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)