**1. Introduction**

Bioleaching is the extraction of metals from ores using the principal components water, air and microorganism [1]. It is the extraction or mobilization of valuable (target) metal from the ore, can also be defined as a process of recovering metals from low grade ore [2, 3], with regard to solubility, bioleaching can be defined as a process of recovering soluble one from insoluble impurities after dissolving sulfide metal as soluble salt in a solution [4] that results toxics and heavy metals removed. It is isolation of metals from their ores, concentrates and mineral wastes under the influence of microorganisms leading to dissolution of metal solutions of leach liquor containing metals [5], followed by solvent extraction, stripping, ion exchange, electro wining to get pure metal.

Both bioleaching and biooxidation leads to recovery target mineral; but there is technical difference between the two technologies. Bioleaching refers to the use of bacteria, the common Thiobacillus Ferrooxidans and other bacterial as a leachant to leach sulfide minerals where the target elements remains in the solution during oxidation process, after the metal recovery the solid left behind regarded as residue and in the contrary biooxodation discard the solution after having metal values in solid phase [6, 7] microorganism also engaged in removal of radionuclides and leaching of metal that are regarded as toxic in some cases and good for bioremediation of soil, the process stops radio nucleation that result the removal of stability of target elements [7].

Bioleaching has been used for a long period of time without regarded as microbial leaching process; it has been used as early as 1000 BC when a man from metal laden recovered copper from a water, passes through copper ore deposit [8]. It was in 1556 at the mine located in Spain at Rio Tinto (Rd River) mine, slurry containing very high concentration of ferric ions leached due to the action of microorganisms [4]. Copper was precipitated from the solution obtained from this river, the very first bio mineralization process was copper dissolution, then the process continued to be developed in countries like Norway, Germany and English at different era of time, in the year 1947 heap and dump leaching was practiced that leads to the development of bacterial bioleaching process [9].

The gram-negative chemolithotroph bacterial, Thiobacillus Ferooxidans was first cultured and isolated from mine water by Colmer and Hinkel [9]. Thiobacillus Ferrooxidans is rod shaped ranging in diameter from 0.3 to 0.8 micrometers (μm), in length from 0.9 to 2 μm, 0.5 μm in width in which its movement is due to a single polar flagellum [10]. Since now this bacteria is the most studied. These bacteria were able to oxidize sulfur to sulfuric acid and ferrous to ferric in acidic environment where pH value is less than 5 [7, 10, 11]. From this point onwards the technology of bioleaching has shown tremendous growth, especially industrial coppers production, which makes annualized world copper production reach up 10% from 0.2%. It was in Chile the first industrial scale copper bioleaching plant was established in 1980 using Thiobacillus bacteria [12] large-scale production begins and bioleaching taken as main manufacturing process as any convection techniques in Chile 1984 [13]. Among the many microorganism involved, bacteria (autotrophic and heterotrophic), fungi and yeasts can be mentioned. The bacterium has these calcification based on their species as Thiobacillus Ferrooxidans, Leptospirillum Ferrooxidans, Thiobacillus Thiooxidans, Sulfolobus, but there are many classifications based on different characteristics reveled by the organisms.

Acidophilic Thiobacillus species are used to leach refractory elements like gold, they generally characterized as aerobic, acidophilic, and autotrophic used to leach sulfide minerals (copper, nickel, zinc and soon). Most common bacteria involved in bioleaching are Acidithiobacillus Ferrooxidans (Thiobacillus Ferrooxidans), Acidithiobacillus Thiooxidans, Leptospirillum Ferrooxidans, Sulpholobus Spp, Sulpholobus Thermosulphidoxidans and Sulpholobus Brierleyi. Acidithiobacillus Ferrooxidans is most vital one, which was named and characterized in 1951. Most common fungi are Aspergillus Niger and Penicillium Simplicissimum. The efficiency of bioleaching depends up on physiological requirement and capability of Thiobacillus to oxidize ferrous ion (Fe2+) and sulfur (S). There are five main species of Thiobacillus, these are Thiobacillus Thioparus, Thiobacillus Dentrificans, Thiobacillus Thiooxidans, Thiobacillus Intermedius, and Thiobacillus Ferrooxidans. On the bases of pH values for growth genus Thiobacillus can be divided into two groups, those that can grow only in neutral pH values are T. Thioparus and T. Dentrificans. The second Thiobacillus species those grow at lower pH value are T. Thiooxidans, *T. intermedius*, and T. Ferrooxidans.

Study of different scholars at the inceptions shows the capability of bacteria (genus Thiobacillus) to oxidize sulfur compounds to sulfuric acid; it can oxidize also range of sulfur compounds (S2−, S0 , S2O4, S2O4 2−, SO4 2−) [11], followed by separation process of the iron and the bacteria Acidithiobacillus Ferrooxidans (Thiobacillus Ferrooxidans) from the solution. A. Ferrooxidans is found in drainage waters and it is commonly identified as pyrite oxidizer [14]. The bacterial (acidophile) obtain energy from inorganic sources, it grows in acidic medium that fixes carbon to the bacteria itself. Most economically important metals like iron, copper, gold, and uranium can be easily extracted by using acidophilic and chemo-litho-autotrophic microorganism. Acidithiobacillus Ferrooxidans is chemoautotrophic microorganism or acidophilic.

*Bio Hydrometallurgical Technology, Application and Process Enhancement DOI: http://dx.doi.org/10.5772/intechopen.94206*

**Figure 1.** *Image of bioleaching bacterial [4].*

Let see the ecology, physiology, availability and genetics of microorganism involved in bioleaching. There are three basic principles for microorganism to leach and mobilize target metals from ore concentrate – redox reaction, formation of organic and inorganic acid and finally the excretion of complexing agent (**Figure 1**) [4].

Here is a generalized reaction used to express biological oxidation of sulfide mineral.

MS + 2O2 → MSO4, where M is bivalent metal and reaction below show a metal sulfide directly oxidize by Acidithiobacillus Ferrooxidans to soluble metal sulfate according to the reaction.

MS + 2O2 → M+2 + SO4 +2 [15].
