1. Novel Advances Using Sewage Sludge in Engineered
Dry Covers for Sulphide Mine Tailings Remediation
Peter Nason
PhD Candidate in Applied Geology
Luleå University of Technology
Division of Geosciences and Environmental
Engineering
peter.nason@ltu.se
Wednesday 18th December 2013
10:00 am
E632
Luleå University of Technology
2. List of Papers
I. Nason P, Alakangas L, Öhlander B (2013) Using sewage sludge as a sealing layer to remediate
sulphidic mine tailings: A pilot-scale experiment, northern Sweden.
Environmental Earth Sciences 70: 3093-3105
II. Nason P, Alakangas L, Öhlander B (2013) Impact of sewage sludge on the groundwater
quality at a formerly remediated tailings impoundment.
Mine Water and the Environment. E-print: DOI 10.1007/s10230-013-0244-6
III. Nason P, Johnson RH, Neuschütz C, Alakangas L, Öhlander B (2013) Alternative waste residue
amendments for passive in-situ prevention of sulphide-mine tailings oxidation: a field-
evaluation. Revised submission to Journal of Hazardous Materials
IV. Jia Y, Nason P, Alakangas L, Maurice C, Öhlander B (2013) Degradability of digested sewage
sludge residue under anaerobic conditions for mine tailings remediation.
Submitted to Environmental Earth Sciences (Under review)
V. Jia Y, Nason P, Alakangas L, Maurice C, Öhlander B (2013) Degradability of digested sewage
sludge residue under aerobic conditions at different temperatures for mine tailings
remediation.
Submitted to International Journal of Environmental Science and Technology (Under review)
VI. Nason P (2013) Advances in using sewage sludge to remediate sulfidic mine tailings – An
overview from pilot- and field-scale experiments, northern Sweden. In: Reliable Mine Water
Technology: Proceedings of the International Mine Water Association Annual Conference
2013, Golden, CO, USA, Brown A, Figueroa L. & Wolkersdorfer C. (Eds.), Volume 1, pp. 681-
686
I. Nason P, Alakangas L, Öhlander B (2013) Using sewage sludge as a sealing layer to remediate
sulphidic mine tailings: A pilot-scale experiment, northern Sweden.
Environmental Earth Sciences 70: 3093-3105
II. Nason P, Alakangas L, Öhlander B (2013) Impact of sewage sludge on the groundwater
quality at a formerly remediated tailings impoundment.
Mine Water and the Environment. E-print: DOI 10.1007/s10230-013-0244-6
III. Nason P, Johnson RH, Neuschütz C, Alakangas L, Öhlander B (2013) Alternative waste residue
amendments for passive in-situ prevention of sulphide-mine tailings oxidation: a field-
evaluation. Revised submission to Journal of Hazardous Materials
IV. Jia Y, Nason P, Alakangas L, Maurice C, Öhlander B (2013) Degradability of digested sewage
sludge residue under anaerobic conditions for mine tailings remediation.
Submitted to Environmental Earth Sciences (Under review)
V. Jia Y, Nason P, Alakangas L, Maurice C, Öhlander B (2013) Degradability of digested sewage
sludge residue under aerobic conditions at different temperatures for mine tailings
remediation.
Submitted to International Journal of Environmental Science and Technology (Under review)
VI. Nason P (2013) Advances in using sewage sludge to remediate sulfidic mine tailings – An
overview from pilot- and field-scale experiments, northern Sweden. In: Reliable Mine Water
Technology: Proceedings of the International Mine Water Association Annual Conference
2013, Golden, CO, USA, Brown A, Figueroa L. & Wolkersdorfer C. (Eds.), Volume 1, pp. 681-
686
3. Project Background: Sulphide Tailings and ARD
Mineral Extraction of sulphide-bearing ores may
generate large volumes of waste material
COG: < 1 %; waste may be > 99 %
Tailings: Waste from hydro-metallurgical processing
Sand-Silt: High surface areas: Very Reactive!
Mineral processing: never 100% efficient
Deposited as a slurry in large-scale impoundments
Acid Rock Drainage:
Chemical Dissolution of Pyrite (FeS2):
𝑭𝒆𝑺 𝟐 +
𝟕
𝟐
𝑶 𝟐 + 𝑯 𝟐 𝑶 → 𝑭𝒆 𝟐+
+ 𝟐𝑺𝑶 𝟒
𝟐−
+ 𝟐𝑯+
Hydrolysis of Ferrous Iron(II):
𝑭𝒆 𝟐+
+
𝟏
𝟒
𝑶 𝟐 + 𝑯+
→ 𝑭𝒆 𝟑+
+
𝟏
𝟐
𝑯 𝟐 𝑶
𝑭𝒆 𝟑+ + 𝟑𝑯 𝟐 𝑶 → 𝑭𝒆(𝑶𝑯) 𝟑 + 𝟑𝑯+
Result: Acid- (<pH 6), sulphate- (>1000mg/L) and
metal-rich solution
Tailings have to be carefully disposed: Avoid
contamination of peripheral environments
Legal Requirements now involved:
European Parliament’s ‘Management of Waste from
Extractive Industries Directive (2006/21/EC)’
Figure 1: Map illustrating the location of operational mines in Sweden
in 2009 (SGU, 2009)
5. Using Sewage Sludge as a Dry Cover Material
“Solid Residue End Product originating from the
treatment process of waste water”
•Anaerobically digested
•Abundant source of an inexpensive waste material
•210 000 t per year from 2100 plants in Sweden
•Hazardous material: requires landfill disposal
•Co-disposal of 2 wastes may solve 2 issues at once
6. How can it be used to Treat Mine Tailings?
Vegetation Substrate Directly
above Fresh Tailings:
Good fertilizer: ↑ N, P and K
nutrients
High Organic-Carbon
amendment
Increases WRC, soil texture pH
and plant-available water
Increases mechanical resistance
that decreases erosion
Proven to support and sustain
long-term vegetation
establishment
Sealing Layer:
Has a Theoretical low H.C. –
decreases oxygen diffusion and
water infiltration
High porosity creates a water-
saturated barrier that further
inhibits oxygen-ingress
The barrier may act as an
organic reactive barrier (ORB)
Uncertainties of degradation of
SL and integrity over time
Vegetation Substrate above
pre-existing cover systems:
Will sewage sludge modify pre-
existing tailings and GW
geochemistry?
19% of Swedish SS exceeded
Cu, Ni, Pb and Zn for agriculture
Eriksson, (2001).
Oxidation of reduced metal
compounds and nitrification of
NH4
+ may release NO3
- and
metals.
NO3
- may oxidise pyrite.
0.3 m
1.5 m
0.3 m
7. Research Questions
What types of sewage sludge applications can be assumed reliable for long-term
sulphide tailings remediation?
Findings will be used to develop new and improved cover systems.
Field and Pilot-scale Aims:
1. To evaluate five different dry cover applications using sewage sludge in dry at
pilot- and field-scale.
2. Can sewage sludge be a viable long-term solution to prevent ARD formation in
underlying tailings?
Laboratory Aims:
1. Calibrate field organic matter biodegradation rates with microcosm laboratory
data.
2. Use the data to predict and model the life-time of a sewage sludge layer by
evaluating aerobic and anaerobic biodegradation rates
Finally: Produce a guide to the most optimum use of sewage sludge in dry cover
systems to prevent ARD formation of tailings in the long-term
Laboratory Field Long-term
8. Pilot- and Field-Scale Experiments (I-III)
Applications of Sewage Sludge:
1. Sealing Layer: Pilot-scale (0-8 years) Paper I
2. Vegetation Substrate Field-scale (0-2 years) Paper II
3. Vegetation Substrate Field-scale (0-2 years) Paper II
4. Vegetation Substrate Field-scale (0-2 years) Paper III
5. Vegetation Substrate Field-Scale (0-6 years) Paper III
9. Field Sites and Sample Collection (I)
• Solid Geochemistry: SSC: Sediment Core UCC: Excavator
• Dissolved Geochemistry: Base drainage and Lysimeter
• Gas Chemistry: Below and above the sealing layer
10. Findings: Sealing Layer (I)
SS Layer Effective to prevent O2 - diffusion:
→ No sulfide oxidation by oxygen or nitrate
0.54 mol-1m-2a-1 O2
Degradation of SS Layer:
→ Top: Aerobic ORB: CH2O + O2 → H2O + CO2
→ Base: Anaerobic ORB: 2CH2O → CH4 + CO2
→ Sulfate reduction
→ P, Cd, Cu, Hg, Pb, Zn removed from SS-SL
→ 85 % loss of OM in 8 years; -20 % SS volume
Underlying Tailings-Metal Accumulation Zone:
→ 0.05m below: +5-11% Fe, Cd, Cu, Ni, Pb, S, Zn
→ pH 7.7-8.2 <1% O2 – Anoxic environment
→ Precipitation as metal-sulfides or within OM
Drainage Geochemistry (2010):
→ <10µg/L Cd, Co, Cu, Ni, Pb, Zn (38mg/L SO4
2-)
→ High buffering capacity – low redox
Uncovered Tailings:
→ 0.35 m oxidation front with typical ARD
11. Field Sites and Sample Collection (II)
• Solid Sewage Sludge Geochemistry
• Dissolved Geochemistry: BAT® Groundwater Wells: Anoxic Sampling
• Visual MINTEQ: Organic Complexation and Speciation Modeling
12. Findings: Vegetation Substrate Above Covers (II)
Sludge-borne Constituent Release
→ -17 % Mass Loss
→ -22 % Organic Matter
→ Depletion in Cu, Ni, Pb and Zn
→ Oxidation of NH4
+: Release of NO3
-
SS on Dry Cover
1. Loss of sludge-borne constituents 0-1 year after application
2. Nitrification of NH4
+ from SS: N03
- released
3. Due to low HC of sealing layer, all constituents travel laterally to
impoundment toe effluent without contacting the impoundment tailings
GW system – no change in well Q geochemistry – only at well L
4. Pulse duration: 1 year – due to rapid vegetation establishment
SS on Water-Saturated Cover
1. Loss of sludge-borne constituents
2. Nitrification of NH4
+ from SS: N03
- released
3. Pulse reached GW system within 1 month due to shallow potentiometric surface of
groundwater
4. Pulse release period: 1 year – due to rapid vegetation establishment
5. However, plume travels slowly laterally: NO3
- oxidises pyrite, increasing Fe and
SO4
2- concentrations with metals
6. Transport controlled by DOC concentrations and dominant GW recharge
7. Plume reaches well Q in 2.2 years; modelled to exit impoundment in 6 years
13. Field Sites and Sample Collection (III)
• Solid Geochemistry using Excavator
• Solid-leachate Geochemistry
• Pore-Water Geochemistry and Paste pH
14. Findings: Single Layer and with Fly-Ash (III)
Uncovered Reference Tailings:
• Oxidation Front: 0.05 m in 2-years
• pH 2.75 and depletion of: Cd>Zn>Pb>Ni>Cu>Fe
2-year SS application onto fresh tailings:
• Oxidation Front: 0.04 m in 2-years
• pH 4.71 and depletion of Cd-Pb-Zn-S = High in pore-water
• Patchy plant establishment: root zone extends to tailings
creating oxygen pathway
• Sludge-borne Cu-Ni-Fe accumulate in upper 0.4 m of
tailings
6-year SS/FA application onto fresh tailings:
• Oxygen diffusion to underlying tailings is prevented
• Sludge-borne metal constituents (Cd-Cu-Ni-Pb-Zn) are
trapped in FA layer
• Nitrate oxidises pyrite in underlying anoxic tailings
creating 0.3 m Oxidation Front
15. Laboratory-Scale Experiments (IV-V)
Anaerobic Experiment:
• Microcosm Experiments
• Laboratory: Fresh (0 yr) and Aged Sample (1 yr)
• Field: Fresh (0 yr) and Aged Sample (8 yr)
• Gas data which is an indicator of biodegradation:
C6H12O6 → 3CH4 + 3CO2
• Time Scales: Laboratory (0-230 d.) Field (586-1076 d.)
• Organic matter contents analysed for BLF or LOI used
Aerobic Experiment:
• Microcosms Experiments
• Different temperatures to simulate accelerated
biodegradation for 156 d.
• Field: 2 Samples: 365 d. and 803 d.
• Dry mass determination (Lab) and gas data
(Field) to indicate aerobic biodegradation:
C6H12O6 + 6O2 → 6CO2 + 6H2O
16. Findings: Anaerobic Biodegradation (IV)
Organic Matter Composition:
• Fresh OM: 72.3 and 78 %
• After 8-years OM: 14 % (-85 % depletion)
• Fresh organic matter consisted of:
1. Cellulose (6.6 %)
2. Hemicellulose (5.2 %)
3. Lignin (48.6 %) - recalcitrant
Gas Composition:
• Gas concentration (mmol/g biosolid)
• Magnitude of gas released is a function of the
amount of readily-biodegradable organic matter
that remained.
• Field biosolid had already undergone peak
degradation prior to data collection
• Model developed :
1. Half-life of degradation: 55.5 days
2. In 230 days: 27.8 % OM degraded
3. Field-estimates: Peak Degradation in 2 yr
0
0.05
0.1
0.15
0.2
500 700 900 1100
Biosolid post-field fresh
CO2
CH4
Experimental Time
CumulatedGasComposition
(mmolgas/gbiosolid)
17. Findings: Aerobic Biodegradation (V)
Organic Matter Composition and Depletion:
• Biodegradation of OM after 156 d:
20-22 C = 14.8 %,
34 C = 27.2 %
50 C = 26.7 %
• Majority (73 %) of TOM was recalcitrant to biodegradation
• Biodegradation rates were dependent on temperature; likely facilitating
higher microbial activities.
• Field biodegradation rates were slower in comparison due to much lower
annual temperatures (0.7 C) than the microcosms, higher water saturation,
and frozen layer formation in the winter months.
• Field TOM depletion:
15.6 % (365 d.)
22.2 % (803 d.)
• Theoretical model indicates 20 % TOM will degrade in 2 years
18. Optimum Approaches to Sewage Sludge use in
sulphide-mine tailings remediation (VI)
Sewage Sludge as a Sealing Layer Barrier Material
• At least a Medium-term solution (~100 years).
• Limitation: Biodegradation of organic matter from combined aerobic and
anaerobic processes: 85 % depletion in 8-years
• Advantages: Effective as ORB and physical barrier due to recalcitrant un-
degradable material fraction
Sewage Sludge as a Vegetation Substrate onto Engineered Composite Dry Cover
• Successful at establishing and maintaining suitable vegetation
• Limitation: 2-year release of elevated sludge-borne nitrate and dissolved metals
• Effluent needs to be collected and treated at the toe in combined temporary
system such as a PRB/ALD to remove dissolved metals
• Biodegradation is not an issue as plant establishment recharges organic matter
Sewage Sludge as combined Engineered Dry Cover with Fly-Ash
• Successful at mitigating both oxygen diffusion and sludge-borne metals from
reaching the tailings
• High yields of vegetation were established, and root zone did not penetrate
through the fly-ash
• Limitation: sludge-borne nitrate oxidised the tailings. Composting of sewage
sludge first, to remove excessive nitrate may be a solution
19. Applications of Sewage Sludge use in sulphide-
mine tailings remediation to be avoided (VI)
Sewage Sludge as a Vegetation Substrate onto Water-Saturated Cover
• Successful at establishing and maintaining suitable vegetation
• Limitation: Elevated sludge-borne nitrate may exacerbate sulphide-oxidation
• Limitation: Elevated sludge-borne metals enter impoundment GW system
• However, effects were temporary, and duration depends on impoundment
hydrogeological regime
Sewage Sludge as a Vegetation Substrate onto bare tailings
• Vegetation is limited by root penetration depth
• Limitation: Large influx of sludge-borne metals to tailings
• Oxygen diffusion is not mitigated
• Sulphide-oxidation and ARD is only postponed
