PROJECT DESCRIPTION
BACKGROUND
In Spain, a considerable amount of slag (siderurgical waste) is generated in the production of Steel. During the process of casting scrap metal in an electric furnace to produce liquid steel, non-metallic residues composed of anhydrous calcium silicates and iron oxides are generated at a volume of 180.000 mt./ year. This is primarily a result of the chemical reactions between the liquid raw materials in the casting process and the lime and dolomite additions, used to trap impurities. While 15.000mt. /year are recovered in the form of iron and reused in the process itself, the majority of the remaining 165.000 mt/year constitute a residue which is difficult to treat, and is usually dumped. This waste product causes serious environmental problems, particularly when one considers that it is a common product for the entire steel sector, generating 1.100.000 mt. a year throughout Spain. Recent studies by the Polytechnic University of Catalunya have suggested that this iron residue could be easily recycled. Because of its excellent hydraulic and mechanical properties, it would be ideal for use in manufacturing concrete slabs with improved resistance, as a complement to conventional dry materials. Various pressed concrete manufacturing companies have showed interest in this possible application, given that the improved resistance of the siderurgical aggregate (65%) would allow for reduced thickness in the tiles, leading to the possibility of new applications such as alveolar pre-casts etc.
OBJECTIVES
The project’s main objective was to develop, on an industrial scale, a new process for transforming slag into dry iron, suitable for use in manufacturing improved resistance concrete tiles. In order to do this, the project would implement a conditioning process which would enable it to obtain granulometric values of between 0.5 and 18mm. This conditioning process would entail classification and magnetic separation of the iron residue and permit the recuperation of an additional amount of iron that is currently not possible through the existing process. Before launching the industrial plant, the project would carry out further rigorous trials on the hydraulic and mechanical properties of the siderurgical aggregate and fine-tune the industrial process and installations. Amongst its expected results, the project aimed to recover an additional quantity of iron (some 5,000 mt/year) for process use as well as achieve the elimination of all siderurgical waste.
RESULTS
The project successfully put into operation an industrial plant for transforming siderurgical waste into reinforced concrete trials, thus offering a completely innovative experience at a European level. The successful implantation of the new process would lead to the entire elimination of siderurgical waste, as well as generating value-added in improved resistance concrete tiles. The trial stage carried out with the Polytechnic University of Catalunya produced several new findings related to the viability of using siderurgical aggregate for obtaining precast concrete. Some of these led to changes in the industrial process proposed. New trials with different, more refined waste granulometry failed in the slag resistance, due to an excess of Aluminum silicate. Moreover, the presence of MgO in the furnace waste could not be related to the concrete expansion since there was no means to identify the chemical form of this oxide. A main conclusion was that in order to avoid expansion problems in the production of concrete slabs from the furnace waste, it must previously be subjected to a stabilization process during 30 hours at 2 atm. pressure. In this way, it could be applied to non-rigid matrix sub-layers such as road construction and hydraulic civic works. In the summer of 2000 a grinding plant was set up. It consisted of an overband magnetic separator and all the elements necessary for conditioning slag and producing different granulometries of high quality siderurgical aggregates. This included a post-hopper feeder, magnetic fraction screen, slag screen, magnetic roller, screen clearing belts, aggregate handling walls and aggregate feeding and clearing shovel. The different final products could be used as ornamental precasts, welded layers for asphalt paving, non-rigid matrix and hydraulic works. As a result of the demand for these applications, the slag residue dump was reduced by 80% by the end of the project. The project supposed an important change in the mentality of the sector, by promoting a series of rational programmed practices in slag treatment, and in considering this material as a valuable product rather than a waste. It therefore offers a high level of reproducibility in the context of the electric furnaces in the foundry sector. The beneficiary helped to ensure this transfer by establishing permanent exchanges of results and cooperation with other related Life projects (Colegio de Arquitectos de Catalunya, Life 95-474 and Instituto Catalan de la Construccion, Life 98-351). The project successfully put into operation an industrial plant for transforming siderurgical waste into reinforced concrete trials, thus offering a completely innovative experience at a European level. The successful implantation of the new process would lead to the entire elimination of siderurgical waste, as well as generating value-added in improved resistance concrete tiles. The trial stage carried out with the Polytechnic University of Catalunya produced several new findings related to the viability of using siderurgical aggregate for obtaining precast concrete. Some of these led to changes in the industrial process proposed. New trials with different, more refined waste granulometry failed in the slag resistance, due to an excess of Aluminum silicate. Moreover, the presence of MgO in the furnace waste could not be related to the concrete expansion since there was no means to identify the chemical form of this oxide. A main conclusion was that in order to avoid expansion problems in the production of concrete slabs from the furnace waste, it must previously be subjected to a stabilization process during 30 hours at 2 atm. pressure. In this way, it could be applied to non-rigid matrix sub-layers such as road construction and hydraulic civic works. In the summer of 2000 a grinding plant was set up. It consisted of an overband magnetic separator and all the elements necessary for conditioning slag and producing different granulometries of high quality siderurgical aggregates. This included a post-hopper feeder, magnetic fraction screen, slag screen, magnetic roller, screen clearing belts, aggregate handling walls and aggregate feeding and clearing shovel. The different final products could be used as ornamental precasts, welded layers for asphalt paving, non-rigid matrix and hydraulic works. As a result of the demand for these applications, the slag residue dump was reduced by 80% by the end of the project. The project supposed an important change in the mentality of the sector, by promoting a series of rational programmed practices in slag treatment, and in considering this material as a valuable product rather than a waste. It therefore offers a high level of reproducibility in the context of the electric furnaces in the foundry sector. The beneficiary helped to ensure this transfer by establishing permanent exchanges of results and cooperation with other related Life projects (Colegio de Arquitectos de Catalunya, Life 95-474 and Instituto Catalan de la Construccion, Life 98-351).
