Dextran derivatives application as flocculants

Abstract

A large variety of hydrophilic and amphiphilic polyelectrolytes based on dextran have been previously tested as coagulating and flocculating agents in model wastewater treatment and the results are presented in this review article. The dextran derivatives are either cationic, bearing (i) pendent quaternary ammonium groups, N-alkyl-N,N-dimethyl-N-(2-hydroxypropyl)ammonium chloride and (ii)1-(2-hydroxypropyl)-3-methyl imidazolium chloride, randomly distributed along the polymer backbone or anionic, (i) dextran monobasic phosphate with HP(O)(OH) groups and (ii) dextran derivatives with carboxylic groups namely, dextran-g-poly(acrylamide-co-sodium acrylates). This paper will give an overview of the main results obtained in the separation of suspensions and emulsions containing either inorganic (clay, titanium dioxide, zirconium silicate (kreutzonit), zinc oxide and ferric oxide (hematite)) or organic (pesticides: Fastac 10EC, Decis, Dithane M45) contaminants. The investigations considered the influence of some polyelectrolyte characteristics (the charge density, the length of the alkyl substituent, the molecular mass), polyelectrolyte dose and initial concentration, as well as the properties of the model suspensions/emulsions (contaminants concentration, dispersion medium composition and pH) on the separation process. Turbidity/absorbance, zeta potential and particle dimensions measurements allowed to determine the polycation dose where the maximum separation efficiency was obtained, the flocculation mechanism and the floc size and distribution for each peculiar system.