Comparative Study of the Effect of Aluminum Chloride, Sodium Alginate and Chitosan on the Coagulation of Polystyrene Micro-Plastic Particles

Abstract

The coagulation of negatively charged polystyrene latex micro-plastic particles is studied in presence of two linear biopolymers (chitosan and sodium alginate) and a trivalent salt, aluminum chloride as coagulants. The performance of the different coagulants, impact of the solution pH, and use of alginate as a coagulant in presence of aluminum chloride, fractal character and compactness of aggregates are investigated by using mainly electrophoretic experiments and image analysis. The coagulant efficiency and coagulation routes and strategies are analyzed by considering the variations of the particle surface charges at variable coagulant concentrations. Optimal coagulant dosage is determined when the surface charge of the latex particle is neutralized. Our results suggest that the biopolymers are in some cases more efficient than AlCl3 for the destabilization of latex micro-plastic particles. Indeed, charge neutralization is more rapidly achieved by chitosan regarding the optimal dosage and chitosan is found to work over a wider range of pH values. Alginate is also found to be a good candidate when particle charge inversion is achieved first with aluminum chloride. We also demonstrate that coagulant dosage is dependent on the initial pH of the suspension. When the initial pH of the dispersion is low, the isoelectric point is obtained for small dosage values. Image analysis indicates that in all situation fractal aggregates are obtained and that biopolymers result in the formation or more compact structures which will increase the sedimentation rates.