Continuous intensified selective extraction of platinum group metals in small channels

Combined small channel extraction for continuous integrated Pd > Pt > Rh separation. Platinum-group metals (PGMs) are essential in various fields, including automotive emission control, process catalysis and emerging green energy technologies, making their efficient recovery crucial for sustainable industrial use. Solvent extraction (SX) is a key technique for the recovery and purification of these metals. This study explores the use of continuous small channel systems to intensify SX, focusing on the selective separation of palladium, platinum, and rhodium. By using two distinct extractants, trioctylamine, a fast outer-sphere ion-pair extractant, and di-n-hexyl sulfide, a slower coordination-based extractant, efficient, selective extraction was achieved. Trioctylamine achieved nearly 100 % extraction of palladium and platinum in just 7 s and 65 s respectively, whereas di-n-hexyl sulfide reached over 40 % palladium extraction within 5 min. In the small channel systems, mass transfer coefficients were found to be up to two orders of magnitude higher than in conventional SX equipment. Additionally, increasing the temperature from 20 °C to 40 °C led to a 50 % increase in mass transfer coefficients for the kinetically slow extraction with di-n-hexyl sulfide. These results suggest that small channel systems hold considerable promise for rapid, selective PGM recovery, supporting sequential multicomponent separation processes.