Two-Stage Airlift Bioreactor System for Efficient Iron Oxidation and Jarosite Precipitation

Abstract:

Continuous high-rate iron oxidation and removal of jarosite precipitates from solution at low pH and ambient temperature and pressure was successfully demonstrated. The bio-catalysed iron oxidation and jarosite precipitation is promising as a unit process for a variety of hydrometallurgical process flow sheets, where it allows for iron removal from ferrous solutions without the requirement for chemical addition and with negligible base metal co-precipitation losses. The process demonstrated performance that could be used in a large scale industry unit. A two-stage airlift bioreactor (ALBR) system comprised of two ALBRs, each with its own settler, was operated for iron oxidation and precipitation at room temperature with a mixed culture of mesophilic iron oxidisers. The two-stage reactor design allowed for optimization of overall reactor kinetics by facilitating the growth of low (430 mV vs Ag/AgCl) and high (517 mV) redox potential iron oxidizers in the respective reactors. The influent (pH 1.5) contained (g L^-1) 15 Fe²⁺, 1.5 Cu, 1.5 Ni, nutrients and trace elements. The hydraulic retention time (HRT) was decreased stepwise to evaluate process performance. With the lowest HRTs (8 h in ALBR1 and 10 h in ALBR2), the overall iron oxidation and precipitation rates of the two-stage system were 0.75 ± 0.02 g L^-1 h^-1 and 0.15 ± 0.01 g L^-1 h^-1, respectively and overall iron oxidation and precipitation efficiencies of 94 ± 3% and 18 ± 1 %, respectively. The percent of influent Fe, S, Cu and Ni removed as precipitates from settlers were 30.9%, 16.7%, 1.1% and 0.2%, respectively. The precipitates were predominately comprised of (>95%) jarosite with potassium jarosite being the dominant form, followed by hydronium, ammonium and sodium jarosites. In conclusion, the two-stage ALBR system allowed efficient iron oxidation and precipitation of the oxidised iron as well settling jarosite with only minor loss of Cu and Ni via co-precipitation.

• Periodical: Advanced Materials Research (Volume 825)
• Pages: 242-245
• DOI: https://doi.org/10.4028/www.scientific.net/AMR.825.242
• Online since: October 2013
• Authors: Anna H. Kaksonen, Christina Morris, Felipe Hilario, Suzy Rea, Jian Li, Kayley Usher, Jason Wylie, Maneesha P. Ginige, Ka Yu Cheng, Chris du Plessis
• Keywords: Airlift, Bioreactor, Iron, Jarosite, Oxidation, Precipitation

References

[1] D.E. Rawlings, Heavy metal mining using microbes. Annual Reviews of Microbiology 56 (2002) 65-91.

[2] J.P. Gramp, F.S. Jones, J.M. Bigham, O.H. Tuovinen, Monovalent cation concentrations determine the types of Fe(III) hydroxysulfate precipitates formed in bioleach solutions. Hydrometallurgy 94 (2008) 29-33.

DOI: 10.1016/j.hydromet.2008.05.019

[3] D.E. Rawlings, H. Tributsch, G.S. Hansford, Reasons why Leptospirillum, -like species rather than Thiobacillus ferrooxidans are the dominant iron-oxidizing bacteria in many commercial processes for the biooxidation of pyrite and related ores. Microbiology 145 (1999).

DOI: 10.1099/13500872-145-1-5

[4] C. du Plessis, W. Slabbert, K.B. Hallberg D.B. Johnson, Ferredox: A biohydrometallurgical processing concept for limonitic nickel laterites. Hydrometallurgy 109 (2011) 221-229.

DOI: 10.1016/j.hydromet.2011.07.005

[5] 3500-Fe. Standard methods for the examination of water & wastewater. 18th Ed. APHA, AWWA, WEF. (1992).

[6] 2540 D. Total Suspended Solids Dried at 103–105 °C Standard methods for the examination of water & wastewater. 20th Ed. APHA, AWWA, WEF. (1998).

[7] 2710 D. Sludge volume index. Standard Methods for the Examination of Water & Wastewater. 20th Ed. APHA, AWWA, WEF. (1998).

[8] H. Wang, J.M. Bigham, O.H. Tuovinen, Formation of schwertmannite and its transformation to jarosite in the presence of acidophilic iron-oxidizing microorganisms. Material Science Engineering C26 (2006) 588-592.

DOI: 10.1016/j.msec.2005.04.009