Mercury removal from aqueous media by aminated polyacrylonitrile beads impregnated with nano-urchin bismuth sulfide particles: Experimental and theoretical analysis under batch and continuous mode

Abstract

The present study encompasses a thorough analysis of aqueous Hg (II) adsorption using aminated polyacrylonitrile beads incorporated with high-capacity surfactant assisted bismuth sulfide nanoparticles. The porous beads provided effective contact between aqueous Hg and the inorganic nano-adsorbent (PBS2) that was encapsulated in the matrix. The macro-sized beads served as suitable packing material for designing a fixed bed adsorption column for continuous mode analysis without significant pressure build up and offered an easy solid–liquid separation after treatment. A marginal negative zeta potential of the adsorbent beads improved the interaction with Hg²⁺ facilitating the sorption. The incorporation of amine groups into the polymeric bead surface via amination increased the adsorption capacity further from 83.30 mg/g to 130.00 mg/g (∼56.00%) at 303 K. The associated parameters of batch kinetics (effective pore diffusivity and mass transfer coefficient) were determined using a first principle-based model available in literature. Mercury was chemisorbed via synergistic lone pair interactions of S and N atoms with Hg, leading to formation of coordination bonds (Hg-S and Hg-N). An established mass transfer model was utilized to generate simulated breakthrough curves for the continuous analysis using synthetic feed. Additionally, the adsorption column showed comparable performance using both synthetic and real water samples (synthetically spiked) maintaining high selectivity. The optimized values of axial dispersion coefficient (E_z) and fixed bed mass transfer coefficient (kƒb) were estimated and subsequently used for the scale up studies to predict column life. The adsorbent beads were regenerated using 0.05 M EDTA aqueous solution and showed good reusability (>95.00%) after 5 cycles of operation. Overall, this work highlights a reusable Hg adsorbent possessing good selectivity and capacity and simultaneously demonstrating real-field applicability.