Abstract
Jarosites are widely used in the hydrometallurgical industry of zinc to eliminate iron and other impurities contained in the concentrates. However, these compounds can also incorporate elements of significant environmental concern such as Tl+, Hg2+, Pb2+, Cd2+, Cr(VI), and As(V). In this work, the characterization of a synthetic mercury jarosite and its thermal decomposition kinetics are reported. XRD and FTIR analyses confirm that a mercury jarosite—Hg0.40(H3O)0.2]Fe2.71(SO4)2.17(OH)4.79(H2O)0.44—was successfully synthesized. Four mass loss events were observed by thermogravimetric analysis at 290 °C, 365 °C, 543 °C, and 665 °C. The third event corresponds to mercury decomposition into mercury oxide, whilst the forth is related to the jarosite to hematite transformation determined by X-ray diffraction starting at around 600 °C. According to the kinetic parameters (activation energy and frequency factor) of the thermal decomposition process, the fourth stage required the highest energy (Ea = 234.7 kJ∙mol−1), which corresponds to elimination of sulfur and oxygen from the jarosite lattice. Results show that jarosite-type compounds have the capability to incorporate heavy metals into their structure, retaining them even at high temperatures. Therefore, they can be used as a remediation strategy for heavy metals, such as mercury and others elements of environmental concern.
Highlights
Mercury is widely known for its high toxicity; in recent years, its concentration levels have increased in several environments [1,2,3]
The synthesis of mercury jarosite was conducted according to the procedure reported by Ordoñez et al [39], in which 1 L of a solution containing 0.27 mol·L−1 Fe2 (SO4 )3 ·nH2 O and 0.58 mol·L−1
Thermogravimetric analyses show four weight losses: the first two attributed to adsorbed water and structural water, the third weight loss relates to attributed to adsorbed water and structural water, the third weight loss relates to transformation of mercury into different species and to desulfonization, and the fourth is associated transformation of mercury into different species and to desulfonization, and the fourth is associated with the sulfur loss due to the formation of different oxides
Summary
Mercury is widely known for its high toxicity; in recent years, its concentration levels have increased in several environments [1,2,3]. The importance of the formation and decomposition of jarosite-type compounds depends on its presence in the soils, sediments, and deposits where it is formed [27]. Jarosites have the capability to incorporate elements of environmental concern—such as Pb2+ , As(V), Cr(VI), Cd2+ , and even Hg2+ —into their structure. Dutrizac and Kaiman, 1976, were the first researchers to synthesize jarosite-type compounds with mercury, which was achieved by incorporation of 14.62 wt. 1981, synthesized jarosite-type compounds with mercury, they incorporated only. The thermal decomposition of jarosite-type compounds containing K+ , Na+ , Pb2+ , H3 O+ , and NH4 + was analyzed by Frost et al 2005, 2006 a, 2006 b [36,37,38]. The present work presents the thermal characterization and subsequent thermal decomposition kinetics of jarosite-type compounds containing mercury. The main objective was to investigate the high temperature behavior of this toxic element in order to propose its thermal decomposition stoichiometry
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