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.

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Exiguobacterium oxidotolerans was found to be effective for dissolving Fe 2+ from hematite via reduction under alkaline conditions. However, the possible mechanism for bacterial reduction of hematite in seawater is still unclear. The present work has investigated the reductive dissolution of iron by the bacteria in two elution systems, namely direct and indirect elution systems. Greater than 30 mg L ¹1 of Fe was dissolved and measured in a direct elution system. Fourier transform infrared (FTIR) and field-emission scanning electron microscopy (FE-SEM) revealed the surface oxidation and particle aggregation in our direct elution system. The obtained results suggest that direct interaction of bacterial cells with hematite facilitates iron elution, probably due to electron transfer to hematite via the cell membrane, resulting in reductive elution of hematite.

It had been reported that iron and manganese oxides in steel slag enhanced the production of humic acid (HA) from low-molecular-weight compounds, such as phenolic acids, amino acids, and saccharides. In the present study, this function of steel slag was applied to the composting of raw organic wastes (ROWs). The degree of humification of HAs is an important factor in evaluating compost quality. Thus, HAs were extracted from the prepared composts and the humification parameters were determined, in terms of elemental compositions, acidic functional group contents, molecular weights, spectroscopic parameters from UV-vis absorption and C NMR spectra. The timing for adding steel slag affected the degree of humification of HAs in the composts. The weight average molecular weight of a HA when slag was added initially (29 kDa) was significantly higher than when slag was added after elevating the temperature of the compost pile (17-18 kDa). These results show that ROWs are decomposed to low-molecular-weight compounds after the pile temperature is elevated and the presence of slag enhances the polycondensation of these compounds to produce HAs with a higher degree of humification. Because the slag used in the present study contained several-tens ng g to several μg g of toxic elements (B, Cu, Cr, and Zn), leaching tests for these elements from the prepared composts were carried out. Levels for leaching boron from composts prepared by adding slag (0.2-0.4 mg L) were obviously higher than the corresponding levels without slag (0.05 mg L).