REMEDIATION OF MINING SITES

JurisdictionUnited States
RCRA and CERCLA
(Apr 1997)

CHAPTER 8A
REMEDIATION OF MINING SITES

Michael R. Thorp
Heller Ehrman White & McAuliffe
Tacoma, Washington
Brian G. Hansen
McCulley Frick & Gilman, Inc.
Missoula, Montana

[Page 8A-2]

Focus: Hard-Rock (Metal) Mining Sites

Overview:

• Variability of Mining Sites

• Environmental Problems Typically Encountered

• Problem Solutions: Proven and Innovative

• RI/FS: Recent Developments

[Page 8A-3]

Hard-Rock (Metal) Mining Sites

Copper, Cadmium, Lead, Zinc, Silver, Gold

Driving Force for Mine Clean Up: Exposure of humans and environmental receptors to heavy metals. Aesthetics comprise a secondary clean up driver.

Key Terms:

Ore — mineral(s) that contains a sufficiently high percentage of the target metal such that a profit may be realized.

Extraction — removal of ore from a deposit.

Waste Rock — rock, to low in metal content to be considered ore, that is removed during the extraction process (e.g., during the installation of a tunnel to access an ore body).

Beneficiation — crushing, grinding, washing, filtration, sorting, sizing, and concentration (gravity and flotation).

Concentrate — the product of beneficiation processes that is ready for processing.

Tailing — waste material from the beneficiation process that is too low in metal content to warrant further treatment.

Processing — smelting and refining of concentrates to prepare a marketable metal product.

Slag — a principal waste product of smelting

[Page 8A-4]

VARIABILITY OF MINING SITES

Factors Affecting Variability:

• Site Setting

• Magnitude of Operation

• Type of Deposit and Extraction Method

• Beneficiation Method

• Processing Method

• Historic Waste Disposal Practices

• Proximity of Population Centers

• Presence of Sensitive Ecological Receptors

[Page 8A-5]

Site Setting

• Climate: Wet or Dry?

• Topography

• Hydrogeology

Magnitude of Operation

• Often linked to extraction / beneficiation method

• Dictates waste quantities

[Page 8A-6]

Type of Deposit and Extraction Method

Placer Deposits

• Fragments from eroded ore body are mixed with other rocks in stream banks and bottoms.

• Nature of Extraction Waste: piles of re-worked stream gravel.

Vein Deposits

• Ore concentrated along an underground fissure; mined by tunneling.

• Nature of Extraction Waste: piles of waste rock.

Disseminated Deposits

• Lower grade deposits where ore minerals are dispersed through a large volume of host rock; mined by open pit methods.

• Nature of Extraction Waste: very large piles of waste rock.

[Page 8A-7]

Beneficiation Method

• Crushing (milling) of ore almost typically is the first step in beneficiation.

• Early beneficiation processes focused on gravity separation ("jigging") of crushed particles; the heavier particles typically contained higher concentrations of the target metal.

• Later beneficiation processes that are in use today focus on flotation methods to concentrate metals.

• Beneficiation includes leaching of crushed gold ore with cyanide ("heap-leach" operations).

• Nature of Beneficiation Waste: range from coarse tailings with high metals concentrations (jig tailings) to very fine grained tailings with low metals concentrations (flotation tailings). Wastes from heap leach operations are piles of spent ore.

[Page 8A-8]

Processing Method

• Processing of metals from concentrate typically involves pyrometallurgical processes (smelting) as a final step to separate the target metal from other minerals.

• Nature of Processing Waste: slag

• Though not regarded as wastes, smelter emissions and fugitive dusts are dispersed from smelting operations.

[Page 8A-9]

Historic Waste Disposal Practices

• Extraction Wastes: waste rock typically piled wherever convenient.

• Beneficiation Wastes: tailings from historic mining/milling operations often were discharged directly to streams. Later practices included discharging tailings to tailings "ponds", where tailings are contained within embankments. Spent ore from heap-leach operations typically is left in place and revegetated.

• Processing Wastes: slag was usually piled near the smelter.

[Page 8A-10]

Proximity of Population Centers

• At some sites residences are commingled with historic mining and metals recovery operations and associated waste accumulations. Exposure risks are correspondingly greater and dictates a more stringent level of clean up relative to remote sites.

Presence of Sensitive Ecological Receptors

• The documented presence of federally designated threatened or endangered species may also dictate...

To continue reading

Request your trial

VLEX uses login cookies to provide you with a better browsing experience. If you click on 'Accept' or continue browsing this site we consider that you accept our cookie policy. ACCEPT