BIOMINING

Biomining is a broad term that describes the processing of metal containing ore sand concentrates of metal containing ore using microbiological technology.

• It is an alternative to more traditional physical-chemical methods of mineral processing. Commercial biomining are usually partitioned into two main process

1. Mineral bio-oxidation= process applied to extract bit expensive metals

2. Bioleaching= applied to the base metal(inexpensive metals)

• Both of these processes are carried out by naturally occurring microorganisms. So, bio-oxidation and

• Bioleaching are commercial and economic alternatives to smelting, roasting, and pressure oxidation.

History• The application of biomining processes predates by

centuries the understanding of the role of micro-organism in metal extraction.

• It appears to have been carried out in China at least 100-200 BC and in Europe and Scandinavia at least as far back as the second century AD.

However, the modern era of biomining began with the discovery of the bacterium Thiobacillus ferrooxidans

• . WHAT MICRO-ORGANISM ARE USED IN BIOMINING PROCESSES?

• The natural habitat of all micro-organism used in bioleaching are acid, hot springs, volcanic areas, natural outcroppings of sulphide minerals etc.

They are single-celled organisms that multiply by simple cell division.

• It derive energy for growth and cell functioning by oxidizing iron and sulfur. Obtain carbon for their cellular bodies from carbon dioxide.

• Require oxygen.

• Requires a sulphuric acid environment to grow. i.e. pH less than 2.

CLASSIFICATION

• The microbes can be conveniently grouped within temperature ranges at which they grow and where they are found in the natural environment: Ambient temperature bacteria(mesophiles), grow and function from 10°C to 40°C .They are cylindrical-shaped about 1 μm long and ½ μm in diameter.

E.g. Acidithiobacillus ferrooxidans

Leptospirillum ferrooxidans

Moderately-thermophilic (heat-loving)bacteria(40-60°C ) somewhat larger than mesophiles.

E.g. species of Sulfobacillus and Acidithiobacilluscaldus

• Extremely thermophilic Archaea.

While similar in size, have different molecular organization, spherical shaped,lack rigid cell wall, instead cell contents are enclosed by a membrane, (60-85°C)

E.g: Acidianus brierleyi, Sulfolobusmetallicus and

Metallosphaera sedula

Fig-1 Fig.2 Fig.3

Fig: 1-Strain of Leptospirillum, Fig: 2- Moderately thermophilic bacteria,Fig: 3- Acidianus brierleyi

BIOLEACHING• Leaching widely used extractive metallurgy

technique which converts metal into soluble salts in aqueous media.

• Bioleaching uses bacterial micro-organisms to extract metals from their ores.

• Bacteria feeds on nutrients in minerals , thereby separating the metal, then the metal can be collected in the solution

• Bioleaching process applied to gold extraction, the extraction of gold from its ore involves numerous ferrous and sulphur oxidizing bacteria, including

• Acidithiobacillus ferroxidans and Acidiobacillusthiooxidans.

Stage 1 Bacteria catalyzes the breakdown of the mineral arseno pyrite by oxidizing sulphur and

metal ( arsenic ions) and reducing di oxygen by H2

and Fe3+ this allows the soluble particle to dissolve.

•

• This process occurs in the bacterial cell membrane.

• The electrons pass into the cell and are used in the biochemical processes to produce energy for the bacteria to reduce oxygen molecules to water.

Reaction involved:

• FeAsS(s) →Fe2+(aq) +As3+(aq) +S6+(aq)

stage 2

bacteria oxidize Fe2+to Fe3+(while reducing O2)

Fe2+→ Fe3+

Then they oxidize metal to higher positive oxidation state. M3+ → M5+ With the electrons gained, they reduce Fe3+to Fe2+ to continue the cycle. Gold is now separated from the ore in solution.

• Advantages and Disadvantages

Advantages:

Ores and concentrates of lower metal concentration can be treated economically.

• Arsenic in the concentrates can be removed in an environmentally stable form.

• Can be applied to smaller deposits in remote locations due to low infrastructures costs.

• Rapid start up, easy and reliable maintenance.

• Process takes place at atm. pressures and low temperatures.

• No emission of SO2 gas.

Disadvantages:

• Bioleaching is a slow process as compared to smelting.

• Toxic chemicals like H2SO4 and H+ions are produced in the process whose leakage into the ground and surface water turns into acidic and causes environmental damage.