Roles of Microbial Activity and Anthraquinone-2,7-disulfonate as a Model of Humic Substances in Leaching of Iron from Hematite into Seawater

Abstract

Fertilization with a mixture of steelmaking slag and compost can affect the supply of dissolved iron used to restore seaweed beds, however, the mechanisms of iron elution from the fertilizer is not well understood. In the present study, the microorganism was isolated from Fe-fertilizer incubated in coastal seawater for 6 months and was identified as Exiguobacterium oxidotolerans T-2-2 by 16S rDNA sequencing. The iron elutability of the bacteria was proved the increasing of dissolved iron by the incubation with Fe 2 O 3 (hematite) under seawater-like condition. The value of ORP was changed by inoculated of the bacteria from ca. 0 mV to ca. -400 mV, which is anticipated to reduction of Fe. The concentration of eluted iron was largely depended on those of organic acids produced by bacteria. From the results, it was proved that E. oxidotolerans is capable of reductive eluting of iron from Fe 2 O 3 into seawater.Anthraquinone-2,7-disulfonate (AQDS), which can play as an electron acceptor/donor between microbe and insoluble Fe 2 O 3 particles, enhanced the effect of iron bio-leaching.

Evaluation of the Effect of Humic Acids on the Reductive Elution of Fe from Fe₂O₃ in a Saline, Seawater-like Medium

“…30,31) This electron shuttling function is largely induced by quinone moieties. 12,16,30,31) The electron shuttling function depends on the structural features of HA. A significantly large amount of aromatic compounds was detected as fragments of the HHA by TMAH-py-GC/MS analysis, in a previous study.…”

“…It is known that the microbial reduction of Fe under anaerobic conditions is a relevant mechanism that explains why soluble Fe(II) can be produced from insoluble Fe(III)-oxides. [10][11][12] The previous study observed reductive Fe elution from Fe 2 O 3 by an anaerobic bacterium, E. oxidotolerans, isolated from the fertilizer, and the reductive Fe elution was enhanced by co-existed antraquinone. 12) Quinone moieties in humic substances would also play a role as an electron acceptor/donor in the natural sediment under aquatic condition.…”

“…[10][11][12] The previous study observed reductive Fe elution from Fe 2 O 3 by an anaerobic bacterium, E. oxidotolerans, isolated from the fertilizer, and the reductive Fe elution was enhanced by co-existed antraquinone. 12) Quinone moieties in humic substances would also play a role as an electron acceptor/donor in the natural sediment under aquatic condition. [13][14][15] Attention has focused on the electron shuttle effect of humic substances which could accelerate the metal reductive reaction in sediments or aquatic environments.…”

“…Fe 2 O 3 , an insoluble Fe(III)-oxide found on the surface of steelmaking slag, was employed as a model of an insoluble Fe source in the fertilizer. 12) Anaerobic bacteria should be employed as a reducing agents, however, specialized isolation and cultivation techniques are required when the bacteria used in the evaluation. Ascorbic acid can also perform a well-reducing agent in seawater condition.…”

Microbial Leaching of Iron from Hematite: Direct or Indirect Elution

“…Our previous study showed that bacteria isolated from Fe-fertilizer are important for iron elution at a pH range of 67. 7) We reported that Exiguobacterium oxidotolerans plays a crucial role in the dissolution of Fe(III) oxide (Fe 2 O 3 , hematite). The interaction between E. oxidotolerans and hematite was monitored, and 23 mg L ¹1 of eluted Fe species was detected after a few days of incubation.…”