Biomining & Bioleaching

Prepared By:Vijay Singh Kunwar1

1 punkvijay@gmail.com

BIOMINING

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

• It is an alternative to more traditional physical-chemical methods of mineral processing.

Biomining plant

• 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)

• These two terms can be used interchangeably. • 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.

We will be dealing with

history of biomining and bioleaching what is the nature of micro-organism used? what are the bio-technical process used to

extract the metal? what advantages and disadvantages of the

process?

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

History (continued)

• 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.

Microorganisms used in biomininghave several things in common

They:

• Are single-celled organisms that multiplyby simple cell division.

• Derive energy for growth and cellfunctioning 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 .• cylindrical-shaped• about 1 micrometer (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

Acidithiobacillus caldus

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, Sulfolobus metallicus

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.2

• 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.

Series of micrographs showing the leaching of pyrite in presence of micro-organisms

Bioleaching process applied to gold extraction

• The extraction of gold from its ore involves numerous ferrous and sulphur oxidizing bacteria, including Acidithiobacillus ferroxidans and Acidiobacillus thiooxidans.

…..continued

Stage 1

• Bacteria catalyzes the breakdown of the mineral arsenopyrite by oxidizing sulphur and metal ( arsenic ions) and reducing dioxygen by H2 and Fe 3+.

• This allows the soluble particle to dissolve.

….continued• 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)

…..continuedStage 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.

…..continued

• 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.

FAQs• Are the microbes used in biominingprocesses genetically altered?

• Are the microbes used in biominingprocesses genetically altered?

• Can biomining be effectively used inextreme environments such as highaltitudes and in cold environments?