Adsorption stands
out as a leading wastewater treatment
method
for ion removal or recovery. Polymeric fibers, notably electrospun
ones, are gaining prominence due to their high capacity and easy recovery.
Electrospinning offers a cost-effective means to produce fibers with
a large surface area and high adsorption capacity. These fibers can
be further functionalized with chemical substances acting as specific
ligands for metal ions, bolstering their adsorption capabilities.
In this study, dithioester-functionalized electrospun fibers were
synthesized as an alternative to conventional sorbents for palladium
recovery from acidic chloride solutions, similar to those used in
hydrometallurgical processes for platinum group metal recovery (Pd,
Pt, Rh···) from spent catalysts. Fibers with identical
chemical composition but varying morphology were examined to assess
their impact on palladium adsorption efficiency (i.e., beads-free
and beads-on-string morphologies). Experimental investigations involved
model solutions with varying palladium concentration, temperature,
acidity (adjusted with HCl content), and salinity (adjusted with NaCl),
utilizing both pure and dithioester-functionalized fibers. Experimental
results demonstrate enhanced adsorption efficiency at lower temperatures
and in 0.1 M HCl, with a negligible influence from solution salinity.
Moreover, both pure polymeric and dithioester-functionalized electrospun
fibers exhibit highly efficient palladium recovery. Furthermore, under
optimal conditions, starting from an 80 mg/L palladium solution, a
95% recovery of palladium can be achieved with a sorbent dosage below
4 g/L of functionalized electrospun fibers. The adsorption data are
well described by the Langmuir isotherm model for the pure polymeric
fibers. At the same time, the contribution of dithioesters has been
separately accounted for to describe the behavior of functionalized
electrospun fibers. Thermal recovery of palladium from the spent sorbents
has also been investigated.
