Simultaneous removal of Ni(II) and Cr(VI) from aqueous solution by froth flotation using PNIPAM-CS intelligent nano-hydrogels as collector

In this work, the feasibility of froth flotation for simultaneous removing Ni(II) and Cr(VI) from aqueous solution by using thermo-responsive intelligent nano-hydrogels consisting of poly(N-isopropylacrylamide) (PNIPAM) and chitosan (CS) as the collector was investigated. PNIPAM-CS nanohydrogels were synthesized by free radical precipitation polymerization and they were characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and laser nanoparticle size tester. Experimental results indicated that CS content had a significant impact on the phase transition behaviors of PNIPAM-CS nano-hydrogels. The suitable mass ratio of PNIPAM and CS was 2:1. The suitable pH of 6 for performing adsorption experiments was determined according to the species distribution of Ni(II) and Cr(VI) at different pH values. The adsorption kinetic data of PNIPAM-CS nanohydrogels towards Ni(II) and Cr(VI) followed the pseudo-second-order model and their adsorption behavior were fitted well to Freundlich equation. Based on X-ray photoelectron spectroscopy (XPS) analysis, the driving forces for adsorption of Ni(II) and Cr(VI) by PNIPAM-CS nano-hydrogels mainly involved electrostatic adsorption, ion exchange and complexation. Finally, froth flotation was performed under the conditions of air flow rate 30 mL/min, cocamidopropyl betaine (CAB) concentration 70 mg/L, temperature 313 K and PNIPAM-CS nano-hydrogels concentration 6.0 g/L. The removal percentages of Ni(II) and Cr(VI) were 86.1% and 91.5%, respectively. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

The study investigated the feasibility of using thermo-responsive intelligent nano-hydrogels for removing Ni(II) and Cr(VI) from aqueous solutions simultaneously. Experimental results showed that the suitable PNIPAM to CS mass ratio was 2:1, with an appropriate pH of 6 for adsorption experiments. XPS analysis revealed that the adsorption of Ni(II) and Cr(VI) by PNIPAM-CS nano-hydrogels mainly involved electrostatic adsorption, ion exchange, and complexation. Froth flotation under specific conditions achieved removal percentages of 86.1% for Ni(II) and 91.5% for Cr(VI).