The Thickeners/Clarifiers are highly effective to separate solid/liquid at very high rates and treat waste water produced in the washing process of sands and minerals. The sludge, clay and fine particles are accumulated in the bottom of the unit, as a concentrate slurry, to the point of discharge while the clarified effluent flows continuously through a peripheral launder located in the top of the tank. The principle of operation of the Tespa Thickeners is similar to the Hi-Rate Thickeners. This equipment has been specially designed for the processing of plastic clay, whereby it makes possible to obtain in one stage clarified water and a high density sludge with water content similar to a cake produced in process filtration. This equipment has been conceived to achieve a thorough dissolution of a dry-solid flocculant at a convenient concentration rate. The prepared solution, after dilution, is later added to the feed pulp at a certain rate in accordance with feed volume.