Thermo-desorption: A valid tool for mercury speciation in soils and sediments?

Abstract

Mercury (Hg) speciation by thermo-desorption is considered an alternative to laborious sequential chemical procedures; hence its popularity has increased in the last years. In this work, steps were taken to improve the information obtained by Hg speciation through thermo-desorption, specifically to improve peak resolution and increase the number of species that can be identified. The thermo-desorption behavior of Hg bound to iron oxides was characterized, as well as a new Hg-humic acid synthetic standard material. In contrast to previous studies, the peak corresponding to the Hg fraction associated with humic acids was clearly separated from the mineral fraction, and identified in some natural samples. With increasing temperature, Hg species are released in the following order: HgCl 2 = Hg associated with Fe 2 O 3 b Hg associated with humic acids b HgS b HgO, with an overlap of HgCl 2 and Hg associated with iron oxides. An evaluation of the effects of sample pre-treatment and storage on Hg speciation was also performed. It was found that sieving to b2 mm improved the sample homogeneity. The importance of fast sample analysis was highlighted, given that after 10 days of storage at room temperature, volatile Hg 0 could no longer be identified in the sample. The suitability of thermo-desorption for mercury speciation in soils and sediments is discussed.

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

“…However, it is still difficult to identify the mode of occurrence 102 of mercury in all types of solids. X-ray adsorption fine structure 103 spectroscopy (EXAFS) [13,14], sequential extraction (SE) [15,16] 104 and temperature programmed desorption (HgTPD) [17][18][19][20][21][22] The new furnace also contains two temperature controllers that 175 allow the heating ramp and the temperature in the zone between Earth's crust. In addition, mercury is also present as HgSe in bitu-247 minous coals.…”

Temperature programmed desorption as a tool for the identification of mercury fate in wet-desulphurization systems

“…One of the most promising of these methods is based on the selective thermal desorption of mercury species from the solid sample, referred to in this work as HgTPD. This method has already been employed to identify the mercury composition of soils, sediments, airborne particulate matter and FGD gypsum among others [17][18][19][20][21]. Nevertheless, it still needs to be validated and the scientific community has yet to demonstrate that the method is reproducible for any solid matrix.…”

Overview and challenges of mercury fractionation and speciation in soils

“…According to Han et al [32], this fraction encompasses Hg 0 , some (unspecified) mercury complexes and minor fraction of Hg2Cl2. However, the presence of the first species is questionable, since, due to its high volatility, Hg 0 is easily lost after the vigorous treatment involved in extraction of mobile and semi-mobile fractions [23]. The application of this extraction scheme allowed inferences to be drawn on the influence of soil properties in mercury fractionation in contaminated areas and has proven to be useful in distinguishing between anthropogenic and geogenic sources [27,64].…”

“…Consequently, research dedicated to mercury speciation/fractionation has gained attention in recent years [15][16][17][18][19][20][21][22][23][24][25][26][27][28][29].…”

“…Several protocols can be found in the literature regarding mercury speciation and fractionation, as reviewed by Issaro et al [29], and three main lines can be identified in mercury speciation/fractionation methodologies: 1) chemical extraction [26,27,[29][30][31][32][33][34]; 2) thermodesorption [23,26,35]; and 3) X-ray absorption techniques [36,37]. X-ray techniques are expensive and require samples with mercury concentration greater than 100 mg kg −1 [37], which strongly limits their applicability in environmental samples, therefore they are not further discussed.…”