Continuous Supply of Bioavailable Iron for Marine Diatoms from Steelmaking Slag

Abstract

Ϫ1, the slag supplied bioavailable Fe to two diatoms for 50 d. The probable duration for which the slag was available as an Fe source was approximately 10 times longer than the reported duration in in situ iron fertilization experiments. These results indicate that continuous Fe fertilization can be achieved by a single addition of the slag, and hence, we can reduce the energy and cost of ocean fertilization and also create a resource of microalgae biofuels.KEY WORDS: biological pump; marine diatom; iron fertilization; steelmaking slag; carbon sequestration; geoengineering. 513© 2011 ISIJ for which continual production of the Fe-binding chelator such as ethylenediaminetetraacetic acid (EDTA) that releases Fe(III)Ј continuously is required. Synthesis of such chelators requires excess energy. In natural seawater, Febinding ligands may act as reducers in instantaneous Fe bioavailability for marine phytoplankton because the uptake of Fe from the Fe-ligand complex is generally several orders of magnitude lower than that of Fe(III)Ј, 9) although they may present an excess concentration compared to dissolved Fe. 14,20) Furthermore, the conditional stability constant of the natural Fe-binding ligand is sufficiently high to limit the growth of phytoplankton. 21) In this study, we conducted phytoplankton culture experiments using steelmaking slag as an Fe source. Steelmaking slag is a by-product of an iron and steelmaking process. Approximately 100 kg of slag is produced per 1 ton of steel. Approximately 14ϫ10 6 tons of slag is produced every year in Japan. 22) A significant amount of the slag is not reused because of its unstable chemical characteristics. Our previous studies showed that steelmaking slag contains elements essential for the healthy growth of marine phytoplankton (especially of diatoms) such as Fe, silicon, and phosphorus. [23][24][25][26] Thus, slag is not a harmful substance; rather, it useful for the growth of marine phytoplankton. Noxious metals such as Pb and Hg were not detected in a solute of slag suspension with seawater.27) Sugie and Taniguchi 25,26) demonstrated the bioavailability of Fe dissolving from slag into ligand-free synthetic seawater. In the present study, we conducted experiments to determine the effect and probable duration for which the steelmaking slag was available as an Fe source for marine diatoms, comparing its availability in the presence or absence of the synthetic chelator EDTA. This kind of bioassay study is essential at present because we cannot directly determine the kinetics and amount of Fe dissolving from the slag in the presence of Fe-binding ligands. Materials and Methods Steelmaking SlagThe steelmaking slag we used was decarburization steelmaking slag (hereafter referred to as slag), containing 17.9% of total-Fe (T-Fe), 14.1% SiO 2 , 43.4% CaO, 3.4% MnO, 8.6% MgO, 2.1% P 2 O 5 , 0.1% S, 2.8% Al 2 O 3 , 0.9% TiO 2 and 6.9% other elements. The ground slag was sieved and the finest fractions of 5-20 mm were obtained in order to weigh smaller amounts precisely and to p...

Influence of Gluconic Acid on Dissolution of Si, P and Fe from Steelmaking Slag with Different Composition into Seawater

“…As common sequestering agents, organic acids can chelate iron species not only to improve its solubility but also to extend its elution life time. For instance, Sugie and Taniguchi 5) convinced ethylenediaminetetraacetic acid (EDTA), as the chelating agent of Fe dissolved from steelmaking slag, having a sufficient duration of bioavailability.…”

A Review on the Effect from Steel Slag on the Growth of Microalgae

“…The maximum growth rates of T. nordenskieldii and T. oceanica were 1.5/d and 2.3/d, respectively. The iron or ferrous ions were released in the steel slag and inorganic iron reagent (FeCl 3 •6H 2 O), both can effectively promote the growth rate of two diatoms [53]. The iron element in the steel slag forms a colloidal iron ion with the solution to maintain the iron ion concentration in the culture medium.…”

Growth promotion of Spirulina by steelmaking slag: application of solubility diagram to understand its mechanism

“…SMS contains minerals, such like Fe, P, Mg, Ca, Mn, that are essential for algal growth (Yokoyama et al 2010 ; Zhang et al 2012 ; Mombelli et al 2014 ). The growth promotion effect of SMS has been reported in not only macroalgae but also in certain seawater microalgae (Nakamura et al 1998 ; Haraguchi et al 2003 ; Sugie and Taniguchi 2011 ). However, investigations on freshwater microalgae required for the commercial production of valuable products are fewer than those on marine microalgae.…”