Papers by Keyword: EAF Dust

Abstract: Zinc is a base metal present in several products of general use, and therefore found in numerous residues and end-of-life products. The two main sources of zinc containing wastes are spent Zn-MnO₂ portable batteries and electric arc furnace (EAF) dusts from steelmaking plants. The recovery of metals from these residues by appropriate recycling processes is mandatory due to environmental, economic and resource conservation issues. Concerning the similar composition of both residues, their simultaneous processing can be envisaged. The research herein described consists on the hydrometallurgical treatment of zinc bearing waste, where several leaching routes for solubilising metals, mainly zinc, are studied. The leaching of shredded batteries and EAF dusts was carried out using three different leaching solutions containing sulfuric acid, hydrochloric acid or ammonium chloride. The acid leaching of zinc in the oxide form (zincite) using both acids, was very efficient and quick, allowing the recovery of practically all Zn contained in batteries and about of 80% of Zn in dusts. Regarding to the leaching media the behaviour of lead oxides present in dusts was different, being insoluble with H₂SO₄ and partially soluble with HCl (40-90% yield, depending on conditions). For battery waste stream, manganese is also other important metal, which oxides were only partially soluble in acid media, attaining a maximum leaching yield of 90% Mn. Iron, considered a contaminant in both residues, was partially leached and required further purification steps. The use of an ammoniacal medium (NH₄Cl) was very selective for zinc, being iron practically insoluble. However, the maximum zinc leaching yield attained for both residues was only near 60%. Under these conditions, manganese contained in batteries was very insoluble while lead from dusts was leached up to 70% due to the relative solubility of lead chloride. This research showed that hydrometallurgical treatment can provide versatile solutions for recycling metals from Zn waste. Ammoniacal leaching allows high selectivity for zinc but less recovery efficiency is attained, while acid leaching allows higher metal recovery yields but unwanted elements like iron are co-dissolved.

Abstract: The dependence of composition and sintering temperature on physical properties of ALA was investigated. Mechanism of black discoloration(sometimes called black core) usually found in the interior cores of artificial lightweight aggregate was also investigated by the optical observations. As a result, the primary cause of black discoloration in the interior of the lightweight aggregate body resulting from incomplete burn-out of carbonaceous impurities and iron-containing materials.In the cross-sectional morphology of ALA, bloating phenomena as well as formation of large pores were found in the samples containing ferrous materials. By increasing content of ferrous materials, both specific gravity and water absorption have been decreased.

Abstract: The EAF Dusts and pickling sludges generated in the stainless steel production contain a lot of valuable metals such as iron, nickel, chromium and manganese. Their compositions are similar to those of laterite nickel ore, and sometimes even better than that at the contents of nickel and chromium. But it is regret that these valuable resources were random piled up or landed fill disposal. In this paper, the typical EAF dusts and pickling sludges and reductant coke powder were mixed in appropriate ratio, and then smelted in a medium frequency induction furnace. In the smelting process, the lime powder and fluorite was added to fluxing, and the ferrosilicon powder was added to strengthen the reduction. The product nickel-chromium-iron can be used as the raw material for stainless steel or cast iron production. The technology has good social and economic benefits.

Abstract: The corrosion behavior of glass and glass-ceramics fabricated with silicate glass frit mixed with 50~70 wt% EAF dust in the acidic solution was analyzed by both heavy metal leaching test and microstructural observation. The crystallization temperature, Tc of glassy specimens was around 850
measured by DTA and the heat treatment temperature to crystallize a glassy specimen was selected as 950
/ 1 hr. The spinel crystal peaks were found in XRD analysis for the glass containing dust > 60 wt%. For the glass-ceramics, however, the spinel peaks in a specimen containing dust > 50 wt% was found with weak willemite peaks. The glass and glass-ceramic specimens showed the first stage of corroding reaction according to Clark models in acidic solution. The glass-ceramic specimens showed much lower a heavy metal leaching concentration than that of glass specimens in the corrosion test in acidic solution of pH=2.95. Especially, the glass-ceramics containing dust 60 wt% showed a heavy metal leaching concentration of 66 % Pb, 60 % Zn and 98 % Fe lower than that of glass specimens due to crystal phases formed, thermodynamically more stable than a glass network structure. From the leaching test that more Zn ion leached out than Fe ion, the spinel crystal phase [ZnFe2O4] showed better corrosion resistant in the acidic solution than the willemite [Zn2SiO4].

Abstract: To recycling the EAF dust as a ceramic raw material, the leaching concentrations of heavy metals (Zn, Pb, Cr, Cd) were analyzed with various pH and mixing ratios for EAF dust-clay bodies. The evaporation amounts of the some heavy metals were evaluated by measuring their total concentrations in the sintered bodies of EAF dust-clay mixtures with various mixing ratio and sintering temperature. TCLP test was conducted for evaluating the chemical stabilities of the heavy metal elements. The heavy metals in EAF dust are 'amphoteric metal' and leached a little at pH10. The leaching concentrations of heavy metal ion were effectively decreased by the formation of PSHP when adding the clay to the EAF dust and controlling the pH of the slurry at 12. Evaporation of heavy metal components were increased with increasing the sintering temperature and the contents of EAF dust. The leaching concentrations of heavy metal components were decreased with increasing the clay content and temperature.

Abstract: Stabilizing characteristics of heavy metals in the silicate glass (SD) and lead silicate glass(PD) containing Electric Arc Furnace(EAF) dust was studied by the toxic characterization leaching procedure(TCLP) test. Dependence of the amount of EAF dust upon structural changes of SD and PD glasses and TCLP results was also investigated by FT-IR spectroscopy. In the TCLP test, the concentration of heavy metals leached from a glass increased with the amount of EAF dust added. The SD series specimens showed heavy metal leaching lower than the PD series specimens, but the Pb leaching from the PD series specimens was the highest owing to the high Pb content in the PD glass composition. The value R(oxygen/network former ion ratio) was used to compare the leaching characteristics of glasses, and the SD had a higer R than PD series specimens to show a better chemical durability. Adding the EAF dust to the SD mother glass decreased the Si-O-Si symmetry and increased the non-bridging oxygen, which weakened the structure and decreased the chemical durability of glasses. It is concluded that SD is more effective in stabilizing the heavy metals of EAF dust than PD series glass.

Abstract: Thermal behaviors of EAF dust, water-washed EAF dust, and EAF dust/heavy clay mixtures with wet mixing process were characterized by TG/ DTA analysis. The ionic concentrations of some metal ions and anions in the supernatant from water-washing process were evaluated by ICP and IC analysis. Weight loss of water-washed EAF dust above the temperature range of 1000°C was significantly decreased because of the washing effect of chloride and sulfate compounds. The variation of volatile ZnO and PbO contents were not detected in 20wt% D dust-80wt% clay sample. The wet mixing process not only enhanced the homogeneous mixing of EAF dust and clay particles, but also reduced the volatilization of heavy metals(Zn, Pb, etc.) at the high temperature range.

Abstract: Brick samples were prepared through vitrification process with two different kinds of EAF dust. Leaching concentrations of various metal ions and anions for the bricks(20wt% EAF dust-80wt% clay) were evaluated by ICP and IC analysis. The results of leaching test showed that the concentration of ions leached from bricks were proportional to the square root of time and saturated with leaching time. The saturated concentrations of alkali and alkali-earth metal ions were 0.1-250ppm; on the other hand, the heavy metal ions were 0-0.084ppm. The efflorescence mechanism of EAF dust-clay bricks was studied by quantitative analysis for the effects of various metal ions and anions. Efflorescence formed on the brick surfaces which were immersed in DI water and dried slowly in the air were characterized by SEM, EDS and XRD. The results of EDS and XRD showed that the main component of the efflorescence was water soluble Na₂SO₄ .