A Quantitative Method to Measure the Kinetics of Elemental Mercury Emissions From Black Shale (Nova Scotia, Canada)

A controlled chamber method using continuous gold trap atomic fluorescence spectroscopy (AFS) (Tekran 2537X) for the analysis of Hg(0) emissions from moderate mass rock samples was developed and tested. A series of black shale and other bedrock samples from Nova Scotia, Canada, were used to test the method and its reproducibility. Hg(0) emissions at 170°C were measured to quantify both free surficial Hg(0) and Hg(0) that had penetrated the rock structure. High volumes of chamber air (45 L) were sampled using 30 min collection times to achieve detectable elemental mercury (Hg(0)) emissions. We found higher percentage masses of Hg(0) were released (1.1%-4.1% of total Hg mass present) in black shale samples as compared to granite and basalt samples from the same region (0.0%-0.3% released) over 350 h of continuous analysis time. The pseudo first order emission rate constants ranged from 0.015-0.245 h^-1 (mean 0.063 h^-1, standard deviation (SD) 0.102) for the black shale samples analyzed and was 0.004 h^-1 for the granite sample. The 24-h zero-order emission rate constants ranged between 0.41 and 3.54 ng h^-1 (mean 1.4 ng h^-1, SD 1.3) for the black shale samples analyzed and were ~ 0.01 ng h^-1 for the granite and basalt samples. This technique has useful implications for examining rock properties and Hg(0) emission rates.