Leaching diffusion batteries

Batch Percolators The batch tank is not unlike a big nutsche filter it is a large circiilar or rectangiilar tank with a false bottom. The solids to be leached are dumped into the tank to a uniform depth. They are sprayed with solvent until their solute content is reduced to an economic minimum and are then excavated. Countercurrent flow of the solvent through a series of tanks is common, with fresh solvent entering the tank containing most nearly exhausted material. In a typical ore-dressing operation the tanks are 53 by 20 by 5.5 m (175 by 67 by 18 ft) and extract about 8200 Mg (9000 U.S. tons) of ore on a 13-day cycle. Some tanks operate under pressure, to contain volatile solvents or increase the percolation rate. A series of pressure tanks operating with countercurrent solvent flow is called a diffusion battery. 

Mass-transfer problems can be solved by two distinctly different methods, one utilizing the concept of equilibrium stages, the other based on diffusional rate processes. The choice of the method depends on the kind of equipment in which the operation is carried out. Distillation, leaching, and sometimes liquid extraction are performed in equipment such as mixer-settler trains, diffusion batteries, or plate towers, which contain a series of discrete processing units, and problems in these areas are commonly solved by equilibrium-stage calculations. Gas absorption and other operations which are carried out in packed towers and similar equipment are usually handled using the concept of a diffusional process. All mass-transfer calculations, however, involve a knowledge of the equilibrium relationships between phases. 

In some solid-bed leaching the solvent is volatile, necessitating the use of closed vessels operated under pressure. Pressure is also needed to force solvent through beds of some less permeable solids. A series of such pressure tanks operated with countercurrent solvent flow is known as a diffusion battery. 

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