Iron Oxidation and Jarosite Precipitation in a Continuous Two-Stage 70°C Archaeal Bioreactor

Abstract:

This study is the first demonstration of a continuous culture bio-catalysed iron oxidation and jarosite precipitation reactor using thermophilic archea, for use in hydrometallurgical process flow sheets. A two-stage continuous stirred tank reactor (CSTR) system comprised of two CSTRs, each with its own settler, was operated for biological iron oxidation and precipitation at 70°C. The two-stage design was to allow the growth of microorganisms that prefer various redox regimes. The bioreactors were inoculated with a mixed culture of extreme thermophilic iron oxidisers from genera Acidianus, Metallosphaera and Sulfolobus. The influent (pH 1.5) contained (g L^-1) 15 Fe²⁺, 1.5 Cu, 1.5 Ni (all as sulfates), nutrients and trace elements. At a hydraulic retention time (HRT) of 6-7 h in each CSTR, the overall iron oxidation rate was 1.0±0.1 g L^-1 h^-1 and percent 97±2%. The pH values were 1.38±0.16 and 1.57±0.05, and redox potentials (Ag/AgCl reference) were474±47 mV and 575±1 mV, in CSTR1 and CSTR2, respectively. The percentages of influent Fe, Cu and Ni removed as precipitates from settlers were 52%, 0.46% and 0.03%, respectively. The precipitates were comprised of jarosite (100%), potassium jarosite being the dominant form (38-51%), followed by hydronium (30-35%), ammonium (13-18%) and sodium jarosites (6-9%). The precipitates had a sludge volume index of 5.8-19 mL g^-1, indicating good settling properties facilitating easy removal through settling. The simultaneous and instantaneous addition of contaminants (g L^-1: 2.0 Al, 0.05 As, 0.05 F, 0.2 Co, 5.0 Mg and 0.4 Mn), potentially contained in hydrometallurgical processing streams, into the influent decreased the iron oxidation (50% overall oxidation with HRT of 26-29 h in each CSTR) and jarosite content in precipitates (85-87%). In conclusion, the two-stage high-temperature CSTR system allowed iron oxidation and precipitation of the oxidised iron in the form of well settling jarosite with only minor loss of Cu and Ni via co-precipitation. However, the bioreactor performance was hampered by the introduction of other transition metals, fluoride and arsenic.

• Periodical: Advanced Materials Research (Volume 1130)
• Pages: 230-233
• DOI: https://doi.org/10.4028/www.scientific.net/AMR.1130.230
• Online since: November 2015
• Authors: Anna H. Kaksonen, Christina Morris, Jason Wylie, Jian Li, Kayley Usher, Felipe Hilario, Chris du Plessis
• Keywords: Archaea, Bioreactor, Contaminant, Iron, Jarosite, Oxidation, Precipitation

References

[1] D.E. Rawlings, Annual Reviews of Microbiology Vol. 56 (2002) 65.

[2] J.P. Gramp, F.S. Jones, J.M. Bigham and O.H. Tuovinen, Hydrometallurgy Vol. 94 (2008) 29.

[3] D.E. Rawlings, H. Tributsch and G.S. Hansford, Microbiology Vol. 145 (1999) 5.

[4] C. du Plessis, W. Slabbert, K.B. Hallberg and D.B. Johnson, Hydrometallurgy Vol. 109 (2011) 221.

[5] A.H. Kaksonen, C. Morris, S. Rea, J. Li, J. Wylie, K. Usher, M.P. Ginige, K.Y. Cheng, F. Hilario and C. du Plessis, Hydrometallurgy Vol. 147-148 (2014) 255.

DOI: 10.1016/j.hydromet.2014.04.016

[6] A.H. Kaksonen, C. Morris, S. Rea, J. Li, K. Usher, R.G. McDonald, F. Hilario, T. Hosken, M. Jackson and C. du Plessis, Hydrometallurgy Vol. 147-148 (2014) 264.

DOI: 10.1016/j.hydromet.2014.04.015

[7] 3500-Fe, Standard methods for the examination of water & wastewater 18th Ed APHA AWWA WEF (1992).

[8] 2540 D, Total Suspended Solids Dried at 103–105°C Standard methods for the examination of water & wastewater 20th Ed. APHA, AWWA, WEF, (1998).

[9] 2710 D, Sludge volume index, Standard Methods for the Examination of Water & Wastewater 20th Ed. APHA, AWWA, WEF, (1998).