Mechano-chemical and thermal treatment of iron bearing waste materials

Abstract

Steel scrap recycling is generally performed by direct smelting of scrap in electric arc furnaces, generating about 2% of dust per charge. Electric arc furnace dust (EAFD) is characterized as a hazardous material, due to its heavy metals content and a powder form. This PhD thesis presents the study of Serbian electric arc furnace dust (EAFD) management trough some conventional and innovative technologies. The investigated EAFD was brought from Serbian carbon steel making and that is way the zinc percentage it was 30.34%, which is in the standard range of typical chemical analysis of EAFD from carbon steelmaking. The analysis also shows that zinc, iron and chromium are mainly present as ferrites which are very resistant against to any kind of treatment. Because of that, it is necessary to use more aggressive conditions (high temperature or stronger leaching reagent) for metals recovery. Solidification/Stabilization (S/S), a widely used treatment technology, of EAFD was investigated in two ways; first as cement replacement in grout mixture and the replacement percent was set up to 80%. Results of compressive strength testing showed that the best maximum replacement of cement with EAFD is 20%. With a higher amount of EAFD in mixture compressive strength decreases rapidly. According to leachability results, Pb was stabilized in a cement matrix even at 80% of cement replacement with EAFD. Second way of (S/S) of EAFD by using cement as the main stabilizer, fly ash as an additive, and controlling the EAFD particle size by milling. EAFD replaced 50 % of fine aggregate and fly ash replaced 10-25% of cement in mixtures, with different milling times applied. S/S samples were tested for compressive strength and heavy metals leachability. The results of compressive strength testing showed that the best maximum EAFD replacement is 15%, after which compressive strength decreases rapidly. The best fly ash compressive strength was attained at 10% replacement of both fine aggregate and cement. The milled EAFD produced the best results at three hours of milling; however, the addition of fly ash resulted in a slight compressive strength decrease in these samples. Leachability results of concrete samples indicated that Zn and Pb were stabilized in the cement matrix even at 30% of fine aggregate replacement with EAFD...