Toward efficient and selective thorium recovery using stable ion-imprinting sorbent − application to processed acidic ore leachate as a case study
Mengjie Zhao, Amr Fouda, Khalid A.M. Salih, Eric Guibal, Yuezhou Wei, Shunyan Ning, Mohammed F. Hamza, Saly R. El Dakkony
Abstract
The recovery of thorium from aqueous industrial effluents is a challenge not only for environmental purpose but also for the valorization of secondary resources. The complexity of these effluents not only require designing highly efficient stable sorbent with highly reactive functional groups but also with good selectivity. Phosphonic groups are efficient for the binding of thorium. Successive grafting of phosphonic groups through one-pot reaction of vinylphosphonic acid with acrylamide-based reagents (as monomer and crosslinker) for polymerizing an efficient sorbent (HVP/NIP) toward Th(IV) recovery in slightly acidic solution. On the other hand, the selectivity objective was reached by adopting an ion-imprinting strategy (HVP/IP). While the templating weakly improves sorption capacity (at 1.46 mmol g−1 at pH close to 3), the most significant benefits concern the uptake kinetics (slightly enhanced; equilibrium being reached in 20–25 min) and more significantly the separation properties of HVP/IP, against base metals and uranium (to a certain extent). The selectivity coefficient (i.e., SCTh/metal) increases twice (against U and Ca) and up to 16-folds against Al, at pH0 3. Fourier-transform infrared and XPS spectroscopy confirm the structural differences for both sorbents (arrangement of reactive groups) and the interactions modes involved in thorium binding mechanisms. The remarkable sorption properties of HVP/IP are also illustrated by the good stability of the sorbent at recycling (loss in sorption less than 2% at the 10th cycle): complete desorption is achieved using 0.3 M HNO3 solution. The ion-imprinted sorbent is successfully applied to the recovery of valuable metals (thorium, uranium, and gallium) from acidic ore leachate at different pH values. The materials are fully characterized using different analytical tools; i.e., FTIR, TGA, XPS, BET, titration, and elemental analysis.