Basaltic Glass Fibers from Industrial Wastes: A Laboratory-Scale Technical Feasibility Study

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This study demonstrated the physical–chemical and technical feasibility of recycling EAF slag granulated by rapid cooling with gas to produce continuous glass fibers with a basalt-like composition. To adjust the chemical composition, a silica fume-based secondary raw material was used, together with other additives. Different compositions were tested: 50% EAF slag and 50% silica fume (sample C1); 40% EAF slag, 50% silica fume and 10% Na2O (sample C2); 40% EAF slag, 50% silica fume, 5% Na2O and 5% K2O (sample C3); 20% EAF slag, 57% silica fume, 10% Na2O and 13% alkali earth oxides (sample C4); 26% EAF slag, 35% silica fume, 7% CaO and 12% Na2O (sample C5); 26% EAF slag, 35% silica fume, 4% CaO and 15% Na2O (sample C6). The last composition allowed obtaining fibers up to 5–6 m long, with a diameter between 60 and 180 µm. The process involved using a refractory material crucible with a calibrated bottom orifice as a single nozzle bushing. The optimal temperature range for fiber forming was between 1115 and 1125 °C, with a linear drawing speed of about 2 m/s. Preliminary mechanical tests were performed. Based on these results, potential further recycling applications of granulated EAF slag in the production of basalt-like glass for noncontinuous fiber production for mechanical reinforcement or for thermal–acoustic insulation can also be foreseen.