flocculation

n. (Geol.) 1. The process by which small particles of fine soils and sediments aggregate into larger lumps. [ 1913 Webster ]

2. The process or event in which masses of a solid substance of perceptible size form in a liquid by aggregation of smaller particles, and usually sediment to the bottom of the containing vessel; as, addition of a cationic polymer can cause flocculation of a negatively charged colloidal suspension. [ PJC ]