Mercury emissions from non-ferrous metal industries are a major environmental concern. Because of the large differences in mercury emission factors depending on the kind of metal ore and the details of the smelting process, detailed information on the behavior of mercury is required to control the mercury emissions. In this study, we investigated removal of mercury using processes involving sulfuric acid during zinc production in an imperial smelting process (ISP) plant in Japan. The total mercury concentration in the flue gases in the chimneystack was found to be in the range 1.7-6.1 mu g/N m(3). Metallic mercury was the predominant mercury species in the flue gases in the chimneystack. The distribution ofmercury in this plant was as follows: 89.1 % in the sludge, 9.29 % in the fly ash, 1.51 % in the sulfuric acid product, and 0.059 % in the flue gases. The overall efficiency of mercury removal by mass was therefore 99.92 %. The overall emission factor was 0.0088 g per ton of zinc produced, which is lower than that reported for other zinc smelting plants. Consequently, the combination of double gas coolers and double wet electrostatic precipitators described in this study is comparable to advanced Boliden-Norzink technology for mercury removal.