Collection and analysis of gas phase mercury from a tailings pile

Abstract

Air samples (150 liters) were taken form the Murray Brook tailings pile located 60 km west of Bathurst, New Brunswick in order to determine if "unnatural" amounts of gas phase mercury (Hg) were being volatized from the pile. In order to collect and analyze these samples it was necessary to design and construct a sampling system as well as an analytical method that was suitable for our analyses. The sampling system consisted of denuder based air-suction system and the analytical analysis was done using cold-vapor atomic absorption (A. AS). Air from within and at the surface of the tailings was drawn through the denuder, which contained gold-plated sand, allowing any mercury present in the air to be absorbed by the gold. The denuder is heated, releasing any trapped mercury, and the mercury vapor is forced into an optical cell within the A.AS. to be analyzed. The results from the analyses obtained are compared to a developed standard curve in order to determine the quantity of mercury present in the samples. The samples collected from the Murray Brook tailings pile were analyzed for their mercury content, however the results obtained were far beyond the analytical range anticipated. This problem could be easily remedied in the future by sampling a much smaller volume of air. By sampling a smaller volume of air, their would be less mercury trapped within the denuder and therefore less mercury to be analyzed. This would allow the results to be within the analytical range of the A. AS. and also within range of the standard curve developed for this situation. This project was, however, successful in regards to the completion of both a sampling system and an analytical method as well as the development of a reproducible standard curve. This project was undertaken knowing that there was little published information on the subject and that this was the first attempt at such a project.