Natural attenuation study of the impact of acid mine drainage (AMD) in the site of Carnoulès
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Weathering of the As-rich pyrite-rich tailings of the abandoned mining site of Carnoulès (southeastern France) results in the formation of acid waters heavily loaded with arsenic. Dissolved arsenic present in the seepage waters precipitates within a few meters from the bottom of the tailing dam in the presence of microorganisms. An Acidithiobacillus ferrooxidans strain, referred to as CC1, was isolated from the effluents. This strain was able to remove arsenic from a defined synthetic medium only when grown on ferrous iron. This A. ferrooxidans strain did not oxidize arsenite to arsenate directly or indirectly. Strain CC1 precipitated arsenic unexpectedly as arsenite but not arsenate, with ferric iron produced by its energy metabolism. Furthermore, arsenite was almost not found adsorbed on jarosite but associated with a poorly ordered schwertmannite. Arsenate is known to efficiently precipitate with ferric iron and sulfate in the form of more or less ordered schwertmannite, depending on the sulfur-to-arsenic ratio. Our data demonstrate that the coprecipitation of arsenite with schwertmannite also appears as a potential mechanism of arsenite removal in heavily contaminated acid waters. The removal of arsenite by coprecipitation with ferric iron appears to be a common property of the A. ferrooxidans species, as such a feature was observed with one private and three collection strains, one of which was the type strain.Weathering of sulfide-rich rocks results in the formation of highly acidic and heavy metal-laden effluents. At the abandoned Pb-Zn mining site of Carnoulès (southeastern France), the pyrite-rich tailings are subject to bioleaching. Consequently, the Reigous spring, which collects the seepage waters from the waste materials, is acid (pH 3) and contains high levels of solubilized metals (Fe, Zn, and Pb) but also extremely high arsenic (As) concentrations (250 mg liter Ϫ1 on average) (26, 27). The extremely high contents of this metalloid are lowered by 2 to 3 orders of magnitude between the bottom of the tailing dam and few hundred meters downstream. The presence in the sediments of bacteria coated with Fe-As-rich material suggested that arsenic attenuation was due to precipitation mechanisms mediated by microorganisms (24,25,26,27). Among them, Acidithiobacillus ferrooxidans was proposed to be involved in the removal of soluble arsenic (9,26,27,35). The role of microorganisms in arsenic attenuation in this ecosystem was evaluated by two different approaches: (i) an A. ferrooxidans strain was isolated from the effluent and its role in arsenic oxidation and/or precipitation was determined (this paper); (ii) arsenite oxidizing bacteria, one of which belongs to the Thiomonas genus, were isolated and characterized (K. Duquesne, A. Yarzabal, J. Ratouchniak, D. Muller, D. Lièvre-mont, M-C. Lett, and V. Bonnefoy, unpublished results).A. ferrooxidans is an acidophilic chemolithoautotrophic gram-negative bacterium commonly encountered in acid mine drainage. This bacterium is resistant to heavy metals and metallo...
Weathering of the As-rich pyrite-rich tailings of the abandoned mining site of Carnoulès (southeastern France) results in the formation of acid waters heavily loaded with arsenic. Dissolved arsenic present in the seepage waters precipitates within a few meters from the bottom of the tailing dam in the presence of microorganisms. An Acidithiobacillus ferrooxidans strain, referred to as CC1, was isolated from the effluents. This strain was able to remove arsenic from a defined synthetic medium only when grown on ferrous iron. This A. ferrooxidans strain did not oxidize arsenite to arsenate directly or indirectly. Strain CC1 precipitated arsenic unexpectedly as arsenite but not arsenate, with ferric iron produced by its energy metabolism. Furthermore, arsenite was almost not found adsorbed on jarosite but associated with a poorly ordered schwertmannite. Arsenate is known to efficiently precipitate with ferric iron and sulfate in the form of more or less ordered schwertmannite, depending on the sulfur-to-arsenic ratio. Our data demonstrate that the coprecipitation of arsenite with schwertmannite also appears as a potential mechanism of arsenite removal in heavily contaminated acid waters. The removal of arsenite by coprecipitation with ferric iron appears to be a common property of the A. ferrooxidans species, as such a feature was observed with one private and three collection strains, one of which was the type strain.Weathering of sulfide-rich rocks results in the formation of highly acidic and heavy metal-laden effluents. At the abandoned Pb-Zn mining site of Carnoulès (southeastern France), the pyrite-rich tailings are subject to bioleaching. Consequently, the Reigous spring, which collects the seepage waters from the waste materials, is acid (pH 3) and contains high levels of solubilized metals (Fe, Zn, and Pb) but also extremely high arsenic (As) concentrations (250 mg liter Ϫ1 on average) (26, 27). The extremely high contents of this metalloid are lowered by 2 to 3 orders of magnitude between the bottom of the tailing dam and few hundred meters downstream. The presence in the sediments of bacteria coated with Fe-As-rich material suggested that arsenic attenuation was due to precipitation mechanisms mediated by microorganisms (24,25,26,27). Among them, Acidithiobacillus ferrooxidans was proposed to be involved in the removal of soluble arsenic (9,26,27,35). The role of microorganisms in arsenic attenuation in this ecosystem was evaluated by two different approaches: (i) an A. ferrooxidans strain was isolated from the effluent and its role in arsenic oxidation and/or precipitation was determined (this paper); (ii) arsenite oxidizing bacteria, one of which belongs to the Thiomonas genus, were isolated and characterized (K. Duquesne, A. Yarzabal, J. Ratouchniak, D. Muller, D. Lièvre-mont, M-C. Lett, and V. Bonnefoy, unpublished results).A. ferrooxidans is an acidophilic chemolithoautotrophic gram-negative bacterium commonly encountered in acid mine drainage. This bacterium is resistant to heavy metals and metallo...
As a hazardous environmental metalloid toxicant, arsenic (As)-at elevated levels in water and soil-has created a major public health concern through its entry into the food chain by accumulation in crops. Among the various methods reported thus far for reclamation of As-contaminated crop fields, bioremediation using bacteria with plantgrowth-promoting traits has been found to be a most promising solution. There is every possibility that bacterial isolates with the ability to remove or immobilize As could be used for successful bioremediation. However, bioremediation needs to define its boundaries between promise and field application, as most studies have been restricted to laboratory results only. Rhizosphere interactions play a critical role in monitoring As bioavailability to crop plants, thus a better understanding of it might improve rhizoremediation technologies. The challenges rely on the application of these novel approaches under field conditions. Despite some limitations, the prospect for successful stimulation and exploitation of microbial metabolism for As rhizoremediation appears to be very promising.
L’anomenat drenatge àcid de mina (AMD) ve generat per l’oxidació de sulfurs i és causa major de contaminació d’aigües a nivell mundial. L’arsènic és un del princiapls contaminants laconcentració del qual pot assolir centenars de mgL-1, és a dir, de 5 a 6 ordres de magnitud més gran que el límit de potabilitat per a l’aigua (10μg L-1) establert per la UE en 1998. En aquesta tesi, s’estudia l’impacte de la mobilització de l’arsènic al llarg de descàrregues de drenatge àcid de mina. L’oxidació de sulfurs que contenen arsènic (tal com l’arsenopirita (AsFeS), la pirita rica en arsènic (FeS2) o la marcassita (FeS2) és una de les principals fonts d’alliberament d’arsènic a l’aigua. En la primera part de la tesi, s’ha estudiat la cinètica de dissolució de l’arsenopirita i de la marcassita a pHs àcids i neutre, utilitzant reactors de flux continu, i s’han valorat els efectes del pH, de l’oxigen dissolt i de la temperatura en la dissolució d’ambdós sulfurs. A partir de les velocitats en estat estacionari establertes, es proposen les respectives lleis de dissolució que tenen en compte el lleu i el fort efecte del pH i de l’oxigen dissolt, respectivament, en llur dissolució. La incorporació d’aquestes lleis cinètiques en les bases de dades del codis geoquímics i de transport reactitu permeten fer prediccions molt més realistes. L’impacte mediambiental causat per l’arsènic alliberat a les aigües depèn de la seva atenuació natural. El principal procés que controla el destí i la mobilitat de l’arsènic aquós és l’adsorció de l’arsenat en fases de ferro precipitades. Per tant, cal tenir en compte el paper que juga l’estat d’oxidació de l’arsènic. En la segona part de la tesi, shan estudiat tant l’oxidació de l’arsènic com l’adsorció de l’arsènic. L’oxidació s’estudia en condicions abiòtiques i biòtiques a pH i composició típics d’aigües àcides de mina, fent servir experiments de tipus batch. S’hi mostra com en condicions biòtiques tenen lloc simultàniament l’oxidació de Fe(II) a Fe (III) i d’arsenit a arsenat, de manera que mentre els bacteris governen la primera, el contingut de Fe(III) domina la segona. En condicions abiòtiques, l’oxidació d’arsenit a arsenat en presència de Fe(III) és lenta, tot i que augmenta augmentant la presència de Fe(III) i de clorur amb llum de dia. L’adsorció d’arsènic en llocs d’AMD, i per tant l’atenuació d’arsènic, ocorre mitjançant l’adsorció d’arsenat en precipitats formats per oxi-hidròxids i oxi-hidròxid-sulfats de ferro (principalment schwertmannita (Fe8O8(OH)5.5(SO4)1.25), K-jarosita (KFe3(SO4)2(OH)6) i goetita (FeOOH)). S’han estudiat les capacitats d’adsorció de la jarosita i de la goetita i s’han comparat amb la de la schwertmannita. Amb aquest propòsit es van fer experiments de tipus batch a pH molt àcid i amb mostres sintetitzades de K-jarosita i de goetita. Sense la competència d’altres anions, la capacitat de la jarosita per eliminar arsenat és més alta que la de la goetita. També s’ha vist que la força iònica té un escàs efecte en l’adsorció d’ambdós minerals, però que la presència de sulfat, que és l’anió més abundant en aigües àcides de mina, minva llurs capacitas d’adsorció. Cal conèixer bé els mecanismes dominants que controlen el contingut d’arsènic en les aigües, no només en condicions de laboratori, sinó també en les condicions de camp. Per tant, en la tercera part de la tesi s’han estudiat el processos d’atenuació de l’arsènic en un sistema natural. Amb aquest objetiu s’han caracterizat exhaustivament l’aigua i els sediments del rieron provinent de la mina abandonada Tinto Santa Rosa, situada a la Faixa Pirítica Ibèrica (IPB). La característica dominant de l’aigua del rierol és un descens del pH aigües avall que va acompanyat d’un decreixement sistemàtic de les concentracions de ferro ferrós i de ferro total, d’arsenit i d’arsenat, així com d’arsènic total. A més a més, els sediments de llit mostren contiguts alts d’arsènic. Els principals mecanismes que dominen el destí i la mobilitat de l’arsènic en aquestes aigües de camp són l’oxidació del ferro i de l’arsènic i la precipitatió de compostos de Fe(III) que adsorbeixen l’arsenat. S’ha proposat un model unidimensional de trasnport reactiu, utilitzant el codi PHREEQC, per explicar i quantificar els processos mencionats que han estat estudiats en condicions de laboratori. Acid mine drainage (AMD) generated by sulfide oxidative dissolution is a major cause of water contamination world-wide. Arsenic is one of the main AMD pollutants whose concentration can reach up to hundreds of mg L-1, i.e. 5-6 orders of magnitude higher than the limit of 10 μg L-1 for potable water established by the European Union in 1998. This thesis is concerned with the impact of arsenic mobilization along AMD discharges. Oxidation of As-bearing sulfides such as arsenopyrite (AsFeS), As-rich pyrite (FeS2) or marcasite (FeS2) is one of the main sources of arsenic release. The first part of this thesis is focused on the dissolution kinetics of arsenopyrite and marcasite at acidic to neutral pH using long term flow-through experiments. The effects of pH, dissolved oxygen and temperature on their dissolution were assessed. The respective dissolution rate laws were proposed on the basis of the steady-state rates, taking into consideration the slight pH effect and the strong dissolved oxygen effect on dissolution. The incorporation of these rate laws into the kinetic databases of geochemical and reactive transport codes allows us to obtain better realistic simulations. The environmental impact of released arsenic into waters depends on its natural attenuation. The arsenic oxidation state is considered given that the main process that controls the fate and mobility of aqueous arsenic is arsenate sorption onto precipitated Fe-phases. The second part of the thesis discusses arsenic oxidation and arsenic sorption. Oxidation was studied by means of batch experiments under abiotic and biotic conditions at typical AMD water pH and water composition. Simultaneous oxidation of Fe(II) to Fe(III) and arsenite to arsenate occurs under biotic conditions, the former mediated by bacteria, and the latter by the presence of Fe(III). Under abiotic conditions, oxidation of arsenite to arsenate in the presence of Fe(III) is slow, but is enhanced by increasing dissolved Fe(III) and chloride concentrations in the presence of light. Arsenic sorption at AMD sites, and hence arsenic attenuation, occurs via arsenate sorption on new iron-oxyhydroxide and iron-oxyhydroxide-sulphate precipitates (mainly, schwertmannite (Fe8O8(OH)5.5(SO4)1.25), jarosite (KFe3(SO4)2(OH)6) and goethite (FeOOH)). The sorption capacity of goethite and jarosite was studied and compared with the one reported for schwertmannite. To this end, batch experiments were conducted using synthetic powders of K-jarosite and goethite at highly acidic pH. In the absence of competitive effects of other anions, K-jarosite presented better removal efficiency for arsenate, and ionic strength and pH had little effect on the sorption capacity of the two minerals. In contrast, these sorption capacities diminished considerably in the presence of sulfate, which is the main anion in AMD waters. A deeper understanding of the dominant mechanisms controlling arsenic content in waters demands the study of the processes not only under laboratory but also under natural conditions. Accordingly, the third part of this thesis deals with the arsenic attenuation processes in a natural system. To this end, the acidic water and sediments of the abandoned Tinto Santa Rosa mine discharge, located in the Iberian Pyritic Belt, were studied. The most striking feature of the water was a pH decrease accompanied by a systematic decrease in ferrous iron, total iron, arsenite, arsenate and total arsenic concentration. Additionally, bed-stream sediments showed high arsenic contents. The main processes that control the fate and mobility of arsenic in waters in the field were iron and arsenic oxidation, precipitation of Fe(III)- minerals and sorption of As(V) onto them. A 1-D reactive transport model using the PHREEQC code was used to explain and quantify the aforementioned processes that had been studied previously under laboratory conditions.
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