Flocculation Of Colloidal Suspensions Research Articles

The use of dielectric spectroscopy in the investigation of the effect of polymer choice on the flocculation of polystyrene particles

The flocculation of colloidal suspensions using synthetic polymeric flocculants is an important operation in separation processes. Optimizing flocculant use requires insight into the underlying mechanisms governing flocculation. As most existing methods for the online characterization of flocculation processes can only be used on dilute suspensions, new methods applicable at high solid content levels are of interest. This study used dielectric spectroscopy to investigate the mechanisms involved in the flocculation of polystyrene particles with three different cationic polymers. We observed that the relaxation time of the dielectric dispersion increased as particle flocculation was initiated. Reduction of particle charge due to polymer addition was found to reduce the magnitude of the dielectric dispersion, whereas the formation of aggregates increased it. This resulted in decreasing magnitude when charge reduction was the primary cause of flocculation, whereas the magnitude increased when the particles were flocculated by bridging.

The use of dielectric spectroscopy for the characterization of polymer-induced flocculation of polystyrene particles

The flocculation of colloidal suspensions is an important unit operation in many industries, as it greatly improves the performance of solid separation processes. The number of available techniques for evaluating flocculation processes on line is limited, and most of these are only functional in dilute suspensions. Thus, techniques usable for flocculation characterization in high-solids suspensions are desirable. This study investigates the use of dielectric spectroscopy to monitor the flocculation of polystyrene particles with a cationic polymer. The frequency-dependent permittivity is modeled and the model parameters are used to describe the particle aggregation. The results show a peak in the modeled time constants of the dielectric relaxation at the onset of flocculation. Further, the adsorption of polymeric flocculant onto the particle surface results in a reduction in particle charge, evident as a decrease in the magnitude of the dielectric dispersion. The use of dielectric spectroscopy is found to be valuable for assessing flocculation processes in high-solids suspensions, as changes in parameters such as floc size and charge can be detected.

Mineral weathering in trachydacitic-derived soils and saprolites involving formation of embryonic halloysite and gibbsite at Mt. Amiata, Central Italy

Mount Amiata is a volcano that has been extinct for 200 ka. It is located in southern Tuscany, central Italy, and is composed largely of trachydacitic rocks. The soils of Mt. Amiata show a dark, carbon-rich A horizon that overlies a slightly structured Bw horizon or, directly, a very thick saprolite, which at a depth of about 3 m still maintains some ellipsoidal cores of coherent material. Mineral weathering in two of these soils, one under beech and the other under chestnut, was studied in detail. The mineralogy of the parent rock consists predominantly of volcanic glass with phenocrysts of feldspar (principally K-feldspar), biotite and pyroxene. The main weathering products are an embryonic form of halloysite and gibbsite, while allophane is usually absent or occurs in minor amounts. SEM evidence indicates that the clay minerals form directly from the weathering of volcanic glass in an environment where Si is preferentially depleted in relation to Al. In the saprolite an anomalous situation is observed where optically fresh ferromagnesian minerals are thickly coated by clay particles whereas the surfaces of the glass and feldspar grains are relatively much cleaner. However, the ferromagnesian minerals are also much more heavily colonised by fungal hyphae and it is proposed that this results in the preferential deposition or flocculation of colloidal suspensions which translocate from higher positions in the weathering profile.