Novel Determination of Elemental Mercury in Silicate Rock by Thermal Desorption

Much importance has been given in the recent literature to the determination and speciation of mercury in contaminated mine waste and soil. Among mercury species, the concentration of elemental mercury is a key parameter for risk assessment. However, at present, a validated analytical method for the quantitation of Hg(0) in solid matrices does not exist. In the present study, the reliability of a thermal desorption technique in quantifying elemental mercury in Hg(0) amended silica glass, a reference shelf standard, and in a Hg(0)-bearing mineralized silicate rock, considered representative of mine tailings, has been addressed. Mercury release has been measured at variable temperature using a thermo-desorption method combined with a mercury vapor analyzer. The results allowed the peak temperature for the emission of free and matrix-bound Hg(0) components to be identified, suggesting that 100 degrees C represents a suitable temperature for Hg(0) isothermal release. Experiments with the shelf standard exposed to a specific sorbent keeping the temperature constant at 100 degrees C provided 90% and 98% Hg(0) recovery after 2 and 24 h, respectively. Experiments with the mineralized rock demonstrated that free elemental mercury was recovered after 6 h, while 60 h were required for the free and matrix bound Hg(0) release. The limits of detection and quantification of the method were 1.3 ng and 3.0 ng, respectively. This approach allows elemental mercury in solid matrices to be determined, allowing the quantification of Hg(0) in contaminated mine tailings and soil.