Study on the Starch-Driven Flocculation Mechanism of Sepiolite in the Presence of Mono- and Divalent Cations Using Microfluidic Device

In this pioneering study, cationic starch (CS) was employed for the first time to flocculate sepiolite (SPT) in aqueous media containing common real-water electrolytes (NaCl, MgCl2, and CaCl2). Floc formation and morphology were monitored using an innovative microfluidic device (FlocChip), marking a novel approach to studying flocculation dynamics. Additionally, the behavior of SPT suspensions was evaluated via turbidimetry, while electrokinetic measurements, adsorption isotherms, and surface analyses provided insight into the underlying flocculation mechanisms. The findings demonstrate that CS is a highly effective natural bioflocculant for removing SPT particles across a broad salinity range (ionic strength: 0.001, 0.01, and 0.1 mol/dm3). Optimal flocculation was achieved with CS dosages between 40 and 400 mg/g, with higher cation concentrations requiring lower polymer doses. The presence of CaCl2 led to the most efficient flocculation and promoted aggregate formation via calcium bridging with oxygen atoms on the sepiolite surface. The newly developed FlocChip enabled precise optimization of flocculant dosage and real-time analysis of flocculation kinetics; it also allows for a 189-fold reduction in reagents’ volume in comparison to turbidimetric methods. These findings provide critical insights into the application of sustainable bioflocculants like CS, paving the way for greener wastewater treatment solutions.