Abstract: A washbox comprising a vessel divided into a stratification compartment and an adjacent reject compartment, a perforate grid plate extending across upper parts of the compartments. First pulsation means activates the water in the stratification compartment, and second pulsation means activates the water in the reject compartment separately and in isolation from the stratification compartment. A divider is mounted above the part of the grid plate which extends over the reject compartment, an upper surface of the divider defining a first outlet channel by which material of a lower density may pass from the washbox, whilst a lower surface of the divider, together with the said part of the grid plate which extends over the reject compartment, defines a second outlet channel along which material of higher density may pass from the washbox.