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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