Commercial importance of biomining

An attempt has been made to make a survey on species that are economically important. Bacteria belonging to genus “ACIDITHIOBACILLUS” are economically important. Previously these species belonged to the genus Thiobacillus. When sequence analysis of this genus was performed it became clear that this is sulfur oxidizing bacteria and it belongs to Proteobacteria.

When this problem was arosed than in order to solve this problem the subdivision of genus Thiobacillus was done and a new genus Acidithiobacillus was obtained and this genus includes those species that are highly acidophilic. The members of this genus are :

·         Acidithiobacillus ferrooxidans.

·         At.thiooxidans.

·         At.caldus.

These bacteria are present in those regions where there is environment suitable for them like sulfur springs as these regions are suitable for their survival.

The first discovered bacteria that had the ability to oxidize sulfur was AT.FERROOXIDANS. The G+C content of this bacteria is about 59%. The percentage of DNA similarity between these species is very low that is almost about50% and this percentage is very less to consider them as separate species.

 There is another strain of T.ferriooxidans and G+C content of this strain is 65% and this specie belongs to another strain whose name is still unknown. The species of this strain are autotrophs and they have growth on formic acid. Formic acid is provided in small amount to them for their consumption and formic acid contains Cl and because of this property formic acid is not consistent with these autotrophic bacteria.

The species of this strain can also use ferrous iron and also sulfur compounds that are reduced. They use reduced form of sulfur as source of electron. This specie At.ferrioxidans has been used as biomining microbe for many years and its operation was at the temperature of 40C or temperature less than this. Till the mid of 1990s this method was considered as sophisticated.

When ferric iron concentration is high than than activity of this specie is high rather than the condition when there is greater concentration of ferrous iron. This specie At-ferrooxidans is mostly present in those environments where:

·         Uranium.

·         Copper sulfide.

·         Ferric iron.

Concentration is high. At-ferrooxidans also have the ability to grow out of the optimum ph range. These bacteria are also tolerant to a variety of metal ions. At-thiooxidans don’t use sulfur as source of electrons and this specie has nutrition similarity with At-ferrooxidans. At-ferrioxidans does not work in acidic ph. Acidiphillim grows in the presence of low oxygen and it uses ferric iron as source of electron accepter.

When acidophilic uses ferric iron as electron accepter than it regenerates ferrous iron. These species are unable to use sunlight. Many types of Co2 is available and also organic and inorganic sources are available for these species to grow as they provide us benefit in mining process. There are many bacteria that are involved in oxidation of minerals.

These bacteria work at the temperature of 70C. As this temperature is used for the mining of minerals so the bacteria that are involved in the mining of minerals they must grow at this temperature. Many new methods have been discovered that use different temperatures for their operation in the mining process and several species that are involved in this process has been also discovered and these will serve in this process.

The species that will serve in this aspect are as follows:

Ø  SULFUBACILLUS:

The temperature range of this specie is about 60C. These are gram positive and we can obtain these species from heaps of waste. The food source for these species is:

·         Ferrous iron.

·         Sulfur compounds.

·         Sulfide minerals.

For their growth they require greater level of Co2 but they can not fix Co2 properly. When we grow them in lab than glucose is provided to them as glucose can also be used as a source of Co2 and this Co2 is essential for their growth and they can also use ferrous iron as acceptor of electron and sulfide compounds as source of donor of electron.

Many species of Sulfobacillus exist but there are only two species of sulfobacillus that have been named and these two species play greater role in the oxidation of several compounds like iron and sulfur compounds.

Ø  FERROPLASMA:

These species are not bacteria but these are arachea. These species don’t have cell wall. The habitat of these species is pyrite. This specie is aerobic and it is involved in the oxidation of ferrous iron and is not involved in the oxidation of sulfur compounds. The temperature range for these species is from 33C to 45C. These species work best at acidic Ph. If we want to obtain these species in a reactor than large amount of these species are obtained when the Ph of reactor becomes acidic.

A related specie to this one has also been isolated from the ores of copper and the temperature for these species is 30C. They are related to a specie from which they were isolated as shown from the sequences of RNA. We can also grow these species on lab media by providing them their required nutrients but they cant be obtained as pure culture.

 

 

 

SULFOLOBUS:

There capability is still confusing because when we studied them previously their cultures were contaminated making their capability unclear. The study of mineral oxidation in lab has been also using this specie. The food source of these species is :

·         Ferrous iron.

·         Inorganic sulfur.

·         Sulfide ores.

This specie is autotrophic. It works best at acidic Ph. They oxidize Chalcopyrite and Arsenopyrite. When we mix greater level of minerals than abrasion is formed and the resistance of this specie to this abrasion is still unclear.

Ø  METALLOSPHAERA:

These species are aerobic and not bacteria as these species are arachea. These species are involved in the oxidation of iron as well as sulfur compounds. We can isolate these species from yeast as they also grow on yeast extract. Mostly these species are involved in the oxidation of minerals. They work best at acidic Ph and their temperature range is about 80C.

As there temperature is sufficiently high so these species can easily work at high temperatures. There RNA was extracted and sequences were obtained but there was a confusion that either this specie belongs to Sulfobacillus or to Metallosphaera.

Ø  ACIDIANUS:

These species are arachea and they are involved in the oxidation of minerals. These species have less industrial importance than other species. These species are both autotrophic and heterotrophic and they are also involved in the oxidation of iron and sulfur. They work best at acidic ph and their temperature range is about 70C. As these species has high temperature so, they can work best at high temperatures.

These species can be aerobic as well as anaerobic. These are Chemolithotrops. These species oxidize as well as reduce.

CURRENT BIOMINING PROCESSES:

Two types of processes exist:

·         Commercial scale process.

·         Irrigation process.

These processes have one thing in common that is there is no requirement of sterility for these processes. The reason for this non-sterility is that such environment is created by the working microbes that is not suitable for the growth of any other type of microbes.

Still efforts are being made to select further new organisms that will prove beneficial to this process. There is further explanation of these processes.

Irrigation process:

This type of process is involved in the recovery of metals specially involved in the recovery of copper. During recovery of copper microbes are applied that work and recover microbes. Usually copper recovery methods are applied in heaps and dumps. This process was started in the year 1960. Four billion ton copper is present in the form of waste. These dumps are than assembled and recovery cycles are applied and than copper is recovered.

In order to recover copper microbes are applied they catalyze different reactions and than convert copper into its insoluble form and in this way copper is recovered. Along with dump leeching of copper, heap leeching of copper is also performed.

Stirred type process:

In this process tanks are used and also increases the efficiency of the process. These tanks are not commonly used because they are very expensive and its difficult to afford them. The arrangement of these bioreactors is in series form. This process is performed in such a way that feed is processed in a flow manner such that it flows from one tank to the next.

When we start the process first of all, tanks are arranged in parallel fashion so that microbes can achieve fast steady rate. The feed that is used in this process is:

·         Mineral concentrate.

·         (NH4)2SO4.

·         KH2PO4.

This processs can also be used for the recovery of gold. This process works on acidic Ph and temperature is about 40C. These are processes are used for the recovery of different metals that are of greater importance for us and these processes use microbes.