Formation Mechanisms and Leachability of Hexavalent Chromium in Cr 2 O 3 -Containing Refractory Castables of Electric Ar
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DUCTION
THERE has been growing attention to health risks for humans and animals because of the existence of heavy metals such as As(V), Cr(VI) and Mo(VI) in the environment. Among the various heavy metals, solid waste containing Cr(VI) is one of the most common toxic pollutants generated by the metallurgical, refractory, chemical, electroplating, leather tanning, pigment, welding and glass industries.[1] In nature Cr generally exists in two most common oxidation states, Cr(III) and Cr(VI) where the latter is 500 times more toxic, mutagenic and
YINGJIANG WU, SHENGQIANG SONG, and ZHENGLIANG XUE are with The State Key Laboratory of Refractories and Metallurgy, Wuhan University of Science and Technology, Wuhan, 430081, China, with the Key Laboratory for Ferrous Metallurgy and Resources Utilization of Ministry of Education, Wuhan University of Science and Technology, Wuhan, 430081, China, and also with the Hubei Provincial Engineering Technology Research Center of Metallurgical Secondary Resources, Wuhan, 430081, China. Contact e-mail: [email protected] MITHUN NATH is with The State Key Laboratory of Refractories and Metallurgy, Wuhan University of Science and Technology. Manuscript submitted May 18, 2018.
METALLURGICAL AND MATERIALS TRANSACTIONS B
carcinogenic than the former.[2,3] Cr(VI) is highly soluble in water,[4,5] resulting in a serious threat to human health and the environment. Solid waste containing Cr(VI) has been classified as one of the most hazardous solid wastes by the US Environmental Protection Agency,[6] as well as the Chinese Environment Protection Bureau.[7] The European Directive 2003/53/EC restricted the use of cement and cement products that contain more than 2 mg/ kg of soluble Cr(VI) in a hydrated state.[8] The maximum permissible limits of Cr(VI) for discharge into potable water, inland surface water and industrial waste water are 0.05, 0.1 and 0.25 mg/L, respectively.[9] Chromium (III) oxide (Cr2O3) is known to have excellent corrosion resistance and thermal shock due to low solubility in molten slags or salts. To improve the properties, it may be present either as a specific addition or as an impurity component in refractory castables. However, Cr2O3 can transform into higher-valent Cr(VI)-compounds at higher temperature under an oxidizing atmosphere and even more readily in the presence of alkali metal or alkaline earth metal oxides, such as CaO, Na2O, and K2O.[10–15] In past decades, chromium-free refractories have been developed rapidly and successfully applied. However there has been no comparison of Cr2O3 in terms of slag corrosion resistance and thus Cr-containing refractories are still being used. One such application area is
Electric Arc Furnace (EAF) cover. The global share of EAF’s output in steel production is increasing every year.[16] In 2016, world steel production was 1628 MT, of which 25.7 pct was produced by EAF.[17] In China, approximately 80 pct of EAF covers contain Cr2O3. The temperature inside the furnace reached 1600 C as a result of electric arc and consequent m
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