Adsorption of elemental mercury vapor by impregnated activated carbon from a commercial respirator cartridge

Abstract

In order to protect workers from the harmful effects of mercury vapor, adsorption technology using impregnated activated carbon is currently in use in respirator cartridges to capture mercury vapor in breathing air. Adsorption onto the activated carbon can be improved through the modification of the carbon surface by impregnation with certain reagents that enhance the bonding of mercury either physically or chemically. The first objective of this study was to characterize the chemisorption behavior of a commercial adsorbent (3M-6009) by measuring the mercury breakthrough using a bench-top apparatus. The second objective was to develop a kinetic model describing the breakthrough behavior. Dynamic breakthrough concentrations were measured using a fixed bed to study the effects of the following adsorption parameters at room temperature: air flow-rate, adsorbent amount, inlet mercury concentration, and bed diameter. A model was developed in which, the rate of irreversible chemisorption was proportional to the concentration of mercury in the airflow, and the concentration of active sites of the surface of the carbon. A model incorporating two different types of the active sites was applied in an effort to differentiate the high initial adsorption rate mediated by readily accessible open sites from the lower adsorption rate mediated by the availability of hindered sites within micro-pores. The model developed herein was superior to a traditional isotherm model for describing the chemisorption behavior of impregnated activated carbon.