Fluidized leaching and washing

The equations derived in Section III for idealized fluidization may be applied to nonideal G/S systems with suitable corrections, much in the manner of the van der Waals corrections to the ideal gas law, as will be shown in Section IX. Direct use of the equations in Section III is for L/S systems, as exemplified by fluidized leaching and washing. 

Conceivably, any granular solid containing a soluble component disseminated in an inert matrix could be leached rather efficiently in the fluidized state to separate the soluble from the insoluble. And the leached pulp, or slurry, could again be washed in the fluidized state for removal of the solution lodged in intraparticular enclaves and occupying interparticular spaces. 

In extractive metallurgy, for instance, certain low-grade copper ores could be leached with acid or ammoniacal solution advantageously in the fluidized state cupriferous iron ores, after sulfatizing roasting, could have their copper values recovered selectively by leaching with a very dilute acid (Yu et al., 1964)  

By comparing this simple diagram with the conventional continuous countercurrent decantation circuit, it is easy to deduce the following characteristics for fluidized leaching and washing  

A typical fluidized leacher/washer. [After Kwauk, 1973,1979a Kwauk and Wang, 1981.] 

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By comparing this simple diagram with the conventional continuous countercurrent decantation circuit, shown in Fig. lb (Coulson and Richardson, 1968, 1978 Treybal, 1955, 1968, 1980) for carrying out the same duty, it is easy to deduce the following characteristics for fluidized leaching and washing ... 

Fluidized leaching and washing is a countercurrent operation with downflow of solids, called counter-down. The following equation for generalized fluidization... 

Kwauk, M., Fluidized Leaching and Washing, (in Chinese), Science Press, Beijing (1979a)... 

Fluidized leaching and washing belong to counter-down, or mode III, operation for simultaneous particle-fluid motion. A basic case for uniform particle size will be established, and it will then be extended to mixed particle sizes. 

Kwauk, M., Fluidized Leaching and Washing (in Chinese). Science Press, Beijing, 1979a. Kwauk, M., Fluidized Roasting of Oxidic Chinese Iron Ores, Sdentia Sinica 22,1265 (1979b) repr. Intern. Chem. Eng. 21,95-115 (1981). 

Figure 2. Fluidized leaching or washing of uniform particles—reduced vessel parameters A, Z and V. (Kwauk, 1973, 1979 Kwaukand Wang, 1981.)...

Zhang, F., and Zheng, X., Polydisperse Behavior of Leached Uranium Ore in Fluidized Classifying and Washing Column, Proc. China-Japan Fluidization Symposium, April 4-9, 1982, Hangzhou. China 1982). 

Liquid fluidization is the basis of both the Oslo (or Krystal) continuous crystalliser (Mullin, 1993) which is used in the production of, for example, sugar or citric acid, and the bioreactors in which immobilised cells or enzymes are fluidized by the reactant solution (Epstein, 2003). It is used in the leaching of vegetable oils from seeds (Rios et al, 1985 Epstein, 2003) and in physical operations such as the washing and preparation of vegetables. 

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