Leaching agitated tanks

Impeller-agitated tanks These can be operated as continuous leaching tanks, singly or in a series. If the sohds feed is a mixture of particles of different setthng velocities and if it is desirable that all particles reside in the leaching tank the same lengths of time, design of a continuous stirred leach tank is difficult and uncertain. 

BioCOP [Biological COPper] A bacterial process for leaching copper from its ores. BioCOP uses an agitated tank for oxidation and leaching of copper sulfides. Developed by BUP Billiton and Codelco, which operated a demonstration plant in Chuquicamata, Chile, from 2003. Several plants have been operated commercially in Chile since then. 

Although the overall processes have evolved for specific metals, and leachants, there are principally only two leaching techniques that provide the pregnant leach solution for metal recovery percolation leaching and agitated tank leaching. 

In agitated tank leaching systems, finely ground ore must be mixed with the lixiviant until the reaction is complete. Liquid/solid separation processes are used to recover the solution and prepare the waste for disposal in a tailing impoundment. Unlike percolation leaching operations, these operations require a large impoundment area to not only handle the solids, but also to neutralize the chemistry and pH of the solutions used to extract the metal value. 

Pressure acid leaching (PAL) combined with atmospheric pressure agitated tank leaching (AL). 

Amongst the options considered were heap leaching [17], agitated tank atmospheric leaching [18, 19,20, 21] and combinations of PAL and atmospheric leaching [22, 23, 24]. 

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. 

Modem manufacturing processes quench the roast by continuous discharge into the leach water held in tanks equipped with agitators. At this point the pH of the leach solution is adjusted to between 8 and 9 to precipitate aluminum and siHcon. The modem leaching operations are very rapid because no or htde lime is used. After separation of the ore residue and precipitated impurities using rotary vacuum filters, the cmde Hquid sodium chromate may need to be treated to remove vanadium, if present, in a separate operation. The ore residue and precipitants are either recycled or treated to reduce hexavalent chromium to Cr(III) before disposal. 

Dispersed-Solids Leacbing Equipment for leaching fine solids by dispersion and separation includes batch tanks agitated by rotating impellers or by air and a variety of continuous devices. 

Batch Stirred Tanks Tanks agitated by coaxial impellers (turbines, paddles, or propellers) are commonly used for batch dissolution of solids in liquids and may be used for leaching fine solids. Insofar as the controlhng rate in the mass transfer is the rate of transfer of mate-... 

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. 

In pharmaceutical processes, leaching by immersion is carried out in simple tanks which may be agitated by a turbine or paddle. If the solids are adequately suspended, intimate contact between the phases promotes efficient extraction. Incomplete extraction due to channeling is avoided and difficulties due to swelling do not arise. Problems arise, however, in the subsequent... 

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