Precipitation / Flocculation
Precipitation and flocculation are chemical water treatment processes that cannot always be clearly distinguished from each other, since they can be caused by the same additives and sometimes also run in parallel. The aim of both processes is to convert dissolved or non-separable water constituents into a separable form. The precipitation / flocculation is thus usually followed by a further processing stage (filtration, sedimentation or flotation) for separating the substances from the water.
During precipitation, chemicals are added to the water, which react chemically with certain dissolved water constituents. As a result of this reaction, the substances are converted into insoluble and thus separable compounds.
Flocculation is about the agglomeration (aggregation) of colloidal and finely suspended substances. If these particles are suspended in the water, in addition to the attractive forces (van der Waal surface forces), repulsive forces (electrostatic forces with the same charge) also act between the particles. The repulsive forces can be overcome by the addition of flocculant, so that agglomeration of the particles occurs. In the field of water treatment, the flocculants are often hydrolyzing iron and aluminum salts. Subsequently, flocculating auxiliaries which improve the flocculation formation or the flocculation properties can also be metered in. Polyelectrolytes are often used here.