1706 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
agent and activator was investigated. This was compared to
PGMs recovery using IX. The extraction loading time of
both processes was also studied.
MATERIALS AND METHODS
Reagents
The chemical reagents used in this work were of analytical
grade and were procured from Merck, Sigma Aldrich, and
ACE (Pty, Ltd). Ultrapure water, hydrochloric acid (32%
w/w), ammonium hydroxide (25% w/w), sodium hydrox-
ide pellets, tin chloride di-hydrate, Triton X-100, thiourea,
palladium chloride, platinum chloride, rhodium chloride,
ferric chloride, aluminium chloride hexahydrate, magne-
sium chloride hexahydrate, and 2-mercaptobenzothiazole
were used without further purification.
Resin Used and Method of Pre-Treatment
A SAR in chloride form that operates in the 0–14 pH range
was used in this study. The functional group on it is a qua-
ternary ammonium type 1 on a macroporous polystyrene
crosslinked with divinylbenzene polymer structure. Its
capacity is 1.15 mol of chloride ions per litre of resin. The
resin was selected based on its selectivity for PGMs chloro
complexes as reported by the supplier, Purolite, and in pub-
lished literature (Silva, Hawboldt, and Zhang 2018).
Spent Autocatalytic Converter Chloride Leach
A synthetic leach solution, based on leaching spent autocat-
alyst in chloride media by other researchers, was prepared
(Saguru 2018 Firmansyah et al. 2019 Kim et al. 2011
Torrejos et al., 2020). The synthetic solution was prepared
by the dissolution of palladium chloride, platinum chloride,
rhodium chloride, ferric chloride, aluminium chloride, and
magnesium chloride in HCl. The metal compositions of
the solution used in this study, solution generated in indus-
try and that of other researchers are shown in Table 1.
The experimental work consisted of two parts, the CPE
and IX experiments which were both done in duplicate.
PGMs Extraction by CPE Procedure
A volume of 40 ml of a PGMs leach solution, at a prede-
termined pH, was placed in a 50 ml centrifuge tube. To it,
1 ml of the surfactant, Triton X-100 (10% m/v), and 1 ml
of the complexing agent, 2-MBT (1% m/v), were added
and left to stand for 15 minutes (Suoranta et al. 2015
Niemelä et al 2009). Afterwards 3 ml of the reducing and
activating agent, tin (II) chloride di-hydrate in 6M HCl
solution was added, and the open centrifuge tubes were
heated in a thermostat-controlled water bath set at 90 °C
to achieve a system equilibration temperature of 75 °C for
an incubation time of 1 hour 55 minutes (Suoranta et al.,
2015). Due to evaporative losses, heated de-ionized water
at 75 °C, which was the equilibration temperature of the
CPE system, was added to ensure constant solution volume
and system behaviour. A sample was collected for analysis
by ICP-MS for PGMs and ICP-OES for Al, Fe and Mg.
The PGMs extraction by CPE was calculated as a percent-
age of PGMs in the surfactant phase to that initially present
in the chloride leach solution as per equation 9.
E% C
C C
100
initial
initial final #=
-
(9)
where Cinitial and Cfinal are the concentration of metals
before and after extraction in the aqueous phase respectively.
Effect of Incubation Time on PGMs Extraction by CPE
The effect of incubation time on CPE extraction was con-
ducted on the leach at 494 ppm (total PGMs), pH 1.00,
1 ml Triton X-100 (10% m/v), 1 ml 2-MBT (1% m/v)
using the CPE procedure at 10 and 20% m/v tin (II) chlo-
ride di-hydrate. The incubation times investigated were 15,
45, 90 and 115 minutes. Aqueous samples were collected
and analysed for PGMs, Al, Mg, and Fe.
PGMs Extraction by Ion Exchange Procedure
A solution to resin volume ratio of 9, within typical indus-
try range, was employed (Goc et al., 2021). A volume of
Table 1. Spent auto-catalyst leach solution composition
Metal Pt (IV) Pd (II) Rh (III) Al (III) Mg (II) Fe (II) Composition Ref
Conc*
(ppm)
72 350 72 11,000 1,500 700 This study
246,000 133,000 41,200 — — 26,000 Industry Asamoah-Bekoe 1998
— 368 33 3,898 555 32 Literature Firmansyah et al. 2019
349 172 51 11,700 1704 520 Literature Kim et al. 2011
390 217 — 12,002 1835 1,226 Literature Torrejos et al. 2020
*Stands for metal concentration

Previous Page Next Page

Extracted Text (may have errors)

1706 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
agent and activator was investigated. This was compared to
PGMs recovery using IX. The extraction loading time of
both processes was also studied.
MATERIALS AND METHODS
Reagents
The chemical reagents used in this work were of analytical
grade and were procured from Merck, Sigma Aldrich, and
ACE (Pty, Ltd). Ultrapure water, hydrochloric acid (32%
w/w), ammonium hydroxide (25% w/w), sodium hydrox-
ide pellets, tin chloride di-hydrate, Triton X-100, thiourea,
palladium chloride, platinum chloride, rhodium chloride,
ferric chloride, aluminium chloride hexahydrate, magne-
sium chloride hexahydrate, and 2-mercaptobenzothiazole
were used without further purification.
Resin Used and Method of Pre-Treatment
A SAR in chloride form that operates in the 0–14 pH range
was used in this study. The functional group on it is a qua-
ternary ammonium type 1 on a macroporous polystyrene
crosslinked with divinylbenzene polymer structure. Its
capacity is 1.15 mol of chloride ions per litre of resin. The
resin was selected based on its selectivity for PGMs chloro
complexes as reported by the supplier, Purolite, and in pub-
lished literature (Silva, Hawboldt, and Zhang 2018).
Spent Autocatalytic Converter Chloride Leach
A synthetic leach solution, based on leaching spent autocat-
alyst in chloride media by other researchers, was prepared
(Saguru 2018 Firmansyah et al. 2019 Kim et al. 2011
Torrejos et al., 2020). The synthetic solution was prepared
by the dissolution of palladium chloride, platinum chloride,
rhodium chloride, ferric chloride, aluminium chloride, and
magnesium chloride in HCl. The metal compositions of
the solution used in this study, solution generated in indus-
try and that of other researchers are shown in Table 1.
The experimental work consisted of two parts, the CPE
and IX experiments which were both done in duplicate.
PGMs Extraction by CPE Procedure
A volume of 40 ml of a PGMs leach solution, at a prede-
termined pH, was placed in a 50 ml centrifuge tube. To it,
1 ml of the surfactant, Triton X-100 (10% m/v), and 1 ml
of the complexing agent, 2-MBT (1% m/v), were added
and left to stand for 15 minutes (Suoranta et al. 2015
Niemelä et al 2009). Afterwards 3 ml of the reducing and
activating agent, tin (II) chloride di-hydrate in 6M HCl
solution was added, and the open centrifuge tubes were
heated in a thermostat-controlled water bath set at 90 °C
to achieve a system equilibration temperature of 75 °C for
an incubation time of 1 hour 55 minutes (Suoranta et al.,
2015). Due to evaporative losses, heated de-ionized water
at 75 °C, which was the equilibration temperature of the
CPE system, was added to ensure constant solution volume
and system behaviour. A sample was collected for analysis
by ICP-MS for PGMs and ICP-OES for Al, Fe and Mg.
The PGMs extraction by CPE was calculated as a percent-
age of PGMs in the surfactant phase to that initially present
in the chloride leach solution as per equation 9.
E% C
C C
100
initial
initial final #=
-
(9)
where Cinitial and Cfinal are the concentration of metals
before and after extraction in the aqueous phase respectively.
Effect of Incubation Time on PGMs Extraction by CPE
The effect of incubation time on CPE extraction was con-
ducted on the leach at 494 ppm (total PGMs), pH 1.00,
1 ml Triton X-100 (10% m/v), 1 ml 2-MBT (1% m/v)
using the CPE procedure at 10 and 20% m/v tin (II) chlo-
ride di-hydrate. The incubation times investigated were 15,
45, 90 and 115 minutes. Aqueous samples were collected
and analysed for PGMs, Al, Mg, and Fe.
PGMs Extraction by Ion Exchange Procedure
A solution to resin volume ratio of 9, within typical indus-
try range, was employed (Goc et al., 2021). A volume of
Table 1. Spent auto-catalyst leach solution composition
Metal Pt (IV) Pd (II) Rh (III) Al (III) Mg (II) Fe (II) Composition Ref
Conc*
(ppm)
72 350 72 11,000 1,500 700 This study
246,000 133,000 41,200 — — 26,000 Industry Asamoah-Bekoe 1998
— 368 33 3,898 555 32 Literature Firmansyah et al. 2019
349 172 51 11,700 1704 520 Literature Kim et al. 2011
390 217 — 12,002 1835 1,226 Literature Torrejos et al. 2020
*Stands for metal concentration

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XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3 1707
45 ml of a 494 ppm PGMs leach solution was added to
5 ml of the Purolite SAR in a glass bottle with a screw top at
25, 45 and 65 °C temperature (Goc et al. 2021 Kononova
et al., 2010). The pH values under study were 1.0, 1.5,
and 2.0, as precipitation occurred from pH 2.5 and above,
a condition, which could prevent the metal from loading
onto the resin. The glass bottles were then placed in a shak-
ing incubator at 150 rpm for 24 hours (Shen et al., 2010).
The solution was then filtered, and a sample collected for
analysis by ICP-MS for PGMs and ICP-OES for Al, Fe,
and Mg. The PGMs extraction by IX was calculated as a
percentage of PGMs on the resin to that initially present in
the chloride leach solution as per equation 10.
E% C
C C
100
i
i f #=
-
(10)
Where Ci and Cf are the concentration of metals before and
after extraction in the aqueous phase, respectively.
Effect of Contact Time on PGMs Extraction by Ion
Exchange
A volume of 90 ml at pH 2 was added to 10 ml of Purolite
SAR in a conical flask (Goc et al., 2021). The reaction was
run at 25 °C and the incubator speed was set at 150 rpm
(Shen et al., 2010). Samples were collected after 15, 45, 90,
115, and 1440 minutes for PGMs, Al, Mg and Fe analysis.
Calculation of CPE and IX Concentration Factors
The concentration factor, CF, of each process was calculated
by dividing the total PGMs concentration in the surfactant
phase by the initial total PGMs concentration in the leach
before CPE, as per equation 11 (Chagnes 2020).
C C
Csurf
F
i
=(11)
Where Csurf and Ci are the total PGMs concentration in
the surfactant phase and the total PGMs concentration in
the aqueous phase respectively. All testwork was conducted
in duplicates.
RESULTS AND DISCUSSION
Cloud Point Extraction Results
Effect of pH on Extraction and Selectivity in the
Presence of 10% Tin (II) Chloride Di-hydrate
The investigation into the pH impact on PGMs CPE was
conducted with a 10% (m/v) concentration of the reducing
and activating agent, tin (II) chloride di-hydrate, follow-
ing the CPE procedure. The results, depicted in Figure 1,
illustrate the effect of pH (1.00 to 5.75) on the extraction
of Pt, Pd, Rh, Al, Fe, and Mg. The influence of pH on
PGMs extraction is significant, affecting the PGMs species
and potential ligands.
At pH 1.00, extractions were 47% Pt, 50% Pd, and
0% for Rh, Al, Fe, and Mg, compared to higher values at
pH 4.00 (99% Pt, 99% Pd, 99% Rh, 11% Al, 45% Fe,
and 45% Mg) and pH 5.75 (87% Pt, 93% Pd, 86% Rh,
22% Al, 21% Fe, and 14% Mg). The low extractions at
pH 1.00 are attributed to the protonation of the N and
exocyclic S donor atoms on the complexing agent, 2-MBT,
which could have resulted in fewer bonding sites available
on the complexing agent (Ghaedi et al., 2009). Another
reason for the low PGMs extractions at pH 1.00 could also
be due to the lower hydrophobicity of the formed PGMs
complexes (Han et al., 2017). The PGMs extraction at pH
4.00 and 5.75 were 99% and this could be due to the high
availability of bonding sites on 2-MBT as the number of
free hydrogen ions to protonate 2-MBT was low. Another
reason for the high PGMs extraction could also be due
to the increased hydrophobicity of the PGMs complexes
formed at pH 4.00 and 5.75 (Han et al., 2017). Under
strong acidic conditions (pH 1.00), only Pt and Pd could
form complexes with 2-MBT due to their stronger affinity
compared to other elements (Galvão et al., 2016).
As pH increased above 1.00, extraction of Rh and
impurities also rose, which is unfavourable for the selectiv-
ity of the CPE process. Therefore, pH 1.00 was chosen for
further study due to its selectivity of Pt and Pd extraction
over Rh, Al, Fe, and Mg. However, the lack of Rh extrac-
tion prompted additional investigation into its recovery,
which involved a higher concentration of the reducing and
activating agent, tin (II) chloride-dihydrate, discussed in
the next section.
Figure 1. Effect of pH on PGMs extraction at 10% m/v tin
(II) chloride di-hydrate

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Extracted Text (may have errors)

XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3 1707
45 ml of a 494 ppm PGMs leach solution was added to
5 ml of the Purolite SAR in a glass bottle with a screw top at
25, 45 and 65 °C temperature (Goc et al. 2021 Kononova
et al., 2010). The pH values under study were 1.0, 1.5,
and 2.0, as precipitation occurred from pH 2.5 and above,
a condition, which could prevent the metal from loading
onto the resin. The glass bottles were then placed in a shak-
ing incubator at 150 rpm for 24 hours (Shen et al., 2010).
The solution was then filtered, and a sample collected for
analysis by ICP-MS for PGMs and ICP-OES for Al, Fe,
and Mg. The PGMs extraction by IX was calculated as a
percentage of PGMs on the resin to that initially present in
the chloride leach solution as per equation 10.
E% C
C C
100
i
i f #=
-
(10)
Where Ci and Cf are the concentration of metals before and
after extraction in the aqueous phase, respectively.
Effect of Contact Time on PGMs Extraction by Ion
Exchange
A volume of 90 ml at pH 2 was added to 10 ml of Purolite
SAR in a conical flask (Goc et al., 2021). The reaction was
run at 25 °C and the incubator speed was set at 150 rpm
(Shen et al., 2010). Samples were collected after 15, 45, 90,
115, and 1440 minutes for PGMs, Al, Mg and Fe analysis.
Calculation of CPE and IX Concentration Factors
The concentration factor, CF, of each process was calculated
by dividing the total PGMs concentration in the surfactant
phase by the initial total PGMs concentration in the leach
before CPE, as per equation 11 (Chagnes 2020).
C C
Csurf
F
i
=(11)
Where Csurf and Ci are the total PGMs concentration in
the surfactant phase and the total PGMs concentration in
the aqueous phase respectively. All testwork was conducted
in duplicates.
RESULTS AND DISCUSSION
Cloud Point Extraction Results
Effect of pH on Extraction and Selectivity in the
Presence of 10% Tin (II) Chloride Di-hydrate
The investigation into the pH impact on PGMs CPE was
conducted with a 10% (m/v) concentration of the reducing
and activating agent, tin (II) chloride di-hydrate, follow-
ing the CPE procedure. The results, depicted in Figure 1,
illustrate the effect of pH (1.00 to 5.75) on the extraction
of Pt, Pd, Rh, Al, Fe, and Mg. The influence of pH on
PGMs extraction is significant, affecting the PGMs species
and potential ligands.
At pH 1.00, extractions were 47% Pt, 50% Pd, and
0% for Rh, Al, Fe, and Mg, compared to higher values at
pH 4.00 (99% Pt, 99% Pd, 99% Rh, 11% Al, 45% Fe,
and 45% Mg) and pH 5.75 (87% Pt, 93% Pd, 86% Rh,
22% Al, 21% Fe, and 14% Mg). The low extractions at
pH 1.00 are attributed to the protonation of the N and
exocyclic S donor atoms on the complexing agent, 2-MBT,
which could have resulted in fewer bonding sites available
on the complexing agent (Ghaedi et al., 2009). Another
reason for the low PGMs extractions at pH 1.00 could also
be due to the lower hydrophobicity of the formed PGMs
complexes (Han et al., 2017). The PGMs extraction at pH
4.00 and 5.75 were 99% and this could be due to the high
availability of bonding sites on 2-MBT as the number of
free hydrogen ions to protonate 2-MBT was low. Another
reason for the high PGMs extraction could also be due
to the increased hydrophobicity of the PGMs complexes
formed at pH 4.00 and 5.75 (Han et al., 2017). Under
strong acidic conditions (pH 1.00), only Pt and Pd could
form complexes with 2-MBT due to their stronger affinity
compared to other elements (Galvão et al., 2016).
As pH increased above 1.00, extraction of Rh and
impurities also rose, which is unfavourable for the selectiv-
ity of the CPE process. Therefore, pH 1.00 was chosen for
further study due to its selectivity of Pt and Pd extraction
over Rh, Al, Fe, and Mg. However, the lack of Rh extrac-
tion prompted additional investigation into its recovery,
which involved a higher concentration of the reducing and
activating agent, tin (II) chloride-dihydrate, discussed in
the next section.
Figure 1. Effect of pH on PGMs extraction at 10% m/v tin
(II) chloride di-hydrate

XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3 1705
phase. This innovative approach provides an efficient and
eco-friendly means of recovering PGMs, particularly at low
metal concentrations 500 ppm with process temperatures
10–15 °C above the cloud point temperature of surfactants
that range from 5 to 85 °C (Quina and Hinze, 1999).
IX is chemical process that involves the exchange of
ions between a solid phase and a liquid phase (Richardson,
Harker, and Backhurst 2002). Termed cation exchange
for positively charged ions and anion exchange for nega-
tively charged ions, the cation and anion exchangers can
be further classified into strong and weak basic and acidic
exchangers (Levan and Carta 2008). Strong anion resins
(SAR) exhibit high loading capacity, operate in the entire
pH range, and have high physicochemical stability and elu-
tion rates, making SAR favourable for PGM recovery from
SACs leach solutions (Silva, Hawboldt, and Zhang 2018).
The chemistries of ion exchange and cloud point extraction
processes are discussed in the sections below.
Chemistry of PGMs Extraction by Ion Exchange
The IX process with SAR takes place without formation of
chemical bonds. Examples of a SAR with type 1 quater-
nary ammonium group reacting with the anionic chloro
complexes of Pd, and Pt are shown in equations (1) and (2)
(Wołowicz and Hubicki 2011 Sun et al., 2015):
2R N
N 2Cl
3 4
2-
3 3 2 4
2-
"-+
-+
+-
+-
^CH
^CH
^resinh ^aqh
^aqh
h3Cl
h 7R 6PdCl
6PdCl
A @^resinh
@
(1)
2R N Cl
N 2Cl
3 3
3 2
"-+
-+
+-
+-
^CH
^CH3h
^resinh
^resinh
^aqh
^aqh
h
7R 6PtCl6@2-
6PtCl6@2-
A
(2)
Chemistry of PGMs Extraction by Cloud Point
Extraction
The process involves the formation of reactive PGMs-tin
chloro complexes from PGMs chloro complexes using
tin (II) chloride as a reducing and activating agent (Le,
Nguyen, and Lee 2018 Zou, Chen, and Pan 1998). The
activation reactions depend on the Sn (II) /PGM ratio.
When the Sn (II) /PGM ratio is 2, unreactive PGMs-
tin chloro complexes are formed as shown in equation (3),
which contain a higher number of Cl– ions which have slow
exchange kinetics compared to the reactive SnCl3– ligands
(Zou, Chen, and Pan 1998).
3SnCl
3 Cl
SnCl SnCl
6
2-
3
3 3
2-
3 3
"+
+
++
-
-
-+
^SnCl
^aqh
^aqh
^aqh
^aqh h@^aqh
6PtCl
6PtCl
@^aqh
(3)
Equations (4), (5) and (6) show the activation reactions for
Rh (III) and Pt (IV) when Sn (II) /PGM ratio is 6 where
the reactivity of the complexes formed is high.
6SnCl
3Cl SnCl
aq
6
3-
3
3 5
4-
6
2-
"+
++
-
-^SnCl
^aqh
^aqh
^^aqh h
h
6RhCl
6Rh
@^aqh
@
(4)
7SnCl
6 Cl
SnCl SnCl
3
3 5
3-
3 3
"+
+
++
-
-
-+
^aqh
^aqh
^aqh
^aqh
^aqh
^aqh
h
6PtCl6@2-
6Pt^SnCl @(5)
6SnCl
5 Cl
SnCl SnCl
6
2-
3
3 4
3-
3 3
"+
+
++
-
-
-+
^aqh
^aqh
^aqh
^aqh
^aqh h
6PtCl
6PtCl^SnCl
@^aqh
@(6)
This is followed by the formation of hydrophobic com-
plexes with the complexing agent via a neutral complexing
mechanism (Yin et al., 2017). Equations (7) and (8) illus-
trate Rh extraction by 1-hexyl-3-methylimidazole-2-thione
(HMImT), a complexing agent related to 2-MBT, which
was used in this study (Yin et al., 2017).
4 4H Rh SnCl H
3 5
4-
3 "$6Rh ++^^SnCl
^aqh ^aqh ^aqh h h5@ 6 @(7)
4 2HMImT
4 2HMImT
H
H
3 5
5
"$6Rh^SnCl
$$
+
^orgh
^orgh h
6Rh^SnCl3h
@^aqh
@
(8)
The hydrophobic PGM complex is extracted to the surfac-
tant phase though in the study referred to by equation 8 it
was an organic phase as SX was used (Yin et al., 2017).
Much of CPE research on PGMs has been on their pre-
concentration for determination in water and fly ash (Kumar
and Shyamala 2019). A look at available literature suggests
that only Makua et al. (2019), Mortada, Hassanien, and
El-Asmy. (2014), and Suoranta et al. (2015) have studied
the recovery of PGMs from SACs using CPE. They studied
the effects of pH, temperature, incubation time, surfactant,
and complexing agent volumes on PGMs extraction inde-
pendently at concentrations 70 ppm. A further look at
literature indicates that there are currently no CPE studies
that have been conducted on SACs leach solutions which
contain 400–600 ppm of PGMs (Firmansyah et al., 2019
Kim et al., 2011 Torrejos et al., 2020). In addition, there
is lack of literature on metal stripping from loaded CPE
surfactant, which is required for commercialization of CPE
(Makua et al., 2019 Suoranta et al., 2015).
In this work, the CPE of PGMs from a synthetic SACs
leach solution using Triton X-100 as the surfactant, 2-MBT
as the complexing agent and SnCl2·2H2O as the reducing

Previous Page Next Page

Extracted Text (may have errors)

XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3 1705
phase. This innovative approach provides an efficient and
eco-friendly means of recovering PGMs, particularly at low
metal concentrations 500 ppm with process temperatures
10–15 °C above the cloud point temperature of surfactants
that range from 5 to 85 °C (Quina and Hinze, 1999).
IX is chemical process that involves the exchange of
ions between a solid phase and a liquid phase (Richardson,
Harker, and Backhurst 2002). Termed cation exchange
for positively charged ions and anion exchange for nega-
tively charged ions, the cation and anion exchangers can
be further classified into strong and weak basic and acidic
exchangers (Levan and Carta 2008). Strong anion resins
(SAR) exhibit high loading capacity, operate in the entire
pH range, and have high physicochemical stability and elu-
tion rates, making SAR favourable for PGM recovery from
SACs leach solutions (Silva, Hawboldt, and Zhang 2018).
The chemistries of ion exchange and cloud point extraction
processes are discussed in the sections below.
Chemistry of PGMs Extraction by Ion Exchange
The IX process with SAR takes place without formation of
chemical bonds. Examples of a SAR with type 1 quater-
nary ammonium group reacting with the anionic chloro
complexes of Pd, and Pt are shown in equations (1) and (2)
(Wołowicz and Hubicki 2011 Sun et al., 2015):
2R N
N 2Cl
3 4
2-
3 3 2 4
2-
"-+
-+
+-
+-
^CH
^CH
^resinh ^aqh
^aqh
h3Cl
h 7R 6PdCl
6PdCl
A @^resinh
@
(1)
2R N Cl
N 2Cl
3 3
3 2
"-+
-+
+-
+-
^CH
^CH3h
^resinh
^resinh
^aqh
^aqh
h
7R 6PtCl6@2-
6PtCl6@2-
A
(2)
Chemistry of PGMs Extraction by Cloud Point
Extraction
The process involves the formation of reactive PGMs-tin
chloro complexes from PGMs chloro complexes using
tin (II) chloride as a reducing and activating agent (Le,
Nguyen, and Lee 2018 Zou, Chen, and Pan 1998). The
activation reactions depend on the Sn (II) /PGM ratio.
When the Sn (II) /PGM ratio is 2, unreactive PGMs-
tin chloro complexes are formed as shown in equation (3),
which contain a higher number of Cl– ions which have slow
exchange kinetics compared to the reactive SnCl3– ligands
(Zou, Chen, and Pan 1998).
3SnCl
3 Cl
SnCl SnCl
6
2-
3
3 3
2-
3 3
"+
+
++
-
-
-+
^SnCl
^aqh
^aqh
^aqh
^aqh h@^aqh
6PtCl
6PtCl
@^aqh
(3)
Equations (4), (5) and (6) show the activation reactions for
Rh (III) and Pt (IV) when Sn (II) /PGM ratio is 6 where
the reactivity of the complexes formed is high.
6SnCl
3Cl SnCl
aq
6
3-
3
3 5
4-
6
2-
"+
++
-
-^SnCl
^aqh
^aqh
^^aqh h
h
6RhCl
6Rh
@^aqh
@
(4)
7SnCl
6 Cl
SnCl SnCl
3
3 5
3-
3 3
"+
+
++
-
-
-+
^aqh
^aqh
^aqh
^aqh
^aqh
^aqh
h
6PtCl6@2-
6Pt^SnCl @(5)
6SnCl
5 Cl
SnCl SnCl
6
2-
3
3 4
3-
3 3
"+
+
++
-
-
-+
^aqh
^aqh
^aqh
^aqh
^aqh h
6PtCl
6PtCl^SnCl
@^aqh
@(6)
This is followed by the formation of hydrophobic com-
plexes with the complexing agent via a neutral complexing
mechanism (Yin et al., 2017). Equations (7) and (8) illus-
trate Rh extraction by 1-hexyl-3-methylimidazole-2-thione
(HMImT), a complexing agent related to 2-MBT, which
was used in this study (Yin et al., 2017).
4 4H Rh SnCl H
3 5
4-
3 "$6Rh ++^^SnCl
^aqh ^aqh ^aqh h h5@ 6 @(7)
4 2HMImT
4 2HMImT
H
H
3 5
5
"$6Rh^SnCl
$$
+
^orgh
^orgh h
6Rh^SnCl3h
@^aqh
@
(8)
The hydrophobic PGM complex is extracted to the surfac-
tant phase though in the study referred to by equation 8 it
was an organic phase as SX was used (Yin et al., 2017).
Much of CPE research on PGMs has been on their pre-
concentration for determination in water and fly ash (Kumar
and Shyamala 2019). A look at available literature suggests
that only Makua et al. (2019), Mortada, Hassanien, and
El-Asmy. (2014), and Suoranta et al. (2015) have studied
the recovery of PGMs from SACs using CPE. They studied
the effects of pH, temperature, incubation time, surfactant,
and complexing agent volumes on PGMs extraction inde-
pendently at concentrations 70 ppm. A further look at
literature indicates that there are currently no CPE studies
that have been conducted on SACs leach solutions which
contain 400–600 ppm of PGMs (Firmansyah et al., 2019
Kim et al., 2011 Torrejos et al., 2020). In addition, there
is lack of literature on metal stripping from loaded CPE
surfactant, which is required for commercialization of CPE
(Makua et al., 2019 Suoranta et al., 2015).
In this work, the CPE of PGMs from a synthetic SACs
leach solution using Triton X-100 as the surfactant, 2-MBT
as the complexing agent and SnCl2·2H2O as the reducing