Speciation and precipitation of heavy metals in high-metal and high-acid mine waters from the Iberian Pyrite Belt (Portugal)

Abstract

Acid mine waters (AMW) collected during high- and low-flow water conditions from the Lousal, Aljustrel, and São Domingos mining areas (Iberian Pyrite Belt) were physicochemically analyzed. Speciation calculation using PHREEQC code confirms the predominance of Me and Me-SO species in AMW samples. Higher concentration of sulfate species (Me-SO) than free ion species (Me, i.e., Al, Fe, and Pb) were found, whereas opposite behavior is verified for Mg, Cu, and Zn. A high mobility of Zn than Cu and Pb was identified. The sulfate species distribution shows that Fe-SO, SO, HSO, Al-SO, MgSO, and CaSO are the dominant species, in agreement with the simple and mixed metal sulfates and oxy-hydroxysulphates precipitated from AMW. The saturation indices (SI) of melanterite and epsomite show a positive correlation with Cu and Zn concentrations in AMW, which are frequently retained in simple metal sulfates. Lead is well correlated with jarosite and alunite (at least in very acid conditions) than with simple metal sulfates. The Pb for K substitution in jarosite occurs as increasing Pb concentration in solution. Lead mobility is also controlled by anglesite precipitation (a fairly insoluble sulfate), where a positive correlation was ascertained when the SI approaches equilibrium. The zeta potential of AMW decreased as pH increased due to colloidal particles aggregation, where water species change from SO to OH species during acid to alkaline conditions, respectively. The AMW samples were supersaturated in schwertmannite and goethite, confirmed by the Me-SO, Me-Fe-O-OH, or Me-S-O-Fe-O complexes identified by attenuated total reflectance infrared spectroscopy (ATR-IR). The ATR-IR spectrum of an AMW sample with pH 3.5 (sample L1) shows well-defined vibration plans attributed to SO tetrahedron bonded with Fe-(oxy)hydroxides and the Me sorbed by either SO or Fe-(oxy)hydroxides. For samples with lower pH values (pH ~ 2.5-samples SD1 and SD4), the vibration plans attributed to Me sorption are not evidenced, indicating its release in solution. The sorption of heavy metals on the first precipitated simple metal sulfates was ascertained by scanning electron microscopy coupled with X-ray spectrometry (SEM-EDX), where X-ray maps of Cu and Zn confirm a distribution of both metals in the melanterite structure.

Environmental Impact Variability of Copper Tailing Dumps in Fushe Arrez (Northern Albania): The Role of Pyrite Separation during Flotation

“…In Figure 6B results were plotted in a Ficklin diagram together with those of waters from Reps tailings, deriving from the nearby dressing plant that enriched ore from several copper mines located within the EOB, and those from the Iberian pyrite belt. This last one is a large VMS copper district in southern Spain and Portugal that was widely studied for its AMD processes [35][36][37][38][39][40]. Background waters conditions are similar in all three areas, with a slightly higher metal content at Reps, probably due to the presence of other mines upstream of the Reps dumps.…”

Mineralogy and Geochemistry (HFSE and REE) of the Present-Day Acid-Sulfate Types Alteration from the Active Hydrothermal System of Furnas Volcano, São Miguel Island, The Azores Archipelago

“…Jarosite formation is limited by the availability of K or Na deriving from feldspar alteration in a more acidic micro-environment [71], being disseminated in the oxidation zone outer of fumarole and hot springs areas. Melanterite is one of the first simple sulfates precipitated in the high SO 4 2− concentration in extreme low pH, especially in acid mine drainage environments where it promotes the speciation of Me n+ with SO 4 2− [72,73]. The dehydration process of melanterite is accompanied by its dissolution, generating acid production upon dissolution and hydrolysis [74].…”

Assessment of the Environmental Impact of Acid Mine Drainage on Surface Water, Stream Sediments, and Macrophytes Using a Battery of Chemical and Ecotoxicological Indicators

“…The results reported in this study, and in other studies that have assessed the environmental impact in the Aljustrel mining area [2-4,9,22,23] can be used to evaluate the benefits of the remediation measures at the site, documenting the "ground zero" Several studies have documented these impacts in rivers and streams, in Aljustrel [3,9,[22][23][24], and also in other mines from the IPB, both in Portugal, for example, the Lousal mine, affecting the Corona stream [18,25,26], São Domingos, affecting the São Domingos stream, a tributary to the Chança river [10,27] and, in Spain, mainly in Tinto and Odiel river basins, affected by different mines, for example, Rio Tinto, Tharsis, and Sotiel-Coronado [15,17,21,[28][29][30][31][32][33], in the Oraque and Meca rivers (Odiel tributaries), affected by the Tharsis mine [33], also affecting the Chanza and Guadiamar rivers [32]. In fact, in specific hydrogeochemical conditions, the environments affected by AMD can be characterized by extreme conditions, for example, negative pH values [33], similar to those found in the Cobica River basin, affected by AMD-polluted waters coming from the Lagunazo mine and the Herrerias mine, where, in addition to the high concentrations of toxic elements, the mean pH value was negative (pH = −1.56) [34].…”

“…Considering Pb, its concentration in the surface water was only detectable at Site 1 and diminished at Sites 2 and 3 to non-detectable values, irrespective of the fact that the stream at those sites was still AMD affected. Durães et al [24] explained the low concentrations found for Pb in waters affected by AMD by its retention in Fe oxyhydroxides or sulphates, with a greater sorption capacity for Pb than for Cu and Zn in waters with low pH, an explanation that can be applied in this case.…”