POST MINING RESTORATION

OF ENVIRONMENT

Acid mine drainage

Lecture #8

Acid Mine Drainage (AMD)

• The majority of extremely acidic

sites now in word-wide have
their origin in human activity,
the mining of metals and coal.

• Acid mine drainage or acid rock

drainage refers to the outflow
water from metal mines or coal
mines.

Copper leaching from tailing

heap

Acid mine drainage (AMD)
occurs at about 70% of the
world’s mine site.

Microbial stalactite

Acid streamer in pyrite mine in
North Wales

Stream running through

the mine

Acid mine drainage (AMD)

• Mining activities result in the

formation of a severe environmental

problem known as acid mine drainage.

• For instance, annually nearly 500 000

000 t waste rock are deposited in

tailing in Canada.

• The chemolithotrophic bacterium

Acidithiobacillus ferrooxidans is one of

the major microorganisms in AMD.

Acid drainage waters

• The acid mine drainage (AMD) is

considered to be the major
environmental problem associated
with mining activities.

• This phenomena is connected with

the biooxidation of pyrite and other
sulphide minerals as a result of which
acidic waters containing sulphuric
acid.

AMD from coal mines

(Western Maryland)

Rio Tinto river

• The Rio Tinto is a long (100 km) river

located in the southwest of Spain,
characterized by a low pH (mean pH -2.3)
and high concentration of transition
metals (iron, copper and zinc) and sulfate.

• The dominant microorganisms in the Tinto

river are all able to catalyse redox
transformation of iron: Leptospirillum
ferooxidans, Acidiphilium Acidithiobacillus
ferrooxidans

Rio Tinto - Spain

Geomicrobiological scheme

of the Tinto River

Acid mine drainage

Main factors

The main factors influencing the

generation of acid drainage can be
distributed into three groups:

- characteristic of the mineral substrate
- physical parameters of the acid-

generation system

- microbiological parameters of acid –

generation system.

Uranium in the environment

• Uranium has been released into the

environmental through

Mining operation
Nuclear testing
Accidents in atomic power plant

Uranium waste

• The present inventory of uranium mill

tailings (UMT) in the United States is
about 240 million tons.

• In a reduced valence state (+IV),

uranium is quite insoluble, The
reduction of soluble U(VI) to insoluble
U(IV) prevents the migration of U with
groundwater.

Uranium

• Uranium plays an important role in

mine and drainage waters. Uranium

was separated from the ore body very

often by bioleaching processes were

the U

was transformed into U

• The acid mine drainage from the

uranium mines contain, apart from the

iron and other heavy metals, also

radioactive elements such as uranium

and radium.

Reduction of U

to U

• A separation of uranium from the mine water

is possible by a

precipitation

after a

reduction

• This reduction can be carried out with sodium

hydrogen sulfide, metallic aluminum or iron.

• [UO

(CO

)

]

+2CO

32-

+ 2H

O + 2e



[U(CO

)

]

+ 4 OH

• [U(CO

)

]

+ 4OH

+ nH

O  U(OH)

O +

5CO

32-

• Processes resulting in the

transformation of U(VI) to U(IV)
decrease uranium mobility in the
environment

AMD from different mines

Coal mining dump drainage

system

Bioremediation

• Commercial application of

bioremediation in the mining
environments involve the immobilization
and recovery of soluble metals from
aqueous waste.

• Bacterial sulfate reduction project to

remove metal ions from water.

• The sulfate-reducing bacteria can reduce

S to precipitate metals as sulfides

Microbial processes

• Microbial processes that generate net

alkalinity are mostly reduced
processes and include:

Denitrification
Methanogenesis
Sulfate reduction
Iron and manganese reduction

Reducing and alkalinity

producing system (RAPS)

AMD flow is forced downwards through a layer of
compost and then through limestone bed.

BioSulphide

Process

• In the process, sulfur-reducing bacteria in an

anaerobic bioreactor produce hydrogen sulfide gas

S).

• The gas is transferred to a contactor tank where it

mixes with the water to be treated under controlled

conditions to selectively precipitate metals as metal

sulfides.

• The precipitated metals and water are pumped to a

clarifier tank where the clean water is separated

from the metal solids and discharged or recycled.

• The metal solids are filtered to remove excess

water, producing a high grade metal product

suitable for refining.

BioSulphide

Process

• Metals that can be recovered into valuable

products include

copper, zinc, nickel

and

cobalt

• Toxic metals such as

arsenic

antimony

lead

cadmium

, and

manganese

are also

removed from the water.

• BioteQ’s BioSulphide® Process is used to

treat acid mine drainage, leach solutions,

industrial wastewater, water in mineral

processing and metallurgical operations,

and contaminated groundwater.

BioSulphide Process

Chem Sulphide

process

Chem Sulphide

process uses chemical sulfide reagents

to remove and recovery metal form solution.

The process operation are the same as in the
BioSulphide

Process

Metal recovery from acid

drainage from a waste rock

dump

Metal recovery from waste

streams at metal smelters and

refining facilities

Benefits of Biosulphide

process

• Produces a low cost sulfide reagent that can be used

for metal recovery or other industrial applications.

• Eliminates or reduces the environmental liability

caused by metal-contaminated water.

• Metal recovery rate is greater than 99%; recovered

metal products are high grade and suitable for

refining.

• Recovered metals can generate revenue to offset

water treatment costs.

• Produces high quality treated water that can be

discharged safely to the environment.

• Saves money compared to alternative processes.
• Easy to scale up and down over a wide range of H

production capacities.

Mine Environment Neutral

Drainage

• Through the Mine Environment

Neutral Drainage (MEND) Program,
Canadian mining companies and
provincial/territorial and federal
departments have reduced the
liability due to acidic drainage by at
least $400 million. This is an
impressive return on an investment
of $17.5 million over eight years.