Reduction of Sn-Bearing Iron Concentrate with Mixed H 2 /CO Gas for Preparation of Sn-Enriched Direct Reduced Iron
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INTRODUCTION
THE stainless steel industry has experienced rapid development, which has resulted in a robust demand for iron ore, steel scrap, and alloying elements (Ni, Cr, Mo, etc.).[1] Generally, tin is considered as a kind of harmful element in steel products. Its drawbacks include hot shortness and temper brittlement, as well as the fact that cracks and fractures occur if the tin content exceeds the limits (Sn < 0.05 pct).[2] The Sn-bearing iron ore is intractable and abundantly reserved in China, Russia, Indonesia, etc. However, this kind of iron ore has not been efficiently used because tin would exert an adverse effect on the ferrous metallurgical processes and on the properties of conventional steel products.[3] Up to now, much effort has been expended to develop more economical and effective ways to recover iron and other valuable elements from Sn-bearing iron ore. Traditional methods primarily focus on separating tin from iron to decrease the Sn content.[3,4] For example, ZHIXIONG YOU is with the School of Minerals Processing & Bioengineering, Central South University, Changsha 410083, Hunan, China, and also with the RM 205, Biology Building, Central South University, Changsha 410083, Hunan, China. GUANGHUI LI is with the School of Minerals Processing & Bioengineering, Central South University, and also with the RM 253, Peace Building, Central South University, Changsha 410083, Hunan, China. Contact e-mail: [email protected] PEIDAN WEN, ZHIWEI PENG, YUANBO ZHANG, and TAO JIANG are with the School of Minerals Processing & Bioengineering, Central South University. Manuscript submitted October 6, 2016. METALLURGICAL AND MATERIALS TRANSACTIONS B
combined physical separation processes are efficient to increase iron grade, while excessive Sn is still left because cassiterite is complexly embedded in magnetite.[5] Selective sulfurization or chlorination roasting processes are effective to separate tin from iron ore, but issues of environmental pollution and equipment corrosion are difficult to avoid.[6–8] Tin is also capable of being removed by conventional coal-based or microwave-assisted carbothermal reduction, in which a wustite pellet was prepared for ironmaking.[4,9,10] Although metallic pellet [direct reduced iron (DRI)] with low Sn content can be prepared via CO reduction, the volatilization of Sn and metallization reduction of iron must be carried out in two separate steps. In addition, the reduction atmosphere for volatilizing SnO should be strictly controlled to keep the residual Sn content below 0.05 pct, because tin oxides are easily over-reduced to metallic tin.[11,12] In recent years, Sn-bearing stainless steel, successfully developed in China, Japan, etc., has proven to have excellent corrosion resistance and machinability.[13–15] The addition of Cr and Ni can be markedly reduced in the Sn-bearing stainless steel after adding a certain amount of Sn. With respect to the Sn-bearing stainless steel of NSSCFW2 (0.3 pct Sn), developed by Nippon Steel & Sumitomo Metal Corporation (NSSC, Tokyo, Japan), about 4
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