Study On Atmospheric Mercury Emissions From Typical Zinc Smelting Process

As a global pollutant mercury has caused significant effects on public health. Mercury pollution has become one of the most important global environmental issues. China is the largest anthropogenic mercury emission source in the world. Zinc smelting is one of the most important sources in China. However, mercury emission estimates for zinc smelters suffer from high uncertainty due to the lack of local emission factors for typical zinc smelting process. To further understand the mercury pollution and set up effective mercury emission control strategy in China, it is essential to study the atmospheric mercury emission characteristics of typical smelting processes and update the mercury emission inventory.In this study, field tests were conducted in two typical zinc smelters to measure the mercury removal efficiencies of air pollution control devices （APCDs）, atmospheric mercury emission factors, and chemical speciation profiles of mercury emissions. Literatures were systematically searched and zinc concentrate samples were collected in 16 provinces to obtain the spatial distributions of mercury concentration in zinc concentrates. With the consumption of zinc concentrates, mercury concentration in zinc concentrate, and the mercury removal efficiencies of APCDs, the mercury emission inventory of zinc smelters in China were updated and its uncertainty was analyzed. The mercury pollution control strategy for zinc smelters was also discussed.According to the field tests, the mercury removal efficiencies of flue gas cleaning tower, electrostatic demister, mercury reclaim tower and acid plant were respectively 42.0%, 31.6%, 88.0% and 98.5%. In the atmospheric mercury emissions, Hg⁰, Hg²⁺ and Hgp respectively accounted for 65%, 30% and 5%. Mercury concentrations of zinc concentrates in China had large variations, ranging from 0.07 g·t^-1 to 2.53×10³ g·t^-1; the arithmetic and geometric mean value were 159 g·t^-1 and 9.45 g·t^-1 respectively. According to the zinc production in 2006, the weighted mean of mercury concentration in China was 82.9 g·t^-1. In 2006, the atmospheric mercury emission from zinc smelting in China was 49.1 t, of which 78% was Hg⁰, 17% was Hg²⁺ and 5% was Hg^p. Analysis of mercury reduction potential indicated that integration of small scale zinc smelters and installation of acid plants may reduce 86% of atmospheric mercury emission from zinc smelters in China.