1708 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
Effect of pH on Extraction and Selectivity in the
Presence of 20% Tin (II) Chloride Di-hydrate
The investigation into the impact of pH on PGMs extrac-
tion using 20% (m/v) concentration of tin (II) chloride di-
hydrate was conducted following the CPE procedure and
the results are presented in Figure 2.
Figure 2 illustrates the effect of pH (1.00 to 5.75) on
the extraction of Pt, Pd, Rh, Al, Fe, and Mg at 20% (m/v)
tin (II) chloride di-hydrate. Extractions at pH 1.00 were
52% Pt, 38% Pd, 40% Rh, 11% Al, 10% Fe, and 12% Mg,
compared to higher values at pH 4.00 (100% Pt, 100%
Pd, 100% Rh, 15% Al, 27% Fe, and 32% Mg) and pH
5.75 (99% Pt, 100% Pd, 94% Rh, 16% Al, 3% Fe, and
13% Mg). A substantial increase in Rh extraction from 0%
to 40% at pH 1.00 is observed when compared to metal
extractions at 10% (m/v) tin (II) chloride di-hydrate in
Figure 1. The increase in the concentration of the activating
agent, tin (II) chloride di-hydrate, changed the activating
agent /PGMs ratio from 9.3 at 10% SnCl2.2H2O to 18.6
at 20% SnCl2.2H2O. It is possible that at low Sn concen-
tration, there was insufficient SnCl3– to reduce and activate
the Rh (III)-aqua chloro complexes to form the reactive
Rh (I)-tin chloro complexes. It is also highly likely that the
Rh-tin chloro complexes formed were less reactive as they
still contained several Cl– or H2O ligands, which exhibit
slow exchange kinetics compared to SnCl3– ligands (Zou,
Chen, and Pan 1998). At higher Sn concentration, possi-
bly a higher number of unreactive ligands were replaced to
form the reactive Rh (I)-tin chloro complexes. These com-
plexes reacted with 2-MBT, forming hydrophobic com-
plexes and 40% of these complexes were extracted into the
surfactant phase
It can also be observed in Figure 2 that at pH 1, Pd
extraction decreased from 50% at 10% (m/v) tin (II) chlo-
ride di-hydrate to 38% at 20% (m/v) of the activating
agent. A similar Pd (II) behaviour was observed in a solvent
extraction system where tin (II) chloride was added to a
PGMs leachate to activate Pt (IV) and Rh (III) (Mhaske
and Dhadke, 2001). The higher concentration of the acti-
vating agent also increased the reactivity of Al, Fe, and Mg
at pH 1.00, where these elements were not extracted at 10%
(m/v) tin (II) chloride di-hydrate, their extraction, at 20%
(m/v), became evident. However, from pH 2.00 to 5.75 at
20% tin, the extraction of the impurities was suppressed.
The reason for such behaviour is currently unknown and
further studies are being undertaken to get a better under-
standing. The investigation at an elevated concentration of
tin (II) chloride di-hydrate has unveiled that the extraction
of Rh at 10% tin (II) chloride di-hydrate was restricted
by the absence of reactive Rh tin-chloro complexes due to
insufficient tin (II) chloride di-hydrate, other than just the
protonation of the complexing agent, 2-MBT.
Furthermore, Figure 2 illustrates a decrease in extrac-
tion efficiency at pH 3, similar to the observations made
in Figure 1, although the decrease in Figure 1 is less pro-
nounced. It is postulated that the PGM-tin-chloro com-
plexes formed at pH 3 seem to be less reactive at this pH
level leading to a decline in PGMs extraction. However,
this phenomenon needs to be investigated further in future
studies.
Effect of Incubation Time
Incubation time plays a crucial role in the formation of
hydrophobic PGMs complexes and their entrapment to
the surfactant rich phase. Figures 3a and 3b show the effect
of incubation time at 10% and 20% m/v tin (II) chloride
di-hydrate respectively.
The effect of incubation time in Figure 3a shows that
only Pt and Pd were extracted at 10% SnCl2 as already
discussed in previous sections. At these conditions the
extraction rate rose steadily from 15 minutes to 115 min-
utes. When the concentration of the activating agent was
doubled as shown in Figure 3b the extraction %for Pt dou-
bled from 20 to 42% in the initial stages of the reaction as
shown at 15 minutes while that for Pd increased from 22
to 29%. The increase in the activating agent improved the
reactivity of all the PGMs but the difference in the reactiv-
ity of Pt (IV) and Pd (II) could also be due to the difference
in their initial concentrations of 72 ppm (Pt) and 350 ppm
(Pd) respectively in the leach. The addition of the activating
agent had a higher impact on Pt (IV) due to the higher ratio
of activating agent to Pt than Pd (II).
Figure 2. Effect of pH on PGMs extraction at 20% m/v tin
(II) chloride di-hydrate
Effect of pH on Extraction and Selectivity in the
Presence of 20% Tin (II) Chloride Di-hydrate
The investigation into the impact of pH on PGMs extrac-
tion using 20% (m/v) concentration of tin (II) chloride di-
hydrate was conducted following the CPE procedure and
the results are presented in Figure 2.
Figure 2 illustrates the effect of pH (1.00 to 5.75) on
the extraction of Pt, Pd, Rh, Al, Fe, and Mg at 20% (m/v)
tin (II) chloride di-hydrate. Extractions at pH 1.00 were
52% Pt, 38% Pd, 40% Rh, 11% Al, 10% Fe, and 12% Mg,
compared to higher values at pH 4.00 (100% Pt, 100%
Pd, 100% Rh, 15% Al, 27% Fe, and 32% Mg) and pH
5.75 (99% Pt, 100% Pd, 94% Rh, 16% Al, 3% Fe, and
13% Mg). A substantial increase in Rh extraction from 0%
to 40% at pH 1.00 is observed when compared to metal
extractions at 10% (m/v) tin (II) chloride di-hydrate in
Figure 1. The increase in the concentration of the activating
agent, tin (II) chloride di-hydrate, changed the activating
agent /PGMs ratio from 9.3 at 10% SnCl2.2H2O to 18.6
at 20% SnCl2.2H2O. It is possible that at low Sn concen-
tration, there was insufficient SnCl3– to reduce and activate
the Rh (III)-aqua chloro complexes to form the reactive
Rh (I)-tin chloro complexes. It is also highly likely that the
Rh-tin chloro complexes formed were less reactive as they
still contained several Cl– or H2O ligands, which exhibit
slow exchange kinetics compared to SnCl3– ligands (Zou,
Chen, and Pan 1998). At higher Sn concentration, possi-
bly a higher number of unreactive ligands were replaced to
form the reactive Rh (I)-tin chloro complexes. These com-
plexes reacted with 2-MBT, forming hydrophobic com-
plexes and 40% of these complexes were extracted into the
surfactant phase
It can also be observed in Figure 2 that at pH 1, Pd
extraction decreased from 50% at 10% (m/v) tin (II) chlo-
ride di-hydrate to 38% at 20% (m/v) of the activating
agent. A similar Pd (II) behaviour was observed in a solvent
extraction system where tin (II) chloride was added to a
PGMs leachate to activate Pt (IV) and Rh (III) (Mhaske
and Dhadke, 2001). The higher concentration of the acti-
vating agent also increased the reactivity of Al, Fe, and Mg
at pH 1.00, where these elements were not extracted at 10%
(m/v) tin (II) chloride di-hydrate, their extraction, at 20%
(m/v), became evident. However, from pH 2.00 to 5.75 at
20% tin, the extraction of the impurities was suppressed.
The reason for such behaviour is currently unknown and
further studies are being undertaken to get a better under-
standing. The investigation at an elevated concentration of
tin (II) chloride di-hydrate has unveiled that the extraction
of Rh at 10% tin (II) chloride di-hydrate was restricted
by the absence of reactive Rh tin-chloro complexes due to
insufficient tin (II) chloride di-hydrate, other than just the
protonation of the complexing agent, 2-MBT.
Furthermore, Figure 2 illustrates a decrease in extrac-
tion efficiency at pH 3, similar to the observations made
in Figure 1, although the decrease in Figure 1 is less pro-
nounced. It is postulated that the PGM-tin-chloro com-
plexes formed at pH 3 seem to be less reactive at this pH
level leading to a decline in PGMs extraction. However,
this phenomenon needs to be investigated further in future
studies.
Effect of Incubation Time
Incubation time plays a crucial role in the formation of
hydrophobic PGMs complexes and their entrapment to
the surfactant rich phase. Figures 3a and 3b show the effect
of incubation time at 10% and 20% m/v tin (II) chloride
di-hydrate respectively.
The effect of incubation time in Figure 3a shows that
only Pt and Pd were extracted at 10% SnCl2 as already
discussed in previous sections. At these conditions the
extraction rate rose steadily from 15 minutes to 115 min-
utes. When the concentration of the activating agent was
doubled as shown in Figure 3b the extraction %for Pt dou-
bled from 20 to 42% in the initial stages of the reaction as
shown at 15 minutes while that for Pd increased from 22
to 29%. The increase in the activating agent improved the
reactivity of all the PGMs but the difference in the reactiv-
ity of Pt (IV) and Pd (II) could also be due to the difference
in their initial concentrations of 72 ppm (Pt) and 350 ppm
(Pd) respectively in the leach. The addition of the activating
agent had a higher impact on Pt (IV) due to the higher ratio
of activating agent to Pt than Pd (II).
Figure 2. Effect of pH on PGMs extraction at 20% m/v tin
(II) chloride di-hydrate