Fractionation and leachability of Fe, Zn, Cu and Ni in the sludge
from a sulphate-reducing bioreactor treating metal-bearing wastewater
P. Kousi, E. Remoundaki, A. Hatzikioseyian, V. Korkovelou & M. Tsezos
Laboratory of Environmental Science and EngineeringSchool of Mining and Metallurgical EngineeringNational Technical University of Athens (NTUA)
ATHENS 2017, 5th International Conference on Sustainable Solid Waste Management21-24 June 2017, Athens, Greece
Process:Microbially mediated sulphate reductionby sulphate-reducing bacteria (SRB)under anaerobic conditions
Process benefit:simultaneous removal of-sulphate-metal ions-acidity-organic carbon
acidity neutralisation
precipitation of metal sulphides
Prevailing mechanism:bioprecipitation of metal sulphides
•A key aspect of the sustainability of the process, besides its effectiveness, is the management of the generated sludge
•Potential scenarios range from disposal via landfilling to further treatment for metal recovery
Metal ion sequestering – Sludge formation
Bioreactor
100 mg/L Fe2+
100 mg/L Zn2+
100 mg/L Cu2+
100 mg/L Ni2+
1,700 mg/L SO42-
pH = 3.5-4.0
Upflow, packed-bed reactorBiofilm established on porous ceramic pipes 1 cm long(Cermec®, JBL Germany)
Operation: batch modefor 6 years at room temperature
Carbon/electron sourceethanol
Issue addressed:Propose sludge management options for overall process sustainability
1.Is the sludge safe for disposal via landfilling?
2.Is the metal content of the sludge recoverable?
Relevant questions:
Issue addressed: sludge management for overall process sustainability
• mineral phasesFormation mechanism
• crystallinity• particle size
Other factors (temp, pH, sulphide)
Sludge stability
Metal mobility
Sludge samples from the bottom of the reactor low redox and neutral pH conditions
Methodology
Physical, chemical, mineralogical characterisation
Laser Diffraction – Low Angle Laser Light Scattering X-Ray Diffraction Thermogravimetry-Differential Scanning Calorimetry Scanning Electron Microscopy / Energy Dispersive X-ray
Spectrometry
Methodology
Metal fractionationSequential extraction method (Tessier)
Metal leachability and environmental stability
EN 12457-2 TCLP pH-time effect
RESULTSParticle size distribution
0.1 1 10 1000.01 10000
1
2
3
4
5
6
7
8
9
10
Tota
l par
ticle
s in
ban
d (%
vol
.)
Equivalent particle diameter (μm)
Total particles in band Cumulative undersize
0
10
20
30
40
50
60
70
80
90
100D90= 45.73μm
D50= 8.31μm
Cum
ulat
ive
unde
rsiz
e (%
vol
.)
D10= 0.20μm
Sludge composition
Parameter Value (wt. %, dw)
Iron 14.80Zinc 18.73Copper 18.24Nickel 17.71Total metal content 69.48Sulphur (total) 31.22Carbon (total) 5.00Volatile solids 14.70
Mineralogy - XRD1 FeS2 pyrite
2 FeCO3 siderite
3 CuS covellite
4 Zn5S5 wurtzite
5 ZnS sphalerite
6 NiS millerite
7 Ni3S2 heazlewoodite
8 Cu4Fe5S8 haycockite
9 Cu2FeS2 bornite
10 CuFe2S3 cubanite
11 CuFeS2 chalcopyrite
0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75
11
10
9
8
76
5
4
32
1
2θ
Mineralogy – SEM/EDS
Metal fractionation
Fe Zn Ni Cu0
20
40
60
80
100Fr
actio
n (%
)
water-soluble exchangeable carbonate Fe/Mn oxides organic/sulphide
Environmental stability
0 20 40 60 80 100 120 140 160 1800
200
400
600
800
1000
1200
1400
1600
Time (h)
Fe Zn Ni Cu pH
Met
al c
once
ntra
tion
(mg/
L)
Time (h)
Initial water pH=2
1
2
3
4
5
6
7
8
9
pH
0 60 120 1800
20
40
60
Fe (mg/L)
Environmental stability (long-term)
Fe Zn Ni Cu S-SO42-
0
10
20
30
40
50
Leac
hed
(%)
pH=2 pH=4 pH=6 pH=9
90 % of the particles are smaller than 47 μm, 50 % of the particles are smaller than 8.5 μm
Amorphous or poorly crystalline phases and aggregates of Fe, Zn, Cu, Ni sulphides
Metal content adds to 70 % dw: Fe (14.8 %), Zn (18.7 %), Ni (17.7 %), Cu (18.2 %)
Main metal sulphides determined: pyrite, covellite, wurtzite/sphalerite and millerite/heazlewoodite
The sludge is characterised as hazardous and inappropriate for disposal via landfilling without any prior treatment.
The sludge fine grain size and poorly crystalline structure, as well as the direct oxidation of sulphide upon exposure to water/air, render the high metal content (70 % dw) of the sludge recoverable.
Remoundaki, E., Kousi, P., Joulian, C., Battaglia-Brunet, F., Hatzikioseyian, A., Tsezos, M.: Characterization, morphology and composition of biofilm and precipitates from a sulphate-reducing fixed-bed reactor. J. Hazard. Mater. 153(1-2), 514-524 (2008)
Kousi, P., Remoundaki, E., Hatzikioseyian, A., Battaglia-Brunet, F., Joulian, C., Kousteni, V., Tsezos, M.: Metal precipitation in an ethanol-fed, fixed-bed sulphate-reducing bioreactor. J. Hazard. Mater. 189, 677-684 (2011)
Kousi, P., Remoundaki, E., Hatzikioseyian, A., Tsezos, M.: Sulphate-reducing fixed-bed bioreactors fed with different organic substrates for metal precipitation. In: Qiu, G., Jiang, T., Qin, W., Liu, X., Yang, Y., Wang, H. (eds.) Biohydrometallurgy: Biotech key to unlock mineral resources value, Proceedings of the 19th International Biohydrometallurgy Symposium (IBS 2011), Changsha, China, 18-22 September 2011, pp. 1078-1084. Central South University Press (2011)