danny santis
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Characterization and in-situmonitoring of large scale heapleach fluid dynamicsDanny Santis Valenzuela, Michael Milczarek, Tzung-mow Yao,Jason Keller
Pilot Heap Leach Design• 500,00 ton copper sulfide heap leach pilot project
– 0.5-inch crushed and agglomerated ore– 18 m height– Approximately 90 m x 90 m leaching area– Drainage system split into 9 modules to monitor outflow– Double aeration system
• Key questions for characterization and monitoring:– Ore permeability?– Solution distribution?– Oxygen content and distribution?– Temperature distribution and evolution?– In-situ solution sampling?
• Operated for 1.3 years
Pilot Heap Leach Characterization
• Daily samples from crusher plant (PSD)– Target < 50% passing the #4 mesh
• Pre-leach and post-leach drilling for deep sub-surface samplecollection– Casing advancement to keep the hole open (and for instrument
placement during pre-leach)
• Sample collection for:– Geochemical/mineralogy testing– Hydraulic and physical property testing (undisturbed samples)
Instrumentation and Monitoring
• 25 monitor well– 0 to 17.5 m below ground surface
• Monitoring parameters– Temperature oxygen/air piezometers (every 3 m)– Moisture content and capillary pressure (tension) (every 6 m)– Water piezometers (one per module)– Suction lysimeters (various)
• Automated data collection w/ telemetry to control room
Leaching Core84 m x 84 m
SolutionCollectionModules30m x 30m
1 4 7
2 5 8
3 6 9
Aeration from East
Aeration from West
Topographic Gradient
Drainage lines
1 4 7
2 5 8
3 6 9
East
West
Slide 6
Suctionlysimeter
In-situ Monitoring InstrumentInstallation
Automated Data Collection
Hourly data collection w/Telemetry to control room
RESULTS
Heap Solution Budget (Average)
0%
5%
10%
15%
20%
25%
30%
11/1/
2007
12/1/
2007
12/31
/2007
1/30/2
008
2/29/2
008
3/30/2
008
4/29/2
008
5/29/2
008
6/28/2
008
7/28/2
008
8/27/2
008
9/26/2
008
10/26
/2008
11/25
/2008
12/25
/2008
Date
Sol
utio
n C
onte
nt (v
/v)
0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
Irrig
atio
n R
ate
(l/m
2 /hr)
Predicted Solution Content (v/v) Avg Daily Irrigation Rate
Start DoubleAeration
Stop DoubleAeration
Temperature at Depth (Center Borehole)
0
1
2
3
4
5
6
2008
-09-
29
2008
-10-
01
2008
-10-
03
2008
-10-
05
2008
-10-
07
2008
-10-
09
2008
-10-
11
2008
-10-
13
2008
-10-
15
2008
-10-
17
2008
-10-
19
2008
-10-
21
2008
-10-
23
2008
-10-
25
2008
-10-
27
2008
-10-
29
2008
-10-
31
2008
-11-
02
Perc
olat
ion
flow
rate
(L/h
/m2)
Date
Module 4 - East aeration grid Module 6 - East aeration grid
Module 4 - West aeration grid Module 6 - West aeration grid
Percolation vs Aeration (direction)
1 4 7
2 5 8
3 6 9
East
West
0.00
0.20
0.40
0.60
0.80
1.00
1.20
1.40
1.60
Single EastAir
Double EastAir
Alt Air-E Alt Air-W No Air
Dra
inag
e/Ir
riga
tion
Mod 1,4,7Mod 2,5,8Mod 3,6,9
North-South Solution Balance(Normalized)
East
West
East
West
4 m bgs Capillary Pressure – DoubleAeration
-40-20
-40
-20
-20
-20
-20
-20
-20
0
00
0
0
0
0
0
0
0
20
20
2020
20
20
20
40 40
40
40
40
40
60
60
60
80 80
80
100
100100
120
120
120140
140
140
160
160
160
180
180
180200
200
200
X (m)
Y(m)
10 20 30 40 50 60 70 80
10
20
30
40
50
60
70
80
200180160140120100806040200-20-40-60-80-100
7/10/2008 - Double Aeration From East, I=3.0 l/hr/m2
4 m bgsCapillary Pressure
(cm)123
456
789
West East
Monitoring Data Summary
• Time dependent behavior– High initial temperatures then temperature decline– Increasing solution balance– Solution samples showed more reducing conditions over time
• Strong preferential solution and air flow• Low aeration efficiency
– Highly variable oxygen contents– Low observed air connectivity under leach
• Positive capillary pressures in heap– Combination of near saturation and CO2 accumulation
Post-leach Ore Sampling andTesting
• Drilled 52 boreholes (sonic drilling)– Samples every 1.5 m– Logging for oxidising and reducing conditions– Physical property and geometallurgical analyses– 12 representative samples for hydraulic property testing
• Determine relationship of PSD, bulk density and hydraulicconductivity
• Results correlated to monitoring data
0
10
20
30
40
50
60
70
80
90
100
0.1 1 10 100
Perc
ent P
assi
ng
Particle Diameter (mm)
Average of All Core Samples
Average of Crush head
#4 mesh
#100 mesh
Average PSD – Before and After Leaching
Percolation vs < #100 Mesh (module avg)y = -0.061x + 22.015
R² = 0.6559
19.0
19.5
20.0
20.5
21.0
21.5
22.0
22.5
0 5 10 15 20
Perc
ent P
assi
ng #
100
Mes
h
Percent of Total Collected Percolation
Modules 1and 4
Module 7
Module 2Module 5 Module 3
Module 9
Module 8
Module 6
0.0%
10.0%
20.0%
30.0%
40.0%
50.0%
60.0%
70.0%
80.0%
90.0%
Perc
ent o
f Tot
al C
ore
Module 1
Module 2
Module 3
Module 4
Module 5
Module 6
Module 7
Module 8
Module 9
Module Avg
Outside Avg
Yellow (Oxidising) Grey (Reducing)
Eastern Modules
4,5,6 Transect
BETTER AERATION/SOLUTION FLOWModule 9
Relative Oxidising Conditions perModule (52 boreholes)
0
2
4
6
8
10
12
14
16
1.0E
-05
1.0E
-04
1.0E
-03
1.0E
-02
1.0E
-01
1.0E
+00
Dep
th (m
bgs
)
Ksat (cm/sec)
Predicted-AllModules2 L/m2/hr
100X SafetyFactor
0
2
4
6
8
10
12
14
16
1.0E
-06
1.0E
-05
1.0E
-04
1.0E
-03
1.0E
-02
1.0E
-01
1.0E
+00
Dep
th (m
bgs
)
Ksat (cm/sec)
Module 1
Module 2
Module 3
Module 4
Module 5
Module 6
Module 7
Module 8
Module 9
Post-Leach Predicted Permeability (Ksat)
1 4 7
2 5 8
3 6 9
East
West
Other factors:• Decrepitation• Aeration/flow domains (initial fingering)• Aeration pipe damage• Earthquake
High Flow in 4, 5, 6, 8 During No Aeration?
Lessons Learned• Bulk densities higher (permeability lower) than predicted:
– Mostly in initial modules (i.e. 9) where crushing criteria was not beingmet
• Solution movement– Permeability contrasts, preferential flow– Decrepitation, particle orientation (and an earthquake)– Drainage layer pressurization by aeration
• Low aeration efficiency– Air loss from sides, pipe damage– More air may not be better
• Greatest oxidation/copper recovery observed in modules withmost air and solution flow
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