HR: 0830h
AN: B41D-0916    [PDF]
TI: Importance of Fe(II)-Hydroxide Complexes For the In-Situ Bioremediation of ARD Sites
AU: * Bilgin, A
EM: azra.bilgin@colorado.edu
AF: University of Colorado, Civil, Environmental & Architectural Engineering Department, Univeristy of Colorado Engineering Center CEAE ECOT 441, Boulder, CO 80309 United States
AU: Silverstein, J
EM: joann.silverstein@colorado.edu
AF: University of Colorado, Civil, Environmental & Architectural Engineering Department, Univeristy of Colorado Engineering Center CEAE ECOT 441, Boulder, CO 80309 United States
AU: Nordstrom, D K
EM: dkn@usgs.gov
AF: United States Geological Survey, USGS 3215 Marine Street Suite E-127, Boulder, co 80303 United States
AB: Enhancing the growth of heterotrophic bacteria such as Acidiphilium cryptum that are indigenous to acid rock drainage (ARD) sources is a potential strategy for in-situ inhibition of pyrite oxidation and acid formation. When biodegradable organic carbon was supplied to A. cryptum, oxygen was consumed by rapidly growing heterotrophs, and bacterial iron reduction observed, accompanied by increasing solution pH. A. cryptum (ATCC 33463) cells were incubated in well-aerated liquid media containing Fe2(SO4)3 and glucose at varying initial pH values from 1.5 to 3.5. No more than 1% of the added ferric iron was detected as soluble Fe3+ for any of the media, indicating that the A. cryptum cells were able to reduce precipitated ferric iron. No organic carbon consumption or iron reduction was observed in flasks incubated at pH 1.5 indicating that A. cryptum may not be able to grow at this low pH. In reactors where the initial pH was 3.5, the pH increased to approximately 5.5 during the experiment accompanied by a 0.4 gl-1 decrease in Fe(III) species after aeration stopped. In reactors where the initial pH was 2.5, final pH values were inconsistent between replicate experiments: pH decreased to 2.3 in one experiment and increased to 2.8 in the second. Dissociation of Fe(OH)2+ complexes at pH values near 2.5 could have acted as a buffer, minimizing pH change during iron respiration. The existence of Fe(OH)2+ complexes was investigated using O-square wave voltametry, a pulse polarography technique which allows for identification of metal complexes and estimation of complex stability constants. The presence of ferric hydroxide complexes at pH near 2.5 was confirmed by pulse polarography. When the initial pH was 3.5, the base neutralizing capacity of the solution decreased due to the replacement of Fe(OH)2+ by Fe(OH)3 resulting in the pH increase of over 2 units.
DE: 0330 Geochemical cycles
DE: 0400 Biogeosciences
DE: 1030 Geochemical cycles (0330)
DE: 1099 General or miscellaneous
SC: Biogeosciences [B]
MN: 2003 Fall Meeting