|Abstract: ||國內電弧爐煉鋼製程之集塵灰產生量每年約18 ~ 22萬噸，其中不銹鋼集塵灰約6萬公噸。電弧爐煉鋼集塵灰經毒性溶出試驗證實，其鉛、鎘、六價鉻等重金屬均超出規定限值，因此環保署將電弧爐煉鋼集塵灰認定為製程有害事業廢棄物，若未妥善處理，將對環境、生物及人體健康造成危害，因此必須以再利用方式回收處理，將其無害化及資源化。目前國內將電弧爐煉鋼集塵灰資源化均是以處理碳鋼集塵灰，並回收其中之氧化鋅為主要目的。對於富含鐵、鉻、鎳等有價金屬之不銹鋼集塵灰，大部分是以固化掩埋方式處理，並無有效將其資源化的處理方式，僅能將有害的集塵灰暫時安定化，掩埋在特定之掩埋場中，無法將其中之有價金屬資源化，且需要大面積土地供其最終掩埋，對地狹人稠的台灣而言，無疑是重大的環境負荷。|
本研究利用高溫熔融還原法（Electric Smelting Reduction Furnace, ESRF）處理國內三家不銹鋼煉鋼廠製程中產生的集塵灰。先行檢測不銹鋼集塵灰之組成分，分析結果得知不銹鋼集塵灰中，具有資源化價值之鐵、鉻及鎳，含量分別為21 ~ 35 %、7.5 ~ 8.7 %及0.8 ~ 2.3 %，可資源化成分約佔30 ~ 40 %之間，實屬都市礦脈之一種。以高溫熔融還原法處理不銹鋼集塵灰之流程是先將集塵灰均勻混合後，再與副原料混鍊造粒，投入1550 ℃之高溫熔融還原爐中，利用焦炭等還原劑將集塵灰中之金屬氧化物予以還原，其中高沸點之金屬鐵、鉻及鎳等，可溶入鋼液中而回收。本研究亦經由控制不同的鹽基度，探討鹽基度對於鉻、鎳回收至銑鐵中之回收率的影響，研究發現當鹽基度控制在1.05 ~ 1.12時，可得到較佳之回收率，鉻回收率在86 ~ 96 %之間，鎳回收率可達90 %以上。而不銹鋼集塵灰中之鐵、鉻、鎳等金屬經高溫熔融後可以鋼液型態回收，經澆鑄成為銑鐵，其中鉻及鎳含量分別為18.1 %及5.1 %，可供不銹鋼煉鋼廠作為原料使用。由爐氣中所收集之二次灰富含氧化鋅，含量約32 %，但仍不足以供煉鋅廠提煉，需再次投入高溫熔融還原爐進一步富集。熔融處理時所產生的爐渣經毒性溶出試驗分析，均符合環保法規標準，可作為營建材料、路基材料或與水泥混合使用。本研究結果顯示，以高溫熔融還原法回收不銹鋼集塵灰中鉻與鎳，不論是在經濟、環境及社會層面考量，均具有正面之效益。;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.