**7. Environmental concerns about the slags use in agriculture**

According to its environmental policy, the European targets concern the environment preservation, protection and its quality improvement, the human health protection and the efficient use of natural resources, by adopting measures for handling environmental issues on global and local level. The use of slags has a crucial significance as regard the environmental aspects. The main problem concerning the utilization of steel slags in agriculture consists of the possible leaching of heavy metals.

Heavy metals are broadly distributed in the Earth's crust and some of their chemical forms can be a potential risk to biosphere, in particular to the water life, because of their solubility. Their bioavailability depends on the plants ability to uptake them from soil and water, due to the secretion by plants roots of chelators compounds; furthermore many heavy metals are transported by sulphur ligands, such as glutathione, and organic acids. Moreover some heavy metals are insoluble and they often interact with soil particles, and therefore they are not available to plants (Babula, P., et al., 2008).

Possible Uses of Steelmaking Slag in Agriculture: An Overview 353

Nevertheless it is important to carry out further investigations focused on the heavy metals behaviour on the soil in order to better understand the effects of long-term use of steelmaking slags in agriculture. In the above-mentioned research project (Kühn et al., 2006), the preliminary investigation, based on the origin of heavy metals in the BF-BOF route, has led to the result that Cr is originated from ore, but it is also influenced by the scrap used, whereas V content is only affected by the iron ore input in the BF. In the second part of the investigation, the analysis of long term effects of Cr and V has showed significant accumulation of their

Results on soil analysis have shown that the highest values for Cr and V have been detected during the 50 years test conducted in St. Peter site (Black Forest), after using of basic slag, where Cr has increased of 40-50 mg Cr/kg of aqua regia soluble and total Cr, whereas V has

It has been shown that both Cr and V, even though they have increased in the top soil, they are stable and immobile in the soil. In addition, after more than 50 years tests, they did not move into the deeper soil and therefore they cannot adversely affect the groundwater and

Plant analysis conducted in pot experiments have shown no significant differences for Cr and V uptake, but in different crops they have shown different results for Cr and V. In particular, the Cr concentrations in rye, rape and winter wheat was about lower of the detection limit (< 0.035 mg kg-1). As far as V is concerned, it could not be measured in rye, rape, spring barley and winter wheat, while it has shown the highest concentration in

Furthermore it has been pointed out that the metals uptake by the plants is affected by the soil properties. For example the Cr and V contents into potatoes are reduced in soils with higher content of organic matter and with an heavy texture. In addition, the uptake of Cr, V

The steel industry is committed to increasing the way for recycling slags generated during the steel production. Since their use as landfill material has almost reached its limit, the pressure for saving natural resources and energy has led steel industry, along with other important technological challenges, to improve and increase the recycling of this byproduct. While in the past steelmaking processes were exclusively design for the production of specific qualities of iron and steel, one of the today's goals for steelmakers is to design processes to produce high quality slags, according to the market requirements. New technologies and/or the improvement of existing technologies have been investigated and developed in order to achieve the ambitious target of "zero-waste" in the incoming years. To this aim, the effective utilisation of slags turns it into high value added product and allows to improve the steel industry competitiveness. On the other hand, the sustainable use of slags contributes to natural resources saving, to CO2 emission reductions and to

The use of steel slags in agriculture produces not only economic but also ecological advantages. A more effective exploitation of natural resources can be achieved in both the

content in the cultivated layer of the soil, after application of converter slag.

consequently the human and animal health.

and Cd by potatoes is favoured by low pH.

consolidate a society founded on the recycling practice.

**8. Conclusion** 

potatoes after basic slag fertilisation of the Austrian field trials.

increased of 60-70 mg V/kg of aqua regia soluble and 63-80 mg V/kg of total V.

Chromium (Cr) is used in different industrial field of applications such as steel industry, wood preservatives, electroplating, metal finishing, leather tanning, textiles and chemical manufacture and it is a frequent contaminant of both surface ground waters. In oxidizing conditions is highly soluble and forms Cr(VI) anions, such as chromates CrO42- or dichromates Cr2O7 2-. Under reducing conditions, through a process involving a chemical reduction and a precipitation, Cr(VI) converts to Cr(III) that is insoluble. Both forms are stable in the environment. The roots plants can absorb both forms Cr3+ and CrO42-, but, according to some date, the Cr(III) forms stable compounds (e.g. hydroxides, oxides and sulphates). Therefore it is less soluble and, consequently, less bioavailable (Srivastava et al., 1994, as cited in Babula, P. et al., 2008). However Huffman et al. has shown as there are not uptake differences between Cr(III) and Cr(VI) by bean (*Phaseolus vulgaris, Fabaceae*) and wheat (*Triticum aestivum, Poaceae*).

Although Cr is an essential element for animal and human health, hexavalent Cr salts have toxic and carcinogenic effects. The plant mechanism of toxic effect of Cr is due to the reaction between Cr-complexes and hydrogen peroxide that produces hydroxyl radicals. They can trigger off DNA alteration (Shi & Dalal, 1990a, b, as cited in Babula, P. et al., 2008), by affecting, for example, its replication and transcription.

Among heavy metals, steelmaking slags contain Vanadium (V). The V content in the processed ore is about less of 2%. During the blowing process into the LD converter the V is transferred to the converter slag as V2O5 (about 5%), which represents the main source for some procedures aiming to extract V from LD converter slag. Due to its heavy metals content and the environmental problems resulting to their release to earth, LD slag is often subjected to treatments, aiming to extract these harmful but also precious elements from it. Because of its physical properties, such as high tensile strength, hardness, and fatigue resistance, V is used in ferrous and non-ferrous alloys. For all these reasons it is desirable to recover this valuable element.

Among some studies about this topic, a recent research aims to investigate on the extraction procedure of V by using salt roasting and sulphuric acid leaching and how some leaching parameters, such as particle size, acid concentration, reaction temperature and solid:liquid ratio (S/L), may influence the kinetics process (Aarabi-Karasgani et al., 2010). The found optimum condition of leaching allows to achieve a maximum V recovery of 95%. Furthermore the size fraction of below of 0.850 mm has shown to be mostly effective in order to attain the maximum extraction. Two leaching stages have been proposed: the first one (the first 15 minutes), when the V leaching is faster, and a second stage (more than 30 min), when the leaching becomes slower. In addition, the leaching rate is controlled by chemical reaction at low temperature while at high temperature it is controlled by the solid product diffusion.

The increasing interest concerning the slags use for soil conditioning has focused the attention on the heavy metal concentrations in these materials. Several investigations carried out in Finland have shown that the concentration of some elements, such as Cr and Zn, are low because of the high temperatures of the processes. On the other hand, long-term experiments in Germany have shown that the application of steel slag as liming material does not increase the content of mobile chromium into the soil and, after using steelmaking slags as fertiliser, significant increases in Cr content have not been found in plants (R. Hiltunen & A. Hiltunen, 2004).

Nevertheless it is important to carry out further investigations focused on the heavy metals behaviour on the soil in order to better understand the effects of long-term use of steelmaking slags in agriculture. In the above-mentioned research project (Kühn et al., 2006), the preliminary investigation, based on the origin of heavy metals in the BF-BOF route, has led to the result that Cr is originated from ore, but it is also influenced by the scrap used, whereas V content is only affected by the iron ore input in the BF. In the second part of the investigation, the analysis of long term effects of Cr and V has showed significant accumulation of their content in the cultivated layer of the soil, after application of converter slag.

Results on soil analysis have shown that the highest values for Cr and V have been detected during the 50 years test conducted in St. Peter site (Black Forest), after using of basic slag, where Cr has increased of 40-50 mg Cr/kg of aqua regia soluble and total Cr, whereas V has increased of 60-70 mg V/kg of aqua regia soluble and 63-80 mg V/kg of total V.

It has been shown that both Cr and V, even though they have increased in the top soil, they are stable and immobile in the soil. In addition, after more than 50 years tests, they did not move into the deeper soil and therefore they cannot adversely affect the groundwater and consequently the human and animal health.

Plant analysis conducted in pot experiments have shown no significant differences for Cr and V uptake, but in different crops they have shown different results for Cr and V. In particular, the Cr concentrations in rye, rape and winter wheat was about lower of the detection limit (< 0.035 mg kg-1). As far as V is concerned, it could not be measured in rye, rape, spring barley and winter wheat, while it has shown the highest concentration in potatoes after basic slag fertilisation of the Austrian field trials.

Furthermore it has been pointed out that the metals uptake by the plants is affected by the soil properties. For example the Cr and V contents into potatoes are reduced in soils with higher content of organic matter and with an heavy texture. In addition, the uptake of Cr, V and Cd by potatoes is favoured by low pH.
