Slag for Agricultural Applications
The acidity of soils is a limiting factor for the development and production of most crops. On the one hand, its harmful action can be felt directly due to the increased concentration of hydrogen and aluminum ions on the soil, which establish adverse conditions to the upper plants and the useful microbial life. But indirectly, that action can also be felt in complex phenomena related to the availability of essential nutrients to the plants, as well as in the impoverishment of the soil exchangeable bases, mainly calcium and magnesium. The crushed carbonated rocks, generically defined as limestone, are materials largely employed in the elimination of those direct and indirect undesirable effects of the acidity.
The Steel Slags are materials that combine the conditions for replacing the usual soil correctives, because in addition to phosphate, magnesium and sulfur, the steel slag contains 35% to 45 % of calcium oxide, which makes it a desirable product as a soil conditioner for renewing the natural equilibrium of acidified soils.
The utilization of steelworks slags as an agricultural consumable product has been studied for some time in many parts of the world, producing satisfactory results. In the USA, their use have been approved by agricultural agencies on a federal basis and licensed by some bodies on a state basis. In some countries of Europe, tests carried out have shown an improvement in the property of acid soils. In France, for instance, the use of slag in the agriculture has been adopted for over 20 years.
Partial view of a field where LD Slag was applied - Sollac Atlantique - Dunquerque - France - Arcelor Group
In Brazil, our legislation foresees the utilization of slag, mainly as soil acidity corrective. Therefore, it establishes standards regarding the quality requirements the corrective must fulfill.
Ministry of Agriculture Law Decree from 4/03/1983.It approves the standards for inspections and surveillance of the production and commerce of fertilizer and correctives meant for the agriculture sector. - As for the slag correctives in general, they shall meet minimum values such as PN 60 % of CaCO³.
Agricultural CorrectiveBesides correcting acid waters, the slag can also be used as a soil corrective. Such use of the Steel Slag, such as soil acidity corrective, can be explained by its high contents of CaO and MgO, and low Al²O³, taking into consideration the fact that compounds like CaO and MgO are obtained in their soluble form by cooling the slag. The hydrolysis of these compounds in water and the presence of acid H+ ions, produce divalent ions (Ca+2 and Mg+2), which then become part of the humus-clay exchange complex in the soil (Balcazar, 1998). The use of slag in this application has a great advantage over the conventional fertilizers, since the lime present in the Steel Slag is chemically combined with silica, iron and manganese. This allows the slow release of lime in order to prevent the "burn" or reversal to carbonate.
This application requires fine particles (0 to 1mm) and dry storage installations.
In this area, the Federal University of Viçosa has carried out the following tests:
- The possibility of using the slag as an agricultural corrective, where the efficiency of this product has been proved by increasing the soil pH level and then making available more nutrients and nitrogen to the plants, thus resulting in an increased growth of both the plant and the production of grains.
- Leaching tests, where the mobility of some heavy metals was tested in the soil as well as the possibility of ground water contamination. In such tests, the absence of neither risk of ground water contamination nor absorption of any type of contamination by the plants was checked. The decreased mobilization of heavy metals and aluminum is due to the higher pH level.
The table bellow shows the benefits brought by the utilization of this product as well as its limiting factors and the competitive products:
| Steel Slags: (accepted use) |
Benefits:
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Limiting factor:
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| Competitive products: | Limestone and agricultural plaster. |
The environmental aspect should also be highlighted, since the agronomical use of this product brings positive factors such as the non-utilization of natural resources, like phosphatic and carbonated rocks;
Contact:Eng. Jairo de Mattos Pereira Filho - Sales Executive
ArcelorMittal Tubarão - Companhia Siderúrgica de Tubarão,
Avenida Brigadeiro Eduardo Gomes, 930 - Jardim Limoeiro,
Serra, Espírito Santo, Zip Code 29163-970. PCE 41
Tel: (+55 27) 3348-1395
E-mail: jairomat@ArcelorMittal.com.br
Siderúrgica produtora de placas de aço, aços planos, bobinas e laminados a quente.
