Tank leaching

In metallurgical processes tank leaching is a hydrometallurgical method of extracting valuable material (usually metals) from ore.

Tank vs. vat leaching

Factors

Tank leaching is usually differentiated from vat leaching on the following factors:

  1. In tank leaching the material is ground sufficiently fine to form a slurry or pulp, which can flow under gravity or when pumped. In vat leaching typically a coarser material is placed in the vat for leaching, this reduces the cost of size reduction;
  2. Tanks are typically equipped with agitators, baffles, gas introduction equipment designed to maintain the solids in suspension in the slurry, and achieve leaching. Vats usually do not contain much internal equipment, except for agitators.
  3. Tank leaching is typically continuous, while vat leaching is operated in a batch fashion, this is not always the case, and commercial processes using continuous vat leaching have been tested;
  4. Typically the retention time required for vat leaching is more than that for tank leaching to achieve the same percentage of recovery of the valuable material being leached;

In a tank leach the slurry is moved, while in a vat leach the solids remain in the vat, and solution is moved.

Processes

Tank and vat leaching involves placing ore, usually after size reduction and classification, into large tanks or vats at ambient operating conditions containing a leaching solution and allowing the valuable material to leach from the ore into solution.

In tank leaching the ground, classified solids are already mixed with water to form a slurry or pulp, and this is pumped into the tanks. Leaching reagents are added to the tanks to achieve the leaching reaction. In a continuous system the slurry will then either overflow from one tank to the next, or be pumped to the next tank. Ultimately the “pregnant” solution is separated from the slurry using some form of liquid/solid separation process, and the solution passes on to the next phase of recovery.

In vat leaching the solids are loaded into the vat, once full the vat is flooded with a leaching solution. The solution drains from the tank, and is either recycled back into the vat or is pumped to the next step of the recovery process. . Vat leach units are rectangular containers (drums, barrels, tanks or vats), usually very big and made of wood or concrete, lined with material resistant to the leaching media. The treated ore is usually coarse.

 The vats are usually run sequentially to maximize the contact time between the ore and the reagent. In such a series the leachate collected from one container is added to another vat with fresher ore

As mentioned previously tanks are equipped with agitators to keep the solids in suspension in the vats and improve the solid to liquid to gas contact.[1] Agitation is further assisted by the use of tank baffles to increase the efficiency of agitation and prevent centrifuging of slurries in circular tanks...

Extraction efficiency factors

Aside from chemical requirements several key factors influence extraction efficiency:

The tank leaching method is commonly used to extract gold and silver from ore, such as with the Sepro Leach Reactor.

References

  1. Altman, K., Schaffner, M., & McTavish, S. (2002). D. J. Barrat; H. N. Doug; A. L. Mular, eds. Mineral Processing Plant Design, Practice and Control. Littleton, Colorado, USA: Society for Mining, Metallurgy, and Exploration, Inc. (SME). pp. 1631–1643.
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