Nutrient Supply to Seawater from Steelmaking Slag: The Coupled Effect of Gluconic Acid Usage and Slag Carbonation
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SEAWEEDS play critical roles in sustaining biodiversity in the marine ecosystem.[1,2] Vanishing of seaweeds at barren ground in coastal areas has gradually become a serious environmental problem worldwide.[3,4] There are many possible reasons, such as global climate change and coastal urbanization. One possible cause is nutrient deficiency in seawater surrounding the seaweeds, especially iron. In the case of Japan, a decrease of river flow into the sea and construction of landslide barriers in coastal regions may result in nutrient deficiency. Suzuki et al. analyzed the coastal seawater in the northern Sea of Japan with barren ground and found that the concentration of dissolved iron is very low (< 0.045 lg L1).[5] The relationship between Fe concentration and seaweed growth has been clarified by Matsunaga et al.,[6] who compared the seaweed growth rate in Fe-limited (0.0616 lg L1) and Fe-rich (11.2 lg L1) actual seawater and confirmed the faster growth of seaweeds in the Fe-rich medium.
YUTA SAKURAI, XIAO YANG, YUTA HISAKA, and FUMITAKA TSUKIHASHI are with the Department of Advanced Materials, Graduate School of Frontier Sciences, The University of Tokyo, Kashiwanoha 5-1-5-501, Kashiwa-shi, Chiba-ken 2778561, Japan. Contact e-mail: [email protected] Manuscript submitted September 16, 2019.
METALLURGICAL AND MATERIALS TRANSACTIONS B
Researchers have proposed fertilization approaches to restore seaweeds. Yamamoto et al. applied Fe humates[7,8] in a coastal area as an Fe source, and the restoration of a seaweed bed was confirmed. Blazevic et al. reported the effect of Fe-humic substances on improving the bioavailability of Fe in oceans.[9] These results suggested the necessity and feasibility of finding a fertilizer that is effective, inexpensive and abundant. Steelmaking slag, containing essential nutrients such as Fe and P in the form of oxides, is probably one of the best underwater fertilizers in terms of cost and quantity. As a major byproduct of the steel manufacturing process, the global output of steelmaking slag in 2017 was estimated at around 170 million tons.[10] Treatment of such a huge amount of solid byproduct remains challenging, although a portion can be recycled as construction material. Proposals or reviews relevant to steelmaking slag treatment or recycling can be found in the literature.[11–14] Utilizing steelmaking slag as a nutrient source to rehabilitate coastal areas may simultaneously address the two challenges of seaweed restoration and byproduct treatment. Meanwhile, because the amount of phosphorus in steelmaking slag is not large, there is no need to worry about overnutrition inducing eutrophication. The ultimate objective of this study is to develop an ocean fertilization technology using steelmaking slag as the nutrient source. The environmental impact of steelmaking slag is a major concern. Nakata et al.[15] and Miki et al.[16] studied the dissolution behaviors of
hazardous elements (F, As, Pb, Cr, Cd, etc.) from different types of steelmaking slags in seawater. The resu
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