Adsorptive Recovery of Iopamidol from Aqueous Solution and Parallel Reuse of Activated Carbon: Batch and Flow Study

This study demonstrates the adsorptive recovery of high-concentration Iopamidol (TOP) from aqueous solution. IOP is a highly valuable X-ray iodinated contrast agent (ICA), and the reuse of the adsorbent activated carbon (AC) is via elution with alcohol. Of the adsorbents selected, coconut powder AC (CPAC) displayed the best adsorption performance for IOP. The results of batch investigation into adsorption kinetics, isotherms, activation energy, and thermodynamic calculations support the occurrence of a physisorption process. The adsorption mechanism has been determined using the intraparticle diffusion model. A Boyd plot has revealed that IOP adsorption onto CPAC was mainly governed by particle diffusion. CPAC also exhibited excellent adsorptive performance toward IOP, which was efficiently eluted and recovered using methanol in a semicontinuous flow system. Moreover, the spent CPAC was efficiently regenerated and reused in five adsorption/desorption cycles. The characterization of CPAC samples by SEM, DRIFT, and TGA shows that IOP is absorbed onto CPAC, leading to significant decreases in the BET surface area and pore volume and shift of the pore diameter. pi-pi, donor-acceptor complex, van der Waals, and hydrogen-bond interactions are governed by the IOP adsorption. Hydrogen-bond interactions between IOP and alcohols play a crucial role in the desorption process. IOP was completely eluted, and the surface properties of CPAC were recovered after elution in the flow system. This study demonstrates that many benefits can be achieved from adsorption/desorption processes, such as those in wastewater treatment and the recovery of valuable compounds, as adsorbent recycling simplifies the operations and reduces treatment costs.