**1. Introduction**

334 Material Recycling – Trends and Perspectives

[17] PENG Yu-chu, HUANG Chau-long. Engineering properties of sintered waste sludge as

[18] Roy DM, Idorn GM. Hydration, structures, and properties of blast furnace slag cements,

[19] Schindler Anton K., Barnes Robert W., Roberts James B., Rodriguez Sergio, Properties of

[20] Sakuraya T. The utilizing condition of metallurgical slag and steel slag for Japanese

[21] Wu X, Zhu H, Hou X, Li H. Study on steel slag and fly ash composite Portland cement.

[22] Whitcomb Brent L., Kiousis Panos D., Development of self-consolidating concrete for

[23] Zhang MH, Bilodeau A, Malhotra VM, Kim KS, Kim JC. Concrete incorporating

to chloride-ion penetration. ACI Mater J 1999;96:181–189.

Ed [ISSN 1671-8224], 2009, 8(4): 231-238.

n 1, p 53-61, January/February 2007.

and Utilization, Beijing, 1999. p. 15–20.

Engineering, v 21, n 10, p 587-593, 2009.

Cem Concr Res 1999;29:1103–1106.

mortars, and concrete. ACI J 1982;82:444–457.

lightweight aggregate in a densified concrete mixture [J]. J Chongqing Univ: Eng

self-consolidating concrete for prestressed members, ACI Materials Journal, v 104,

Refinery Steel Industry. The International Associate of Metallurgical Slag Recycle

thin wall applications including validation, Journal of Materials in Civil

supplementary cementing materials: effect on compressive strength and resistance

Slags are the main by-products generated during iron and crude steel production and the steel industry is committed to increasing and improving their recycling.

Over the past decades, the steel production has increased and, consequently, the higher volumes of by-products and residues generated have driven to the reuse of these materials in an increasingly efficient way. In recent years new technologies have been expanded, and some of them are still under developing, in order to improve the recovery rates of slags. On this subject material separation technologies and carbon sequestration could dramatically reduce CO2 emissions from steelmaking processes. On the other hand, the increase of slags recovery and use in different fields of application, such as in agriculture, allowed to reduce landfill slags and to preserve natural resources. In addition to the environmental achievements, these practices produced economic benefits, by providing sustainable solutions that can allow the steel industry to achieve its ambitious target of "zero-waste" in the incoming years (worldsteel, 2008).

Steel is produced by mean two main ways:


In both BOF and EAF the reactions between oxygen, carbon (carbon as gaseous carbon monoxide), silicon, manganese, phosphorus and some iron as liquid oxides produce oxidized compounds that react with lime or dolomitic lime to form slag. At the end of the

Possible Uses of Steelmaking Slag in Agriculture: An Overview 337

Bessemer or Thomas processes, as phosphating and/or liming agent started in 1880

The traditional use of slag as landfill material, after the increase of steel production since the mid-1970's, has reached its limit and the pressure for natural resources and energy saving have driven steel industry to increase the recycling of this material, by facing other important challenges (such as technologies development, production facilities maintenance and ferrous slag products certification) in order to improve their application in different

Slags coming from both BF and steelmaking processes are consumed at steelworks, used in cement, roadbed material, ground improvement material, civil engineering material and fertiliser. Once slags were dumped; nowadays they are considered marketable products and

In the past steelmaking processes were exclusively designed for the production of specific quality of iron and steel. One of the current steelmakers' goal is to design processes to produce high quality slags, both prior to and during the slags production, according to the market requirements, in order to satisfy environmental and technical requirements of international and national standards (Euroslag, 2006). On one hand, selling by-products produces revenues for steelmakers, that in turn generate economic development for the worldwide industry. On the other hand, the sustainable use of slags contributes to natural resources saving, to CO2 emissions reduction, to energy consumption reduction, to the formation of a society founded on the recycling practice (as landfilling is avoided) and to the promotion of the steel industry sustainability. Therefore potential economic and environmental benefits make slags by-products that can be further recovered and used. For all these reasons, the effective utilisation of slag turns it into high value added product and

This chapter intends to review the state of the art related to the use in agriculture of steel slag, mainly coming from BOF process using basically Linz-Donawitz (LD) converter, in different worldwide contexts. The review covers different aspects by summarizing its use as

sectors (The Japan Iron and Steel Federation – Nippon Slag Association, 2006).

only a small percentage is processed as industrial waste in landfills.

allows to improve competitiveness of the steel industry.

(Geiseler, 1996).

Fig. 2. The scrap-based steelmaking.

refining operation, after steel pouring into a ladle, the slag is poured into a vessel and is subsequently tapped into a slag pot.

Fig. 1. The iron ore based steelmaking.

The main by-products resulting by ironmaking and steelmaking are slags (that represent 90% of the total by-products), dusts and sludges. On the average about 200 kg of byproducts per ton of steel result from the steel production through electric arc furnace, while about 400 kg of by-products per ton of steel production through BF/BOF (World Steel Association, n.d.).

The use of by-products from steel industry goes back to many centuries ago. In 350 BC Aristotle already stated "When iron is purified by fire, there forms a stone known as iron slag. It is wonderfully effective in drying out wounds and results in other benefits". In later centuries slag has been used as construction material. The discovery of the hydraulic properties of granulated BF slag gave birth to a new era in slag exploitation: slag has been used as binding agent and/or addition for concrete. The use of steelmaking slag, from Basic-

refining operation, after steel pouring into a ladle, the slag is poured into a vessel and is

The main by-products resulting by ironmaking and steelmaking are slags (that represent 90% of the total by-products), dusts and sludges. On the average about 200 kg of byproducts per ton of steel result from the steel production through electric arc furnace, while about 400 kg of by-products per ton of steel production through BF/BOF (World Steel

The use of by-products from steel industry goes back to many centuries ago. In 350 BC Aristotle already stated "When iron is purified by fire, there forms a stone known as iron slag. It is wonderfully effective in drying out wounds and results in other benefits". In later centuries slag has been used as construction material. The discovery of the hydraulic properties of granulated BF slag gave birth to a new era in slag exploitation: slag has been used as binding agent and/or addition for concrete. The use of steelmaking slag, from Basic-

subsequently tapped into a slag pot.

Fig. 1. The iron ore based steelmaking.

Association, n.d.).

Bessemer or Thomas processes, as phosphating and/or liming agent started in 1880 (Geiseler, 1996).

Fig. 2. The scrap-based steelmaking.

The traditional use of slag as landfill material, after the increase of steel production since the mid-1970's, has reached its limit and the pressure for natural resources and energy saving have driven steel industry to increase the recycling of this material, by facing other important challenges (such as technologies development, production facilities maintenance and ferrous slag products certification) in order to improve their application in different sectors (The Japan Iron and Steel Federation – Nippon Slag Association, 2006).

Slags coming from both BF and steelmaking processes are consumed at steelworks, used in cement, roadbed material, ground improvement material, civil engineering material and fertiliser. Once slags were dumped; nowadays they are considered marketable products and only a small percentage is processed as industrial waste in landfills.

In the past steelmaking processes were exclusively designed for the production of specific quality of iron and steel. One of the current steelmakers' goal is to design processes to produce high quality slags, both prior to and during the slags production, according to the market requirements, in order to satisfy environmental and technical requirements of international and national standards (Euroslag, 2006). On one hand, selling by-products produces revenues for steelmakers, that in turn generate economic development for the worldwide industry. On the other hand, the sustainable use of slags contributes to natural resources saving, to CO2 emissions reduction, to energy consumption reduction, to the formation of a society founded on the recycling practice (as landfilling is avoided) and to the promotion of the steel industry sustainability. Therefore potential economic and environmental benefits make slags by-products that can be further recovered and used. For all these reasons, the effective utilisation of slag turns it into high value added product and allows to improve competitiveness of the steel industry.

This chapter intends to review the state of the art related to the use in agriculture of steel slag, mainly coming from BOF process using basically Linz-Donawitz (LD) converter, in different worldwide contexts. The review covers different aspects by summarizing its use as

Possible Uses of Steelmaking Slag in Agriculture: An Overview 339

The marketed BF slag can be subdivided into three main types, depending how they are

• The Granulated BF Slag (GBFS) is produced by injecting high pressure water, followed by quenching and granulating it. It is used as material in cement, as fine aggregate for concrete and in civil engineering works, exhibiting better long-term strength, better

• The Air-cooled BF Slag (ABFS) is discharged to a cooling yard and naturally cooled with moderate sprinkling. The crystallized slag, after crushing, sieving and removing magnetic matter, can be used as construction aggregate, concrete products, road bases

• The third type of cooled BF slag is represented by Pelletised Slag, with a vesicular texture, used as a lightweight aggregate and, when it is fine grounded, as cementitious

Steelmaking slags include slags from BOF and EAF. Since at this stage the steel production processes vary, depending on the steel being made, the slags chemical properties change as well. This results in a more difficult use of steel slags compared to the BF slag. They are discharged to a cooling yard or to a slag ladle and they are naturally cooled with moderate sprinkling. After crushing, sieving and removal of magnetic matter, they achieve granularity appropriate to different applications. Because of their lime contents they expand in reaction with water. After this expansion they are stabilised by "natural ageing" for long periods outdoors in natural rainfall and other weather or "steam ageing", through high-temperature

Steelmaking slag deriving from BOF process (using the Linz-Donawitz (LD) converter) comes from the pig iron refining process, which converts molten pig iron and steel scraps into high quality steel. Most slags from steel plant derive from this process, with an average of 150-200 kg of slag generated per tonne of steel produced. X-ray diffraction studies have shown that the major phases present in LD slag are dicalcium ferrite, calcium alluminate

resistance to chemical attack, and it brings down the cost of cement.

**Others 1%**

**Final deposit 2%**

**Road construction 38%**

Fig. 3. The uses of different types of slags in Europe.

and surface and clinker raw material.

**Internal use for metallugical purposes 3%**

**Interim storage 5%**

**Hydraulic engineering 1%**

cooled:

material.

vapour.

**Fertilizer 2%**

> **Cement production 48%**

fertiliser and as liming agent, its potential use as amending material for soils, and by paying attention also to different technologies and methodologies aiming to improve the quality of the slag, in order to increase and make progress in its use in agriculture. On one hand, studies based on the use of slag in agriculture will be considered, which treat the use of steel slags for amending acid soils and as source of important factors and growing agents (not only calcium and magnesium compounds, but also other elements such as silicon, providing important beneficial effects for some crops and increasing the plant yields) and its use as Fe source for reducing Fe chlorosis in different crops. Moreover, investigations will be described concerning the heavy metals contained into the slags and their behaviour on the soil, in order to evaluate possible harmful effects after slag application for agricultural purposes and to avoid their possible negative environmental impacts, as well as the use of steel slags for metal stabilisation in contaminated soils. On the other hand, investigations focused on the obtaining a slag with high phosphorus content to be used as fertiliser (together with other slags with a low content in phosphorus to be recycled inside the steelmaking process) will be discussed.
