Pachuca tanks

The Dorr agitator (Coulson and Richardson, loc. cit.) consolidates in one unit the principles of the thickener and the Pachuca tank. Resembling a rake-equipped thickener, it differs in that the rake is driven by a hollow shaft through which the solids-liquid suspension is lifted and circulated by an air stream. The rake moves the pulp to the center, where it can be entrained by the air stream. The unit may be operated batchwise or continuously. 

Pachuca tank The simplest and most inexpensive device for agitating the pulp. Agitation is achieved by the injection of air under pressure into the bottom of a tall tank. The rising gas draws the surrounding liquid with it to the surface... 

An example of an agitated vessel in which compressed air is used is the Pachuca tank, shown in Figure 10.8. This is a cylindrical tank with a conical bottom, fitted with a central pipe connected to an air supply. Continuous circulation is obtained with the central pipe acting as an air lift. Additional air jets are provided in the conical portion of the base and are used for dislodging any material which settles out. 

The pulp-water systems encountered in the agitation of paper stock represent a highly specialized case of solid-liquid agitation, discussed in a few papers (CIO, K5, 04), which will not be reviewed here. Lamont (L2) discusses the operation of pachuca tanks, used for ore-leaching operations, in which agitation results from air introduced at the tank bottom. 

Pachuca Tanks Air-agitated Pachuca tanks were widely used in mineral processing until the 1960s when the industry concluded that mechanical agitation was more economical and more effective for solids suspension. A description of Pachuca tanks can be found in previous editions of Perry s Handbook. 

Finely divided solids can be suspended in leaching solvents by agitation, and for batch operation a variety of agitated vessels are used (see Chaps. 6 and 11). The simplest is the Pachuca tank (Fig. 13.5), which is employed extensively... 

Figure 13.5 Pachuca tank. (Fran liddell, Handbock of Non-ferrous Metallurgy," 2d ed, McGraw-Hill Book Cortytany, New York, 1945. Used by permission of the publisher.)...

The leaching is 50—60°C without external heating. The cone-bottom tanks are equipped with a pipe from just above the solution level to near the bottom through which air is blown forming bubbles which lower the density of the slurry. These leach tanks, caHed Pachucas, are fairly efficient and are stiH popular although many plants employ mechanical agitators. Most plants use 3—5 tanks in series with acid and calcine being fed to the first and, in some cases, downstream from the first tank as weH. 

Pachuca.—This type of agitator, similar to the Dorr in. what it attempts to accomplish, has in recent years been almost completely replaced by other types. It consists of a very high tank with a conical bottom. Reaching from the top of the tank to the center of this cone is a pipe to be used as an air lift as in the Dorr, the idea being that as the particles sink they strike this conical bottom and slide... 

Fig, 2.3. Pachuca leaching tanks at Western Reefs Uranium Plant, South Africa (Arden, T.V. Ref. 1). 

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