Mobilization of Ag, heavy metals and Eu from the waste deposit of the Las Herrerias mine (Almería, SE Spain)

Potentially harmful elements pollute soil and vegetation around the Atrevida mine (Tarragona, NE Spain)

Mining activity is one of the main sources to pollute soil, water and plants. An analysis of soil and plant samples around the Atrevida mining area in Catalonia (NE Spain) was preformed to determine potentially harmful elements (PHEs). Soil and plant samples were taken at eight locations around the mining area. The topsoil (0-15 cm) samples were analysed for physico-chemical properties by standard methods, by ICP-MS for Cd, Co, Cr, Cu, Fe, Ni, Pb and Zn, and were microwave-digested. Plant, root and shoot samples were digested separately, and heavy metals were analysed by AAS. Translocation factor (TF), biological concentration factor (BCF) and biological accumulation factor (BAF) were determined to assess the tolerance strategies developed by native species and to evaluate their potential for phytoremediation purposes. Soil pH was generally acid (5.48-6.72), with high soil organic matter (SOM) content and a sandy loamy or loamy texture. According to the agricultural soil values in southern Europe, our PHEs concentrations exceeded the toxicity thresholds. The highest root content of the most studied PHEs appeared in Thymus vulgaris L. and Festuca ovina L., while Biscutella laevigata L. accumulated more PHEs in shoots. The TF values were > 1 in B. laevigata L., but BAF obtained < 1, except Pb. B. laevigata L., and can be considered potentially useful for phytoremediation for having the capacity to restrict the accumulation of large PHEs amounts in roots and Pb translocation to shoots.

Fe-Rich Fossil Vents as Mars Analog Samples: Identification of Extinct Chimneys in Miocene Marine Sediments Using Raman Spectroscopy, X-Ray Diffraction, and Scanning Electron Microscopy-Energy Dispersive X-Ray Spectroscopy

On Earth, the circulation of Fe-rich fluids in hydrothermal environments leads to characteristic iron mineral deposits, reflecting the pH and redox chemical conditions of the hydrothermal system, and is often associated with chemotroph microorganisms capable of deriving energy from chemical gradients. On Mars, iron-rich hydrothermal sites are considered to be potentially important astrobiological targets for searching evidence of life during exploration missions, such as the Mars 2020 and the ExoMars 2022 missions. In this study, an extinct hydrothermal chimney from the Jaroso hydrothermal system (SE Spain), considered an interesting geodynamic and mineralogical terrestrial analog for Mars, was analyzed using Raman spectroscopy, X-ray diffraction, and scanning electron microscopy coupled with energy dispersive X-ray spectroscopy. The sample consists of a fossil vent in a Miocene shallow-marine sedimentary deposit composed of a marl substrate, an iron-rich chimney pipe, and a central space filled with backfilling deposits and vent condensates. The iron crust is particularly striking due to the combined presence of molecular and morphological indications of a microbial colonization, including mineral microstructures (e.g., stalks, filaments), iron oxyhydroxide phases (altered goethite, ferrihydrite), and organic signatures (carotenoids, organopolymers). The clear identification of pigments by resonance Raman spectroscopy and the preservation of organics in association with iron oxyhydroxides by Raman microimaging demonstrate that the iron crust was indeed colonized by microbial communities. These analyses confirm that Raman spectroscopy is a powerful tool for documenting the habitability of such historical hydrothermal environments. Finally, based on the results obtained, we propose that the ancient iron-rich hydrothermal pipes should be recognized as singular terrestrial Mars analog specimens to support the preparatory work for robotic in situ exploration missions to Mars, as well as during the subsequent interpretation of data returned by those missions.

Comparison of the effectiveness of biochar vs. magnesite amendments to immobilize metals and restore a polluted soil

Here we addressed the remediation of a soil severely contaminated by Cu, Cd, Pb and Zn. In this regard, we tested the capacity of magnesite and biochar, inorganic and organic soil amendments, respectively, to reduce metal availability and improve soil properties. To this end, 1-kg pots containing the polluted soil were amended with either magnesite or biochar. Metal availability and soil properties were then measured at days 15 and 75. Also, to evaluate the impact of the two treatments on plant growth, we conducted experimental trials with Brassica juncea L. and compost addition. Both amendments, but particularly magnesite, markedly decreased metal availability. Soil properties were also enhanced, as reflected by increases in the cation exchangeable capacity. However, plant growth was inhibited by magnesite amendment. This observation could be attributable to an increase in soil pH and cation exchange capacity as well as a high Mg concentration. In contrast, biochar increased biomass production but decreased the quantity of metals recovered when the plants are harvested. In conclusion, on the basis of our results, we propose magnesite as a suitable approach for stabilizing contaminated soils (or even spoil heaps) where revegetation is not a priority. In contrast, although biochar has a lower, but still significant, capacity to immobilize metals, it can be used to restore natural soil properties and thus favor plant growth.

Short-term experiment for the in situ stabilization of a polluted soil using mining and biomass waste

Mining and biomass waste were used to remediate a brownfield affected by As, Cd, Cu, Pb and Zn pollution in a pilot scale experiment, and a plant used for phytoremediation purposes was used as an indicator of possible toxicological effects. To carry out the experiments, plots in field conditions were treated with magnesite (mining waste), magnesite-sludge compost, and magnesite-biochar respectively, while untreated soil was used as a control. The plots were then irrigated and left for one week, after which seeds of the ryegrass Lolium perenne L. were sown. Soil properties such as metal(loid) availability, pH, phosphorus availability, total nitrogen, organic carbon, and nutrients were monitored for two months. Finally, the ryegrass was harvested and pollutant concentrations were analyzed in the aerial parts. Magnesite proved to be an excellent amendment for metal(loid) immobilization, although the notable increase in soil pH and Mg content inhibited plant growth. However, the application of magnesite in combination with the sludge compost (rich in N and P) favored plant growth and also immobilized metals, although As availability increased. In contrast, the analysis of plants in this treatment revealed lower As and metal concentrations than those grown in the untreated soil. In turn, the application of magnesite and biochar was also effective in reducing metal(loid) availability; however, the plants did not grow under these conditions, probably due to the low N and P content of biochar. In this regard, the combined application of mining waste and sludge compost emerges as a useful nature-based solution for soil remediation in the context of the circular economy.

Acid Generation and Heavy Metal Leachability from Lignite Spoil Heaps: Impact to the Topsoils of Oropos Basin, North Attica, Greece

The disposal of lignite spoil and tailings poses a major environmental problem in lignite mining sites which is associated with the oxidation of sulfide minerals contained in the primary ore. This process renders acidic effluents. Lignite mining in the Oropos Neogene basin, North Attica, Greece operated since the last century and ceased in the late 1960s. Piles of complex waste material are dispersed close to the mining sites. The high sulfur content and low Net Neutralization Potential, i.e. values < - 20 CaCO₃ kg/t in most analyzed waste samples, indicate that the waste is prone to acid generation. The leachates (EN12457) from the lignite spoils showed high concentrations in Ni and Zn exceeding the EU regulatory limits for the non-hazardous wastes. GIS-based geochemical maps of the topsoil showed enrichment in Ni (Cr, V) associated with the regional geogenic enrichment but also local accumulation around the hot spot sites of lignite spoil heaps.

Mineralogical and geochemical characterization of mining wastes: remining potential and environmental implications, Muteh Gold Deposit, Iran

Muteh Gold Deposit is the biggest active gold district in Iran consisting of two mines, Senjedeh and Chah-Khatoun, and seven mineral occurrences. Senjedeh has been mined about 20 years ago and was recently closed because of the depletion of the reserves. Chah-Khatoun went into operation few years ago. During the previous decades, more than 22 Mt of low-grade wastes has been produced from both mines. The wastes are assumed to be a possible source of gold, especially with recent increase in the world gold prices. In this research, 62 surface and subsurface samples were taken from four waste dumps in Senjedeh and two dumps in Chah-Khatoun mines. The optical mineralogy, XRD, ICP-MS analysis, SEM, and electron probe microanalysis (EPMA) studies were carried out to investigate the mineralogical and geochemical characteristics of the waste rocks. In addition to identification of major and minor primary and secondary phases, the mode of occurrence of minerals and also the content of precious and economic elements have been studied. The main opaque mineral was found to be pyrite. Among the economic elements, Au was recognized in the pyrite lattice as well as electrum. The Au grades are higher than 0.5 mg/kg in some waste piles. Zinc and Cu revealed concentrations above 5000 and about 1400 mg/kg, respectively. It is for the first time that electrum is reported in Muteh. Therefore, regarding the economically recoverable content of Au, the studied waste rocks may be considered as potential ores of coming years. Among the environmentally significant elements, As showed concentrations of up to 25 mg/kg which may be of pollution concerns.

Spatio-temporal distribution of major and trace metals in estuarine sediments of Dhamra, Bay of Bengal, India--its environmental significance

The research depicts the spatial and temporal variation of major and trace metals in marine sediments at various monitoring stations of Dhamra estuary, Bay of Bengal, Odisha. The concentration and distribution of selected metals in surface sediments of the estuary were studied in order to assess the spatial extent of anthropogenic inputs viz., mining activities and to estimate the effects of seasonal variations on geochemical processes in this particular tropical estuarine system. Surface sediments reflect the presence of trace and major metals in parts per million, and the concentrations vary in the range of Cu (0.083 to 127.2), Ni (17.35 to 122.8), Co (1.2 to 31.58), Pb (0.8 to 95.86), Zn (12.1 to 415), Cd (0 to 11) and Cr (35.21 to 5,890), Fe (7,490 and 169,100), Mn (20 to 69,188), Ca (10 to 10,520), Mg (990 to 28,750), Na (300 to 51,700), and K (1,100 to 30,010). The comparison of spatial distribution of metal contents using GIS in marine sediments indicates that there is a substantial anthropogenic input in the Dhamra estuary. The enrichment of Cr is ascribed to the sedimentation of Brahmani River, passing through the mining region and discharging Cr pollutant to the sea. Similarly, the sources of Cd are attributable to corrosion-resistant paints used by a large number of trawlers. Contamination factor has been calculated for various metals to assess the degree of pollution. As per Hakanson's classification, Cr indicates very high contamination with considerable contamination of Cd, whereas moderate contamination of Pb, Zn, and Mn are observed in marine sediments. Pollution load index also indicate that there is deterioration of site quality in premonsoon season, which almost attains the baseline level in post monsoon and perfection in monsoon season (Tomlinson et al. (Helgolander Wissenschaftliche Meeresuntersuchungen, 33, 566-572, 1980)). The geoaccumulation index shows that the metal concentrations in sediments can be considered as background levels except Cr and Cd. The geoaccumulation index shows that Cr is moderately contaminated and it is higher in offshore region in post monsoon and monsoon than premonsoon season. All the calculated indices show that Cr and Cd levels are more than the desired limits in the marine sediments. Multivariate statistical analysis evaluates the plausible sources of contaminants, attributing to mining, industrial, and urban wastes by way of Brahmani River discharging to the estuarine region.