Table 1. Life cycle inventories: Material and energy input and outputs for open-pit and alluvial mining techniques.
Gold mining techniques
|
Alluvial
|
Open-pit
|
Unit
|
Emissions released to:
|
Input
|
Water
|
a9.79X1007
|
l5.70X1007
|
ton/year
|
|
Energy (electricity)
|
b2.53X1011
|
m2.03X1012
|
kJ/year
|
|
Energy (natural gas)
|
c1.60X1007
|
n1.68X1010
|
kJ/year
|
|
Energy (petrodiesel)
|
d1.12X1009
|
o1.15X1012
|
kJ/year
|
|
Oxygen (air from cylinders)
|
e40
|
p3.75X1005
|
ton/year
|
|
Others (services/chemicals)
|
*318.8
|
** 1.01X1006
|
ton /year
|
|
Output
|
Inert material removed (sterile mineral)
|
f1.06X1008
|
q 6.94X1007
|
ton/year
|
soil
|
Vegetation cover (clearing and stripping)
|
g60
|
r 1.33X1003
|
ton/year
|
soil
|
Sludge tails (wet weight)
|
h4.52X1003
|
s 2.42X1007
|
ton/year
|
tailing pond (stored)
|
Energy losses
|
i4.74X1010
|
t1.24X1012
|
kJ/year
|
air
|
Emissions of substances to air by combustion, detonation, trituration, leakage etc.
|
---
|
u2.204X103
|
|
---
|
Stored material with mineral of interest
|
---
|
v3.98X1007
|
ton/year
|
soil
|
Metal ferrous co-product (dry weight, 55% iron)
|
1.55
|
---
|
ton/year
|
|
Silver co-product (dry weight)
|
---
|
w21.55
|
ton/year
|
|
Gold (dry weight)
|
j3.10
|
x19.05
|
ton/year
|
|
Recycling
|
Water
|
k4.42X1005
|
y4.79X1007
|
ton/year
|
|
aWater in alluvial mining technology (ton/year): Exploration (1.25X1002), clearing and stripping (1.15X1006), float up of suction dredger (1.00X1007), mechanical screening (7.46X1007), hydraulic jigs (1.12X1007), sluice boxes (4.84X1005), Physical separation (4.46X1005), Waste Tailings Treatment Plant (3.80X-01), Services (9.38X1003 water for domestic use, not used into operational process).
b Electrical energy in alluvial mining technology (kJ/year): clearing and stripping (9.98X1010), dipper dredger (6.86X1010), mechanical screening (4.47X1010), hydraulic jigs (2.33X1010), sluice boxes (2.76X1009), physical separation (1.92X1008), filtration-separation (7.67X1007), chemical separation (1.15X1008), Waste Tailing Treatment Plant (WTTP) (4.77X1007), tailings pond (6.95X1007), services (1.35X1010 to support suction dredger, dipper dredger and administrative offices). Hydropower run-of-river electricity production supplies 100% of the energy demand from alluvial mining,
c Gas energy (propane) in alluvial mining technology (kJ/year): drying and separation of ferrous minerals (1.60X1007).
d Diesel fuel (derived from petroleum) in alluvial mining technology (kJ/year): Exploration (2.86X1008), Casting and molding (4.33X1006), Services (8.34X1008 to support suction dredger, dipper dredger).
e Oxygen (air) in alluvial mining technology (ton/year): drying and separation (20), tailings pond (20)
f Inert material removed (sterile mineral in dry weight) in alluvial mining technology (ton/year): reserves evaluation, exploration (5.61X1002); reserves evaluation, clearing and stripping (3.65X1007); mineral extraction, dipper dredger (6.95X1007).
g Vegetation covered harbors in alluvial mining technology (ton/year): clearing and stripping (60 corresponding to 140 hectares)
h Sludge tails (wet weight) in alluvial mining technology 4.52X1003 with 98.7% humidity.
i Energy losses in alluvial mining technology (KJ/year): clearing and stripping (9.98X1009), dipper dredger (6.86X1009), mechanical screening (2.41X1010), hydraulic jigs (2.33X1009), sluice boxes (7.73X1008), physical separation (1.92X1007), filtration-separation (2.15X1007), chemical separation (3.22X1007), WTTP (1.34X1007), tailing pond (1.94X1007), services (3.10X1009 to support suction dredger, dipper dredger and administrative offices), drying and separation of ferrous minerals (1.60X1006), Exploration (1.80X1008), Casting and molding (1.99X1003). Note: energy losses are calculated on equipment efficiency.
j Gold (dry weight) in alluvial mining technology (ingot/year): 155 each 20kg.
k Recycling in alluvial mining technology, water treated from WTTP to physical separation.
l Water consumption in open-pit Mining Technology (ton/year): clearing and stripping (5.65X1006 water for irrigation to minimize Total Suspended Particles in the air), mineral excavation (5.08X1006 spray irrigation systems to minimize Total Suspended Particles in the air), secondary milling (3.59X1007), gravimetric separation (8.32X1006), floatation (2.08X1006), elution (6.96X1005). Primary crushing step is not significant in spray irrigation systems, and is not quantified.
* Others in alluvial mining technology (ton/year): 1. Services (7.3 organic material in domestic wastewater). 2. Chemicals: chemical separation (emulsifying agent 0.1; foaming agent 0.23; flotation agent 0.48), WTTP (coagulating agent 0.45), Casting and molding (Sodium borate 232.68 as a fluxing agent; calcium carbonate 77.56).
m Electrical energy in open-pit mining technology (kJ/year): mineral excavation (8.08X1010), primary crushing (7.82X1010), secondary milling (1.36X1012), gravimetric separation (2.15X1009), floatation (1.97X1011), leaching (4.45X1010), carbon adsorption (8.05X1009), detoxification (2.02X1008), tailings pond (5.34X1010), elution and carbon regeneration (3.90X1010), casting and electro-winning (7.99X1009), other services such as administrative offices, public services (1.55X1011).
n Gas energy (liquefied petroleum gas) in open-pit mining technology (kJ/year): other services (1.68X1010).
o Diesel fuel (derived from petroleum) in open-pit mining technology (kJ/year): mineral excavation (1.14X1012), casting and electro-winning (1.35X1009), other services (5.35X1009 lightweight vehicles).
p Oxygen (air) in open-pit mining technology (ton/year): floatation (2.27X1004), leaching (3.75X1005).
q Inert material removed (sterile mineral in dry weight) in open-pit mining technology (ton/year): reserves evaluation, clearing and stripping (1.09X1003); mineral excavation (6.93X1007).
r Vegetation covered harbors in open-pit mining technology (ton/year): clearing and stripping (1.33X1003 vegetation covered harbors).
s Sludge tails (wet weight) in open-pit mining technology (ton/year): 2.42X1007 with 2.36X10-04 % humidity.
t Energy losses open-pit mining technology (KJ/year): mineral excavation (7.48X1011), primary crushing (1.49X1010), secondary milling (2.59X1011), gravimetric separation (2.15X1008), floatation (5.50X1010), leaching (4.45X1009), carbon adsorption (3.62X1009), detoxification (5.64X1007), tailings pond (5.34X1009), elution and carbon regeneration (1.09X1010), casting and electro-winning (1.65X1009), other services (1.39X1011 administrative offices, public services). Note: energy losses are calculated on equipment efficiency.
u Emissions, Total Suspended Particles in open-pit mining technology (ton/year): mineral excavation (1.75X1003), primary crushing (2.41X1001), secondary milling (7.09X1001), tailings pond (3.75X1002).
v Stored material with mineral of interest (ton/year): 55% of the extracted material (3.98X1007) with a significant gold concentration is stored (3.98X1007) for future beneficiation.
w Silver (dry weight) in open-pit mining technology (ingot/year): Average 1078 each 20kg.
x Gold (dry weight) in open-pit mining technology (ingot/year): Average 952 each 20kg.
y Recycling in open-pit mining technology, water treated from WTTP to all the process.
** Others in open-pit mining technology (ton/year): 1. Chemicals: mineral excavation (1.41X1004 Ammonium Nitrate - Fuel Oil ANFO, 95% ammonium nitrate and 5% kerosene), chemical separation (1.08X1001 NaOH; 8.99X1001 NaCN), floatation (Potassium Ammonium Xanthate 5.29X1002; 4.37X1002 flotation agent), leaching (1.87X1003 NaCN, 2.19X1003 CaO), carbon adsorption (2.67X1003 activated carbon), detoxification (1.5X1002 CaO; 1.10X1000 H2O2; 1.27X1002 Na2S2O5), tailings pond (flocculating agent 3.11X1002), elution and carbon regeneration (9.91X1005 inorganic chemicals)
Note: --- data not considered in this study. Both mining are legally constituted entities (not considered as informal ones).
Table 2. Comparison of gold mining processes according to mid-point impact categories.1
Impact categories aggregated
|
Impact categories
|
Alluvial mining technology
|
Open-pit mining technology
|
Ecoinvent 3.1. database Peru
|
Ecoinvent 3.1. database Papua New Guinea
|
Ecoinvent 3.1. database Rest of the World
|
Non-normalized values (units/year)
|
Normalized values (units/year)
|
Non-normalized values (units/year)
|
Normalized values (units/year)
|
Non-normalized values (units/year)
|
Normalized values
(units/year)
|
Non-normalized values (units/year)
|
Normalized values (units/year)
|
Non-normalized values (units/year)
|
Normalized values (units/year)
|
Ecosystem (soil)
|
agricultural land occupation, (m2a)
|
1.81X1004
|
3.33X1000
|
2.65X1002
|
4.88X10-02
|
4.13X1002
|
7.61X10-02
|
1.24X1003
|
2.29X10-01
|
6.06X1002
|
1.12X10-01
|
natural land transformation, (m2)
|
4.64X1002
|
3.86X1001
|
1.93X1001
|
1.60X1000
|
5.17X1000
|
4.29X10-01
|
9.45X1000
|
7.86X10-01
|
6.60X1000
|
5.49X10-01
|
urban land occupation, (m2a)
|
4.21X1002
|
5.43X10-01
|
1.30X1003
|
1.68X1000
|
1.09X1003
|
1.41X1000
|
1.20X1003
|
1.55X1000
|
1.09X1003
|
1.40X1000
|
terrestrial acidification, (kg SO2 eq)
|
8.05X10-01
|
2.11X10-02
|
2.07X1002
|
5.42X1000
|
1.90X1002
|
4.98X1000
|
2.54X1002
|
6.66X1000
|
2.41X1002
|
6.31X1000
|
terrestrial ecotoxicity, (kg 1,4-DB eq)
|
1.15X10-02
|
1.94X10-03
|
1.03X1001
|
1.74X1000
|
2.20X1000
|
3.72X10-01
|
1.95X1000
|
3.28X10-01
|
2.53X1000
|
4.27X10-01
|
Ecosystem (water)
|
freshwater ecotoxicity (kg 1,4-DB eq)
|
1.29X1001
|
3.01X1000
|
7.39X1004
|
1.72X1004
|
1.41X1004
|
3.28X1003
|
6.33X1003
|
1.47X1003
|
1.24X1004
|
2.89X1003
|
freshwater eutrophication, (kg P-eq)
|
4.20X10-02
|
1.45X10-01
|
4.94X1002
|
1.71X1003
|
3.80X1002
|
1.31X1003
|
1.70X1002
|
5.87X1002
|
3.24X1002
|
1.12X1003
|
marine ecotoxicity (kg 1,4-DB eq)
|
1.14X1001
|
4.63X1000
|
2.11X1004
|
8.57X1003
|
1.25X1004
|
5.08X1003
|
9.07X1003
|
3.68X1003
|
1.18X1004
|
4.79X1003
|
marine eutrophication, (kg N-eq/m3)
|
3.94X10-01
|
5.37X10-02
|
8.55X1001
|
1.16X1001
|
1.06X1002
|
1.44X1001
|
1.20X1002
|
1.64X1001
|
1.26X1002
|
1.72X1001
|
water depletion (m3)2
|
2.82X1004
|
|
4.91X1002
|
|
1.89X1001
|
|
1.23X1003
|
|
1.34X1002
|
|
Resources
|
fossil depletion, (kg oil eq)
|
4.29X1001
|
3.32X10-02
|
3.94X1003
|
3.06X1000
|
2.48X1003
|
1.92X1000
|
9.82X1003
|
7.61X1000
|
5.06X1003
|
3.92X1000
|
metal depletion (kg Fe-eq)
|
7.00X1004
|
1.57X1002
|
8.29X1004
|
1.86X1002
|
8.23X1004
|
1.85X1002
|
8.14X1004
|
1.83X1002
|
1.01X1005
|
2.28X1002
|
Human health
|
climate change (kg CO2 eq)
|
1.66X1002
|
2.41X10-02
|
1.51X1004
|
2.19X1000
|
8.07X1003
|
1.17X1000
|
2.90X1004
|
4.22X1000
|
1.57X1004
|
2.28X1000
|
ozone depletion, (kg CFC-11 eq)
|
1.63X10-05
|
4.34X10-04
|
1.06X10-03
|
2.81X10-02
|
1.07X10-03
|
2.84X10-02
|
3.46X10-03
|
9.18X10-02
|
2.04X10-03
|
5.43X10-02
|
particulate matter formation (kg PM10 eq)
|
6.91X10-01
|
4.92X10-02
|
1.65X1002
|
1.18X1001
|
6.56X1001
|
4.67X1000
|
1.04X1002
|
7.41X1000
|
8.44X1001
|
6.00X1000
|
photochemical oxidant formation (kg NMVOC)
|
7.86X10-01
|
1.38X10-02
|
2.18X1002
|
3.84X1000
|
2.34X1002
|
4.12X1000
|
3.15X1002
|
5.55X1000
|
2.87X1002
|
5.05X1000
|
human toxicity (kg 1,4-DB eq)
|
7.35X1001
|
2.25X10-01
|
5.56X1005
|
1.70X1003
|
6.42X1005
|
1.97X1003
|
2.88X1005
|
8.82X1002
|
5.47X1005
|
1.68X1003
|
1 The results are expressed per 1.00 kggold.
2 ReCiPe (v. 1.11) does not include a normalization factor for water depletion
Table 3. Environmental performance of open-pit and alluvial mining systems according to end-point indicators to the total environmental impacts in points.
Indicator
|
Open-pit mining [points]
|
Alluvial mining [points]
|
Percentage
open-pit mining [%]
|
Percentage
Alluvial mining [%]
|
Ecosystem quality [points]
|
6.02X1002
|
2.37X1003
|
6.0
|
99.3
|
Human health [points]
|
8.98X1003
|
9.35X1000
|
89.2
|
0.4
|
Resources [points]
|
4.88X1002
|
7.43X1000
|
4.8
|
0.3
|
Single indicator:
total [points]
|
1.01X1004
|
2.38X1003
|
100.00
|
100.00
|
Note: Total points values are already weighted in the previous aggregation step under hierarchist perspective (ecosystem weight: 400. Human health weight: 300, resources weight: 300) ReCiPe (v. 1.11).