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
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