XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3 3177
flotation, it becomes crucial to eliminate this binder to
restore graphite and CAMs’ distinct wettability properties.
Several researchers proposes various techniques for binder
removal before flotation, including mechanical and thermal
treatments. Mechanical treatment includes ambient tem-
perature grinding (Yu et al., 2018) and cryogenic grinding
at –196°C (Liu et al., 2020), and ultra-high shear forces to
delaminate PVDF from surfaces of active materials (Shin et
al., 2020 Zhan et al., 2020). As PVDF degrades at temper-
ature around 400–500 °C (de Jesus Silva et al., 2020 Kuila
et al., 2015), thermal treatment has demonstrated effective-
ness in partially removing PVDF and improving flotation
efficiency (Kim et al., 2004 Zhang et al., 2018 Zhang et
al., 2019 Zhan et al., 2021 Vanderbruggen et al., 2022
Qiu et al., 2022 Salces et al., 2022). The biggest concern
surrounding PVDF decomposition is the generation of
toxic off-gas such as hydrogen fluoride, polynuclear aro-
matic hydrocarbons, and halogenated hydrocarbons (Ji et
al., 2022 Rensmo et al., 2023). During thermal treatment,
carbothermic reduction of CAMs has also been reported
(Lombardo et al., 2019, 2021), hindering the possibility
of direct recycling. Water leaching of lithium in wet recy-
cling processes also results in Li losses in effluent streams
(Li et al., 2016 Xiao et al., 2017 Schwich et al., 2021
Balachandran et al., (2021) Zhang et al., 2022, Rouquette
et al., 2023).
Dihydrolevoglucosenone ((1S,5R)-6,8-Dioxabicyclo
[3.2.1]octan-4-one) or commercially known as Cyrene ™
has been identified as a green and non-toxic dipolar aprotic
solvent capable of dissolving PVDF. It is derived from bio-
mass and possesses the capability to dissolve various poly-
meric materials, as elaborated in the study by Kong &
Dolzhenko (2022). PVDF dissolution with Cyrene has been
reported to occur only at temperatures exceeding 80°C (Bai
et al., 2020). Similar findings were observed in the work of
Zhou et al., (2021) where Cyrene replaced NMP for NMC
811 cathode electrode preparation. In this work, Cyrene is
implemented to dissolve PVDF from CAM particles before
flotation. The flotation efficiency of the Cyrene pre-treated
black mass is compared to the same material pre-treated
mechanically and thermally. The ultimate goal is to estab-
lish the groundwork for an environmentally friendly flota-
tion pre-treatment step to separate CAMs from graphite
before downstream recycling processes.
METHODOLOGY
For this study, pristine NMC111 (LiNi0.33Mn0.33Co0.33O2,
MSE supplies, Product No. PO0126) and spheroidized
natural graphite (ProGraphite GmbH, product No.
1112‑1) powders were mixed at an 80:20 mass ratio to
create a model black mass (MBM), simulating binder-free
and completely liberated particles. An industrial black mass
(IBM) was provided by Envirostream Australia Pty Ltd and
mainly sourced from consumer batteries with dominating
chemistries of lithium cobalt oxide (LCO) and lithium
nickel manganese cobalt oxide (NMC). The industrial
black mass contains 38.5% C, 2.8% Li, 10.4% Ni, 3.4%
Mn, 12.9% Co (26.6% Ni+Mn+Co), 3.4% Al, and 2.2%
Cu. In its original conditions, the IBM is ‘mechanically
treated’ (M-IBM) being subjected only to shredding and
sieving. The Cyrene pre-treatment was achieved by mixing
the 80 g IBM and 400 mL Cyrene using an overhead stir-
rer at 25°C. The mixture was heated to 100 °C and held
for 1 hr, followed by hot vacuum filtration inside a drying
cabinet (as shown in Figure 1). To remove Cyrene residue,
the filter cake was further washed with hot de-ionized water
yielding C-IBM. The IBM was also pyrolyzed at 550°C
under N2 gas for 3 hours to produce P-IBM.
Flotation was conducted using a laboratory-scale
mechanically stirred flotation device (GTK Labcell from
Outotec) with automatic scraping in a 1-L cell. The
parameters were fixed and based on previous studies of
Vanderbruggen et al., (2022). For attrition, a dispersing
instrument (T25, IKA ULTRA-TURRAX ®) was utilized at
an agitation speed of 16,000 rpm for 10 min. After each
pre-treatment, the treated black mass was dispersed in tap
water. Ekofol 440 and diesel were added at a concentra-
tion of 500 g/t as a promoter, aiming at increasing the
hydrophobicity of graphite. Methyl isobutyl carbinol was
used as a frother at a concentration of 250 g/t. The airflow
rate and impeller speed were kept constant at 5 L/min and
1000 rpm, respectively. The overflow products were col-
lected after 1, 2, and 10 min. After drying in an oven for
12 h at 45°C, representative samples were analyzed for their
metal content by inductively coupled plasma-atomic emis-
sion spectroscopy (Optima 8300, PerkinElmer) and carbon
analysis (Series II CHNS/O Analyzer 2400, PerkinElmer).
The lithium concentration in the process water was mea-
sured using flame-atomic absorption spectroscopy (con-
traAA 700, Analytik Jena). The flotation recoveries were
calculated using Eq. (1).
R Ff
Cc
i
i
i =(1)
where Ri is the recovery of component i, C is the overflow
product mass, ci is the grade of element i in the overflow
product, F is the feed mass, and fi is the grade of compo-
nent i in the feed.
flotation, it becomes crucial to eliminate this binder to
restore graphite and CAMs’ distinct wettability properties.
Several researchers proposes various techniques for binder
removal before flotation, including mechanical and thermal
treatments. Mechanical treatment includes ambient tem-
perature grinding (Yu et al., 2018) and cryogenic grinding
at –196°C (Liu et al., 2020), and ultra-high shear forces to
delaminate PVDF from surfaces of active materials (Shin et
al., 2020 Zhan et al., 2020). As PVDF degrades at temper-
ature around 400–500 °C (de Jesus Silva et al., 2020 Kuila
et al., 2015), thermal treatment has demonstrated effective-
ness in partially removing PVDF and improving flotation
efficiency (Kim et al., 2004 Zhang et al., 2018 Zhang et
al., 2019 Zhan et al., 2021 Vanderbruggen et al., 2022
Qiu et al., 2022 Salces et al., 2022). The biggest concern
surrounding PVDF decomposition is the generation of
toxic off-gas such as hydrogen fluoride, polynuclear aro-
matic hydrocarbons, and halogenated hydrocarbons (Ji et
al., 2022 Rensmo et al., 2023). During thermal treatment,
carbothermic reduction of CAMs has also been reported
(Lombardo et al., 2019, 2021), hindering the possibility
of direct recycling. Water leaching of lithium in wet recy-
cling processes also results in Li losses in effluent streams
(Li et al., 2016 Xiao et al., 2017 Schwich et al., 2021
Balachandran et al., (2021) Zhang et al., 2022, Rouquette
et al., 2023).
Dihydrolevoglucosenone ((1S,5R)-6,8-Dioxabicyclo
[3.2.1]octan-4-one) or commercially known as Cyrene ™
has been identified as a green and non-toxic dipolar aprotic
solvent capable of dissolving PVDF. It is derived from bio-
mass and possesses the capability to dissolve various poly-
meric materials, as elaborated in the study by Kong &
Dolzhenko (2022). PVDF dissolution with Cyrene has been
reported to occur only at temperatures exceeding 80°C (Bai
et al., 2020). Similar findings were observed in the work of
Zhou et al., (2021) where Cyrene replaced NMP for NMC
811 cathode electrode preparation. In this work, Cyrene is
implemented to dissolve PVDF from CAM particles before
flotation. The flotation efficiency of the Cyrene pre-treated
black mass is compared to the same material pre-treated
mechanically and thermally. The ultimate goal is to estab-
lish the groundwork for an environmentally friendly flota-
tion pre-treatment step to separate CAMs from graphite
before downstream recycling processes.
METHODOLOGY
For this study, pristine NMC111 (LiNi0.33Mn0.33Co0.33O2,
MSE supplies, Product No. PO0126) and spheroidized
natural graphite (ProGraphite GmbH, product No.
1112‑1) powders were mixed at an 80:20 mass ratio to
create a model black mass (MBM), simulating binder-free
and completely liberated particles. An industrial black mass
(IBM) was provided by Envirostream Australia Pty Ltd and
mainly sourced from consumer batteries with dominating
chemistries of lithium cobalt oxide (LCO) and lithium
nickel manganese cobalt oxide (NMC). The industrial
black mass contains 38.5% C, 2.8% Li, 10.4% Ni, 3.4%
Mn, 12.9% Co (26.6% Ni+Mn+Co), 3.4% Al, and 2.2%
Cu. In its original conditions, the IBM is ‘mechanically
treated’ (M-IBM) being subjected only to shredding and
sieving. The Cyrene pre-treatment was achieved by mixing
the 80 g IBM and 400 mL Cyrene using an overhead stir-
rer at 25°C. The mixture was heated to 100 °C and held
for 1 hr, followed by hot vacuum filtration inside a drying
cabinet (as shown in Figure 1). To remove Cyrene residue,
the filter cake was further washed with hot de-ionized water
yielding C-IBM. The IBM was also pyrolyzed at 550°C
under N2 gas for 3 hours to produce P-IBM.
Flotation was conducted using a laboratory-scale
mechanically stirred flotation device (GTK Labcell from
Outotec) with automatic scraping in a 1-L cell. The
parameters were fixed and based on previous studies of
Vanderbruggen et al., (2022). For attrition, a dispersing
instrument (T25, IKA ULTRA-TURRAX ®) was utilized at
an agitation speed of 16,000 rpm for 10 min. After each
pre-treatment, the treated black mass was dispersed in tap
water. Ekofol 440 and diesel were added at a concentra-
tion of 500 g/t as a promoter, aiming at increasing the
hydrophobicity of graphite. Methyl isobutyl carbinol was
used as a frother at a concentration of 250 g/t. The airflow
rate and impeller speed were kept constant at 5 L/min and
1000 rpm, respectively. The overflow products were col-
lected after 1, 2, and 10 min. After drying in an oven for
12 h at 45°C, representative samples were analyzed for their
metal content by inductively coupled plasma-atomic emis-
sion spectroscopy (Optima 8300, PerkinElmer) and carbon
analysis (Series II CHNS/O Analyzer 2400, PerkinElmer).
The lithium concentration in the process water was mea-
sured using flame-atomic absorption spectroscopy (con-
traAA 700, Analytik Jena). The flotation recoveries were
calculated using Eq. (1).
R Ff
Cc
i
i
i =(1)
where Ri is the recovery of component i, C is the overflow
product mass, ci is the grade of element i in the overflow
product, F is the feed mass, and fi is the grade of compo-
nent i in the feed.