Case Studies Chapter 7

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1. The Argo Tunnel - Pulsed Limestone Bed Treatment
2. Bisbee No. 7 stockpile – BioSulphide process
3. Equity Silver – High Density Sludge Treatment Plant
4. Keystone Mine – Constructed Wetlands

1. The Argo Tunnel - Pulsed Limestone Bed Treatment

(Demonstration)

Background

The Argo Tunnel is located in Idaho Springs, Clear Creek County, Colorado, approximately 30 miles west of Denver. The tunnel was constructed to provide drainage and transportation for several connected gold mines. The tunnel continues to drain acidic mine water at an average rate of 280 gallons per minute. The environmental media affected are surface water and, to a much lesser extent, groundwater.

Treatment Applied

A conventional lime water treatment plant was constructed in 1998 and has been operating continuously. Primary contaminants include acidity and a host of heavy metals, including aluminum, copper, iron, manganese and zinc.

A pilot treatment system was operated and studied periodically from 2004 through 2007 by the United States Geological Survey (USGS) Leetown Science Center utilizing a pulsed limestone bed treatment system at 230 L/min.

Pulsedlimestonebedtreatmentsystem.gif

Performance

Metals removal for iron and aluminum was >98%. Copper had removals of 50 to >99%, while zinc had removals from 5 to 65%. Manganese concentrations were generally unaffected. The effluent of the limestone reactor required post-treatment with lime to raise the pH high enough to remove zinc and manganese to dischargeable levels. The sludge from the limestone/lime treatment scheme had settled volumes that were 60% of the lime treatment alone.

Reference

Sibrell, P. L., T. R. Wildeman, M. Frienmuth, M. Chambers, and D. Bless. 2005. “Demonstration of a Pulsed Limestone Bed Process for the Treatment of Acid Mine Drainage at the Argo Tunnel Site.” Abstract. www.epa.gov/aml/news/argo.htm.


2. Bisbee No. 7 stockpile – BioSulphide process

Background

The Copper Queen Mine closed in the 1970s after nearly one hundred years of mining. One of the major issues at this site was drainage from a large ore stockpile (No. 7). This drainage was optimal for BioSulphide treatment due to its flow rate and copper concentration. The plant was commissioned in 2004.

Treatment Applied

BioteQ and Phelps Dodge have a Joint Venture to use the process to recover copper at Bisbee, Arizona. The fully commissioned BioSulphide® plant recovers copper from dump drainage. The resulting concentrate (50% Cu) reports to the Miami smelter for profitable water treatment. The plant has a design capacity of 3.6 tonnes Cu/day

BioSulphidePlantDiagram.gif


BioSulphidePlantPhotos2.jpg

Performance

The feed water to the plant contains 0.5 to 2 g/L iron and 340 mg/L copper at a pH of 2.2. After treatment, the effluent contains less than 1 mg/L copper and iron. The plant is currently recovering more than 2 tonnes Cu per day.

Reference

Nelson L. Ashe, Ian McLean, and Max Nodwell. 2008. “Review of Operations of the Biosulphide® Process Plant at the Copper Queen Mine, Bisbee, Arizona”. In Hydrometallurgy 2008 - 6th International Symposium - Honoring Robert Shoemaker. Editors Courtney A. Young, Patrick R. Taylor, Corby G. Anderson - 2008 - Technology & Engineering - 1186 pages


3. Equity Silver – High Density Sludge Treatment Plant

Background

The Equity Silver mine is a former open pit and underground mine, located 35 kilometres southeast of Houston in north central British Columbia. The Equity Silver mine operated from 1980 to 1994 and then closed due to depletion of the economic resource. The mining occurred from three open pits and a small underground mine. Copper, silver and gold were extracted through a conventional mill flotation circuit plus a cyanide leach circuit.

Shortly after the mine opened, acidic drainage was found to be occurring from the oxidization of sulphide minerals contained in the mined rock. Equity Silver’s original low density sludge process was unable to handle the usually large runoff events so a new high density sludge (HDS) plant was commissioned to treat acidic drainage post closure.

Treatment Applied

Installation of a conventional high density planted was completed in 2004 at a cost of $10M. The 600 m3/h water treatment plant started up in December 2004, with placement of the treatment sludge in an abandoned pit. The plant was designed for full automation and remote control.

Parameters

Design Feed

Permit Limits

pH

2.4

6.5 to 9.5

Acidity

13,500

Al (mg/L)

650

0.5

Cu (mg/L)

280

0.05

Fe (mg/L)

2000

0.3

Zn (mg/L)

350

0.2

SO4 (mg/L)

12,500

Cd (mg/L)

1.2

0.01

As (mg/L)

2.5

0.05


Performance

The effluent discharge consistently meets regulatory compliance.

Treatment Statistics

2008

2007

Lime(t)

4,014

7,290

Drainage treated (m3)

793,459

1,629,420

Average acidity (mg/L)

9,004

8,404

Sludge produced (m3)

99,240

125,930

Water discharges (m3)

1,476,793

3,836,848


Reference

Goldcorp. 2008. Sustainability Report. http://csr.goldcorp.com/docs/2008_report.pdf


4. Keystone Mine – Constructed Wetlands

Background

The Keystone Mine was owned by Silver King Mines Inc., of Salt Lake City, Utah. The mine produced mainly copper from 1923 to 1925 and includes two adits and 2,000 ft of drifts and crosscuts in an area of 15 acres. The extraction of large quantities of ore from the mine resulted in extensive development of the underground workings. These workings discharge two miles upstream of the confluence with Lake Shasta, with copper, cadmium, and zinc the constituents of concern.

Treatment Applied

The typical metal concentrations and ranges of discharge are shown below.


In 1989, a constructed wetlands treatment system was commissioned. It consists of a vertical flow of water treated using anaerobic conditions at the base to precipitate heavy metals as sulphides. The technology is designed to treat the drainage in perpetuity. The system uses a ditch design with a topsoil substrate. The retention time through the 4200 square meter (1 m deep) system is 0.3 days at a flow rate of 8600 L/minute. The treatment system was constructed for $2M US. Operation and maintenance (O&M) are estimated at $10,000 per year indefinitely.

Performance

The constructed wetlands system has an efficiency of 90%. Details of its performance are presented below.


References

Robert S. Hedin, Robert W. Nairn, and Robert L. P. Kleinmann. . Passive Treatment of Coal Mine Drainage. U.S. Dept. of the Interior, Bureau of Mines, 1994 - Technology & Engineering - 35 pages. http://www.hedinenv.com/pdf/ptcmd.pdf

ITRC website - retrieved on May 5, 2012 from - http://www.itrcweb.org/miningwaste-guidance/cs22_24_keystone_rising.htm