Abstract

Flocculating agents are chemical additives that cause suspended solids to form aggregates called flocs. These agents are used in water treatment, municipal and industrial waste treatment, mineral processing, and papermaking. Flocculating agents are either inorganic salts or water-soluble organic polymers. They act by shrinking the ionic double layer, or neutralizing the surface charge of suspended particles, or bridging between particles. The type of flocculant used depends on the type of solid–liquid separation being performed. The physical properties and size of the flocs as well as the rate of floc formation are the critical parameters in this process. Flocculants are usually selected by the results of laboratory-scale experiments. The manner in which the flocculating agent is mixed with the substrate can affect the results. Special analytical methods are used for some flocculating agents. Some agents or impurities in them may present toxicological or environmental problems. The general economic trend is the replacement of inorganic salts with organic polymers, which give improved performance.