Method and apparatus for separating fast settling particles from slow settling particles

A hydroseparator for separating particles based on the differences in settling rates such as for separating fly ash from gypsum includes a substantially cylindrical side wall closed at its bottom end by a floor. A laminar upflow is created through the hydroseparator by adding dilution water to the bottom of the hydroseparator and removing most of the added dilution water from the top of the hydroseparator. The remaining volume of liquid is removed in an underflow. The hydroseparator is divided into at least two sections by a baffle that extends about the interior of the side wall. An inlet is disposed in the center of the hydroseparator slightly above the baffle such that the material added to the hydroseparator to be separated is inserted into the section of the hydroseparator completely surrounded by the baffle. The velocity of the upflow is controlled such that it is not fast enough to cause the faster-settling gypsum particles to rise but is fast enough to cause the slower-settling fly ash particles to rise with the upflow. The upflow thus separates the fly ash from the gypsum and floats the fly ash to the top of the hydroseparator where it is removed in the overflow. An agitator is provided in the lower portion of the hydroseparator to evenly distribute wash water and to keep the gypsum fluid.