**3.4 In situ bioleaching**

In situ leaching requires making the ore permeable for a solution and air to be circulated through the ore body. It does not require metal containing material to be removed from the ground [18]. It employs a method of recovering target minerals from the leach solution. The acid solution percolates until it reaches to impermeable layer. In situ includes recovery of minerals from the intact ore. The resulting metal-enriched solutions are recovered through wells drilled below the ore body. In case of in situ leaching the main concern is pollution of ground water, with this regard there are three types of ore bodies generally considered for in situ leaching: surface deposits above the water table, surface deposits below the water table and deep deposits below the water table. It is burden materials, establish permeability allowing air to pass in which metal bearing solution collected in the sumps [7]. It is combined with mineral recovery operation time and again to pull out the minerals from recovered fluid or pregnant solution or leachant. Acidified leach solutions, applied to the top surface of the entire ore zone, infiltrate through the fragmented ore due to the blast. The leaching bacteria become established and facilitate metal extraction. Metal-rich solutions or large volume of solution is circulated with the aid of gravity flow and pumped and recovered in sumps then again pumped to the surface for metal recovery, the returning fluids to the extraction operation are known as "barren solution". Metal recovery depends on two major things first the bacteria used (Acidithiobacillus Ferrooxidans) and permeability of the ore-body, which can be increased by fragmenting of ores in place, called "rubblizing". Due to the ground water pollution this leaching process becomes less used and less popular [18] on the contrary it has been said that it is a best substitute for open pit and shaft mining operation, basically when in situ leaching is applied, no gangue or tailing is byproduct, it also called green mining or mine of the future [33].
