Los Pozuelos is a closed basin in the Puna region of NW Argentina. In this semi-arid region close... more Los Pozuelos is a closed basin in the Puna region of NW Argentina. In this semi-arid region closed basins are the most important feature for the hydrologic systems. The basin center is occupied by a fluctuating playa lake called Los Pozuelos lagoon, which is a UNESCO Biosphere Reserve. Local original communities use groundwater for drinking and cooking. Lowest concentrations of As and dissolved solids are in the rivers (1.46-27 mg/L) and the highest concentrations are in the lagoon (43.7-200.3 mg/L). In groundwater, arsenic also reach high concentrations (3.82-113 mg/L), especially during the dry season where Na/K mass ratios (0.2 and 0.3), and formation of Na-rich efflorescent salts suggest that high evaporation rates increase As concentration. As(V) is the dominant species in all the water types, except for the lagoon, where As(III) occasionally dominates because of organic matter buildup. There are four potential sources of As: i) oxidation of As sulfides in Pan de Azúcar mine wastes, and discharge into the basin; ii) weathering and erosion of mineralized shales; iii) weathering of volcanic eruptive non-mineralized rocks, and iv) weathering of gold mines. Because it is a closed basin, the arsenic released from the natural and anthropogenic sources is transported in solution and in fluvial sediments and finally accumulates in the center of the basin where the concentration in water increases by evaporation with enhancement by organic matter reducing conditions. Remediation methods should be applied in wells with high As concentrations.
Environmental Science and Pollution Research, Jan 22, 2009
Background, aim and scope In the region of the Apuseni Mountains, part of the Western Carpathians... more Background, aim and scope In the region of the Apuseni Mountains, part of the Western Carpathians in Romania, metal mining activities have a long-standing tradition. These mining industries created a clearly beneficial economic development in the region. But their activities also caused impairments to the environment, such as acid mine drainage (AMD) resulting in long-lasting heavy metal pollution of waters and sediments. The study, established in the context of the ESTROM programme, investigated the impact of metal mining activities both from environmental and socioeconomic perspectives and tried to incorporate the results of the two approaches into an integrated proposition for mitigation of mining-related issues. Study site The small Certej catchment, situated in the Southern Apuseni Mountains, covers an area of 78 km 2. About 4,500 inhabitants are living in the basin, in which metal mining was the main economic sector. An open pit and several abandoned underground mines are producing heavy metal-loaded acidic water that is discharged untreated into the main river. The solid wastes of mineral processing plants were deposited in several dumps and tailings impoundment embodying the acidic water-producing mineral pyrite. Methods The natural science team collected samples from surface waters, drinking water from dug wells and from groundwater. Filtered and total heavy metals, both after enrichment, and major cations were analysed by inductively coupled plasma optical emission spectroscopy (ICP-OES). Major anions in waters, measured by ion chromatography, alkalinity and acidity were determined by titration. Solid samples were taken from river sediments and from the largest tailings dam. The latter were characterised by X-ray
Journal of South American Earth Sciences, Aug 1, 2021
Abstract Pan de Azucar is an inactive Pb–Ag–Zn mine in the semi-arid Puna region of NW Argentina ... more Abstract Pan de Azucar is an inactive Pb–Ag–Zn mine in the semi-arid Puna region of NW Argentina at 3600 m above sea-level. The mine is situated in Los Pozuelos basin, which is a UNESCO Biosphere Reserve. Substantial pyrite and few carbonate minerals are present in the tailings. The generated acid mine drainage (AMD) has low pH (1.92–4.06) and is mainly Fe–Zn–SO4 type water with high concentrations of metals that in order of relative abundance vary as: Al ≫ Cd > As(T) > Ni > V > Cu > Co > Sb > Cr > Pb > Sn > Ag. The strong annual cycle of dry and wet seasons in the Puna generates a significant influence on AMD geochemistry. In the dry season, there is no runoff and AMD drains mainly in the form of seepages with low pH (1.92–2.21), high concentrations of metals, and the formation of metal-rich soluble efflorescent salts is favored by strong evaporation. At the beginning of the wet season, the efflorescent salts rapidly dissolve and metals concentrations in AMD increase significantly, creating the most hazardous period for the surrounding fluvial environment. At the end of the wet season the pH increases (3.44–4.06) and the concentration of metals decreases, especially arsenic associated with ferric iron precipitates. As a consequence of the DC3 dam restoration, a large volume of AMD is retained forming an acid pond, in which processes of AMD mixing, secondary minerals precipitation, and sulfide oxidation were quantified by inverse modeling with mixing. Jarosite and schwertmannite precipitates in the surface of the pond and favors the attenuation of As and Pb. However, subaqueous oxidation of sulfide minerals, hydrolysis of silicates, and mixing with upstream AMD seepage increases the concentrations of SO42-, Fe(II), and the other metals in the seepage of the pond that migrates downstream. The results of this study indicate the necessity to improve the remediation methods of Pan de Azucar mine. It is expected that other sulfide mines in the Puna region will have a similar variability of the AMD geochemistry, which should be considered for mine closure, remediation, and monitoring of water quality in mining.
The geochemical and mineralogical study of the Quiulacocha tailings impoundment has shown that th... more The geochemical and mineralogical study of the Quiulacocha tailings impoundment has shown that the hydrological connection of the three mine-waste systems at Cerro de Pasco (Excelsior, Quiulacocha, Ocroyoc) is the most critical concern for the waste management. The Quiulacocha tailings cover 114 ha, comprising 79 Mt of tailings, which contain ~ 50 wt% pyrite. The tailings are located at 4340 m altitude in a tropical puna climate with about 1025 mm/a rainfall. The tailings are partially overlain by the Excelsior waste-rock dump, which contains about 26,400,000 m 3 of waste rocks that cover 94 ha and contain ~60 wt% of pyrite. In the Quiulacocha impoundment there are two different types of tailings recognized: 1) Zn-Pb-rich tailings and 2) Cu-rich tailings. During the sampling campaign, the Zn-Pb-rich part of Quiulacocha was not producing important excess of acid mine drainage (AMD) from the oxidation zone, where pH is increased to near neutral values at 1 m depth. The underlying tailings were still able to neutralize the acidity, produced in the oxidation zone through sulfide oxidation, by the underlying carbonates (dolomite and siderite). The main source of AMD in this mine-waste system is from the Excelsior waste-rock dump. Its acid seepage infiltrates into Quiulacocha forming a Fe-Zn-Pb plume with a pH 5.5-6.1 and containing up to 7440 mg/L Fe, 627 mg/L Zn, and 1.22 mg/L Pb. The plume was detected between 10 m to 13 m depth in the stratigraphy of Quiulacocha. Additionally, the AMD seepage from the base of the Excelsior waste-rock dump is channelled on the tailings surface to the pond of Quiulacocha (pH 2.3), which covers Cu-rich tailings. Infiltration of this Fe(III)-rich AMD increases oxidation of tailings in the southwestern part of the impoundment and subsequently liberates As by enargite oxidation. Additionally, the AMD collected in the Quiulacocha pond was pumped into the active Ocroyoc tailings impoundment, where sulfide oxidation was strongly enhanced by the input of dissolved Fe(III). Therefore, the AMD management and a hydrological separation of the different mine-waste systems might be a first step to prevent further extension of the AMD problem. Figure 1. Overview of the Quiulacocha tailings impoundment with the overlying Excelsior waste-rock dump on the right and the AMD pond in the southwestern part of the tailings impoundment.
CHAPTER3 3 Methodology used for sequential extraction applied to geochemical investigations of su... more CHAPTER3 3 Methodology used for sequential extraction applied to geochemical investigations of sulfidic mine tailings by combination of dissolution kinetics and mineralogical control of dissolved phases by x-ray diffraction (XRD) and differentiai x-ray diffraction (DXRD) .
We present data of the time-evolution of a remediation approach on a marine shore tailings deposi... more We present data of the time-evolution of a remediation approach on a marine shore tailings deposit by the implementation of an artificial wetland. Two remediation cells were constructed: one in the northern area at sea-level and one in the central delta area (above sea-level) of the tailings. At the beginning, the "sea-level" remediation cell had a low pH (3.1), with high concentrations of dissolved metals and sulfate and chloride ions and showed sandy grain size. After wetland implementation, the "sea-level" remediation cell was rapidly water-saturated, the acidity was consumed, and after four months the efficiency of metal removal from solution was up to 79.5%-99.4% for Fe, 94.6%-99.9% for Mn, and 96.1%-99.6% for Zn. Al and Cu concentrations decreased below detection limit. The "above sea-level" remediation cell was characterized by the same pH (3.1) and finer grain size (clayey-silty), and with some lower element concentrations than in the "sea-level" cell. Even after one year of flooding, the "above sea-level" cell was not completely flooded, showing ongoing sulfide oxidation in between the wetland cover and the groundwater level; the pH increased only to 4.4 and metal concentrations decreased only by 96% for Fe, 88% for Al, 51% for Cu, 97% for Mn, and 95% for Zn. During a dry period, the water level dropped in the "sea-level" cell, resulting in a seawater ingression, which triggered the desorption of As into solution. These data show that the applied
Preliminary results on mineralogical and geochemical changes at the transition between oxidiation... more Preliminary results on mineralogical and geochemical changes at the transition between oxidiation and primary (sulfide) zone in copper flotation tailings located in Chile are presented. The tailing Cauquenes (El Teniente) and Piuquenes (La Andina) were sampled down to a depth of 10,4 m with percussion drilling. In both tailings, results of sequential digestions analyses show a similar distribution. In the oxidation zone (jarosite zone) Cu, Ca, Co, Mg, Mn, Pb, Zn are almost completely leached out. Fe and Mo display relatively high values in the oxalic acid and H202 fractions of the oxidation zone indicating that they have been fixed in Fe(III)hydroxides subsequently to the breakdown of sulfides. K is fixed in jarosite. As, Al, and Ba show relatively high values in the oxalic acid fraction in the oxidation zone. The underlying precipitation zone (gypsum zone) is characterized by enrichment of elements leached from the oxidation zone in particular Cu, Co, and Mo. In the basal primary zone, carbonates (e.g. siderite) and sulfides are still stable and no secondary mineral formation is recognize
Sulphidic mine tailings are among the largest mining wastes on Earth and are prone to produce aci... more Sulphidic mine tailings are among the largest mining wastes on Earth and are prone to produce acid mine drainage (AMD). The formation of AMD is a sequence of complex biogeochemical and mineral dissolution processes. It can be classified in three main steps occurring from the operational phase of a tailings impoundment until the final appearance of AMD after operations ceased: (1) During the operational phase of a tailings impoundment the pH-Eh regime is normally alkaline to neutral and reducing (water-saturated). Associated environmental problems include the presence of high sulphate concentrations due to dissolution of gypsum-anhydrite, and/or effluents enriched in elements such as Mo and As, which desorbed from primary ferric hydroxides during the alkaline flotation process. (2) Once mining-related operations of the tailings impoundment has ceased, sulphide oxidation starts, resulting in the formation of an acidic oxidation zone and a ferrous iron-rich plume below the oxidation front, that re-oxidises once it surfaces, producing the first visible sign of AMD, i.e., the precipitation of ferrihydrite and concomitant acidification. (3) Consumption of the (reactive) neutralization potential of the gangue minerals and subsequent outflow of acidic, heavy metal-rich leachates from the tailings is the final step in the evolution of an AMD system. The formation of multi-colour efflorescent salts can be a visible sign of this stage.
Mining is a vital part of the Global economy, but the extraction of metals, metalloids, and other... more Mining is a vital part of the Global economy, but the extraction of metals, metalloids, and other mineral products generates vast quantities of liquid and solid waste. Currently the volume is estimated at several thousand million tons per annum, but is increasing exponentially as demand and exploitation of lower-grade deposits increases. The high concentrations of potentially toxic elements in these wastes can pose risks to ecosystems and humans, but these risks can be mitigated by implementing appropriate management or remediation schemes. Although there are a large number of such schemes available, there is still a need to research the processes, products, and effectiveness of implementation, as well as the nature of the mine wastes themselves. This Special Issue is aimed at bringing together studies in the areas of mine waste characterization, management, and remediation, to review the current state of knowledge and to develop improvements in current schemes. Fourteen manuscripts are published for this Special Issue, and these are summarized below. Due to the large-scale nature of mine wastes, characterization is often done at regional scales. In this regard, Buzzi et al. [1] describe a method whereby hyperspectral high spatial resolution HyMap data can be used to map mainly abandoned massive sulfide mine wastes from the Iberian Pyrite Belt, Southwest Spain. Pattelli et al. [2] describe the flood-related mobilization of sediment-borne Hg from the Mount Amiata mining district in southern Tuscany, Italy, the fourth largest Hg district worldwide, which produced 102,000 metric tons of Hg from the 1860s to 1980. The processes and products of contaminant mobility at redox-transition zones, leading to diffuse metal contaminant inputs into river systems, is reviewed by Lynch et al. [3].
Sea level rise is able to change the geochemical conditions in coastal systems. In these environm... more Sea level rise is able to change the geochemical conditions in coastal systems. In these environments, transport of contaminants can be controlled by the stability and adsorption capacity of iron oxides. The behavior of adsorbed and co-precipitated arsenic in jarosite, schwertmannite, ferrihydrite, and goethite in sea water (common secondary minerals in coastal tailings) was investigated. The aim of the investigation was to establish As retention and transport under a marine flood scenario, which may occur due to climate change. Natural and synthetic minerals with co-precipitated and adsorbed As were contacted with seawater for 25 days. During this period As, Fe, Cl, SO 4 , and pH levels were constantly measured. The larger retention capability of samples with co-precipitated As, in relation with adsorbed As samples, reflects the different kinetics between diffusion, dissolution, and surface exchange processes. Ferrihydrite and schwertmannite showed good results in retaining arsenic, although schwertmannite holding capacity was enhanced due its buffering capacity, which prevented reductive dissolution throughout the experiment. Arsenic desorption from goethite could be understood in terms of ion exchange between oxides and electrolytes, due to the charge difference generated by a low point-of-zero-charge and the change in stability of surface complexes between synthesis conditions and natural media.
Understanding geochemical processes in mining environments are essential to waste management deci... more Understanding geochemical processes in mining environments are essential to waste management decisions including remediation. In an attempt to understand geochemical processes, chemical data have m ...
Shewanella is a genus of marine bacteria capable of dissimilatory iron reduction (DIR). In the co... more Shewanella is a genus of marine bacteria capable of dissimilatory iron reduction (DIR). In the context of deep-sea mining activities or submarine mine tailings disposal, dissimilatory iron reducing bacteria may play an important role in biogeochemical reactions concerning iron oxides placed on the sea bed. In this study, batch experiments were performed to evaluate the capacity of Shewanella loihica PV-4 to bioreduce different iron oxides (ferrihydrite, magnetite, goethite and hematite) under conditions similar to those in anaerobic sea sediments. Results showed that bioreduction of structural Fe(III) via oxidation of labile organic matter occurred in all these iron oxides. Based on the aqueous Fe (II) released, derived Fe(II)/acetate ratios and bioreduction coefficients seem to be only up to about 4% of the theoretical ones, considering the ideal stoichiometry of the reaction. A loss of aqueous Fe (II) was caused by adsorption and mineral transformation processes. Scanning electron microscope images showed that Shewanella lohica was attached to the Fe(III)-oxide surfaces during bioreduction. Our findings suggest that DIR of Fe(III) oxides from mine waste placed in marine environments could result in adverse ecological impacts such as liberation of trace metals in the environment.
Los Pozuelos is a closed basin in the Puna region of NW Argentina. In this semi-arid region close... more Los Pozuelos is a closed basin in the Puna region of NW Argentina. In this semi-arid region closed basins are the most important feature for the hydrologic systems. The basin center is occupied by a fluctuating playa lake called Los Pozuelos lagoon, which is a UNESCO Biosphere Reserve. Local original communities use groundwater for drinking and cooking. Lowest concentrations of As and dissolved solids are in the rivers (1.46-27 mg/L) and the highest concentrations are in the lagoon (43.7-200.3 mg/L). In groundwater, arsenic also reach high concentrations (3.82-113 mg/L), especially during the dry season where Na/K mass ratios (0.2 and 0.3), and formation of Na-rich efflorescent salts suggest that high evaporation rates increase As concentration. As(V) is the dominant species in all the water types, except for the lagoon, where As(III) occasionally dominates because of organic matter buildup. There are four potential sources of As: i) oxidation of As sulfides in Pan de Azúcar mine wastes, and discharge into the basin; ii) weathering and erosion of mineralized shales; iii) weathering of volcanic eruptive non-mineralized rocks, and iv) weathering of gold mines. Because it is a closed basin, the arsenic released from the natural and anthropogenic sources is transported in solution and in fluvial sediments and finally accumulates in the center of the basin where the concentration in water increases by evaporation with enhancement by organic matter reducing conditions. Remediation methods should be applied in wells with high As concentrations.
Environmental Science and Pollution Research, Jan 22, 2009
Background, aim and scope In the region of the Apuseni Mountains, part of the Western Carpathians... more Background, aim and scope In the region of the Apuseni Mountains, part of the Western Carpathians in Romania, metal mining activities have a long-standing tradition. These mining industries created a clearly beneficial economic development in the region. But their activities also caused impairments to the environment, such as acid mine drainage (AMD) resulting in long-lasting heavy metal pollution of waters and sediments. The study, established in the context of the ESTROM programme, investigated the impact of metal mining activities both from environmental and socioeconomic perspectives and tried to incorporate the results of the two approaches into an integrated proposition for mitigation of mining-related issues. Study site The small Certej catchment, situated in the Southern Apuseni Mountains, covers an area of 78 km 2. About 4,500 inhabitants are living in the basin, in which metal mining was the main economic sector. An open pit and several abandoned underground mines are producing heavy metal-loaded acidic water that is discharged untreated into the main river. The solid wastes of mineral processing plants were deposited in several dumps and tailings impoundment embodying the acidic water-producing mineral pyrite. Methods The natural science team collected samples from surface waters, drinking water from dug wells and from groundwater. Filtered and total heavy metals, both after enrichment, and major cations were analysed by inductively coupled plasma optical emission spectroscopy (ICP-OES). Major anions in waters, measured by ion chromatography, alkalinity and acidity were determined by titration. Solid samples were taken from river sediments and from the largest tailings dam. The latter were characterised by X-ray
Journal of South American Earth Sciences, Aug 1, 2021
Abstract Pan de Azucar is an inactive Pb–Ag–Zn mine in the semi-arid Puna region of NW Argentina ... more Abstract Pan de Azucar is an inactive Pb–Ag–Zn mine in the semi-arid Puna region of NW Argentina at 3600 m above sea-level. The mine is situated in Los Pozuelos basin, which is a UNESCO Biosphere Reserve. Substantial pyrite and few carbonate minerals are present in the tailings. The generated acid mine drainage (AMD) has low pH (1.92–4.06) and is mainly Fe–Zn–SO4 type water with high concentrations of metals that in order of relative abundance vary as: Al ≫ Cd > As(T) > Ni > V > Cu > Co > Sb > Cr > Pb > Sn > Ag. The strong annual cycle of dry and wet seasons in the Puna generates a significant influence on AMD geochemistry. In the dry season, there is no runoff and AMD drains mainly in the form of seepages with low pH (1.92–2.21), high concentrations of metals, and the formation of metal-rich soluble efflorescent salts is favored by strong evaporation. At the beginning of the wet season, the efflorescent salts rapidly dissolve and metals concentrations in AMD increase significantly, creating the most hazardous period for the surrounding fluvial environment. At the end of the wet season the pH increases (3.44–4.06) and the concentration of metals decreases, especially arsenic associated with ferric iron precipitates. As a consequence of the DC3 dam restoration, a large volume of AMD is retained forming an acid pond, in which processes of AMD mixing, secondary minerals precipitation, and sulfide oxidation were quantified by inverse modeling with mixing. Jarosite and schwertmannite precipitates in the surface of the pond and favors the attenuation of As and Pb. However, subaqueous oxidation of sulfide minerals, hydrolysis of silicates, and mixing with upstream AMD seepage increases the concentrations of SO42-, Fe(II), and the other metals in the seepage of the pond that migrates downstream. The results of this study indicate the necessity to improve the remediation methods of Pan de Azucar mine. It is expected that other sulfide mines in the Puna region will have a similar variability of the AMD geochemistry, which should be considered for mine closure, remediation, and monitoring of water quality in mining.
The geochemical and mineralogical study of the Quiulacocha tailings impoundment has shown that th... more The geochemical and mineralogical study of the Quiulacocha tailings impoundment has shown that the hydrological connection of the three mine-waste systems at Cerro de Pasco (Excelsior, Quiulacocha, Ocroyoc) is the most critical concern for the waste management. The Quiulacocha tailings cover 114 ha, comprising 79 Mt of tailings, which contain ~ 50 wt% pyrite. The tailings are located at 4340 m altitude in a tropical puna climate with about 1025 mm/a rainfall. The tailings are partially overlain by the Excelsior waste-rock dump, which contains about 26,400,000 m 3 of waste rocks that cover 94 ha and contain ~60 wt% of pyrite. In the Quiulacocha impoundment there are two different types of tailings recognized: 1) Zn-Pb-rich tailings and 2) Cu-rich tailings. During the sampling campaign, the Zn-Pb-rich part of Quiulacocha was not producing important excess of acid mine drainage (AMD) from the oxidation zone, where pH is increased to near neutral values at 1 m depth. The underlying tailings were still able to neutralize the acidity, produced in the oxidation zone through sulfide oxidation, by the underlying carbonates (dolomite and siderite). The main source of AMD in this mine-waste system is from the Excelsior waste-rock dump. Its acid seepage infiltrates into Quiulacocha forming a Fe-Zn-Pb plume with a pH 5.5-6.1 and containing up to 7440 mg/L Fe, 627 mg/L Zn, and 1.22 mg/L Pb. The plume was detected between 10 m to 13 m depth in the stratigraphy of Quiulacocha. Additionally, the AMD seepage from the base of the Excelsior waste-rock dump is channelled on the tailings surface to the pond of Quiulacocha (pH 2.3), which covers Cu-rich tailings. Infiltration of this Fe(III)-rich AMD increases oxidation of tailings in the southwestern part of the impoundment and subsequently liberates As by enargite oxidation. Additionally, the AMD collected in the Quiulacocha pond was pumped into the active Ocroyoc tailings impoundment, where sulfide oxidation was strongly enhanced by the input of dissolved Fe(III). Therefore, the AMD management and a hydrological separation of the different mine-waste systems might be a first step to prevent further extension of the AMD problem. Figure 1. Overview of the Quiulacocha tailings impoundment with the overlying Excelsior waste-rock dump on the right and the AMD pond in the southwestern part of the tailings impoundment.
CHAPTER3 3 Methodology used for sequential extraction applied to geochemical investigations of su... more CHAPTER3 3 Methodology used for sequential extraction applied to geochemical investigations of sulfidic mine tailings by combination of dissolution kinetics and mineralogical control of dissolved phases by x-ray diffraction (XRD) and differentiai x-ray diffraction (DXRD) .
We present data of the time-evolution of a remediation approach on a marine shore tailings deposi... more We present data of the time-evolution of a remediation approach on a marine shore tailings deposit by the implementation of an artificial wetland. Two remediation cells were constructed: one in the northern area at sea-level and one in the central delta area (above sea-level) of the tailings. At the beginning, the "sea-level" remediation cell had a low pH (3.1), with high concentrations of dissolved metals and sulfate and chloride ions and showed sandy grain size. After wetland implementation, the "sea-level" remediation cell was rapidly water-saturated, the acidity was consumed, and after four months the efficiency of metal removal from solution was up to 79.5%-99.4% for Fe, 94.6%-99.9% for Mn, and 96.1%-99.6% for Zn. Al and Cu concentrations decreased below detection limit. The "above sea-level" remediation cell was characterized by the same pH (3.1) and finer grain size (clayey-silty), and with some lower element concentrations than in the "sea-level" cell. Even after one year of flooding, the "above sea-level" cell was not completely flooded, showing ongoing sulfide oxidation in between the wetland cover and the groundwater level; the pH increased only to 4.4 and metal concentrations decreased only by 96% for Fe, 88% for Al, 51% for Cu, 97% for Mn, and 95% for Zn. During a dry period, the water level dropped in the "sea-level" cell, resulting in a seawater ingression, which triggered the desorption of As into solution. These data show that the applied
Preliminary results on mineralogical and geochemical changes at the transition between oxidiation... more Preliminary results on mineralogical and geochemical changes at the transition between oxidiation and primary (sulfide) zone in copper flotation tailings located in Chile are presented. The tailing Cauquenes (El Teniente) and Piuquenes (La Andina) were sampled down to a depth of 10,4 m with percussion drilling. In both tailings, results of sequential digestions analyses show a similar distribution. In the oxidation zone (jarosite zone) Cu, Ca, Co, Mg, Mn, Pb, Zn are almost completely leached out. Fe and Mo display relatively high values in the oxalic acid and H202 fractions of the oxidation zone indicating that they have been fixed in Fe(III)hydroxides subsequently to the breakdown of sulfides. K is fixed in jarosite. As, Al, and Ba show relatively high values in the oxalic acid fraction in the oxidation zone. The underlying precipitation zone (gypsum zone) is characterized by enrichment of elements leached from the oxidation zone in particular Cu, Co, and Mo. In the basal primary zone, carbonates (e.g. siderite) and sulfides are still stable and no secondary mineral formation is recognize
Sulphidic mine tailings are among the largest mining wastes on Earth and are prone to produce aci... more Sulphidic mine tailings are among the largest mining wastes on Earth and are prone to produce acid mine drainage (AMD). The formation of AMD is a sequence of complex biogeochemical and mineral dissolution processes. It can be classified in three main steps occurring from the operational phase of a tailings impoundment until the final appearance of AMD after operations ceased: (1) During the operational phase of a tailings impoundment the pH-Eh regime is normally alkaline to neutral and reducing (water-saturated). Associated environmental problems include the presence of high sulphate concentrations due to dissolution of gypsum-anhydrite, and/or effluents enriched in elements such as Mo and As, which desorbed from primary ferric hydroxides during the alkaline flotation process. (2) Once mining-related operations of the tailings impoundment has ceased, sulphide oxidation starts, resulting in the formation of an acidic oxidation zone and a ferrous iron-rich plume below the oxidation front, that re-oxidises once it surfaces, producing the first visible sign of AMD, i.e., the precipitation of ferrihydrite and concomitant acidification. (3) Consumption of the (reactive) neutralization potential of the gangue minerals and subsequent outflow of acidic, heavy metal-rich leachates from the tailings is the final step in the evolution of an AMD system. The formation of multi-colour efflorescent salts can be a visible sign of this stage.
Mining is a vital part of the Global economy, but the extraction of metals, metalloids, and other... more Mining is a vital part of the Global economy, but the extraction of metals, metalloids, and other mineral products generates vast quantities of liquid and solid waste. Currently the volume is estimated at several thousand million tons per annum, but is increasing exponentially as demand and exploitation of lower-grade deposits increases. The high concentrations of potentially toxic elements in these wastes can pose risks to ecosystems and humans, but these risks can be mitigated by implementing appropriate management or remediation schemes. Although there are a large number of such schemes available, there is still a need to research the processes, products, and effectiveness of implementation, as well as the nature of the mine wastes themselves. This Special Issue is aimed at bringing together studies in the areas of mine waste characterization, management, and remediation, to review the current state of knowledge and to develop improvements in current schemes. Fourteen manuscripts are published for this Special Issue, and these are summarized below. Due to the large-scale nature of mine wastes, characterization is often done at regional scales. In this regard, Buzzi et al. [1] describe a method whereby hyperspectral high spatial resolution HyMap data can be used to map mainly abandoned massive sulfide mine wastes from the Iberian Pyrite Belt, Southwest Spain. Pattelli et al. [2] describe the flood-related mobilization of sediment-borne Hg from the Mount Amiata mining district in southern Tuscany, Italy, the fourth largest Hg district worldwide, which produced 102,000 metric tons of Hg from the 1860s to 1980. The processes and products of contaminant mobility at redox-transition zones, leading to diffuse metal contaminant inputs into river systems, is reviewed by Lynch et al. [3].
Sea level rise is able to change the geochemical conditions in coastal systems. In these environm... more Sea level rise is able to change the geochemical conditions in coastal systems. In these environments, transport of contaminants can be controlled by the stability and adsorption capacity of iron oxides. The behavior of adsorbed and co-precipitated arsenic in jarosite, schwertmannite, ferrihydrite, and goethite in sea water (common secondary minerals in coastal tailings) was investigated. The aim of the investigation was to establish As retention and transport under a marine flood scenario, which may occur due to climate change. Natural and synthetic minerals with co-precipitated and adsorbed As were contacted with seawater for 25 days. During this period As, Fe, Cl, SO 4 , and pH levels were constantly measured. The larger retention capability of samples with co-precipitated As, in relation with adsorbed As samples, reflects the different kinetics between diffusion, dissolution, and surface exchange processes. Ferrihydrite and schwertmannite showed good results in retaining arsenic, although schwertmannite holding capacity was enhanced due its buffering capacity, which prevented reductive dissolution throughout the experiment. Arsenic desorption from goethite could be understood in terms of ion exchange between oxides and electrolytes, due to the charge difference generated by a low point-of-zero-charge and the change in stability of surface complexes between synthesis conditions and natural media.
Understanding geochemical processes in mining environments are essential to waste management deci... more Understanding geochemical processes in mining environments are essential to waste management decisions including remediation. In an attempt to understand geochemical processes, chemical data have m ...
Shewanella is a genus of marine bacteria capable of dissimilatory iron reduction (DIR). In the co... more Shewanella is a genus of marine bacteria capable of dissimilatory iron reduction (DIR). In the context of deep-sea mining activities or submarine mine tailings disposal, dissimilatory iron reducing bacteria may play an important role in biogeochemical reactions concerning iron oxides placed on the sea bed. In this study, batch experiments were performed to evaluate the capacity of Shewanella loihica PV-4 to bioreduce different iron oxides (ferrihydrite, magnetite, goethite and hematite) under conditions similar to those in anaerobic sea sediments. Results showed that bioreduction of structural Fe(III) via oxidation of labile organic matter occurred in all these iron oxides. Based on the aqueous Fe (II) released, derived Fe(II)/acetate ratios and bioreduction coefficients seem to be only up to about 4% of the theoretical ones, considering the ideal stoichiometry of the reaction. A loss of aqueous Fe (II) was caused by adsorption and mineral transformation processes. Scanning electron microscope images showed that Shewanella lohica was attached to the Fe(III)-oxide surfaces during bioreduction. Our findings suggest that DIR of Fe(III) oxides from mine waste placed in marine environments could result in adverse ecological impacts such as liberation of trace metals in the environment.
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Papers by Bernhard Dold