Promotion of In-House Zero Emissions
By-products generated and their final disposal amount
In the iron-making process, over 600 kg of by-products are generated for every ton of iron produced. In fiscal 2017, NSSMC produced 40.67 million tons of crude steel and generated 23.29 million tons of by-products. We strove to reduce the final disposal to less than 260,000 tons, an amount based on the government’s target, such as by recycling the majority of these by-products inside and outside the company. As a result, our final disposal of industrial wastes amounted to approximately 230,000 tons and we maintained a very high recycling rate of 99%.
By-products and Recycling
|By-product||Process of generation||Amount generated
(wet weight million tons)
|Recycling application||Recycling rate|
|Blast furnace slag||Components other than iron melted in blast furnace||12.29||11.90||Blast furnace cement, concrete, fine aggregate, road base, etc.||100％||100％|
|Steelmaking slag||Substances other than steel generated in the steelmaking process||5.33||5.14||Road base, civil engineering materials, fertilizer, etc.||99％||99％|
|Dust||Fine dust collected with a dust collector||3.30||3.10||Raw materials for use in-house and also zinc refining||100％||100％|
|Sludge||Water treatment sludge, residue from plating solution, road cleaning sludge||0.41||0.40||Raw materials for in-house use||89％||85％|
|Coal ash||Ash from coaled-fired power plants||0.48||0.47||Cement raw materials||100％||100％|
|Waste furnace materials||Refractories from steelmaking facilities and furnace facilities||0.27||0.34||Reuse, road base, etc.||66％||76％|
|Others||Scale, etc.||1.71||1.94||In-house use, others||97％||99％|
|Total||23.80||23.29||Total recycling rate||99％||99％|
Effective use of steel slag
Geo-Tizer™ is in the granular form
and easy to handle with less dust.
Steel slagSlag is a by-product that is separated and recovered from molten metal during metal refining. It is used as road base material and raw material for cement. is almost entirely utilized. Approximately 70% of blast furnace slag is used for cement, while steelmaking slag is used for materials for road bases, civil engineering work, fertilizer, soil improvement, etc.
“Blast furnace cement,” a mixture of pulverized blast furnace slag and ordinary portland cementHydraulic cement. Gypsum is added to clinker produced by calcinating raw materials containing silica, alumina, iron oxide and lime, and then the mixture is made into powder., contributes to a 40% reduction of CO2 emissions during manufacturing, since the cement-making process can be omitted. It also exhibits superior long-term strength and is registered as an Eco Mark product. Due to the effects of reduction in mining of natural crushed stone and less energy consumption in the cement making process, steel slug products are designated as a “designated procurement item” under the Green Purchasing Law, and included in the Common Specifications for Civil Engineering Work compiled by the Ministry of Land, Infrastructure, Transport and Tourism.
NSSMC’s pavement materials, KATAMA™ SP, taking advantage of characteristics of steel slag, are used for forest roads and farm roads, as well as for weed preventive pavement to be installed near mega-solar panel installations and other locations.
Geo-Tizer™ made of steel slag can be mixed with soft soil (mud, such as surplus excavated soil from construction sites or farmland soil) to reform the soil to make it usable. Unlike conventional soil-improvement materials (i.e., cement and lime), this soil produces less dust, significantly controls CO2 emissions, and is less expensive, enabling reduction of construction cost. The remediated soil is outstanding in compacting and can also be easy to be dug again, without being excessively solidified.
Calcia modified soil, a mixture of steelmaking slag and dredged soil, has the beneficial effects of improving the strength and inhibiting the elution of phosphorus, the generation of hydrogen sulfide, etc. in dredged soil. It has also been used to improve the marine environment, including restoration of seaweed beds and creation of wetlands and tideland. In addition, NSSMC’s Beverly™ iron supply units, which are composed of steel slag and humus made from waste wood, provides iron needed for seaweeds to flourish, promoting regeneration of an area of the sea bed that had lost much of its living organisms.
Moreover, as steel slag contains nutrition that helps plants grow, it is also widely used as fertilizer, contributing to improving farming productivity.
Message from Innovators
Development of “iron” supply unit to prevent ocean desertification
NSSMC promotes the “creation of marine forest” to counteract the “rocky-shore denudation,” which has been a nation-wide environmental concern in recent years.
One of the causes of the “rocky-shore” phenomenon is the decreased supply of iron hich is necessary for kelp and seaweed to grow hrough rivers as a result of deforestation and upstream development. To cope with this problem, in 2004, we developed an iron supply unit containing humic substances made of iron/ steel slag and waste wood. Since then, we have been working on creating a seaweed bed (marine forest).
NSSMC also opened a “Sea Laboratory” (marine environment simulator) at the Technical Development Bureau in Futtsu City, Chiba Prefecture. We are working to scientifically clarify the usefulness and safety of using steel slag to create marine forest.
Recycling of dust and sludge
To recycle the dust and sludge generated in the iron manufacturing process to be used as raw materials, NSSMC has a dust reduction kiln (RC: Resource circulating oven) at Kashima Works and a rotary hearth reduction furnace (RHF) at Kimitsu Works, Hirohata Works, and Hikari WorksTransferred to Nippon Steel & Sumikin Stainless Steel Corporation.. This enables us to recycle all internally-generated dust. In March 2009, we obtained special approval for RHF under the Waste Disposal Act to carry out recycling of externally-generated dust as well.