1703
A Comparison of Cloud Point Extraction and Ion Exchange in
Recovery of Pt, Pd, and Rh from Spent Autocatalytic Converters
Chloride Leach Solutions
C.W. Baleti A. Shemi, and S. Ndlovu
School of Chemical and Metallurgical Engineering, University of the Witwatersrand, Johannesburg, South Africa
DSI/NRF SARChI: Hydrometallurgy and Sustainable Development,
University of the Witwatersrand, Johannesburg, South Africa
ABSTRACT: Although solvent extraction (SX) and precipitation (PPT) are utilized in the recovery of PGMs
from ore concentrate leach solutions, these processes are not very efficient for the direct recovery of PGMs from
spent autocatalytic converters (SACs) leachates due to the lower metal solution concentration. In this study,
Cloud Point Extraction (CPE), a laboratory liquid-liquid extraction method that utilizes a surfactant and a
complexing agent to extract metal ions is investigated as an alternative technique for the recovery of PGMs
from SACs leach solutions. While CPE has shown capability of PGMs recovery at trace levels, CPE studies
from PGM SACs leach solutions and elution of the PGMs from the CPE surfactant rich phase (SRP) are scarce.
In this work, the CPE of PGMs from a synthetic SACs leach solution was investigated, using Triton X-100 as
the surfactant, 2-mercaptobenzothiazole (2-MBT) as the complexing agent and SnCl2.2H2O as the activator.
This was compared to PGMs recovery using ion exchange (IX). The leach solution concentration was based on
literature with a composition (ppm) of: Pt (IV)-72, Pd (II)-350, Rh (III)-72, Al (III)-11000, Mg (II)-1500, and
Fe (III)-700. Under optimal conditions, CPE extractions obtained were 99% Pt, 99% Pd and 94% Rh while
IX extractions were 99% Pt, 98% Pd and 36% Rh. From the results, CPE’s ability to recover metals from trace
level concentrations suggest the possibility of integrating it with other metal recovery techniques to reduce feed
solution recycles and cut down on industrial costs.
Keywords: PGMs Cloud point extraction Ion Exchange Spent autocatalytic converter.
INTRODUCTION
The extraction of PGMs has become more costly due to
challenges such as lower-grade ores, increased mining
depth, and higher energy costs (Mudd, Jowitt, and Werner
2018). Given the critical role of PGMs in modern society,
efforts have intensified to recover them from end-of-life
(EOL) products like SACs (Hong et al., 2020). At the end
of their life cycle, SACs and other EOL products contain-
ing PGMs become valuable resources, offering a high-grade
concentration of 2000–4000 ppm, compared to 1–15
ppm in ores (Yakoumis et al., 2018). In 2019 there was
a deficit of about 40 tonnes of PGMs (Johnson Matthey,
2020). Their recovery from SACs and other EOL products
can alleviate such shortages. EOL sources have, therefore,
A Comparison of Cloud Point Extraction and Ion Exchange in
Recovery of Pt, Pd, and Rh from Spent Autocatalytic Converters
Chloride Leach Solutions
C.W. Baleti A. Shemi, and S. Ndlovu
School of Chemical and Metallurgical Engineering, University of the Witwatersrand, Johannesburg, South Africa
DSI/NRF SARChI: Hydrometallurgy and Sustainable Development,
University of the Witwatersrand, Johannesburg, South Africa
ABSTRACT: Although solvent extraction (SX) and precipitation (PPT) are utilized in the recovery of PGMs
from ore concentrate leach solutions, these processes are not very efficient for the direct recovery of PGMs from
spent autocatalytic converters (SACs) leachates due to the lower metal solution concentration. In this study,
Cloud Point Extraction (CPE), a laboratory liquid-liquid extraction method that utilizes a surfactant and a
complexing agent to extract metal ions is investigated as an alternative technique for the recovery of PGMs
from SACs leach solutions. While CPE has shown capability of PGMs recovery at trace levels, CPE studies
from PGM SACs leach solutions and elution of the PGMs from the CPE surfactant rich phase (SRP) are scarce.
In this work, the CPE of PGMs from a synthetic SACs leach solution was investigated, using Triton X-100 as
the surfactant, 2-mercaptobenzothiazole (2-MBT) as the complexing agent and SnCl2.2H2O as the activator.
This was compared to PGMs recovery using ion exchange (IX). The leach solution concentration was based on
literature with a composition (ppm) of: Pt (IV)-72, Pd (II)-350, Rh (III)-72, Al (III)-11000, Mg (II)-1500, and
Fe (III)-700. Under optimal conditions, CPE extractions obtained were 99% Pt, 99% Pd and 94% Rh while
IX extractions were 99% Pt, 98% Pd and 36% Rh. From the results, CPE’s ability to recover metals from trace
level concentrations suggest the possibility of integrating it with other metal recovery techniques to reduce feed
solution recycles and cut down on industrial costs.
Keywords: PGMs Cloud point extraction Ion Exchange Spent autocatalytic converter.
INTRODUCTION
The extraction of PGMs has become more costly due to
challenges such as lower-grade ores, increased mining
depth, and higher energy costs (Mudd, Jowitt, and Werner
2018). Given the critical role of PGMs in modern society,
efforts have intensified to recover them from end-of-life
(EOL) products like SACs (Hong et al., 2020). At the end
of their life cycle, SACs and other EOL products contain-
ing PGMs become valuable resources, offering a high-grade
concentration of 2000–4000 ppm, compared to 1–15
ppm in ores (Yakoumis et al., 2018). In 2019 there was
a deficit of about 40 tonnes of PGMs (Johnson Matthey,
2020). Their recovery from SACs and other EOL products
can alleviate such shortages. EOL sources have, therefore,