Impacts of Sulfuric Acid Leaching

The electro-winning system [SX-EW] of extracting copper 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 soil and air pollution. Howver, SX-EW 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 over some 15 years.

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. 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.

Ideally, this system is a closed circuit and is considered environmentally safe. However, there are two conduits to environmental 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, spills of the sulfuric acid and the leach solution, which is laden with heavy metals, including radionuclides that are present with metals in Arizona, can spill as they are piped around the facility.

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 or dripped onto fresh ore on the leach pads.

These ponds are not appropriate for a natural setting where birds and animals should have some priority. Are the open ponds a danger to animals and birds? In general, it appears that they are not, for it the critters seem to have an instinct about such toxic places. However, this does not mean that an errant bird, lizard, frog or snake could not happen by and fall in. Any evidence would be dissolved in a split second.

The data on the table below shows the "Characteristics of Leach Solution, which is classifed as hazardous waste. Whereas these ponds are an inevitable part of mining and are considered to be an improvement over tailings impoundments and smelting, it is questionable if they are appropriate for a National Forest setting with its requirements for beneficial use.

Facility/Sample Location	Bailey Lake (D-03)	B-Pond (D-07)	Duval Canal (D-29)	SX-3 Drain Pond (D-31)	SX-1 Drain Pond (D-33)	SX-1 Tank Farm Pond (D-34)	Reclaim Pond	D Pond (D-45)
Date Sampled	4/22/98	4/22/98	9/15/98	4/15/99	4/15/99	4/15/99	4/15/99	6/30/98
Conductance (umhos/cm)	16,300	8,270	2,425		629	104,000	3450	2540
pH, field (su.)	2	2.88	7.34				10.49
pH, lab (su.)	2.1	3	6.9	1.8	7	1.4	10.4	6.3
Total Dissolved Solids (mg/ltr)	47,500	15,900	2140	3870	629	37,000	3270	2270
Sulfate (mg/ltr)	23,000	9280	1220	3310	190	35,600	1820	1240
Arsenic (mg/ltr)	0.15	0.13	ND	0.03	0.06	ND	0.052	0.049
Calcium (mg/ltr)	522	667	541	125	68.3	141	645	432
Magnesium (mg/ltr)	3680	1380	82.9	95.1	9	176	0.5	32.4
Sodium (mg/ltr)	405	383	144	98.4	60.9	147	276	53.1
Potassium (mg/ltr)	65	11	38.9	19.2		490	59.3	19.2
Chloride (mg/ltr)	3540	2050	92	140	16	620	320	170
Fluoride (mg/ltr)	260	78	1.4	6	0.9	240	1.3	1.5
Nitrate (mg/ltr)	6.8	0.03	1.58	2.38		3.6	2.23	0.33
Beryllium (mg/ltr)	1.06	0.312	0.01	0.0008	0.0008	0.03	ND	ND
Cadmium (mg/ltr)	1.17	0.522	0.015	0.0181	0.0022	0.0392	0.014	0.046
Chromium (mg/ltr)	1.1	0.1	ND	0.36	ND	ND	ND	ND
Cobalt (mg/ltr)	10.7	3.6	0.06	0.21	ND	15.3	ND	ND
Copper (mg/ltr)			3.2	845	55.3	5700		0.51
Iron (mg/ltr)	710	282	49.9	49.5	2.72	342	ND	0.23
Lead (mg/ltr)	0.023	0.015	0.136	0.0627	0.041	0.298	ND	0.002
Manganese (mg/ltr)	501	227	6.65	9.27	0.35	23.1	ND	2.53
Molybdenum( mg/ltr)	1	>0.5	0.6	0.26	0.07	2	3.71	11.3

2) Spills of solution and acid: The solution is transferred to and from the leach solution ponds to the leach pads using pipelines. This presents a danger of leaks and spills due to breaking of the pipes. This happens regularly, including Sierrita, although that they use every measure possible to avoid such "incidents." Further, it is possible for the equipment to fail and a pond to overflow as happened in Silver Bell Operations, 2002. Whereas the milling areas and ponds are on private land in these two cases, at Rosemont the mill will be on public land.

As called out in the Rosemont Plan, Augusta is well aware of the problem of "accidents" and "incidents," which they cannot and do not guarantee will not occur.

9/06/05 8,058 lbs. Sulfuric Acid (Report)

9/24/05 1,000 lbs. Sulfuric Acid (Report)

3/23/96 3,000 lbs. Sulfuric acid

2/21/96 1,850 lbs. Leach Solution (spent electrolyte)

12/19/94                     5,000 gals.            Leach Solution

11/03/94                     7,000 gals.            Sulfuric acid

9/19/90                       2,000 gals.            Diesel fuel

3/16/90                       1,500 gals.            Hydrochloric acid

9/8/88                             10 gals.            PCB’s

The Hazardous Waste Incidents at Bagdad mine are of particular interest for a proposed mine that will need to truck in various chemicals and truck out copper concentrate to a smelter. These spills of extremely toxic chemicals and copper concentrate seriously impact the roadways and soils, as well as potentially pollute ground or surface water, on Forest Service, BLM and State Trust Land. Apparently, there was a winding road to the railroad junction, and eventually another route was used.

How Sulfuric Acid Spills Impacted Public Supply Water Wells
in Green Valley, Arizona

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!

It 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

* These are approximate because Community Water was only testing semi-annually during part of this period.