Characteristics of Acid Leach Solution
in Sierrita Ponds
In the Heap Leach process chemicals—sulfuric acid in the case of copper mining—are applied to low-grade ore that has been crushed and deposited on a specially designed pad, lined with synthetic materials or compacted clay. The solution is collected and sent to a solvent extraction (SX) plant to remove the copper. SX is a two step process. In the first step the solution (PLS=pregnant leach solution) is mixed with an organic solvent that selectively binds to copper to separate it out, leaving the other heavy metals including uranium in the solution.
This solution, known as raffinate, is recycled back to the leach process, which saturates the solution even further with the unwanted heavy metals, including uranium. Following is the analysis of the raffinate ponds at the Sierrita mine. Note that their data did not include any radioactive chemicals.
Facility/Sample Location |
Headwall No.1 |
Bailey Lake |
B-Pond (D-07) |
Headwall No. 3 |
Headwall No. 5 |
Duval Canal |
SX-3 Drain Pond |
SX-1 Drain Pond |
SX-1 Tank Farm Pond |
Reclaim |
D Pond |
Headwall #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, field (su.) |
2 |
2 |
2.88 |
3 |
4.72 |
7.34 |
10.49 |
2.11 |
||||
pH, lab (su.) |
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 (mg/ltr) |
47,600 |
47,500 |
15,900 |
41,200 |
9.890 |
2140 |
3870 |
629 |
37,000 |
3270 |
2270 |
48,000 |
Sulfate (mg/ltr) |
15,300 |
23,000 |
9280 |
24,100 |
5600 |
1220 |
3310 |
190 |
35,600 |
1820 |
1240 |
31,100 |
Arsenic (mg/ltr) |
0.15 |
0.15 |
0.13 |
<0.1 |
0.08 |
ND |
0.03 |
0.06 |
ND |
0.052 |
0.049 |
ND |
Calcium (mg/ltr) |
526 |
522 |
667 |
570 |
518 |
541 |
125 |
68.3 |
141 |
645 |
432 |
533 |
Magnesium(mg/ltr) |
3740 |
3680 |
1380 |
3580 |
1070 |
82.9 |
95.1 |
9 |
176 |
0.5 |
32.4 |
3570 |
Sodium (mg/ltr) |
400 |
405 |
383 |
440 |
393 |
144 |
98.4 |
60.9 |
147 |
276 |
53.1 |
435 |
Potassium(mg/ltr) |
55 |
65 |
11 |
45 |
17 |
38.9 |
19.2 |
490 |
59.3 |
19.2 |
52 |
|
Chloride (mg/ltr) |
3340 |
3540 |
2050 |
3470 |
51 |
92 |
140 |
16 |
620 |
320 |
170 |
3090 |
Fluoride (mg/ltr) |
270 |
260 |
78 |
200 |
60 |
1.4 |
6 |
0.9 |
240 |
1.3 |
1.5 |
200 |
Nitrate (mg/ltr) |
5.5 |
6.8 |
0.03 |
9.4 |
250 |
1.58 |
2.38 |
3.6 |
2.23 |
0.33 |
11 |
|
Beryllium (mg/ltr) |
1.08 |
1.06 |
0.312 |
0.98 |
0.81 |
0.01 |
0.0008 |
0.0008 |
0.03 |
ND |
ND |
0.882 |
Cadmium (mg/ltr) |
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 (mg/ltr) |
1.4 |
1.1 |
0.1 |
0.9 |
ND |
ND |
0.36 |
ND |
ND |
ND |
ND |
1 |
Cobalt (mg/ltr) |
10.5 |
10.7 |
3.6 |
9.5 |
1.47 |
0.06 |
0.21 |
ND |
15.3 |
ND |
ND |
10.1 |
Copper (mg/ltr) |
3.2 |
845 |
55.3 |
5700 |
0.51 |
|||||||
Iron (mg/ltr) |
743 |
710 |
282 |
411 |
0.13 |
49.9 |
49.5 |
2.72 |
342 |
ND |
0.23 |
612 |
Lead (mg/ltr) |
0.012 |
0.023 |
0.015 |
0.021 |
0.006 |
0.136 |
0.0627 |
0.041 |
0.298 |
ND |
0.002 |
ND |
Manganese(mg/ltr) |
486 |
501 |
227 |
465 |
60.6 |
6.65 |
9.27 |
0.35 |
23.1 |
ND |
2.53 |
476 |
Molybdenum(mg/ltr) |
1.2 |
1 |
>0.5 |
0.8 |
0.25 |
0.6 |
0.26 |
0.07 |
2 |
3.71 |
11.3 |
|