1710 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
mentioned in the previous section, which have slow ligand
exchange kinetics. These characteristics lead to low Pt and
Rh extractions in the initial stages of the reaction. The
competition for adsorption sites, potentially arising from
chloride ions released after Pd (II) adsorption and [FeCl4]–,
as indicated in Table 2, could result in the delayed adsorp-
tion of Pt (IV) and Rh (III). Among the two kinetically
inert PGMs, Rh (III) is more inert, with more water
and hydroxyl ligands, making its extraction much slower
(Bernardis, Grant, and Sherrington 2005 Shelimov et al.,
2000).
In Figure 4, at 115 minutes, Pd (II) extraction exceeded
98%, while Pt ((IV) extraction was at 76%, and Rh (III)
extraction was less than 1%. The increase in Pt extrac-
tion could be attributed to the formation of more extract-
able anionic species from the chloride ions released by Pd
adsorption. Notably, the extraction of Rh (III) increased
after 24 hours of incubation time to 37%, and since Rh has
more aqua chloro species, a longer time is required for the
unreactive ligands to be replaced to form more extractable
species, extending up to 7 days (Kononova et al., 2010).
Concentration Factors for CPE and IX, and CPE’s
Potential Integration in PGMs Refineries
At 10% concentration of the activating agent, CPE had
a total PGMs concentration factor of 14.10 and 15.21 at
pH 1.00 and pH 4.00–5.75 respectively compared to total
PGMs concentration factors of 13.40 and 15.92 at 20%
tin (II) chloride di-hydrate at similar pH values respec-
tively. IX had a concentration factor of 8.04. The higher
CPE concentration factor indicates a potential of a smaller
processing plant for PGMs recovery, which would result in
lower capital costs, compared to IX.
Current commercial PGMs recovery processes have Pd
and Pt raffinates ranging from 100–600 ppm (Crundwell
et al., 2011). Treatment involves boiling down to attain
solution concentration before reprocessing raising refinery
costs. The CPE results in this study suggest its potential
integration in PGM refineries to lower process costs.
CONCLUSIONS AND FURTHER
RECOMMENDATIONS
This study aimed to compare the efficiency of extracting Pt,
Pd, and Rh from a spent autocatalytic converter chloride
leach solution using Cloud Point Extraction (CPE) and
Ion Exchange (IX). CPE demonstrated optimal selectivity
at low pH and achieved high extractions under near-neutral
pH in a single step. In contrast, the impact of pH on IX was
minimal. Both processes exhibited low selectivity for indi-
vidual PGMs, with CPE at 10% tin (II) chloride showing
the best selectivity, but Pt and Pd recovery was only 50%
at pH 1, and Rh was not extracted. Increasing the reducing
agent in CPE to 20% improved Rh extraction but activated
the recovery of Al, Fe, and Mg.
IX required a shorter incubation time for Pd and Pt
extraction compared to CPE, but it needed 24 hours for
37% Rh extraction, while CPE at 20% tin (II) chloride
achieved 40% extraction in 115 minutes. While these find-
ings suggest the feasibility of CPE for SACs leach metal
concentrations, further comprehensive investigations are
necessary for a robust comparison with existing PGM
extraction methods.
Further work requires exploring the effect of pH on
PGMs and impurity metal extraction in the pH range of
7–14. It is also recommended to extend CPE application to
low-concentration solutions like PGM industry process raf-
finates and waste streams. In addition, research on the recy-
clability of the surfactant phase and impurity scrubbing is
essential. To validate CPE’s commercial potential, piloting,
cost-benefit analyses, and process costing for comparison
with established technologies like solvent extraction is also
recommended.
ACKNOWLEDGMENTS
The authors would like to thank the Department of
Science and Innovation (DSI) and the National Research
Foundation (NRF) for funding under SARChI grant num-
ber 98350.
Figure 4. Effect of contact time on PGMs extraction by IX
mentioned in the previous section, which have slow ligand
exchange kinetics. These characteristics lead to low Pt and
Rh extractions in the initial stages of the reaction. The
competition for adsorption sites, potentially arising from
chloride ions released after Pd (II) adsorption and [FeCl4]–,
as indicated in Table 2, could result in the delayed adsorp-
tion of Pt (IV) and Rh (III). Among the two kinetically
inert PGMs, Rh (III) is more inert, with more water
and hydroxyl ligands, making its extraction much slower
(Bernardis, Grant, and Sherrington 2005 Shelimov et al.,
2000).
In Figure 4, at 115 minutes, Pd (II) extraction exceeded
98%, while Pt ((IV) extraction was at 76%, and Rh (III)
extraction was less than 1%. The increase in Pt extrac-
tion could be attributed to the formation of more extract-
able anionic species from the chloride ions released by Pd
adsorption. Notably, the extraction of Rh (III) increased
after 24 hours of incubation time to 37%, and since Rh has
more aqua chloro species, a longer time is required for the
unreactive ligands to be replaced to form more extractable
species, extending up to 7 days (Kononova et al., 2010).
Concentration Factors for CPE and IX, and CPE’s
Potential Integration in PGMs Refineries
At 10% concentration of the activating agent, CPE had
a total PGMs concentration factor of 14.10 and 15.21 at
pH 1.00 and pH 4.00–5.75 respectively compared to total
PGMs concentration factors of 13.40 and 15.92 at 20%
tin (II) chloride di-hydrate at similar pH values respec-
tively. IX had a concentration factor of 8.04. The higher
CPE concentration factor indicates a potential of a smaller
processing plant for PGMs recovery, which would result in
lower capital costs, compared to IX.
Current commercial PGMs recovery processes have Pd
and Pt raffinates ranging from 100–600 ppm (Crundwell
et al., 2011). Treatment involves boiling down to attain
solution concentration before reprocessing raising refinery
costs. The CPE results in this study suggest its potential
integration in PGM refineries to lower process costs.
CONCLUSIONS AND FURTHER
RECOMMENDATIONS
This study aimed to compare the efficiency of extracting Pt,
Pd, and Rh from a spent autocatalytic converter chloride
leach solution using Cloud Point Extraction (CPE) and
Ion Exchange (IX). CPE demonstrated optimal selectivity
at low pH and achieved high extractions under near-neutral
pH in a single step. In contrast, the impact of pH on IX was
minimal. Both processes exhibited low selectivity for indi-
vidual PGMs, with CPE at 10% tin (II) chloride showing
the best selectivity, but Pt and Pd recovery was only 50%
at pH 1, and Rh was not extracted. Increasing the reducing
agent in CPE to 20% improved Rh extraction but activated
the recovery of Al, Fe, and Mg.
IX required a shorter incubation time for Pd and Pt
extraction compared to CPE, but it needed 24 hours for
37% Rh extraction, while CPE at 20% tin (II) chloride
achieved 40% extraction in 115 minutes. While these find-
ings suggest the feasibility of CPE for SACs leach metal
concentrations, further comprehensive investigations are
necessary for a robust comparison with existing PGM
extraction methods.
Further work requires exploring the effect of pH on
PGMs and impurity metal extraction in the pH range of
7–14. It is also recommended to extend CPE application to
low-concentration solutions like PGM industry process raf-
finates and waste streams. In addition, research on the recy-
clability of the surfactant phase and impurity scrubbing is
essential. To validate CPE’s commercial potential, piloting,
cost-benefit analyses, and process costing for comparison
with established technologies like solvent extraction is also
recommended.
ACKNOWLEDGMENTS
The authors would like to thank the Department of
Science and Innovation (DSI) and the National Research
Foundation (NRF) for funding under SARChI grant num-
ber 98350.
Figure 4. Effect of contact time on PGMs extraction by IX