Preparation and flocculation performance study of a novel amphoteric alginate flocculant

Sodium alginate is a natural biomacromolecule with promising applications as a flocculant for wastewater treatment due to its biodegradability and non-toxicity. To enhance the flocculating efficiency, simplify the synthetic process of the flocculants and expand the application scope of alginate, a novel amphoteric flocculant was synthesized through reaction of alginate with 3-chloro-2-hydroxypropyltrimethyl ammonium chloride under alkaline conditions. The structures of the flocculants were characterized using various methods. The flocculants demonstrated nanoparticle sizes with a narrow distribution. The amphoteric flocculant could not only effectively remove the positively-charged Pb 2+ from wastewater, but also removed the negatively-charged humic acid. Under optimum conditions, the removal rates reached 92.32% and 95.18% for Pb 2+ and humic acid, respectively. Compared with unmodified alginate, the amphoteric flocculant had significantly improved flocculation for the heavy metal ions and negatively-charged pollutants. The flocculating mechanism for heavy metals was chelating, and was confirmed by X-ray photoelectron spectroscopy, and the flocculating mechanism for humic acid was electric neutralization. The adsorption isotherm could be described by a Langmuir model. The flocculation process accorded with quasi-second-order kinetics equation. This novel amphoteric flocculant has promising applications as an environmentally-friendly treatment agent for wastewater.