web version of this article.)
B. Makuza et al.

5
2CoO + C = 2Co + CO2(g)ΔGo
= − 0.144T + 36.18 ( − 50.2kJ / mol at 600o
C) (7)
CoO + CO(g) = Co + CO2(g) ΔGo
= 0.0164T − 43.98 ( − 34.1 kJ / mol at 600o
C) (8)
2Mn3O4 + C = 6MnO + CO2(g) ΔGo
= − 0.251T − 0.139 ( − 150.7 kJ / mol at 600o
C) (9)
Mn3O4 + CO(g) = 3MnO + CO2(g) ΔGo
= − 0.0368T − 62.13 ( − 84.2 kJ / mol at 600o
C) (10)
2MnO + C = 2Mn + CO2(g) ΔGo
= − 0.149T + 334.79 (245.4 kJ / mol at 600o
C) (11)
MnO + CO(g) = Mn + CO2(g)ΔGo
= 0.0141T + 105.33 (113.8 kJ / mol at 600o
C) (12)
2NiO + C = 2Ni + CO2(g) ΔGo
= − 0.179T + 31.93 ( − 75.5 kJ / mol at 600o
C) (13)
NiO + CO(g) = Ni + CO2(g) ΔGo
= − 0.0012T − 46.1 ( − 46.8 kJ / mol at 600o
C) (14)
(iii) Oxidation reactions
C + O2(g) = CO2(g) ΔGo
= − 0.0018T − 394.47( − 395.6 kJ / mol at 600o
C) (15)
2C + O2(g) = 2CO(g)ΔGo
= − 0.179T − 270.34 ( − 377.7 kJ / mol at 600o
C) (16)
(iv) Boudouard reaction
C + CO2(g) = 2CO(g) ΔGo
= − 0.177T + 124.13 (17.9 kJ / mol at 600o
C) (17)
Regarding the oxidation reactions of carbon (reactions 15–17), as
envisaged in the thermodynamic calculations (Fig. 4a), reaction (15) is
favored at temperatures lower than 700 ◦
C, whereas reaction (16) is
expected to dominate at 700 ◦
C and above, which aligns with the TG-
DTA result (Fig. 4b) as significant CO(g) evolution occurred from 700
◦
C onwards.
Roasting is essential to facilitate the carbothermic reduction of the
decomposed cathode material as the ΔG values of reactions (7), (9–11),
and (13) become more negative with increasing temperature. The
resultant metal oxides from the decomposition of the active cathode
material can be reduced by C and CO(g). NiO and CoO can be fully
reduced by C and CO(g) to form Ni and Co respectively, Mn3O4 is reduced
to form MnO, which cannot be reduced further to Mn within the tem
perature range plotted, and the decomposition product Li2O reacts with
CO2(g) to form Li2CO3. However, reaction (18) shows an increase in ΔG
with increasing temperature, which implies that increasing the roasting
temperature further might not benefit the generation of Li2CO3 and
above 962 ◦
C, the formed Li2CO3 can be reduced by graphite forming
Li2O (reaction 19).
(v) Formation of lithium carbonate
Li2O + CO2(g) = Li2CO3 ΔGo
= 0.134T − 174.80 ( − 94.4 kJ / mol at 600o
C) (18)
(vi) Carbothermic reduction of lithium carbonate
Li2CO3 + C = Li2O + 2CO(g) ΔGo
= − 0.311T + 299 (112.4 kJ / mol at 600o
C) (19)
The decomposition profile and the carbothermic reduction of the
decomposed cathode material can be split into 3 distinct regions
(Fig. 4b). There is no mass loss in Region I, and the off-gas results show
no traces of gas evolution. Mass loss started in Region II at around 190
◦
C, resulting in the evolution of CO2. As reported by Toma et al. (2020),
the decomposition of LiNiO2 starts around 200–220 ◦
C (reaction 6),
generating O2 gas. Thus the CO2 evolution around 190 ◦
C (Fig. 4b) is
presumably from the oxidation of graphite by O2 gas generated from
reaction 6. The total absence of mass loss in the TG-DTA results by Yue
et al. (2018) depicted that LiCoO2 material was not decomposed at a
temperature below 650 ◦
C. According to Massarotti et al. (2002), the
decomposition of LiMn2O4 commences around 600 ◦
C, and the decom
position product after 800 ◦
C is reduced completely into Mn3O4 and
MnO. Thus the mass loss in the temperature range of 600–900 ◦
C and its
corresponding CO and CO2 evolution are likely associated with the
decomposition of LiCoO2 and LiMn2O4 (reactions 4 and 5) and subse
quent oxidation of graphite by the resultant O2 gas (reactions 15 and
Fig. 4. a) Plot of the relationship between ΔG◦
(kJ/mol) and temperature ( ◦
C) for reactions (7–19), b) TG-DTA analysis of the mixture of the anode and cathode
material (Heating rate = 10 ◦
C/min; Argon flow rate = 50 mL/min).
B. Makuza et al.

6
16). The endothermic peak at 830 ◦
C is a significant carbothermic
reduction process as it takes place simultaneously with the highest in
tensity of CO(g) evolution and abrupt mass loss (6.64%). Based on the
analysis, the influence of carbothermic reduction roasting temperature
in the range of 500–1000 ◦
C was investigated, aiming to attain
maximum selective recovery of Li2CO3.
3.2. Effect of roasting temperature
The effect of roasting temperature on the leaching efficiency of Li, Ni,
Mn, Co, Cu, Al, and Fe was investigated under the following roasting
conditions: roasting temperature of 500− 1000 ◦
C at 100 ◦
C intervals
and 60 min roasting time. The temperature profile during the roasting
process and the corresponding CO and CO2 concentrations in the off-gas,
the particle size distribution, and the x-ray diffractogram of the roasted
product for the range 500–1000 ◦
C are illustrated in Fig. 5a-d.
The temperature profile illustrates that the fast heating and the rapid
cooling mechanism was achieved (Fig. 5a) and, intense CO2 and CO
peaks appeared shortly after the target temperature was reached
(Fig. 5b). The peaks were attributed to the interaction of the thermally
decomposed cathode material with graphite, represented by Eqs. (7-
17). At 700 ◦
C and 800 ◦
C, the CO peaks show a surge, which could
result from multiple consecutive and parallel reactions coinciding. CO2
is the most dominant gas product at temperatures below 800 ◦
C, as seen
in Fig. 5b, and it also conforms with the thermodynamic computation
and TG-DTA result (Fig. 4b). Thus, stronger reducing conditions are
produced at higher reaction temperatures, while lower temperatures
result in less reducing conditions and slower kinetics (Barker et al.,
2003).
With increasing roasting temperature, the particle size increased
attributed to particle agglomeration (Fig. 5c and Figure S3) (Chen et al.,
2010). For instance, the particle size distribution (PSD) shows 50%
passing 14.845 µm after CTR at 600 ◦
C (Figure S3b), and it rises to
23.341 µm after CTR at 1000 ◦
C for 60 min (Figure S3f), which proves
particle agglomeration. Since there is more reduction with increasing
temperature, at lower temperatures, we are prone to attain metal oxides,
and at high temperatures, we obtain alloy(s) as depicted by the transi
tion from metal oxide to metallic form in Figure S4a-f. Moreover, the
different distribution of elements before and after roasting shows that
the heavy metals in the untreated cathode material were transformed to
alloy form with increasing temperature, as illustrated in Figure S4a-f.
The heavy metals distribution after reduction roasting transitioned from
random distribution (Figure S1) to a uniform distribution (Figure S4),
which confirms the transition from lithiated metal oxide to alloy as
depicted by the positioning of the metals in the same region
(Figure S4a-f).
Fig. 5. Carbothermic reduction roasting of the black mass for the temperature range 500–1000 ◦
C for 60 min: a) temperature profile, b) the corresponding CO(g) and
CO2(g) concentration in the off-gas, c) particle size distribution, and d) X-ray diffractogram and corresponding mass loss change at each temperature: d1) 500 ◦
C, d2)
600 ◦
C, d3) 700 ◦
C, d4) 800 ◦
C, d5) 900 ◦
C, and d6) 1000 ◦
C. (For interpretation of the references to colour in this figure legend, the reader is referred to the web
version of this article.)
B. Makuza et al.

7
According to Fig. 5d, the roasting temperature significantly in
fluences the weight loss of the roasted material (Liu et al., 2019). The
differences in the weight loss (Δwt%) of the roasted samples depict that
the weight loss increases with increasing roasting temperature. At 1000
◦
C, there is a weight loss of approximately 30%, almost triple the weight
loss at 500 ◦
C. The cumulative CO formation with increasing roasting
temperature reduced the decomposed metal oxides further, which also
contributed to increased weight loss with increasing roasting tempera
ture (Fig. 5d). The off-gas peaks are gradually getting broader with
increasing temperature, and this corresponds to the increasing weight
loss with increasing temperature illustrated in Fig. 5d.
The XRD peaks of the active cathode material before roasting are
indexed to be LiCoO2, LiMn2O4, and LiNiO2 (Fig. 1), and they disappear
after reduction roasting in the temperature range 500− 1000 ◦
C. Instead,
some diffraction peaks of Li2CO3, Ni, Co, CoO, and MnO are observed
(Fig. 5d). These significant phases of the cathode materials observed
after reduction roasting are consistent with the XRD analysis results by
Liu et al. (2019) and Lombardo et al. (2019). The results depict that
lower temperatures were associated with less reduction as significant
CoO peaks were observed at 500 ◦
C and 600 ◦
C. At 600 ◦
C, the CoO
peaks gradually reduced and finally disappeared afterward. The XRD
peak intensity for graphite in the roasted mixture is relatively large, and
this was expected because of the excessive amount of graphite present in
the mixture; hence, the graphite would not be wholly consumed. How
ever, the high graphite content in the reduced product is susceptible to
deter maximum selective extraction of Li2CO3 as it gets absorbed by the
graphite (Lombardo et al., 2020; Makuza et al., 2021).
Fig. 6a,b shows the water leaching efficiency of Li and acid leaching
efficiency of the target metals after roasting. The leaching efficiency in
the temperature range of 500–1000 ◦
C remained above 77% (Fig. 6a)
because the active cathode material had been entirely decomposed, as
seen from the absence of peaks ascribed to the cathode material in the
XRD patterns (Fig. 5d).
Maximum recovery of Li (84.08% Li) was attained at 600 ◦
C, after
which a steady and slow decrease in the leaching efficiency with
increasing roasting temperature was observed. By utilizing thermody
namic calculations (reaction 18), higher roasting temperatures deter
the formation of Li2CO3, which is augmented by the decrease in the
Li2CO3 peaks with increasing roasting temperature and ultimately the
absence of Li2CO3 peaks at 900 ◦
C and 1000 ◦
C (Fig. 5d). At 400 ◦
C, the
Li leaching efficiency was a mere 30% because the active cathode ma
terial had not been wholly decomposed, clarified by the presence of
peaks ascribed to LiCoO2 and LiMn2O4 in the XRD pattern (Figure S5).
On the contrary, higher roasting temperatures have adverse effects
on the extent of sulphuric acid dissolution reactions (Liu et al., 2019).
Fig. 6b shows that an increase in the roasting temperature deters the
acid leaching efficiency of the target metals significantly. The acid
leaching efficiency of the high-value metals was greater than 99% at 500
◦
C but dropped sharply with a continuous increase in the roasting
temperature (Fig. 6b). For instance, the acid leaching efficiency of the
high-value metals Ni, Co, and Mn dropped to 19.98%, 45.76%, and
96.56%, respectively, after roasting at 800 ◦
C and further dropped to
18.33%, 25.98%, and 24.10%, respectively after roasting at 1000 ◦
C.
The drop in the leaching efficiency of the target metals can be partially
attributed to calcine agglomeration with increasing temperature
(Fig. 5c) (Chen et al., 2010). Furthermore, the transition to alloy form is
possibly another important reason for the drop in the leaching efficiency
(Figure S4).
Considering energy conservation, enhanced selective recovery of
Li2CO3, and the maximized recovery of the high-value metals (Fig. 6),
the optimum roasting temperature was fixed at 600 ◦
C for the following
experiments.
3.3. Development of dry grinding and CUAWL process for enhanced
recovery of high-value metals
The roasted product was ground for 1 min at 3000 rpm and subjected
to ultrasonic-assisted water leaching under a continuous bubbling of
carbon dioxide gas to investigate the influence of dry grinding and
CUAWL method on the selective recovery of Li and the maximized acid
recovery of the high-value metals. The results are shown in Fig. 7.
The water leaching efficiency of Li in the absence of dry grinding and
CUAWL was 84.08%, and it increased to 85.60% after grinding for 1 min
at 3000 rpm. The combination of grinding and sonication further
increased the Li leaching efficiency to 87.14%. A positive effect was also
noted from the combination of grinding, sonication, and carbonation as
the leaching efficiency further increased to 89.13% under the same
leaching conditions.
In order to further analyze the products of carbothermic reduction
roasting and dry grinding - CUAWL, XPS analysis was performed on the
roasted black mass before and after dry grinding - CUAWL (Fig. 8).
Fig. 8a-f shows the appearance of relevant peaks corresponding to
Li2CO3, Ni, MnO, CoO, and graphite. The C 1 s spectrum before dry
grinding - CUAWL showed peaks at 283.90 eV and 288.63 eV. The
283.90 eV peak was attributed to graphite present in the mixture, and
the 288.63 eV peak was Li2CO3. There are only two peaks of O 1 s, which
are 528.98 eV and 531.36 eV, respectively. By utilizing confirmations by
Verdier et al. (2007), we can ascertain that the peak near 531.36 eV
corresponds to Li2CO3, and the peak near 528.98 eV is the characteristic
peak of metal oxide, resulting from the reduced active cathode
Fig. 6. Leaching efficiency of the black mass roasted at 500–1000 ◦
C for 60 min: a) water leaching efficiency of the roasted black mass in the absence of dry grinding
- CUAWL as a function of the roasting temperature, b) acid leaching efficiency of the metals in the water leaching residue (leaching temperature 80 ◦
C, acid
concentration 4 M, leaching time 3 h).
B. Makuza et al.

8
materials. After dry grinding and CUAWL, the peak shape of the Li 1 s
(54.93 eV) became narrow (peak area reduced to about 25%), and the
peak intensity became much weaker, which shows that the majority of Li
had been leached out. The detectable O–C bond in C 1 s (~285 eV) after
dry grinding and CUAWL is attributed to adventitious carbon contami
nation from grinding and exposure to the atmosphere.
The Co 2p core peak before dry grinding and CUAWL is divided into
Co 2p1/2 and Co 2p3/2 as the split spin-orbit components (Δmetal =
16.68 eV), each of which has a satellite peak. In the Co2p spectra,
802.36 eV, 795.79 eV, 784.32 eV, 779.93 eV correspond to the average
oxidation states of Co2+
observable from the apparent satellite features
and 778.20 eV represents cobalt. The CoO had not been completely
reduced as there was still a vast amount of Co2+
. The Mn 2p core peak is
divided into Mn 2p1/2, and Mn 2p3/2 as the split spin-orbit components
(Δmetal=11.16 eV), and it has a satellite peak (~647 eV) that is not
present for either Mn2O3 or MnO2, and thus it should represent MnO.
The Ni 2p3/2 peak (852.6 eV) is attributed to metallic nickel, and the Ni
2p peaks of the reduced LiNiO2 after dry grinding and CUAWL has a
complex structure that is a combination of core-level and satellite
features.
The XPS spectra of Ni 2p, Mn 2p, Co 2p, and O 1 s after dry grinding
and CUAWL increase in peak width and reveal a shift in their peak po
sitions towards the higher binding energy side attributed to a decrease in
particle size after grinding. This effect is well known in XPS, giving rise
to size-dependent binding energy (BE) shifts relative to the BE for bulk
metal. The binding energy of core orbitals is strongly size-dependent due
to size effects on screening and relaxation in the XPS core-hole final state
(Dai et al., 2017).
3.3.1. Effect of roasting time
The effect of roasting time on the leaching efficiency of Li, Ni, Mn,
Co, Cu, Al, and Fe was investigated under the following roasting con
ditions: roasting time of 15–120 min and roasting temperature of 600 ◦
C.
Fig. 9a-d shows the water leaching efficiency of Li, the acid leaching
efficiency of the target metals, CO and CO2 off-gas concentrations during
CTR, and the x-ray diffractogram of the roasted product.
The Li water leaching efficiency gradually decreased with an in
crease in roasting time. As observed in Fig. 9a, the maximum recovery of
Li (91.68% Li) could be attained after 15 min of roasting, which implies
that the CTR rate was rapid. With the holding time increased to 30 min,
the lithium leaching efficiency was stagnated at 91.66%. A continuous
increase in the holding time to 60 and 120 min resulted in a further
decrease in Li leaching efficiency to 89.14%.
A decrease in the acid leaching efficiency of the high-value metals
with prolonged roasting time was also observed in Fig. 9b, which could
be attributed to the resultant formation of metallic phases after CTR. An
increase in particle size with prolonged heating was also noted as the
particle size analysis shows 50% passing 14.731 µm after roasting for 30
min (Figure S6a), and it rose to 14.845 µm after roasting for 60 min
(Figure S3b). The CO2 and CO peaks were alike (roughly 5.25% CO2 and
1.25% CO) for 15, 30, 60, and 120 min of roasting (Fig. 9c), contributing
Fig. 7. The effect of grinding, sonication, and carbonation on the selective
recovery of lithium (roasting temperature = 600 ◦
C, roasting time = 60 min,
grinding time = 1 min, grinding speed = 3000 rpm, leaching time = 3 h, CO2
flow rate = 100 mL/min, ultrasound frequency = 40 kHz).
Fig. 8. XPS spectra of a) Li 1 s, b) C 1 s, c) O 1 s, d) Ni 2p, e) Mn 2p, and f) Co 2p core peaks of the black mass after roasting and after dry grinding - CUAWL (roasting
temperature = 600 ◦
C, roasting time = 60 min, grinding time = 1 min, grinding speed = 3000 rpm, leaching time = 3 h, CO2 flow rate = 100 mL/min).
B. Makuza et al.

9
to the insignificant weight loss change (Δwt%) and microstructural
changes with prolonged roasting time (Fig. 9d).
Considering energy conservation, enhanced selective recovery of
Li2CO3, and the maximized recovery of the high-value metals (Fig. 9),
the optimum roasting time was fixed at 30 min for the following
experiments.
3.3.2. Effect of leaching duration
The effect of dry grinding and CUAWL time on the leaching effi
ciency of Li is illustrated in Fig. 10, which shows that dry grinding and
CUAWL improved the leaching efficiency of Li, especially in the initial
stages.
A rapid recovery rate of Li was observed within the first 30 min of the
leaching process, with 85.59% of Li being leached within the first 30
min, which is higher than the Li recovery achieved after 3 h in the
absence of dry grinding and CUAWL. After that, the recovery rate of Li
increases steadily. The faster leaching rate for dry grinding and CUAWL
could be attributed to the reduced particle size, ultrasonic cavitation,
and enhanced Li2CO3 solubility.
3.3.3. Effect of milling
The effect of milling on the water leaching efficiency of Li and the
recovery rate of high-value metals is illustrated in Fig. 11a-c.
An increase in the leaching efficiency with decreasing particle size
Fig. 9. Analysis of the black mass after roasting at 600 ◦
C for 15–120 min: a) dry grinding and CUAWL efficiency as a function of the roasting time (grinding time =
1 min, grinding speed = 3000 rpm, CO2 flow rate = 100 mL/min, ultrasound frequency= 40 kHz), b) acid leaching efficiency of metals in the water leaching residue
(leaching temperature 80 ◦
C, acid concentration 4 M, leaching time 3 h), c) corresponding CO and CO2 off-gas concentrations during roasting and d) X-ray dif
fractogram and weight loss after roasting: d1)15, d2) 30, d3) 60, and d4)120 min.
Fig. 10. Effect of leaching duration on the selective recovery of lithium by dry
grinding and CUAWL (roasting temperature = 600 ◦
grinding time = 1 min, grinding speed = 3000 rpm, CO2 flow rate = 100 mL/
min, ultrasound frequency = 40 kHz).
B. Makuza et al.

10
was observed, which conforms with the theory (TaysserLashen et al.,
2016). Before grinding, the particle size distribution was 50% passing
14.8 µm, and dropped to 14.1 µm and ultimately 13.4 µm after 1 and 2.5
min of grinding, respectively (Figure S6a-c). The Li water leaching ef
ficiency increased accordingly from 88.91% before grinding to 91.68%,
92.25%, and 92.60% after 1, 2.5, and 10 min of grinding, respectively
(Fig. 11a). As the metal particle size decreased, the total surface area of
particles and the active spots of the reaction increased, which sped up
the reaction. However, after 10 min of grinding, the particle size dis
tribution increased to 50% passing 18.3 µm (Figure S6d), attributed to
strong inter-particle aggregation promoted by intensive grinding
(negative milling)(Guzzo et al., 2015). A similar aggregation
phenomenon has been reported during the synthesis of LiFePO4 cathode
material after prolonged milling time (Zhang et al., 2010).
The positive effect of grinding on the recovery of high-value metals
could be further extended to the black mass roasted at 1000 ◦
C. Before
grinding, the roasted material had limited solubility in sulphuric acid.
However, after grinding for 1 and 2.5 min, the particle size decreased
from 23.3 µm before grinding to 16.1 µm and 14.8 µm respectively, after
grinding (Figure S7a-c). The leaching efficiency of the high-value
metals increased sharply after l minute of grinding and progressed
with a steady increase from 2.5 min onwards (Fig. 11c). The leaching
efficiency of Mn, Ni, and Co increased from 24.10%, 18.33%, and
25.98% before grinding to 75.53%, 56.22%, and 80.68% after 10 min of
grinding at 3000 rpm, respectively. Since grinding is an energy-intensive
process, especially for extremely fine material (used in this study),
therefore, 2.5 min was chosen as the optimum grinding time for further
experiments.
3.3.4. Effect of water leaching temperature
The effect of water leaching temperature on the leaching efficiency
of Li and target metals is illustrated in Fig. 12a,b. Fig. 12a shows that
high temperatures are more favorable for the dissolution of Li2CO3 in the
water leaching solution because of the increased kinetics. A maximum
recovery of Li (92.25% Li) was attained at 50 ◦
C, and the Li recovery rate
gradually decreased with a decrease in leaching temperature up to a
recovery rate of 85.54% at 20 ◦
C (Fig. 12a).
The solubility of CO2(g) in water increases with a decrease in tem
perature (Wiebe and Gaddy, 1940), and Eqs. (20-23) illustrate the
carbonation mechanism.
CO2(g) + H2O = CO2(aq) + H2O (20)
CO2(aq) + H2O = H2CO3 (21)
Li2CO3 + H2CO3 = 2LiHCO3 (22)
H2CO3⇄ HCO−
3 + H+
⇄CO2−
3 + 2H+
(23)
When the temperature was lowered from 50 ◦
C, the concentration of
CO2(aq) increased, forcing reaction 23 to the right, which lowered the
pH of the water leaching solution and ultimately led to the dissolution of
heavy metals (Fig. 12a). The recovery of heavy metals in the water
leaching solution leached at 50 ◦
C was minimum, and a gradual increase
was observed with a continuous decrease in leaching temperature. At 50
◦
C the leaching efficiencies for Ni, Mn, Co, Cu, Al, and Fe was 0.43%,
0.52%, 0.49%, 0.04%, 0.11%, and 0.29%, respectively, and it increased
to 1.43%, 6.61%, 0.87%, 13.95%, 11.07%, and 3.39%, respectively,
after water leaching at 20 ◦
C which showed the negative effect of lower
leaching temperatures on the selective recovery of Li2CO3 (Fig. 12a). By
fixing the water leaching temperature at 50 ◦
C, high purity Li2CO3 could
be obtained.
3.3.5. Effect of CO2 flow rate
The effect of CO2 flow rate on the leaching efficiency of Li and re
covery of target metals is illustrated in Fig. 13a,b. As shown in Fig. 13a,
the increase of the CO2 flow rate enhanced the dissolution of Li2CO3. The
increase in the leaching efficiency with increasing CO2 flow rate could
be attributed to the increase of the volumetric mass transfer coefficient
of the liquid to solid phases (Wang and Hu, 2020; Yi et al., 2011). The
recovery efficiency of the high-value metals hardly shows any change, as
the CO2(g) flow rate does not affect the leaching efficiency, given that
water leaching temperature is fixed above 50 ◦
C (Fig. 13b).
3.3.6. Further separation and refining
After dry grinding and CUAWL, the recovered filtrate was subjected
to evaporative crystallization at 95 ◦
C to obtain Li2CO3. High-purity
Li2CO3 was attained (99.2%) without any prior purification process,
Fig. 11. Effect of milling time on the: a) selective recovery of lithium by dry
grinding and CUAWL (roasting temperature = 600 ◦
grinding speed = 3000 rpm, CO2 flow rate = 100 mL/min, ultrasound fre
quency = 40 kHz, leaching time = 3 h), b) acid leaching efficiency of metals in
the water leaching residue for the black mass roasted at 600 ◦
C and, c) acid
leaching efficiency of metals in the water leaching residue for the black mass
roasted at 1000 ◦
C (leaching temperature 80 ◦
C, acid concentration 4 M,
leaching time 3 h).
B. Makuza et al.

11
which was much higher than the other reported methods with a purity of
90.0% (Yang et al., 2016), 93.8% (Torres et al., 2020), and 95% (Guzolu
et al., 2017). Fig. 14 shows the x-ray diffractogram and SEM micrograph
of the recovered Li2CO3 and the acid leaching residue.
The x-ray diffractogram of the Li2CO3 recovered after evaporative
crystallization of the LiHCO3 solution is consistent with the standard
PDF card of Li2CO3 (JCPDS Card No. 22–1141), indicating that the ob
tained Li2CO3 has well-crystallized particles (Yan Wang et al., 2019).
The SEM micrograph shows that the Li2CO3 produced has small particles
with a compact cauliflower-like spherulite morphology made of
plate-like facets. The fine Li2CO3 particle size (about 1–5 µm)(Fig. 14b)
promotes the interfacial reaction during cathode regeneration (Liu et al.,
2014). Furthermore, the spherulite product is favorable for the pro
duction of battery-grade lithium carbonate as it improves the flowability
and compressibility of the Li2CO3 product (Yang et al., 2019), and such
spherical and uniform morphology when retained in the cathode ma
terial after regeneration results in promising electrochemical property
(Sa and Sisson, 2015).
The high-value metals remaining in the water leaching residue were
recovered by sulphuric acid leaching (leaching temperature 80 ◦
C, acid
concentration 4 M, leaching time 3 h). The as-obtained filtrate is rich in
high-value metals (Ni 1.93 g/L, Co 14.9 g/L, Mn 4.29 g/L), and it can be
further treated using separation technologies such as precipitation
(Dutta et al., 2018), solvent extraction, and ion exchange (Nguyen and
Lee, 2018) according to the preferred cathode material regeneration
method (Makuza et al., 2021). According to Fig. 14c, the x-ray dif
fractogram of the acid leaching residue shows the absence of peaks
attributed to metal oxides. Instead, a major graphite characteristic peak
at 2θ = 26.4◦
is observed and perfectly matches the graphite pattern
(JCPDS No. 41–1487). SEM image shows that the graphite particles have
an irregularly shaped micrometer size flake-like morphology with a
smooth surface. The EDS results depict that most metals were digested
and contain a scanty amount of trace metal elements (Ni 0.04%, Co
0.05%, Mn 0.00%, Al 0.75%, Cu 0.05%, and Fe 0.05%). The market for
recycled graphite material has expanded, and this graphite residue can
be recycled back into products such as brake linings and thermal insu
lation (U.S. Geological Survey, 2019).
4. Conclusions
This paper proposed a rationale for the controllable carbothermic
reduction method for enhanced selective recovery of Li2CO3 and maxi
mized acid recovery of high-value metals. The developed method in
corporates carbothermic reduction roasting, dry grinding - carbonated
ultrasound-assisted water leaching (CUAWL), and sulfuric acid leaching.
1 The microstructural analysis results depict that the black mass
(mixture of anode and cathode materials) after roasting under opti
mum conditions of 600 ◦
C for 30 min was primarily transformed into
Li2CO3, Ni, Co, CoO, and MnO.
Fig. 12. Effect of leaching temperature on the a) selective recovery of lithium by dry grinding and CUAWL (roasting temperature = 600 ◦
grinding time = 2.5 min, CO2 flow rate = 100 mL/min, ultrasound frequency = 40 kHz, leaching time = 3 h), b) acid leaching efficiency of the metals in the water
leaching residue (leaching temperature 80 ◦
C, acid concentration 4 M, leaching time 3 h).
Fig. 13. Effect of CO2 flow rate on the a) selective recovery of lithium by dry grinding and CUAWL (roasting temperature = 600 ◦
C, roasting time = 30 min, grinding
time = 10 min, grinding speed =1800 rpm, ultrasound frequency= 40 kHz, leaching time = 3 h), b) acid leaching efficiency of the metals in the water leaching
residue (leaching temperature 80 ◦
C, acid concentration 4 M, leaching time 3 h).
B. Makuza et al.

12
2 High-speed grinding enhanced the selective recovery of Li2CO3 and
maximized the acid recovery of high-value metals.
3 The ultrasonic cavitation effects induced by sonication (frequency
40 kHz) enhanced the Li leaching efficiency attributed to the
chemical impacts and mechanical action between solid and liquid
interfaces, thereby facilitating desorption and separation of the
roasted products.
4 Carbonation transformed the lowly soluble Li2CO3 into more soluble
LiHCO3 (CO2 flow rate 100 mL/min, leaching time 3 h, leaching
temperature 50 ◦
C). The recovered leach solution (LiHCO3) is sub
jected to evaporative crystallization to attain high-purity Li2CO3
(99.2%). Subsequently, the water-leached residue was digested by 4
M H2SO4 at 80 ◦
C for 3 h. The optimized experimental results ach
ieved improved leaching efficiencies of up to 92.25% Li, and over
99% of the high-value metals Ni, Mn, and Co could be leached out
from the reduced active cathode materials without adding reductant.
The developed method demonstrated its flexibility in recycling spent
lithium-ion batteries as it was performed on a black mass of various
cathode material combinations (LiCoO2, LiMn2O4, and LiNiO2) and
anode material which is representative of the actual situation in the
industrial recycling facilities. Furthermore, the dry grinding and CUAWL
process is a self-sustaining, environmentally benign process that does
not require external additives.
CRediT authorship contribution statement
Brian Makuza: Investigation, Methodology, Software, Writing –
original draft. Dawei Yu: Conceptualization, Methodology, Resources,
Writing – review & editing, Supervision, Funding acquisition. Zhu
Huang: Visualization, Investigation. Qinghua Tian: Supervision,
Funding acquisition. Xueyi Guo: Supervision, Funding acquisition.
Declaration of Competing Interest
The authors declare that they have no known competing financial
interests or personal relationships that could have appeared to influence
the work reported in this paper.
Acknowledgments
This research was funded by the National Natural Science Founda
tion of China (Grant 51904350, 51922108, and 51874371), Hunan key
research and development program (Grant 2020SK2005), and the
Hunan Natural Science Foundation (Grant 2019JJ20031).
Supplementary materials
Supplementary material associated with this article can be found, in
the online version, at doi:10.1016/j.resconrec.2021.105784.
Fig. 14. a) X-ray diffractogram and b) SEM micrograph of the recovered Li2CO3 (roasting temperature = 600 ◦
C, roasting time = 30 min, grinding time = 2.5 min,
CO2 flow rate = 100 mL/min, ultrasound frequency = 40 kHz, leaching time = 3 h, evaporative crystallization temperature 95 ◦
C); c) X-ray diffractogram and d) SEM
micrograph of the acid leaching residue (leaching temperature 80 ◦
C, acid concentration 4 M, leaching time 3 h). (For interpretation of the references to colour in this
figure legend, the reader is referred to the web version of this article.)
B. Makuza et al.

13
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