5-7 OCTOBERISFR2011

189

TOLEDO (SPAIN)

CHARACTERIZATION OF IRON ELUTION IN THE METHOD OF RESTORATION OFSEAWEED BEDS WITH STEELMAKING SLAG AND HUMUS MATERIALS
Mitsuo Yamamoto1, and Dan Liu2
1College of Arts and Sciences, The University of Tokyo, 3-8-1 Komaba, Meguro, Tokyo 153-8902, Japan
2Ariake National College of Technology, 150 Higashihagio-Machi, Omuta, Fukuoka 836-8585, Japane-mail:mitsuo@eco.c.u-tokyo.ac.jp

Abstract
Barren grounds in coastal area are serious problems in Japan and other parts of the world. It has been developed a methodthat the mixture of steelmaking slag and humus materials, such as composts, were supplied in seawater for restoring
seaweed beds. A concentration of dissolved iron can be increased in the method, since complexes, iron-humates, areproduced from iron in steelmaking slag and humic substances in compost. The effect of this method was already confirmedin the field test. In this study, we evaluated the effect of the mixing humus materials with steelmaking slag in this method forincreasing dissolved iron concentration. Iron elution tests in actual seawaters were attempted by using three kinds ofsamples for iron elution, only steelmaking slag, only compost, and a mixture of steelmaking slag and compost. We found thatthe mixture of steelmaking slag and compost was more effective for extending the lifetime of iron elution besides increasingiron concentration in seawater.

Keywords: humus materials, compost, steelmaking slag, iron elution, seaweed bed restoration

1. Introduction
Seaweed depletion in barren grounds is a serious
problem along the coast of Japan and other parts of theworld. Although several factors, such as elevatedseawater temperature and grazing by herbivorous
animals, have been proposed to account for barren
ground, we have especially focused on the lack ofdissolved iron (Fe) in seawater for restoring seaweed
beds. It has been developed a method that a mixture ofsteelmaking slag (slag) and humus materials, such ascomposts, were supplied to coastal areas of barren
grounds [1, 2]. This method contributes not only to therestoration of seaweed populations, but also to theeffective use of industrial by-products and unutilizedbiomass.
The mixture of slag and compost was applied to acoastal area in Mashike (Hokkaido, Japan) in 2004 forconfirming the actual availability of this method. Threeplots on barren ground were considered in the field test.
The first was treated with slag, the second was treatedwith a mixture of slag and compost, and the third plot
was left untreated (control plot). The types of seaweed
and their fresh weights were recorded in the threesubsequent years. Restoration of a seaweed bed wasespecially confirmed at the location, treated with themixture of slag and compost. The amount of restored
seaweed and the restored area at the site with the slagcompost mixture were significantly larger than other sites.
The Fe concentrations at the site with slag-compost
mixture were also greater than those with the other sites.
It was found that applying a mixture of slag and humus

interiores libro.indd 189

materials was an effective technique for restoring
seaweed in a coastal area.
Although field tests with this method have been carriedout in other coastal areas in Japan, further fundamental
studies are required for understanding the mechanism of
Fe supply to a coastal area and translating this method
into practical applications. Especially, the understandingof characterization of Fe elution from the mixture of slag
and compost (Fe supply unit) is one of the mostimportant issues for practical use. Although we alreadyevaluated the effect of humic substances on Fe elusionin this method [3], additional evaluations are needed forunderstanding the characterization of Fe elution andimproving the method.
In this study, we made an attempt at further laboratorial
Fe elution tests by using actual and artificial seawaters.
The characteristic of Fe elution from Fe supply unit wasevaluated. Meanwhile, the effect of the kinds of composts
also has been investigated. We introduce one of themain results of Fe elution tests in this abstract.

2. Materials and Methods
The following three samples were used in the experiment.
(1) Only slag(2) Only compost(3) Slag : compost = 1 : 1 (in volume)
The amount of each sample is the same based onvolume. The volume of 40g slag (sample (1), V0) is thestandard of this experiment. The volumes of samples (2)and (3) are the same as V0, respectively. The kind of slag
is the same as that used in the field test in Mashike,
Hokkaido [1, 2]. The morph of calcium on the surface ofslag is changed from Ca(OH)2 to CaCO3 in order to

26/9/11 13:13:26

190

6th International Symposium on Feedstock Recycling of Polymeric Materials

3. Results and Discussion

Fe concentration
cooncentration [Ǵg/L][Ǵg/L]]

Fig.1 shows the time dependence of dissolved Feconcentration of three samples. Initial Fe concentration
was extremely small (1.2μg/L). However, Fe
concentrations of three samples increased after one
week. Especially, Fe concentrations of sample (1) andsample (2) were increased drastically. Meanwhile, Feconcentration of sample (2) was larger than that ofsample (3). This implies that Fe elution rate fromcompost is larger than that from slag. As the amount ofcompost in sample (3) was half as small as that insample (2), Fe concentration of sample (2) in seawater
was larger than that of sample (3).

Time [weTime[week][week]kٟ SlagSlً Slag + Compost‫ ع‬CompostCompost٨ BlankTimTimem [week][wweek]
eekekek]

Table 1 shows the amount of Fe elution and the Feelution rate from three samples until 21 weeks. The
amount of Fe elution from sample (2) was the largest andFe elution rate of sample (2) was also largest. However,total amount of Fe elution of sample (1) and sample (2)are smaller than double amount of Fe elution of sample(3). This implies that the mixing of slag and compost
accelerate the Fe elution from both slag and compost.
Meanwhile, compost is the most effective in respect of
the amount of Fe elution and Fe elution rate, if we install
respectively. Meanwhile, compost is the most useful inTable 1 The amount of and rate of Fe elution from sample

interiores libro.indd 190

٨ Sample٤ No sample
samplpe٠ BlankFig.2 The time dependence of dissolved Fe concentration
concentraationt after
13 weeks
kFig.1 The time dependence of dissolved Fe concentration

The amount ofFe elution [μg]Fe elution rate
[μg/day]

the same volume of the sample. However, the content of
total Fe in compost is only 2.55wt%, although that in slag
is 22.2wt% [3]. In respect of lifetime of Fe elution,compost is disadvantage. It was confirmed in this study
that the mixture of slag and compost was more effective
for extending the lifetime of Fe elution, in addition to theincrease of iron concentration in seawater.
Fe elution rates in Table 1 are expected to be smaller
than the true value of Fe elution rate, because bothoxidation and sedimentation of Fe was expected inseawater under this experimental condition. Fig.2 shows
the time dependence of dissolved Fe concentration in thecondition of removing slag-compost sample (no sample)
after 13 weeks compared to that in the condition of notremoving the sample. We found that dissolved Feconcentration was decreased after removing the sample.
This indicates that true Fe elution rate is larger thanthose in Table 1. We should take account of this result in
the case of estimating the lifetime of Fe supply unit.

Fe concentration
concentra
ntra
ntrt tiontio
on [[Ǵg/L]
Ǵg/L]decreasing the alkalis component. The compost in thisexperiment was produced from wood waste (bark) with acomposting accelerator (Tateyama Engineering Co. Ltd.)obtained by fermenting sewage sludge containing
microorganisms capable of growth in an anaerobic
environment [4].
Each sample was installed in a small tank filled with 11L
actual seawater, respectively. The seawater wascollected in Omura bay, Nagasaki prefecture. Asseawater had not been changed during the experiment,
aeration system was used in each tank in order not toputrefy seawater. Fe concentrations in seawaters wereanalyzed with spectrophotometric method [3] every per 7days.

slag

compostslag+ compost

20610

360

0.162

4.12

2.48

4. Conclusions
Characteristic of Fe elution from the mixture of slag andcompost in the method of restoration of seaweed beds
was evaluated in this study. It was found that the mixture(Fe supply unit) was more effective not only forincreasing iron concentration in seawater but forextending the lifetime of Fe elution.

References[1] M. Yamamoto et al. Recovery from Barren Ground bySupplying Slag and Humic Substances. Journal of the Japan
Institute of Energy, 85 (2006) 971-978.
[2] M. Yamamoto, M. Fukushima, E. Kiso, T. Kato, M. Shibuya,S. Horiya, A. Nishida, K. Otsuka, and T Komai. Application ofIron Humates to Barren Ground in a Coastal Area for Restoring
Seaweed Beds, Journal of Chemical Engineering of Japan, 43(2010) 627-634.
[3] M. Yamamoto, M. Fukushima, and D. Liu. Effect of Humic
Substances on Iron Elution in the Method of Restoration of
Seaweed Beds with Steelmaking Slag, Tetsu-to-Hagane, 97(2011) 159-164.
[4] M. Fukushima, K. Yamamoto, K. Ootsuka, T. Komai, T.
Aramaki, S. Ueda, S. Horiya. Effects of the maturity of wood
waste compost on the structural features of humic acids,Bioresour. Technol., 100 (2009) 791-797

26/9/11 13:13:26