A new approach to mercury speciation in solids using a thermal desorption technique

• A new device based on thermal desorption allows the identification of Hg species.
• Hg species in carbonaceous samples are identified without any interference from the matrix.
• Hg species in low rank coals are associated to organic matter and/or pyritic sulphur.
• Hg species in anthracites are mainly associated to sulphur.
• The new method is a useful tool for understanding the Hg-activated carbon mechanism.

Identification of the chemical form of mercury in coals and during the entire combustion process is essential for successfully controlling mercury emissions. However, the speciation of mercury in coal and, in general, in carbonaceous samples has so far proved elusive because of the limitations of current analytical techniques as a consequence of the detection limits of the equipment or interferences originating from the matrix. In this work a new device based on temperature programmed desorption (HgTPD) has been developed to identify mercury species in carbonaceous materials. The samples studied were coals of different rank obtained from around the world and activated carbons that had previously been used as mercury sorbents in simulated coal combustion atmospheres. The mercury species present in both types of sample were identified without any interference from the matrix. This achievement is extremely important as it will contribute to a better understanding of (i) the behavior of mercury species in coal utilization processes and (ii) the retention mechanisms and subsequent stability of the mercury species captured by carbon sorbents.

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