environmental impact of sulfuric acid leaching

the electro-winning system [sx-ew] is a step in the right direction as the mining industry attempts to develop methods that have less of an impact on the environment. really, it's a huge step since it eliminates tailings impoundments, which are unsightly and can cause water pollution, and smelting, which can cause air pollution. it only works on oxide ore, whereas the majority of the ore at rosemont is sulfide and will not dissolve into solution in a reasonable period of time. therefore, leaching can be used on some 14% of the ore, or approximately 59 million tons.

sulfuric acid, the leaching agent, is brought on site in large tankers. the sulfuric acid is diluted and sprayed or dripped over oxide ore, which dissolves the oxidized minerals completely in the solution. the solution, “pregnant” with the dissolved metals, is then piped to the sx-ew plant that separates out the copper into 99% pure bars. the copper is ready with no need for smelting. the waste solution is piped to on-site holding ponds, which are securely lined, awaiting the next load of oxide ore to be placed on the leach pads.

pads for leaching ore with sulfuric acid

ideally, this system is a closed circuit and is considered environmentally safe. however, there are two conduits to environment impact. first, the leach solution is stored in open ponds (until the mine is closed then it is put in barrels and taken to toxic waste dumps). second, the leach solution and the sulfuric acid can spill as they are piped around the facility. there is data to show that these spills impact groundwater—even two miles away.

1) toxic ponds:

as the leach solution is reused, the unwanted metals concentrate into a very toxic solution, which sits out in open ponds, waiting to be piped back to be sprayed on fresh ore on the leach pads.

holding ponds for leach solution

the data on the table on the following page shows the "characteristics of leach solution, which is a toxic hazard. whereas these ponds are an inevitable part of mining and are considered to be an improvement over tailings impoundments, it is questionable if they are appropriate for a national forest setting with its requirements for beneficial use.

characteristics of leach solution in named ponds at sierrita mine
(metals measured in mg/ltr)

facility/sample location

headwall no.1

bailey lake

b-pond

headwall no. 3

headwall no. 5

duval canal

sx-3 pond

sx-1 pond

sx-1
pond

reclaim pond

d-pond

headwall no. 2

date sampled

4/22/98

4/22/98

4/22/98

4/22/98

4/22/98

9/15/98

4/15/99

4/15/99

4/15/99

4/15/99

6/30/98

9/28/98

conductance (umhos/cm)

14,800

16,300

8,270

13,100

5,040

2,425

 

629

104,000

3450

2540

25,940

ph, lab

2.2

2.1

3

2.4

4.3

6.9

1.8

7

1.4

10.4

6.3

2.4

total dissolved   solids

47,600

47,500

15,900

41,200

9.890

2140

3870

629

37,000

3270

2270

48,000

  sulfate

15,300

23,000

9280

24,100

5600

1220

3310

190

35,600

1820

1240

31,100

  arsenic

0.15

0.15

0.13

<0.1

0.08

nd

0.03

0.06

nd

0.052

0.049

nd

  calcium

526

522

667

570

518

541

125

68.3

141

645

432

533

  magnesium

3,740

3680

1380

3580

1070

82.9

95.1

9

176

0.5

32.4

3570

  sodium

400

405

383

440

393

144

98.4

60.9

147

276

53.1

435

  potassium

55

65

11

45

17

38.9

19.2

 

490

59.3

19.2

52

  chloride

3340

3540

2050

3470

51

92

140

16

620

320

170

3090

  fluoride

270

260

78

200

60

1.4

6

0.9

240

1.3

1.5

200

  nitrate

5.5

6.8

0.03

9.4

250

1.58

2.38

 

3.6

2.23

0.33

11

  beryllium

1.08

1.06

0.312

0.98

0.81

0.01

0.0008

0.0008

0.03

nd

nd

0.882

  cadmium

1.05

1.17

0.522

1.02

0.133

0.015

0.0181

0.0022

0.0392

0.014

0.046

1.11

  chromium

1.4

1.1

0.1

0.9

nd

nd

0.36

nd

nd

nd

nd

1

  cobalt

10.5

10.7

3.6

9.5

1.47

0.06

0.21

nd

15.3

nd

nd

10.1

  copper

 

 

 

 

 

3.2

845

55.3

5700

 

0.51

 

  iron

743

710

282

411

0.13

49.9

49.5

2.72

342

nd

0.23

612

  lead

0.012

0.023

0.015

0.021

0.006

0.136

0.0627

0.041

0.298

nd

0.002

nd

  manganese

486

501

227

465

60.6

6.65

9.27

0.35

23.1

nd

2.53

476

  molybdenum

1.2

1

>0.5

0.8

0.25

0.6

0.26

0.07

2

3.71

11.3

 


2) records of spills and their impact on groundwater

spills at sierrita mine (date order with most recent first)

all spills were on-site in mill region, principally due to broken pipes. leach solution content varies according to the step of the process, as is seen by table above.

date of spill

amount of spill

content of spill

4/19/03

8,722 lbs.

sulfuric acid

1/31/02

39,375 gals.

sulfuric acid

7/3/01

1,209 lbs.

sulfuric acid

5/22/00

5,350 gallons

leach solution*

5/05/98

40,000 gallons

leach solution* (includes copper)

5/04/98

120,000 gallons

leach solution* (includes copper)

7/11/97

2,798 lbs

sulfuric acid

3/29/97

8,000 lbs

sulfuric acid-93%

8/11/96

100 gallons

sulfuric acid

7/22/96

3,000 lbs

sulfuric acid

6/12/96

13,263 lbs

leach solution (spent)

3/23/96

3,000 lbs

sulfuric acid

2/21/96

1,850 lbs

leach solution*

1/10/96

2,000 lbs

sulfuric acid

1/8/96

4,000 lbs

sulfuric acid

12/19/94

5,000 gallons

leach solution*

11/03/94

7,000 gallons

sulfuric acid

9/19/90

2,000 gallons

diesel fuel

3/16/90

1,500 gallons

hydrochloric acid

9/8/88

10 gallons

pcb’s

9/6/88

10 gallons

pcb’s

see actual reports at www.savethesantacruzaquifer.info/hazardous material incident sierrita.htm

spills at bagdad operations

since bagdad operations did not have a railway to the site, the chemicals and copper concentrate had to be trucked in and out of the milling/leaching area. there was a mountainous road that contributed to a number of truck accidents.

bagdad operation is using an alternative route at this time.

date of spill

amount of spill

content of spill

owner of property

12/07/04

7,484 lbs

leach solution

on-site

9/10/04

354 gals

sulfuric acid

on-site

12/04/00

<200 gals

sulfuric acid

state trust

9/18/00

5,850 gals

xanthate (flotation chemical)

federal

3/11/99

?

cyanides, acids

federal

3/07/99

12,000 gals

effluent (treated ww)

federal

3/01/99

200 gals

sulfuric acid

state

2/21/99

misc

glacial acetic, nitric acid

federal

7/27/98

?

sulfuric acid

state

1/01/98

50,000 lbs

copper concentrate

state

12/12/97

40,000 lbs

copper concentrate

state

9/17/97

7/7200 lbs

sulfuric acid

on-site

6/11/97

50,000 lbs

copper concentrate

bagdad town

3/09/97

1,500 lbs

sulfuric acid

on-site

7/18/96

3.57 lbs

mercury

bagdad town

6/18/96

3/40,000 lbs

copper concentrate

state/private

8/31/95

35,000 lbs

copper concentrate

state

7/21/95

48,100 lbs

lead sulfide/cu conc.

county

11/22/94

2,100 gals.

diesel

county

3/02/94

60 gals

sulfuric acid

state

6/11/93

600 gals

sulfuric acid

state

5/26/93

200 gals

diesel

private prop

2/22/92

1,200 gals

sulfuric

on-site

5/09/91

?

sodium cyanide

state

9/18/90

13 gals

pcb

on-site

12/17/87

1,500 gals

sulfuric acid

state

11/09/87

2/2,500 gals

sulfuric acid

state

9/20/86

50-60 gals

sulfuric acid

state

see actual reports on www.savethesantacruzaquifer.info/hazardous material incident bagdad.htm

how these spills impact the groundwater

there is data to show from community water company, which wisely did extra water testing for sulfates, that the spills do impact groundwater, even though the groundwater table is at several hundred feet. i noticed spikes in sulfate and tds in the community water company. naturally, i wondered what caused them. it was later that i found out about the spills and wondered if there was any correlation.

they did not appear to be testing errors because

1) they did not necessarily occur on the same test date.

2) there was a gradual increase, a spike, then a decrease.

3) the increase was of sulfate, but not of other common metals.

the sudden increases, then lowering of the levels, are not indicative of a traditional sulfate plume, or of a testing abnormality.

the problem in analyzing the data was finding the time frame that the sulfuric acid would flow from the spill in the mill/leach area to the public supply wells. i finally found the magic number!

the trip takes 39 months. of six correlations available, four in a row were 39 months, then 24 months, then 21 months. it could be expected that with time the spills make a path to make the trip faster.

date correlation of sulfuric acid spills and spikes in sulfates in community water well #8

spill date

date of spike in water testing data

travel time to wells, ± 2 miles

 

 

 

11/12/94

first known spill

1/03/96

4/02/99

39 months

7/08/96

10/26/99

39 months

7/97

10/18/00

39 months

5/98

8/04/01

36 months

5/00

4/8/02

23 months

7/01

4/21/03

21 months


community water company water testing data

well number 8
drilled 7/94

year of test or spill*

hardness

calcium
mg/l

sulfate
mg/ltr

tds

percentage of sulfate in tds

6/1/94 (1 st)

65

70.6

94.5

266

35%

6/1/94 (4 th)

146

46.7

59.8

286

21%

11/03/94

7,000 gallons

sulfuric acid

 

 

 

12/19/94

5,000 gallons

leach solution

 

 

 

10/05/95

160

59.96

--

422

 

11/20/95

 

 

138

396

35%

1/08/96

4,000 lbs.

sulfuric acid

 

 

 

1/10/96

2,000 lbs.

sulfuric acid

 

 

 

2/21/96

1,850 lbs.

spent electrolyte

 

 

 

3/23/96

3,000 lbs.

sulfuric acid

 

 

 

4/15/96

 

 

210

376

55.6%

6/12/96

13,263 lbs.

spent electrolyte

 

 

 

7/22/96

3,000 lbs.

sulfuric acid

 

 

 

8/07/96

 

 

131

470

28%

8/11/96

100 gallons

sulfuric acid

 

 

 

9/11/96

 

 

374

546

69%

10/21/96

 

 

--

406

 

1/13/97

 

 

233

640

36.4%

3/29/97

8,000 lbs.

sulfuric acid-93%

 

 

 

7/11/97

2,798 lbs.

sulfuric acid

 

 

 

7/16/97

 

 

297

564

52.6%

10/27/97

 

 

337

728

46.3%

12/23/97

 

 

329

616

53.4%

2/09/98

 

 

340

613

55.5%

5/04/98

120,000 gallons

sulfuricacid/cu

 

 

 

5/05/98

40,000 gallons

sulfuricacid/cu

 

 

 

6/22/98

 

 

356

873

40.7%

8/10/98

 

 

360

748

48.1%

11/30/98

 

 

553

696

79.5%

2/10/99

381

131

371

741

50.0%

4/12/99

 

 

820

1280

64.1%

7/15/99

 

 

405

766

52.8%

10/26/99

502

170

521

808

64.5%

1/11/00

521

179

390

757

51.5%

4/19/00

 

 

409

768

53.3%

5/22/00

5,350 gallons

sulfuricacid/cu

 

 

 

8/14/00

 

 

442

880

50.2%

10/18/00

 

 

456

704

64.7%

1/30/01

488

164

428

780

54.9%

4/04/01

 

 

430

--

 

7/03/01

1,209 lbs.

sulfuric acid

 

 

 

8/14/01

 

 

474

826

57.4

10/15/01

 

 

479

896

53.5

1/31/02

39,375 gallons

sulfuric acid

 

 

 

2/06/02

488

166

475

922

51.5

4/08/02

 

 

476

776

61.3

7/10/02

 

 

481

863

55.7

11/05/02

 

 

487

908

53.6

2003

565

190

547

956

57.2

2/04/03

519

175

504

871

57.9

4/19/03

8,722 lbs.

sulfuric acid

 

 

 

4/21/03

 

 

508

820

62.

2004

587

 

502

952

52.7

*note: spill data given in red.

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