Precipitation of solids from a liquid is effected in a confined contact zone by passing the liquid downwardly through a rising stream of hot gas. A number of light weight spheres are confined within and freely movable throughout the zone. The upper and lower limits of the zone are defined by partitions each composed of a horizontal foraminous divider and an imperforate wall. The imperforate wall extends upwardly and outwardly from the divider and terminates at a wall defining the side limit of the zone. The velocity of the rising gas is highest as it passes through the divider and decreases upwardly therefrom. The gas causes the spheres resting on the divider to move upwardly and outwardly until the gas velocity is no longer capable of keeping the spheres in suspension whereupon the spheres fall downwardly along the side wall and imperforate wall scouring solids precipitated thereon.
