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

Abstract

• PMAA-PD showed better separation ability for Ni(II) versus Co(II) than M4195. • PMAD-PD could adsorb Ni(II) (0.920 mmol/g) and Co(II) (0.605 mmol/g) at pH 1.0. • The reagent costs of PMAA-PD and PMAD-PD were only 15%-20% of that of M4195. • Cu(II) owned much more stable binding to picolylamine-based resins than other HMCs. • Inorganic salts promoted the HMCs adsorption by weakening electrostatic repulsion. 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 bis-picolylamine 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 α 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 self-synthesized picolylamine-based chelate resins are promising to efficiently separate HMCs from specific acidic industrial media and thus achieve the purification or decontamination.