Surface chemistry of mercury on zinc and copper
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NTRODUCTION
MERCURY is a toxic element, damaging not only to humans, but also to the environment. As a result, international regulations are now being implemented to phase out its use in products and processes.[1] Dealing with mercury emissions from industrial sources has also become an important problem. Emissions levels are now being monitored more closely and, in some cases, companies have been forced to reduce their mercury emission levels.[2] For steel plants fed by scrap metal, viz. electric arc furnace (EAF) steel plants, mercury emissions are particularly hard to control and predict. Because mercury can be found in devices such as electric switches in cars and batteries, scrap metal must be extremely well sorted to remove the sources before the metal is melted down. It is also believed that mercury may adsorb on the surface of zinc (Zn) present on the surface of the galvanized automobile plates in the scrap and copper (Cu) stored at subzero temperatures, thereby entering the production line with the raw material.[3] As the scrap is fed into the EAF, mercury is flashed off in the furnace because of its high vapor pressure compared to other metals. These discharges are partially collected in the emissions-control systems. Previous investigations have been made to correlate mercury emissions with a specific raw material, but have shown that this correlation is difficult to accomplish.[3] Specific raw materials, such as dolomite, are known to contribute to mercury emissions in EAF steelmaking.[4] Gas and coal are finding increased use in the production of stainless steel, and it has been shown that even these raw materials contain small amounts of mercury.[5] However, the trace amounts of mercury that these materials contribute are not believed to account for the elevated levels of mercury found in residues, slag, and exhaust fumes. Currently, D. ROSEBOROUGH, Doctoral Student, and S. SEETHARAMAN, Professor, are with the Department of Materials Science and Engineering, Royal Institute of Technology, 10044 Stockholm, Sweden. Contact ¨ THELID, Associate Professor, and e-mail: [email protected] M. GO P. PALMGREN, Doctoral Student, are with the Materials and Semiconductor Physics Department, Royal Institute of Technology, 16440 Kista, Sweden. Manuscript submitted November 23, 2005. METALLURGICAL AND MATERIALS TRANSACTIONS B
it is not well understood how mercury enters the EAF and which forms are the most significant. With the rise of galvanized steel products since the 1980s,[6] more and more Zn has been entering the EAF with the steel scrap. Over the same time interval, mercury emissions have been noted to be increasing.[7] This may, in part, be due to more diligent mercury emissions measurements, but it is also based on a real increase in mercury emissions. The relationship between increased galvanized metals in the scrap and the increase in mercury emissions has, as yet, not been firmly established. The motivation for studying mercury adsorption at different temperatures and surface conditions, therefore, stems from the
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