Characteristics and settling behaviour of particles from blast furnace flue gas washing. (1st May 2016)

• Record Type: Journal Article
• Authors: Kiventerä, Jenni; Leiviskä, Tiina; Keski-Ruismäki, Kirsi; Tanskanen, Juha
• Is Part Of: Journal of environmental management. Volume 172(2016)
• Page Start: 162
• Page End: 170
• Publication Date: 2016-05-01
• Subjects: Scrubber wash water -- Sludge -- Size fractionation -- Settling -- Flocculation; Environmental policy -- Periodicals; Environmental management -- Periodicals; Environment -- Periodicals; Ecology -- Periodicals; 363.705
• DOI: 10.1016/j.jenvman.2016.02.037
• Languages: English
• ISSNs: 0301-4797

Abstract

Abstract: A lot of particles from iron-making are removed with blast furnace off-gas and routed to the gas cleaning system. As water is used for cleaning the gas, the produced wash water contains a large amount of particles such as valuable Fe and C. However, the presence of zinc prevents recycling. In addition, the high amount of calcium results in uncontrolled scaling. Therefore, the properties of the wash water from scrubber and sludge, from the Finnish metal industry (SSAB Raahe), were evaluated in this study. Size fractionation of wash water revealed that Fe, Zn, Al, Mn, V, Cr and Cd appeared mainly in the larger fractions (>1.2 μm) and Na, Mg, Si, Ni, K, Cu and As appeared mainly in the smaller fractions (<1.2 μm) or in dissolved form. Calcium was found both in the larger fractions and dissolved (∼60 mg/L). Most of the particles in wash water were included in the 1.2–10 μm particle size and were settled effectively. However, a clear benefit was observed when using a chemical to enhance particle settling. In comparison to 2.5 h of settling without chemical, the turbidity was further decreased by about 94%, iron 85% and zinc 50%. Coagulation-flocculation experiments indicated that both low and high molecular weight cationic polymers could provide excellent purification results in terms of turbidity. Calcium should be removed by other methods. The particles in sludge were mostly in the 2–4 μm or 10–20 μm fractions. Further sludge settling resulted in high solids removal. Graphical abstract: Highlights: Wash water and sludge from a blast furnace flue gas cleaning system were analysed. Most of the particles in the wash water were found in the particle size 1.2–10 μm. Zinc appeared in the same size fractions as iron. Both the cationic flocculant and cationic coagulants performed well in wash water. Sludge settled well without the addition of chemical.