Agitated vessels leaching

Three particle collision mechanisms can occur in an agitated vessel. These are (a) particle-vessel, (b) particle-impeller and (c) particle-particle. Most of the work on collisions has been related to secondary nucleation, but there are other systems where mechanical abrasion following impact may occur and may be undesirable, e.g. breakdown of friable catalysts, or in mammalian cell culture on microcarriers or desirable, e.g. removal of an impervious outer skin which forms on ore particles during some leaching processes. 

Finely ground solids may be leached in agitated vessels or in thickeners. The process can be unsteady-state batch or the vessels can be arranged in a series to obtain a... 

Droplet breakup and coalescence occur in parallel in most industrial processes. An example is found in the mining industry, where metals are extracted from leach solutions by contacting with an organic phase. In both agitated vessels and static mixers, there are two stages of contacting. The first is with high specific... 

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 13.4 Agitated batch leaching vessels (see also Chap. 11).

For more fibrous solids, such as sugar cane, which is leached with water to remove the sugar, it has been shown [35] that leaching is generally more efficient in a thoroughly agitated vessel than by percolation, probably because the large amount of static liquid holdup (see Chap. 6) makes important amounts of solute unavailable. 

Ryon, Daley, and Lowrie [Chem. Eng. Ftog., 55(10), 70, (1959), U.S. AFC ORNL-2951, I960]. Continuous extraction of uranium from sulfate-ore-leach liquors and kerosine -t- trihiityl phosphate and di(2-ethylhexyl)-phosphoric acid baffled vessels, turbine agitated. There is strong evidence of the influence of a slow chemical reaction. 

In a pilot scale test using a vessel 1 m3 in volume, a solute was leached from an inert solid and the water was 75 per cent saturated in 100 s. If, in a full-scale unit, 500 kg of the inert solid containing, as before, 28 per cent by mass of the water-soluble component, is agitated with 100 m3 of water, how long will it take for all the solute to dissolve, assuming conditions are equivalent to those in the pilot scale vessel Water is saturated with the solute at a concentration of 2.5 kg/m3. 

It is frequently possible to design the leaching process on a continuous co-current basis, where acid, water and ore are fed into a vessel continuously, or at regular intervals, and discharged in a similar manner. In these circumstances the agitation system is usually designed to suspend the solids sufficiently in the liquid phase so as to allow them both to overflow from... 

Assuming steady-state conditions and efficient agitation in a single cocurrent leaching vessel, it is easily shown that the probability of a particle remaining in the vessel after time t is equal to exp(—r/7. ... 

The sodium reduction of titanium tetrachloride was actually carried out as early as 1939 in Germany, and about 670 kg was produced by the Deutsche Gold and Silber Scheideanstalt, during the 1939-45 war. The process, now obsolete, involved reduction in a molten bath of 50 per cent sodium chloride and 50 per cent potassium chloride at 800°C in an atmos phere of hydrogen. The reactors consisted of expendable welded sheet-iron cylindrical vessels, 50 cm diameter by 70 cm deep and 2 mm thick. These rested loosely in a stout iron crucible, fitted into a gas-fired furnace. A portable stirrer was used to agitate the reactor contents. Approximately 20 kg batches of titanium were reduced by distilling 85 kg of titanium tetrachloride at a controlled rate into a melt of 15 kg sodium chloride and 15 kg of potassium chloride, covered with a layer of 46 kg of molten sodium. The titanium sank to the bottom of the molten salts, and at the end of the reaction was recovered from the crushed solidified melt by leaching with dilute hydrochloric acid, in a ceramic-lined vessel. It was finally washed in water and dried at a moderate temperature. The same plant was also used for the production of zirconium metal by the sodium reduction of potassium fluorozirconate (KaZrF ]. 

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