Antimony weathering products in mine wastes: A case study in Pezinok (Slovakia)

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Antimony is classified as a priority pollutant; it is known to be toxic and probably also carcinogenic. Nevertheless, little attention is paid to this pollutant in comparison with its geochemical cousin, the element arsenic. At abandoned or active mining sites, the primary Sb minerals (mostly stibnite, Sb2S3) weather to form Sb oxides, Sb-rich hydrous ferric oxide, or to release Sb into the environment. Here I propose a meticulous study of the mineral products of this process by a combination of complementary bulk and micro-analytical techniques. The samples for our study come from two waste impoundments near an abandoned Sb deposit Pezinok in Slovakia. The samples were taken from several boreholes, representing the entire weathering profile of the impoundments, and investigated in a great detail with respect to the speciation and migration of As. In the proposed work, we will determine the bulk mineralogy of the borehole samples by X-ray diffraction and optical microscopy. Selected grains will be then analyzed by an electron microprobe for their chemical composition, micro-diffraction for their crystal structure, and micro-X-ray absorption (at the Sb L,,, edge) for the Sb oxidation state. Suitable bulk samples will also be studied; these are hydrous ferric oxide materials with up to 28.3 wt% As2O5 and 2.7 wt% Sb. We will perform bulk X-ray absorption (XAS) experiments at the Sb K edge to determine the local environment of Sb in these samples. Of particular interest is the association or competition of As and Sb for adsorption sites when they occur simultaneously in large amounts. To complement the XAS experiments and to improve the information on Sb speciation, we will also attempt to carry out bulk 121Sb Mössbauer experiments. In conclusion of the project, we will hold a complete data set on the chemical composition, crystal structure (or lack thereof) of the most important Sb weathering products and the chemical state of Sb within them. Such information is currently missing because the existing studies did not use all techniques simultaneously or they focused on the speciation of Sb from a geochemical point of view (e.g., by sequential extractions).