The surface behavior of mercury on iron systems
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NTRODUCTION
MERCURY is a toxic element and has no biological function in nature. For this reason, several laws and guidelines have been adopted per the United Nations to control the discharge of mercury into the environment.[1] Today mercury can be found in devices such as electric switches in cars, batteries, cameras, and metallic scrap and from industries that use mercury in their production. The global mercury production did, however, fall 37 pct between 1990 and 1996, with a larger drop in the United States and Western Europe,[2] as a result of a world-wide effort to phase out mercury use and reduce existing stockpiles.[3] Because mercury is used in electrical applications, mercury tends to follow metal scrap during recycling. In electric arc furnace (EAF) steelmaking, this metallic scrap is melted and any mercury present will vaporize into the atmosphere because of its significantly high vapor pressure. It is also believed that mercury may adsorb on the surface of iron and steel scrap, thereby entering the production line with the raw material. However, previous investigations have shown that it is difficult to correlate mercury emissions with a specific raw material.[4] Additionally, the temperature dependence of atmospheric mercury deposition is not well understood. Another possibility for mercury contamination in the EAF is through the addition of other raw materials such as dolomite.[5] Gas and coal are finding increased use in the production of stainless steel, and it has been shown that even these raw materials contain significant amounts of mercury.[6] Nevertheless, major substances such as lime, fuel, and scrap are listed as having only trace amounts of mercury. These do not account for the elevated levels of mercury found in residues, slag, and exhaust fumes. However, when mercury leaves the steel and becomes concentrated in the waste, amounts present in the raw materials may become significant. Currently, little is known about how and in which forms mercury significantly enters the EAF, and also how mercury behaves during melting operations. D. ROSEBOROUGH, Doctoral Student, R.E. AUNE, Associate Professor, and S. SEETHARAMAN, Professor, are with the Department of Materials Science and Engineering, Royal Institute of Technology, 10044 ¨ THELID, Stockholm, Sweden. Contact e-mail: [email protected] M. GO Associate Professor, is with the Materials and Semiconductor Physics Department, Royal Institute of Technology, 16440 Kista, Sweden. Manuscript submitted November 2, 2005. METALLURGICAL AND MATERIALS TRANSACTIONS B
The present article aims to investigate the factors affecting the mechanism of mercury adsorption on the surface of polycrystalline iron, as well as the effects of chlorine and oxygen modifications on the adsorption mechanism and mercury bonding. Oxygen was selected as a coadsorbate because of its presence on iron surfaces in nature. Chlorine was chosen because of its known reactivity with mercury in the atmosphere.[7,8] The iron substrate is to be studied systematically at low temperatures (LTs) to
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