Original paper

Determination of Hg binding forms in contaminated soils and sediments: state of the art and a case study approaching abandoned mercury mines from Mt. Amiata (Siena, Italy)

Malferrari, Daniele; Brigatti, Maria Franca; Elmi, Chiara; Laurora, Angela

Abstract

This paper, after an introduction about the state of the art in the methods for the evaluation of Hg chemical speciation, focuses on Hg polluted soils and sediments from Siele mining area (Piancastagnaio, Siena, Italy). In particular, the mineralogical composition was evaluated via X-ray powder diffraction, total Hg was determined via inductively coupled plasma optical emission spectroscopy on acid digested samples, and Hg binding forms were investigated both via sequential selective extraction and pyrolytic extraction. Solutions obtained via sequential selective extraction were checked for Hg content using inductively coupled plasma optical emission spectroscopy, whereas to carry out pyrolytic extraction a thermogravimetric analyser coupled with an evolved gas mass spectrometer was used. To our knowledge, this last method was never used for this purpose on natural samples. Experimental results enhance that: i) Hg detection via thermal analyses can qualitatively distinguish among different Hg compounds. ii) The temperature of Hg thermal release is affected by both the sample matrix and the Hg bond type. iii) Thermal analyses fail in the attempt of a quantitative determination of the evolved species; this goal is better achieved via the selective chemical leaching. iv) Most of the Hg is related to HgS-like bonds, thus pointing to the presence of very stable Hg compounds. v) Only in some samples we found also organo-complexed Hg-like compounds and, in a limited amount, hydrosoluble Hg and/or Hg species soluble in weakly acid environment. vi) No correlation between sampling point and both total Hg and/or Hg speciation was observed.

Keywords

cinnabarevolved gas mass spectrometrymercurymonte amiatapyrolytic extractionsequential selective extractionsiele minethermal analyses