Encapsulation of steel foundry bag house dusts in cement mortar

The purpose of this study was to investigate the properties of bag house dusts generated by steel foundries when stabilized with Portland cement at high levels of cement addition. The main bag house dust studied was obtained as a byproduct of steel manufacture, at Pacific Steel Limited in Auckland, New Zealand, whereas others were sourced from BHP New Zealand Steel, Masport, and A&G Price foundries. The main examination techniques used in this study were leachate testing, scanning electron microscopy, X-ray diffraction, and compressive strength measurements. The findings showed that all the dusts investigated varied in their composition and physical makeup. Those bag house dusts that contained elevated levels of zinc severely retarded the hydration of cement within the first 2 weeks, but accelerated the strengths at late ages (28 days). The zinc was predominantly in the form of zinc oxide, which, when mixed with cement, produced the complex, calcium zinc hydrate. When cement was doped with zinc oxide, it was also found to display the same type of retardation as Was found with the high ZnO bag house dusts. Lead also displayed a slight accelerating phenomena at 28 days, but the retention of lead in stabilized materials, as measured by the toxicity characteristic leaching procedure, was higher than that for zinc. The Masport, A&G Price, and two BHP New Zealand Steel bag house dusts did not show accelerating characteristics; however, Pacific Steel and the other two BHP New Zealand Steel zinc oxide-containing bag house dusts did. (C) 1999 Elsevier Science Ltd. All rights reserved.