Evaluation of sequential and selective extraction methods for determination of mercury speciation and mobility in mine waste

Sequential and selective extraction procedures for determining Hg speciation in substrates were evaluated and applied to an extraction protocol to assess Hg mobility in samples of mine waste. Pyrolytic methods were applied to determine volatile phases; leaching with Cl-solutions was utilized to determine soluble or mobile species; and acid digestions were used to extract strongly bound Hg species and for total Hg analyses. Pyrolytic extractions at greater than 80 degreesC were found to significantly over estimate elemental Hg. The organic content of a substrate was found to confound sequential extraction results. Inorganic amendments such as iron Fe and vermiculite also influenced extraction results but not as strongly as organic matter. This study demonstrated that sequential and selective extractions for identification of specific Hg phases should be used with caution. Comparison of HF, aqua regia, and 3 H2SO4 : 7 HNO3 digestions revealed that aqua regia was as effective as the HF digestion for determining total Hg. The 3 H2SO4 : 7 HNO3 digestion was significantly less effective for determining total Hg on silicified samples. Analysis of Hg in mine waste indicated that introduced Hg and naturally occurring Hg minerals are relatively immobile in terms of the percent of leachable and volatile Hg verses the total Hg concentration. Extraction methods were found to overestimate Hg released from mine waste when compared to in situ measurements. (C) 2002 Elsevier Science Ltd. All rights reserved.