Dialysis technology supporting the preparation of acid-resistant picolylamine-based hydrogel sphere for selectively recycling copper, nickel and cobalt from strongly acidic wastewaters

Due to the inhibition from high-concentration proton, acid-resistant adsorbents (especially hydrogels) for directly recycling heavy metal cations (HMCs) from strongly acidic wastewaters (pH < 2.0) are rarely reported yet. Herein, the pyridine-functionalized polyethylenimine polymer (PEIPD) was synthesized and then purified with dialysis technology, based on which a double-network hydrogel sphere PEIPD-CaA (CaA for calcium algi-nate) was prepared. At pH 1.0, PEIPD-CaA adsorbed Cu2+, Ni2+ and Co2+ through deprotonation-chelation processes in maximally 1.844 +/- 0.044, 1.312 +/- 0.063 and 0.712 +/- 0.047 mmol/g respectively, which was unat-tainable by other known adsorbents at this acidity, and the adsorption processes displayed good resistance to interferences of even 500 mmol/L common inorganic salts or sufficient organics (EDTA, citric acid and tartaric acid). The bis-picolylamine group from PEIPD component of this hydrogel proved indispensable for chelation, and X-ray photoelectron spectroscopy revealed that the O donors (ether bond, hydroxyl, etc.) from its calcium alginate component assisted the bis-picolylamine group in coordinating Cu2+ and Co2+ but not Ni2+, because Ni2+ possessed a smaller ionic radius and softness. Additionally, other coexisting HMCs (Zn2+, Fe2+, Pb2+, etc.) caused negligible interferences in the adsorption of Cu2+, Ni2+ or Co2+. Dynamic column test further demon-strated that PEIPD-CaA could highly selectively capture nickel from stainless steel rinsing wastewater (pH 1.5) by raising the nickel purity from 10.5% in wastewater to 91.8% in obtained eluent. Therefore, this acid-resistant hydrogel displays great potential in the selective recycling of Cu2+, Ni2+ and Co2+ from strongly acidic waste-waters, helping realize their direct decontamination and secondary utilization.