Hydroclassification

Hydroclassification is a separation process that uses fluid flow and particle settling to divide a suspension into fractions by particle size, and, in some contexts, by density. It encompasses methods and equipment designed to exploit hydrodynamic forces to classify solids in liquids, with applications in mineral processing, environmental engineering, and soil science. The term can refer to industrial classification with devices such as hydrocyclones, as well as the laboratory-based hydrometer or pipette methods used to determine grain-size distributions in soils.

In mineral processing, hydroclassification typically employs hydrocyclones or other inline classifiers. Feed slurry enters a conical chamber where a vortex creates centrifugal forces that retain coarser particles in the underflow while finer particles exit with the overflow. By adjusting parameters such as feed density, pressure, cone angle, and cone size, operators control the cut size and the size distribution of each stream, enabling downstream processes like flotation and milling to handle appropriate particle ranges.

In soil science and sedimentology, hydroclassification often refers to the hydrometer or pipette method for determining particle-size distribution, especially for sub-sieve-size fractions. The technique uses settling rates governed by Stokes’ law: at specified times, a hydrometer measures suspension density, which is converted into percent finer than given sizes. Combined with sieve analysis for coarser fractions, hydroclassification yields a complete grain-size distribution used in geotechnical and engineering evaluations.

Standards and practice vary by industry, but the concept remains the same: classify particles by size through controlled fluid-based separation, with equipment and methods tailored to the material and required cut points.