Highly effective and selective removal of lead ions by polymer-grafted silica-coated acid-resistant magnetic chitosan composites

Separation and recovery of lead resources from lead-containing wastewater is very important to achieve reuse of lead(II) and environmental protection. Herein, a novel magnetic separation adsorbent, polymer-grafted silica -coated acid-resistant magnetic chitosan composite (PMSC), was facilely constructed and applied for the efficient and selective adsorption of Pb(II) from aqueous solutions. The adsorption results in the Pb(II) mono -contaminated system showed that the adsorption process of PMSC on Pb(II) was significantly pH-responsive and increased with increasing pH, reaching a qmax value of 88.03 mg g-1 at pH 6.0, which was more than 6 times of MSC (14.47 mg g-1). More interestingly, the adsorbent with inert silica coated on the core has a higher acid resistance, with almost no iron leaching from PMSC at pH 1.0, while PMC has 3.99 mg L-1 of iron leaching. The results of adsorption isotherms and kinetics of Pb(II) by PMSC showed that Langmuir and pseudo-second -order kinetics can better describe the adsorption behavior, indicating that the adsorption process was mainly controlled by chemisorption and the maximum monolayer adsorption capacity can reach 111.12 mg g-1 at 298.15 K. Furthermore, PMSC maintained about 80 % of the initial adsorption capacity after five cycles of repeated use, demonstrating its good regenerative cycling performance. Also, PMSC showed excellent selective adsorption of Pb(II) in the coexistence solutions of multiple metal ions with the SPb up to 85.83 %, which was far more than that of MSC (23.55 %), indicating that the polymer grafting had a significant enhancement on the selective performance of the adsorbent. This work could provide design and preparation insights for the development of novel, acid-resistant, recyclable and fast magnetic separation adsorbents for the efficient se-lective separation of lead ions.