Innovative Approaches to Remediate Waterways contaminated with Mercury in a Mining Area in the Iberian Pyritic Belt, SW Portugal

Abstract

Heavy metal pollution is the biggest environmental issue facing the mining industry worldwide. Whenever the target is metal ores, it is generally associated with acid mine drainage (AMD), a multi-factor pollution formed from complex chemical, physical, and biological interactions that takes place under ambient conditions in abandoned and active mines. In areas impacted by mining of metallic sulphides, mercury (Hg) is one of the most critical contaminants in the environment, due to its potential toxicity and the ease with which it leads to widespread contamination over a wide area. This is the case of mining areas in the Iberian Pyritic Belt (IPB), a well-known volcanogenic massive sulfide mining district of worldwide significance in southwest Europe, where many abandoned mines prevail, leaving behind large accumulations of oxidizing sulfide-bearing mine wastes, without suitable corrective measures. One of the most serious examples in Portugal is Caveira mine, where the occurrence of stable forms of Hg reported at the surface around the mine is responsible for generating Hg-rich fluxes of AMD that represent a potential focus related to water quality degradation. The main purpose of this study is to assess the present impact of Hg on local populations around Caveira mining area through (1) the assessment of the most potentially mobile and/or toxic fractions of Hg in the sediments of the aquatic systems in the surrounding area, and (2) based on the greater or lesser mobility of Hg, to test the effectiveness of different types of geomaterials in retaining Hg from the drainage water and which could also be used as cover materials in areas of sediments with a higher degree of contamination.