Continuous adsorption of metal ions based on an elastic and reusable polydopamine-modified foam

Given the limited resources and the growing demand for critical metals as well as the strict environmental regulations, it is essential to develop new metals recovery technologies (more efficient, less expensive and environmentally friendly) especially concerning the treatment of high volume of diluted wastes. In this sense, continuous flow processes appear as the best alternative. But this approach requires suitable adsorbents in term of low pressure drop and ability to adsorb ppm or even ppb traces of metal which are sine qua non key-features. Herein, we have modified the surface of a commercially available open cell melamine foam using the mussel inspired chemistry through an original and ultrafast process. This non-toxic bioinspired coating is based on the polymerization of polyphenols such as dopamine leading to a commonly called polydopamine (PDA) layer resulting to me@PDA adsorbent. Using Pb(II) as model, we have demonstrated its efficient adsorption even from ppb level, leading to a capacity of 1.2 mmol.g(-1) determined from a continuous process. By increasing the path passing through me@PDA, it is observed an increase of the Pb(II) loading capacity concomitantly with the PDA mass. Since me@PDA is an elastic adsorbent, its compression in the filtration column to insert more foam results in an increase of Pb(II) adsorbed without significant increase of the pressure drop. Furthermore, desorption is obtained using a flow of acid solution. Finally, the similarity of three successive cycles of adsorption-desorption of Pb(II) highlights the repeatability of the process and the chemical robustness of the adsorbent me@PDA as designed.