Impactful modulation of micro-structures of acid-resistant picolylamine-based chelate resins for efficient separation of heavy metal cations from strongly acidic media

The efficient separation of heavy metal cations (HMCs) from strongly acidic media (pH 2.5) by adsorption is admittedly challengeable due to the obvious protonation. Aiming at this problem, two acid-resistant picolylamine-based chelate resins PMAA-PD and PMAD-PD with different micro-structures were prepared based on the intermediate modification with ethylenediamine or tetraethylenepentamine (TEPA). The reagent costs for preparing PMAA-PD and PMAD-PD were estimated to be only 15%-20% of that for the same-type commercial resin Dowex M4195 (M4195), but their maximum adsorption capacities of Ni(II) (1.535 and 1.713 mmol/g) at pH 2.0 exceeded that of M4195 by 37.54% and 53.49%, respectively. The combination of amide oxygen and bispicolylamine functionality in PMAA-PD was verified to form more stable binding to Ni(II) relative to the single bis-picolylamine functionality in M4195, resulting in its separation factor alpha Ni(II)/Co(II) of 50.9 being 79.31% higher than that of M4195 and making it more adequate to separate Ni(II) from acidic cobalt-rich liquid to produce high-purity cobalt ( 99.99%). Additionally, PMAD-PD showed the better acid resistance and a versatile decontamination capacity toward Cu(II), Ni(II), Co(II), Zn(II), Cd(II), Fe(II) and Fe(III) for complex strongly acidic wastewater, as its special micro-structure characterized by plentiful small-size pores (<4 nm) and long TEPA skeleton caused abundant synergetic chelation. Moreover, coexisting inorganic salts promoted the HMCs adsorption onto both PMAA-PD and PMAD-PD by weakening electrostatic repulsion. Therefore, the selfsynthesized picolylamine-based chelate resins are promising to efficiently separate HMCs from specific acidic industrial media and thus achieve the purification or decontamination.

Automated summary

In this study, two acid-resistant picolylamine-based chelate resins were prepared and shown to efficiently separate heavy metal cations from strongly acidic media at lower costs compared to commercial resins. These resins exhibited higher adsorption capacities and selectivity for Ni(II) compared to the commercial resin Dowex M4195, making them promising for wastewater treatment and purification purposes.