Application of three methods for determining mercury speciation in mine waste

Three methods, pyrolytic and chemical extractions (PCE), extended X-ray adsorption fine structure spectroscopy (EXAFS) and solid-phase-Hg-thermo-desorption (SPTD) were applied to determine mercury speciation in amended substrates and mine waste samples. Although these three methods determine Hg speciation by fundamentally different processes, comparison of the results are useful for validation of the three methods. PCE uses pyrolysis and weak leaches to determine relative percentages of volatile, ‘soluble’ and residual Hg in substrate. The results are operationally defined and specific species cannot be determined with this method. EXAFS is a nondestructive method which uses high energy synchrotron-sourced X-ray radiation to identify specific species based on scattering patterns. Least squares data analysis is done to link patterns to a database of model compounds. This method is most useful for identification of specific species, given that they are included in the model database. Identification of Hg 0 is difficult using EXAFS. SPTD identifies Hg species by incremental heating and comparison of thermal release patterns to a database of compounds. SPTD allows the identification of a more limited number of specific species than EXAFS, but is the best of the three methods for the identification of Hg 0 . Overlapping release patterns make the identification of species, such as HgS and some forms of matrix-bound Hg, difficult. Results of PCE analyses indicate that volatile and leachable forms of Hg in mine waste are low relative to the total Hg concentration. This was supported by EXAFS and SPTD analysis which identified HgS as the primary component of mine waste. In contrast, analysis of tailings from mills that utilized Hg to amalgamate Au and Ag from ores yielded conflicting results. The results of this study illustrate the importance of using multiple analytical methods for the evaluation of Hg in the substrate.