Tailings by SM Ajon

8/6/2019 Tailings by SM Ajon

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By Sarah Mae B. Ajon


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consist of ground rock and process effluentsthat are generated in a mine processing plant

mechanical and chemical processes are used

to extract the desired produ

ct from the runof the mine ore and produce a waste stream

waste product that has no financial gain to amineral operator at that particular point intime

The disposal of tailings is commonlyidentified as the single most importantsource of environmental impact for manymining operations


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a final storage area where unrecoverable anduneconomic metals, minerals, chemicals,

organics and process water are discharged


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CONVENTIONALIMPOUNDMENT

BACKFILLOFTAILINGSTOUNDERGROUND

WORKINGS

IN-PITTAILINGSSTORAGE


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surface retaining structure designed to store

both tailings and mine water, with the aim of

reclaiming the water for use in the

processing plant as required two types of surface impoundments:

1. Water Retention Type Dam

2. Raised Embankment


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used for mineral operations that plan to

store high volumes of water

Water storage may be required to keep a

processing plant operational during the dryseason or where surface water inundation

can occur especially if the impoundment is in

a catchment area.


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most common construction technique used

in tailings storage facilities

most common materials used for

embankment raises are waste mine rock,natural borrow soils, underground roadway

development material, cycloned tailings

(coarse fraction) and hydraulically deposited

tailings three principal designs are upstream,

downstream and centreline structures


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lowest initial cost and most popular design

most common design to fail

key failure mode of upstream embankments

is a static/transient load inducedliquefaction flowslide event

suited to areas where the climate is arid

not suited to areas of seismic activity

Excessive rates of rise (of upstreamembankments) is the underlying cause for

many upstream tailings impoundment

failures


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developed to reduce the risks associated

with the upstream design, particularly when

subjected to dynamic loading as a result of

earthquake shaking very versatile for a range of site specific

design parameters and behaves similarly to

water retention dams

main advantage is that the downstreamdesign can have unrestricted heights

main disadvantage is the cost of raising theembankment


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a compromise between both the upstream

and downstream designs

more stable than the upstream method but

does not require as much constructionmaterial as the downstream design

When subsequent raising is required,

material is placed on both the tailings and

the existing embankment cannot be used as a large water retention

facility cannot be used as a large waterretention facility


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STORED BELOW GROUND IN PREVIOUS WORKED OUTVOIDS

MIXED WITH A BINDER,USUALLY CEMENT,AND THEN

PUMPED UNDERGROUND TO FILL VOIDS AND HELP

SUPPORT AN UNDERGROUND MINE


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1. THE TAILINGS ARE STORED UNDERGROUND AND THUSPREVENT SURFACE DISTURBANCE.THIS IS MOREENVIRONMENTALLY FRIENDLY AS AREAS OF LAND

DONT HAVE TO BE USED FOR A SURFACE TAILINGSSTORAGE AREA.

2. ORE RICH PILLARS AND SUPPORTS CAN BE

EXTRACTED.

3. THE BACKFILL HELPS TO SUPPORT THE MINE


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4. BACKFILL REDUCES THE RISK OF ROCK BURSTSOCCURRING AS PRESSURES ARE NOT FOCUSED ON

PILLARS AND SUPPORTS.

5. IMPROVES THE VENTILATION CIRCUIT IN THE MINE.

6. PREVENTS ROOF FALLS FROM BLASTING (AIR OVERPRESSURE (AOP))

7. BINDERS HELP TO MINIMISE GROUNDWATERCONTAMINATION


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1. HIGH COSTS,PARTICULARLY IF BINDERS ARE USED.

2. THE TAILINGS NEED TO BE DEWATERED,

INCREASING COSTS.

3. HOLD UPS IN EXTRACTION STRATEGIES.

4. RISKS OF LIQUEFACTION OF THE TAILINGS IFSATURATION LEVELS ARE HIGH,AND A TRIGGER(SEISMIC VIBRATION)ARE PRESENT.


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5. SEEPAGE OF TAILING EFFLUENT INTOGROUNDWATER,THUS CONTAMINATION.

6. EXTRA MANPOWER AND EQUIPMENT.

7. ORE DILUTION FROM POOR QUALITY FILLS.


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process of backfilling abandoned open pit

surface mines with tailings

worked out voids can be filled at a fraction

of the costs the tailings do not require retaining walls,

thus the risks associated with embankment

instability are eliminated

main disadvantage to in-pit storage oftailings is that the potential for

groundwater contamination below andaround the void can be very significant


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1. Rapid rates of rise occur particularly in theearly stages of deposition when the pit is at its

deepest and the exposed surface area the

smallest.

2. The stability of underground mines in the

vicinity to an in-pit tailings facility may bejeopardised.

3. Poor consolidation can result in long durations

of surface deformation after a pit has beenfilled.

4. Groundwater bores will have to be installed

around the pit to monitor the seepage plumes.


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Problems arise when accelerated weathering

process generates toxic levels that createshort and long term tailings management

challenges. Example: Acid Mine Drainage/Acid Rock

Drainage - acid generation and metal

mobilisation occur that eventually find their

way into the surrounding environmentthrough runoffor seepage


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The design of a tailings storage facility

should therefore be optimised to preventweathering and the mobilisation of

contaminants, whilst also increase thedegradation rates of reagents stored in the

tailings facility.

It may be more economical to hold water for

longer periods of time to allow naturaldegradation of reagents rather thanpromoting rapid degradation.


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In the Philippines, there is really no detailed

and specific regulatory legislation relatingto tailings management

Each mine has an EnvironmentalCompliance Certificate (ECC) thatessentially reinforces the prevention of

impacts to the environment from a tailings

facility.


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(From: Guidelines for miners: tailings andtailings storage facilities in South Australia)

1. Site and tailings characterisation

2. Identification of potentialimpacts/hazards

3. Development of controls for identifiedimpacts/hazards and estimation of

residual risk4. Documentation


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involves a comprehensive description of theenvironment, location and relevantfeatures of the proposed location

is a progressive process.Information is required in respect of:

the local community

land use

proximity to housing and infrastructure

amenity

noise, dust and air quality

topography and landscape

climate


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geohazards

hydrology

groundwater

vegetation, weeds and plant pathogens

fauna

topsoil and subsoil

heritage proximity to conservation areas

pre-existing site contamination and

disturbance


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Particular attention needs to be paid to:

1. geographic location of the proposed site

2. Chemical, radiological and physicalcomponents of the tailings

3. Where a tailings dam is to hold radioactive

waste, baseline radiological conditions

need to be determined prior toconstruction


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May include impacts on or hazards to:

surface, ground and nearby marine waters

air quality

flora and fauna

humans, such as amenity, public safety,

health and wellbeing

post mining land use including on adjacent

properties


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This stage should include:

optimal tailings management methods

tailings delivery

tailings containment design, construction,operation and decommissioning

management of odour, dust and gasemissions

opportunities for underground or open pit

backfilling

closure and post closure issues


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Site characterisation, the development of

controls for identified impacts/hazards and

estimation of residual risk are to be

documented consistently.


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Tailings by SM Ajon