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. Agitation is further assisted by the use of tank baffles to increase the efficiency of agitation and prevent centrifuging of slurries in circular tanks...