| dc.description.abstract | The yield of EAF dust collected is around 180k to 220k tons annually in Taiwan, including 60k tons of stainless steel dusts. However, relevant research shows that the amounts of Pb, Cd, and Cr(VI) leached form the EAF dust have exceeded the limits. Taiwan EPA has characterized EAF dust as hazardous industrial waste. If the waste is not treated properly, it will bring harms to the environment, biological system, and human beings. To avoid those harms, the EAF dusts should be properly recycled and treated to reduce the adverse impact. At present, the EAF dust recycling is based on processing carbon steel dust and recycling zinc oxide is the main objective. For stainless steel dust which is rich in Fe, Cr, Ni, and other valuable metals, the majority solution is only burying the solid waste in specific landfill. It is not an effective process to reuse those elements but just temporally stabilizes the harmful dusts. This method is space-consuming since the landfill required large size of place, which is also not suitable for somewhere with limited land, such as Taiwan.
Electric Smelting Reduction Furnace (ESRF) is applied to treat the EAF dusts collected from three major domestic stainless steel plants. First, the content and composition of the stainless steel dust is identified and quantified. The results of analysis indicat that there are 21-35% of iron (Fe), 7.5-8.7% of chromium (Cd), and 0.8-2.3% of nickel (Ni) in the stainless steel dust. Total portion of reusable resources are 30-40% of all dust. Afterwards, the dusts are mixed uniformly and fed into the ESRF for granulation with 1550 ℃ of heat inside the reduction furnace, where the coke is used as a reducing agent to reduce the metallic oxides in the dust. Those metals with high boiling points like iron, chromium, and nickel, will be liquefied and dissolved into the stainless steel fluid and recycled. By controlling the basicity, the rate of chromium and nickel recovered can be optimized. The results of research show that better rate of recycle is achieved when the basicity is controlled between 1.05 -1.12. The recycle rate for chromium is 86-96% and above 90% for nickel. There are also 18.1% of chromium and 5.1% of nickel been recycled from the high temperature liquefied stainless steel by using ESRF. The recycled chromium and nickel can be reused as the material in the form of cast iron for steel mill after casting process. The secondary dust collected from the furnace gas contains 32% of zinc oxide, but the content is not high enough for zinc refining from smelter. It needs to be put back into the ESRF for refining and enrichment. The slag produced from ESRF has been tested and confirmed that the metals leached from the slag meet the TCLP standards. It can be used as building materials, roadbed material, and mixed in cement. This study shows the advantages of recovering chromium and nickel in stainless steel dust by electric smelting reduction process.
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