Caracterización de los sedimentos de tres embalses de Empresas Públicas de Medellín, Colombia

Bottom sediments in the reservoirs “La Fe, Riogrande II and Porce II” properties of EPM, were characterized for environmental quality through the determination of heavy metals (iron, manganese, lead and chromium), the content of bases (calcium, magnesium, sodium and potassium), the concentrations of total nitrogen (Kjeldahl) and phosphorus, sediment granulometry and mineralogy and the classification of diatoms. “La Fe” reservoir presents the best water quality (oligomesotrophic) compared to “Riogrande II” (mesotrophic-eutrophic) and “Porce II” (Eutrophic to hypertrophic); All three share similar characteristics in terms of total nitrogen (NTK) content which is in lower concentration relative to the total phosphorus (PT). The high abundance and occurrence of Spicaticribra kingstonii and D. stelligera in “La Fe”, Fragilaria familiaris and Discostella stelligera in “Riogrande II” and A. granulata in “Porce II”, were good indicators for the water quality at the reservoirs “La Fe” and “Riogrande II” and for the permanent eutrophy at “Porce II”.La caracterización de los sedimentos de fondo en los embalses “La Fe, Riogrande II y Porce II” de EPM, a través de la determinación de metales pesados (hierro, manganeso, plomo y el cromo), el contenido de bases (calcio, magnesio, sodio y potasio), la presencia de nitrógeno y fosforo, su granulometría y mineralogía y la clasificación de diatomeas como indicador ambiental permitió establecer la calidad ambiental de estos, siendo el embalse La Fe el que presenta mejor calidad de agua (oligomesotrófico) comparado con Riogrande II (mesotrófico–eutrófico) y Porce II (eutrófico a hipertrófico); los tres comparten características similares en cuanto al contenido de nitrógeno total Kjeldahl que está en menor concentración con relación al fosforo total. La alta abundancia y ocurrencia de Spicaticribra kingstonii y D. stelligera en La Fe, de Fragilaria familiaris y Discostella stelligera en Riogrande II y de A. granulata en Porce II, en el sedimento de fondo, fue un indicador del deterioro de la calidad para los embalses La Fe y Riogrande II y el mantenimiento de ese estado para el caso de Porce II

Compréhension des processus (bio)géochimiques qui contrôlent la libération, la spéciation et le fractionnement isotopique du chrome dans les environnements ultramafiques impactés par les activités minières

Ultramafic systems are often synonym of high chromium (Cr) content in rocks, which is naturally leached to surface and groundwater. Due to this natural enrichment, ultramafic areas are massively mined. The mining process includes exploitation and beneficiation activities, in which large amount of metal-rich residues, such as overburden, waste rock and tailings, stored in open air, are produced. These processes may considerably increase the amount of both trivalent (Cr(III)) and hexavalent chromium (Cr(VI)) released to the environment. The later (Cr(VI)), known to be highly soluble in water, bioavailable and toxic. Within these mining residues, many chemical and biological processes may take place, which will control Cr speciation, mobility and availability. The present work was conducted on i) the nickel exploitation and metallurgic area of Barro Alto (BA, Goiás state, Brazil); ii) the antique chromite exploitation area of Cromínia (CA, Goiás State, Brazil) and iii) the current chromite mine in the Sukinda valley (Odisha, India). The main focus of this research is the identification of the impact of mining activities (nickel and chromium mining) on Cr mobility and availability in ultramafic environments, through the use of isotopic techniques. The chemically and isotopically exchangeable pools of Cr(VI) (ECr(VI)) were higher in BA ore samples, where the enrichment in light chromium isotopes (-0.76 to -0.16‰) was attributed to the loose of isotopically heavy and exchangeable Cr(VI) during weathering. Astonishingly, heavy δ53Cr values were also found in saprolitic ores in BA and in mining-affected soils in CA up to +3.9‰, strongly enriched in Cr(III). The main causes have been attributed to the existence of hydrothermal chromite in CA and/or to natural weathering followed by Cr(VI) reduction that induces reprecipitation of mobile and isotopically heavy Cr. In such a mining context, the accelerated weathering would play an important role in this process. Chromium in the leachate, of BA lateritic and saprolitic ores samples, was present as Cr(VI) isotopically enriched in heavy isotopes (up to +4.84‰), consistently with the exchangeable Cr (ECr(VI)) (up to +4.37‰). These values were in the same range as isotopic compositions measured in the fresh waters (streams and ponds) in the ultramafic area. These results imply that Cr is mainly released as the toxic Cr(VI) specie, which availability increases from i) the soil profile to ii) the ores and iii) the mining residues. This also suggests that δ53Cr could be used as a tracer of Cr leaching in environmental studies in the dissolved phase.In bioleaching tests on tailings with Acidithiobacillus thiooxidans (pH ~ 2) or Pseudomonas putida (pH ~ 9), Cr was initially extracted as Cr(VI) and later reduced to Cr(III). In the experiments with A. thiooxidans the Cr reduction is due to the production of a series of sulfur compounds with high reducing power, while for P. putida probably uses a variety of electron acceptor for chromate reduction, enhanced by the presence of extracellular polymeric substances. Those mechanisms together with the increase of natural organic matter (NOM) and mineral carbonation, could explain the lower exchangeable pool of Cr(VI) in stockpiled chromite tailings compared to fresh tailings. Through the use of isotopic exchange, the contribution of SPM to the transport of exchangeable chromium and the impact of colloids containing Cr-bearing phases on the determination of the exchangeable pool of Cr associated to SPM (EWCr) was highlighted. Larger particles (>0.2 μm) were dominant in the impacted area, while chromium was mainly associated with colloids (1 kDa–500 kDa) in the pristine area. The presence of organic and inorganic colloids containing non-exchangeable chromium induces an overestimation of the EWCr values, which can be over-come thanks to a worst-case scenario correctionLes systèmes ultramafiques sont souvent synonymes de fortes teneurs en chrome (Cr) dans des roches, qui est naturellement lixivié vers les eaux de surface et souterraines. En raison de cet enrichissement naturel, les zones ultramafiques font souvent l’objet d’extractions massives. Le processus minier inclut l'exploitation et les activités d'enrichissement, dans lesquelles la grande quantité de résidus produits riches en métaux, tels que les gangues et les terrils, sont stockés à l’air libre. Ces processus peuvent considérablement augmenter les teneurs en Cr trivalent (Cr (III)) et hexavalent (Cr (VI)) disséminé dans l'environnement. Ce dernier (Cr (VI)), est connu pour être fortement soluble dans l'eau, biodisponible et toxique. Ce travail de thèse a porté sur i) la zone d’exploitation minière du nickel de Barro Alto (BA, Etat du Goiás, Brésil); ii) la zone d'exploitation minière historique de chromite de Cromínia (CA, Etat du Goiás, Brésil) et iii) une exploitation minière actuelle dans la vallée de Sukinda (Odisha, l'Inde). Le principal objectif de ces travaux est l'identification de l'impact d'activités minières (extraction du nickel et du chrome) sur la mobilité de Cr et sa disponibilité dans des zones ultramafiques, à l'aide des techniques isotopiques. Les compartiments chimiquement et isotopiquement échangeables de Cr(VI) (ECr (VI)) les plus hauts ont été mesurés dans des échantillons de minerai à BA, où l'enrichissement en isotopes légers de Cr (-0.76 à -0.16 ‰) a été attribué à la perte de Cr isotopiquement lourd et échangeable Cr(VI) pendant l’altération. Des valeurs étonnamment lourdes de δ53Cr ont été aussi trouvées dans des minerais saprolitiques à BA et dans des sols affectés par l’extraction à CA, jusqu’à +3.9 ‰ alors qu’ils étaient fortement enrichis en Cr(III). Les causes principales ont été attribuées à l'existence de chromite hydrothermale à CA et/ou à l’altération naturelle suivie par la réduction de Cr(VI), induisant la reprécipitation de Cr mobile et isotopiquement lourd. Le chrome était présent dans les lixiviats des échantillons de minerais saprolitiques et lateritiques de BA, sous la forme de Cr(VI) isotopiquement lourd (jusqu’à +4.84 ‰), en cohérence avec le Cr échangeable (ECr(VI)) (jusqu’à +4.37 ‰). Ces valeurs étaient dans la même gamme de compositions isotopiques que celles mesurées dans les eaux douces de surface (ruisseaux et réservoirs) situés dans la zone ultramafique. Ces résultats impliquent que Cr est principalement disséminé sous sa forme toxique Cr(VI), dont la disponibilité augmente depuis i) le profil de sol ii) les minerais et iii) les résidus miniers. Lors de tests de bioaltération réalisés sur les terrils avec Acidithiobacillus thiooxidans (pH~2) ou Pseudomonas putida (pH~9), Cr a été initialement extrait sous sa forme Cr(VI) puis réduit en Cr (III). Dans les expériences avec A. thiooxidans, la réduction du chrome est dû à l’important pouvoir réducteur d'une série de composés soufrés, tandis que P. putida utilise probablement pour la réduction des chromates une variété d'accepteurs d’électrons. Ces mécanismes, de même que l’augmentation de la concentration en matière organique et la carbonatation minérale, pourraient expliquer la plus faible concentration en Cr(VI) échangeable dans les terrils âgés par rapport aux terrils récents. Par la technique d’échange isotopique, la contribution des SPM au transport du chrome échangeable, ainsi que l’impact des colloïdes contenant des phases porteuses de Cr sur la mesure de ce compartiment échangeable associé aux SPM (EWCr) a été mise en évidence. Les plus grosses particules (> 0.2 µm) jouent un rôle prépondérant dans la zone impactée par l’activité minière, tandis que le chrome est principalement associé aux colloïdes (1 kDa-500 kDa) dans la zone vierge. La présence de colloïdes organiques et inorganiques contenant du chrome non-échangeable induit une surestimation de la valeur de EWCr, qui peut être corrigée par le biais d’un scénario du pir

ANÁLISIS COMPARATIVO DE LA REMOCIÓN DE UN SUSTRATO ORGÁNICO

Se evaluó el potencial de dos macrófitas acuáticas para remover Ftalato Ácido de Potasio (FAP), en sistemas batch con aireación permanente e iluminación de 12 horas, con demandas químicas de oxígeno teóricas iniciales de 250, 500 y 1000 mg/L. En términos de remoción de DQO, el tratamiento con Pistia stratiotes logró remociones promedio de 77,45% para la DQO más baja, 84,25% para la DQO intermedia y 93,47% para la DQO teórica de 1000 mg/L. El tratamiento con Egeria densa alcanzó remociones de 79,80%, 85,25% y 92,5% respectivamente, lo cual indica que la macrófita sumergida E. densa alcanzó remociones superiores a las de P. satratiotes debido a su capacidad para absorber nutrientes por la superficie de las hojas. Estos resultados evidencian que a mayor DQO, hay mayor remoción. Otros parámetros fisicoquímicos fueron monitoreados a lo largo de los bioensayos: Temperatura del agua, Conductividad Eléctrica (CE), Oxígeno Disuelto (OD), Potencial de Hidrógeno (pH), Alcalinidad total y Dureza total. La CE se incrementó diariamente en el periodo de 15 días al igual que la dureza total y el pH. Por su parte la alcalinidad fluctuó con tendencia general a disminuir en los tratamientos de menor carga y a aumentar en el de mayor carga tanto para Pistia como para Egeria

ANÁLISIS COMPARATIVO DE LA REMOCIÓN DE UN SUSTRATO ORGÁNICO

Se evaluó el potencial de dos macrófitas acuáticas para remover Ftalato Ácido de Potasio (FAP), en sistemas batch con aireación permanente e iluminación de 12 horas, con demandas químicas de oxígeno teóricas iniciales de 250, 500 y 1000 mg/L.
 En términos de remoción de DQO, el tratamiento con Pistia stratiotes logró remociones promedio de 77,45% para la DQO más baja, 84,25% para la DQO intermedia y 93,47% para 
 la DQO teórica de 1000 mg/L. El tratamiento con Egeria densa alcanzó remociones de 79,80%, 85,25% y 92,5% respectivamente, lo cual indica que la macrófita sumergida E. densa alcanzó remociones superiores a las de P. satratiotes debido a su capacidad para absorber nutrientes por la superficie de las hojas. Estos resultados evidencian que a mayor DQO, hay mayor remoción. 
 Otros parámetros fisicoquímicos fueron monitoreados a lo largo de los bioensayos: Temperatura del agua, Conductividad Eléctrica (CE), Oxígeno Disuelto (OD), Potencial de Hidrógeno (pH), Alcalinidad total y Dureza total. La CE se incrementó diariamente en el periodo de 15 días al igual que la dureza total y el pH. Por su parte la alcalinidad fluctuó con tendencia general a disminuir en los tratamientos de menor carga y a aumentar en el de mayor carga tanto para Pistia como para Egeria

Mechanistic studies on the bioremediation of Cr(VI) using Sphingopyxis macrogoltabida SUK2c, a Cr(VI) tolerant bacterial isolate

International audienceBioremediation studies of toxic hexavalent chromium (Cr(VI)) were investigated using an indigenous bacterial strain namely, Sphingopyxis macrogoltabida SUK2c, isolated from water samples collected from the Sukinda Valley in Odisha, India. A maximum Cr(VI) biosorption of about 55% could be achieved using the isolate for an initial Cr(VI) concentration of 4 mg L-1. The Cr(VI) biosorption isotherm was found to follow a typical Langmuirian behaviour. The Gibbs free energy value of Cr(VI) biosorption obtained was -25.6 kJ/mol, indicative of the involvement of chemical binding forces. The Cr(VI) biosorption process followed pseudo second order kinetics. FTIR spectral studies revealed that carboxyl, hydroxyl, amino and phosphate groups present on bacterial surface were involved in the complexation process. XPS studies confirmed the involvement of Cr(III) in addition to Cr(VI) ions with the bacterial cell surface. Zeta potential studies showed that the bacterial cells became less negative after interaction with Cr(VI), which further corroborated the binding of positively charged Cr(III) on the cell surface. The marginal shift in iso-electric point for Cr(VI) interacted bacteria further testified to the involvement of chemical binding forces in the bioremediation process. The results of the chromate reductase and Bradford protein assay tests performed on the extracellular component of the isolate also confirmed the involvement of extracellular protein in the reduction of Cr(VI) to Cr(III)

Assessing chromium mobility in natural surface waters: Colloidal contribution to the isotopically exchangeable pool of chromium (E w Cr value)

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(Bio)leaching Behavior of Chromite Tailings

International audienceChromite beneficiation operations in Sukinda valley (India) produce large amounts of tailings, which are stored in open air. In this study, bioleaching experiments were carried out in batch reactors with Acidithiobacillus thiooxidans or Pseudomonas putida in order to determine the potential leachability of metals contained in these tailings due to biological activity. Acidic and alkaline pH resulted from the incubation of tailings with A. thiooxidans and P. putida, respectively. Tailings were characterized by X-ray diffraction (XRD), X-ray fluorescence (XRF), and scanning electron microscopy (SEM), and chemical extraction of Cr(VI) with KH 2 PO 4 was performed. Mineralogical investigations showed that tailings are mainly composed of chromite, hematite, lizardite, chlorite, and goethite, which are all known as Cr-bearing phases. During the leaching with A. thiooxidans and P. putida, total Cr was initially extracted as Cr(VI) due to the presence of phosphates in the medium, and subsequently decreased because of Cr(VI) adsorption and reduction to Cr(III). Reduction was associated with bacterial activity, but also with the presence of ferrous iron. Despite the occurrence of siderophores in the tailings after incubation with P. putida, under acidic conditions, Fe extracted remained higher. Extracted Ni, Mn, and Al concentrations also increased over time. Given the significant amount of chromite tailings produced every year, this study shows that tailings storage and leachability represent a potential source of chromium. However, our findings suggest that the presence of bacterial communities, as well as physicochemical processes, favor Cr(VI) reduction

Chromium mobility in ultramafic areas affected by mining activities in Barro Alto massif, Brazil: An isotopic study

International audienceThis work studies the potential release of Cr from solids to surface water and groundwater, and the related isotopic compositions, in a nickel laterite ore deposit from Barro Alto in Brazil (in the State of Goiás). This ultramafic system is characterized by elevated concentrations of chromium (Cr). Even largely immobile Cr may be naturally leached from weathering profiles such as laterite to the surface and groundwater. This system is exploited for metal production, and both mining and metallurgical activities result in a significant increase in the trivalent (Cr(III)) and hexavalent chromium (Cr(VI)) concentrations released into the environment via runoff. Among all the samples collected, ores contained higher amounts of chemically and isotopically exchangeable Cr(VI) (ECr(VI)) with values as high as 104 (± 8) mg kg−1. δ53Cr increased from −0.28 (± 0.01)‰ to −0.05 (± 0.01)‰ and the ECr(VI) value was up to 30 times higher in deep soils than at the surface (up to 7 (± 1) mg kg−1). Chemically extracted Cr(VI) (ECr(VI)-KH2PO4) displayed positive δ53Cr value (1.69 (±0.03) ‰) with a similar Cr isotopic composition as the ones measured in freshwater sampled in and around the mine area. It appears that Cr is primarily released as Cr(VI), i.e. the toxic species, and becomes increasingly more available as it moves from the soil profile to the ores and mining residues. Based on the differences in the Cr isotopic composition, this study proves that δ53Cr can be used in environmental studies to trace Cr leaching

Mexico ants: incidence and abundance along the Nearctic–Neotropical interface

International audienceto explore different aspects of the population and community research of ants at different spatial scales, and to aid in the establishment of conservation policies and actions. There are no copyright restrictions. Please cite this data paper when using its data for publications or teaching events