Biomining

Subject: Environment

Section: Pollution

Context- Urban local bodies need a comprehensive policy for reuse of reclaimed land.

Concept-

The Union Ministry of Housing and Urban Affairs recognised that the unlined dumpsites in India are creating various irreversible environmental hazards. The major sources of pollution are:
- Puddles of leachate flowing through the adjacent area and reaching the water table Long-term issues of greenhouse gas emissions
- Surface water and groundwater pollution
- Dumpsite surface fires
- Limitations on urban development that make this mode of disposal unmanageable
The Centre has earmarked Rs 1,41,600 crore under its flagship Swachh Bharat Mission 2.0 (SBM 2.0), with a goal of achieving “garbage-free cities”. The focus of the mission is on remediation of all legacy dumpsites in the country by biomining.

What is Biomining?

Biomining is mineral processing with microbes.
Biomining is the process of using microorganisms (microbes) to extract metals of economic interest from rock ores or mine waste.
Biomining techniques may also be used to clean up sites that have been polluted with metals.
Valuable metals are commonly bound up in solid minerals. Some microbes can oxidize those metals, allowing them to dissolve in water. This is the basic process behind most biomining, which is used for metals that can be more easily recovered when dissolved than from the solid rocks.
A different biomining technique, for metals which are not dissolved by the microbes, uses microbes to break down the surrounding minerals, making it easier to recover the metal of interest directly from the remaining rock.

What metals are currently biomined?

Most current biomining operations target valuable metals like copper, uranium, nickel, and gold that are commonly found in sulfidic (sulfur-bearing)
Microbes are especially good at oxidizing sulfidic minerals, converting metals like iron and copper into forms that can dissolve more easily.
Other metals, like gold, are not directly dissolved by this microbial process, but are made more accessible to traditional mining techniques because the minerals surrounding these metals are dissolved and removed by microbial processes.
When the metal of interest is directly dissolved, the biomining process is called “bioleaching,” and when the metal of interest is made more accessible or “enriched” in the material left behind, it is called “biooxidation.”

What processes are used to biomine?

Heap leaching: freshly mined material is moved directly into heaps that are then bioleached.
Dump leaching: low-value ore or waste rock is placed in a sealed pit and then bioleached to remove more of the valuable metals from the waste pile.
Agitated leaching: crushed rocks are placed into a large vat that is shaken to distribute the microbes and material evenly and speed up the bioleaching process.
Leaching times vary from days to months, making this process slower than conventional mineral extraction techniques.
Dump and heap leaching are the oldest and most established biomining techniques, but the use of agitated leaching is becoming more common for minerals that are resistant to leaching, including some copper sulfides like chalcopyrite.

What are the environmental risks of biomining?

the release of the microbes themselves into the local environment are considered to be relatively small.
The greatest environmental risks are related to leakage and treatment of the acidic, metal-rich solution created by the microbes.
This risk can be managed by ensuring that biomining is conducted under controlled conditions with proper sealing and waste management protocols.

How common is biomining?

Biomining is currently a small part of the overall mining industry.
worldwide, 10-15% of copper is extracted using bioleaching.
Biomining is also important in the gold industry, where roughly 5% of global gold is produced using biooxidation.