In situ investigation of the effect of functional groups in polymeric flocculants on the adsorption of kaolin and Pb2+

Flocculation technique is extensively adopted in the tackling of sulfide mineral processing wastewater, which contains abundant suspended solids and heavy metal ions. The functional groups of polymeric flocculants significantly influence the interactions between flocculants and pollutants. Herein, self-assembled monolayers (SAMs) terminated with − NH 2 , − OH, − COOH, and − CH 3 and in situ polymerization coating of acrylamide exclusively containing − CONH 2 were fabricated via the vapor-phase deposition, self-assembly molecular membrane, and atomic transfer radical polymerization methods. X-ray photoelectron spectroscopy, water contact angle measurements, and AFM imaging were utilized for the characterization of functionalized surfaces. The adsorption behavior of kaolin and Pb 2+ on these surfaces was explored using quartz crystal microbalance with dissipation (QCM-D). The amount of kaolin adsorbed on functionalized surfaces followed the sequence of − CONH 2 (∆ f of − 1360.55 Hz) >   −  NH 2 (∆ f of − 395.43 Hz) >   −  OH (∆ f of − 181.31 Hz) >   −  COOH (∆ f of − 1.75 Hz) >   −  CH 3 (∆ f of − 0.1 Hz). The polymer coating with acrylamide (CONH 2 -functionalized surface) with a specific molecular weight exhibited strong bridging effect, capturing quantities of kaolin. The amino group underwent protonation to form NH 3 + , combining with the negatively charged kaolin through electrostatic attraction. These indicated that both the bridging effect of flocculants and the electrical neutralization between flocculants and particles were critical factors influencing the settlement of kaolin. For Pb 2+ , its adsorption amount on functionalized surfaces followed the order of − COOH (∆ f of − 1.53 Hz) >   −  OH (∆ f of − 1.27 Hz) >   −  CH 3 (∆ f of − 0.34 Hz). The carboxyl group played a critical role in facilitating the adsorption of Pb 2+ through chelation and electrostatic interaction, confirming its function as an active site. Our findings provide profound insights into the structure–activity relationship of flocculants, underscoring the importance of designing efficient flocculants for wastewater treatment. Graphical