TYPES OF VAT LEACHING

Vat leaching can be divided in three types since the time that was  introduced in the mining world: initial, traditional and continuous vat.

1) Initia l Vat. This type of vat leaching was used since the first years of the last century and its application was discarded in the ‘30s. It has been considered like the precursor of the heap leaching process.

These vats were rounded with a diameter 3 to 5 times its height. Also, the bottom had a false floor made of holed wood. The ore to be processed should be crushed and the vat was filled with the ore. The cyanide solution passed from the false floor until the top of the vat so that the ore were totally flooded. After a time, the pregnant solution was collected. This cycle could be repeated several times.

When the ore was clayey or had many fine particles was necessary a previous classification where the fine material could be treated by agitation and the coarse particles could be used in the vat.

2) Traditional vat. Since 1980, by using agglomeration and more sophisticated equipment was possible built vat leaching plants with major efficiency. Some plants were built in several parts of the world:

• In 1981. Colorado, United States; were built 4 vats for treating 1000 tons of gold ores. The recovery was 90%.
• In 1983. Sudan, were built 4 vats with capacity of 350 tons. The material treated was old tailings.
• In 1986. Bakit Young Gold Mines, Sudan.
• In 1987. Arirahua, Peru, were built 2 vats for treating 500 tons. The material processed was oxidized ore and old dumps.

Traditional vat has three alternatives.

Fig.1 Vat leaching systems

Alternative A is a Vat with low height and presents a ramp on the leaf side and a vertical wall on the right side. Figure 2 shows a sectional cut of vat indicating how the ore was deposited.

Alternative B is a Vat with low height and presents two ramps. However, there are some disadvantages: first, the required area is major than alternative A, and second, the ore on the ramps could no be leached with the same efficiency as was leached the ore present in the middle.

Alternative C is Vat employed in Sudan. This vat has a floodgate driven by a crane or a similar system.

Traditional vat involves fours stages