Kinetics of adsorption of mercuric chloride vapors on sulfur impregnated activated carbon

Injection of activated carbon impregnated with sulfur or iodine compounds into the flue gases is a promising technique to control mercuric chloride emissions from the combustion of municipal solid wastes. In the present paper the attention is focused on the adsorption of HgCl2 on activated carbon and on the same carbon impregnated with Na2S. The study was performed at laboratory scale, varying the HgCl2 concentration in the inlet stream to the bed in the range of 1-4 mg/m3 and keeping the bed temperature at 150°C. Three different adsorbents were used, i.e. raw commercially available activated carbon and two impregnated activated carbons (7.8% w/w and 18.7% w/w of Na2S). The experimental runs led to the determination of the breakthrough curves for the fixed bed and of the adsorption isotherms for the three materials at 150°C. The results showed that, while "raw" activated carbon is capable of removing mercuric compounds, the impregnation process definitely enhances its adsorption capacity, probably due to a stronger interaction between sulfur and mercury. The adsorption isotherms, which have a characteristic "Langmuir" shape, were used to evaluate the Langmuir parameters for the three different materials under investigation. Eventually the Langmuir parameters were used to solve the adsorption equations for the bed, leading to the individuation of the kinetic constants of the process.