Drainage minier acide | EPFL Graph Search

thumb|Exemple de drainage acide. thumb|Précipitation d'hydroxydes de fer dans un affluent du Missouri recevant des DMA d'une mine de charbon. thumb|Les eaux très acides (pH 2,2) du Río Tinto semblent incapables d'abriter de la vie. Quelques espèces extrêmophiles (bactéries aérobies et acidophiles) y survivent pourtant. Elles sont responsables de la couleur de la roche et de l'eau. thumb|right|Río Tinto, Espagne. thumb|La dissolution d'un cube cristallin de pyrite (qui était dans le bloc au centre de l'image) n'a laissé que quelques particules d'or. Le drainage minier acide (DMA) ou encore drainage rocheux acide (DRA) est un phénomène d'oxydation des sulfures produisant une solution acide s'écoulant régulièrement dans les cours d'eau. De l'acide sulfurique est produit lorsque des sulfures métalliques (pyrite, galène, sphalérite...) entrent en contact avec l'oxygène atmosphérique, à l'occasion de grandes excavations (carrières) et travaux miniers ou de stockage de déchets miniers. Ce pr

Sulfide oxidation and acid mine drainage formation within two active tailings impoundments in the Golden Quadrangle of the Apuseni Mountains, Romania

Linda Frei

Sulfidic mine tailings have to be classified as one of the major source of hazardous materials leading to water contamination. This study highlights the processes leading to sulfide oxidation and acid mine drainage (AMD) formation in the active stage of two tailings impoundments located in the southern part of the Apuseni Mountains, in Romania, a well-known region for its long-term gold-silver and metal mining activity. Sampling was undertaken when both impoundments were still in operation in order to assess their actual stage of oxidation and long-term behavior in terms of the potential for acid mine drainage generation. Both tailings have high potential for AMD formation (2.5 and 3.7 wt.% of pyrite equivalent, respectively) with lesser amount of carbonates (5.6 and 3.6 wt.% of calcite equivalent) as neutralization potential (ABA = -55.6 and -85.1 tCaCO(3)/1000 t) and showed clear signs of sulfide oxidation yet during operation. Sequential extraction results indicate a stronger enrichment and mobility of elements in the oxidized tailings: Fe as Fe(III)oxy-hydroxides and oxides (transformation from sulfide minerals, leaching in oxidation zone), Ca mainly in water soluble and exchangeable form where gypsum and calcite are dissolved and higher mobility of Cu for Ribita and Pb for Mialu. Two processes leading to the formation of mine drainage at this stage could be highlighted (1) a neutral Fe(II) plume forming in the impoundment with ferrihydrite precipitation at its outcrop and (2) acid mine drainage seeping in the unsaturated zone of the active dam, leading to the formation of schwertmannite at its outcrop. (C) 2011 Elsevier B.V. All rights reserved.

2011

Poisoning of Mn-Ce/AC catalysts for low-temperature NH3-SCR of NO by K+ and its counter-ions (Cl- /NO3- /SO42- )

Davide Ferri, Jie Yang

Mn-Ce/AC catalysts for low-temperature NH3-SCR of NOx were deliberately loaded with various potassium salts (KCl, KNO3, and K2SO4) to investigate the influence of the counter-ions on the poisoning impact. Whereas K salts poisoning had only marginal impact on the textural properties of the catalysts, but it altered the chemical properties of the catalysts significantly. Potassium addition lowered the relative surface concentration of Mn4+ and M-O in Mn-Ce/AC catalyst, suggesting that K might occupy the oxygen vacancies around Mn atoms, thereby weakening the NH3 adsorption. The extent of inhibition strongly depended on the anion, with Cl- causing a higher degree of poisoning than that of either NO3- or SO42- . While K+ could hinder NH3 adsorption, both NO3and SO42- provided new acid sites that could offset the deactivation.

ELSEVIER2022

Characterization of surface functional groups present on laboratory-generated and ambient aerosol particles by means of heterogeneous titration reactions

Michel Guillemin, Michel Rossi

A Knudsen flow reactor has been used to quantify surface functional groups on aerosols collected in the field. This technique is based on a heterogeneous titration reaction between a probe gas and a specific functional group on the particle surface. In the first part of this work, the reactivity of different probe gases on laboratory-gene rated aerosols (limonene SOA, Pb(NO3)(2), Cd(NO3)(2)) and diesel reference soot (SRM 2975) has been studied. Five probe gases have been selected for the quantitative determination of important functional groups: N(CH3)(3) (for the titration of acidic sites), NH2OH (for carbonyl functions), CF3COOH and HCl (for basic sites of different strength), and O-3 (for oxidizable groups). The second part describes a field campaign that has been undertaken in several bus depots in Switzerland, where ambient fine and ultrafine particles were collected on suitable filters and quantitatively investigated using the Knudsen flow reactor. Results point to important differences in the surface reactivity of ambient particles, depending on the sampling site and season. The particle surface appears to be multi-functional, with the simultaneous presence of antagonistic functional groups which do not undergo internal chemical reactions, such as acid-base neutralization. Results also indicate that the surface of ambient particles was characterized by a high density of carbonyl functions (reactivity towards NH2OH probe in the range 0.26-6 formal molecular monolayers) and a low density of acidic sites (reactivity towards N(CH3)(3) probe in the range 0.01-0.20 formal molecular monolayer). Kinetic parameters point to fast redox reactions (uptake coefficient y(0) > 10(-3) for O-3 probe) and slow acid-base reactions (gamma(0) < 10(-4) for N(CH3)(3) probe) on the particle surface. (C) 2009 Elsevier Ltd. All rights reserved.

2009

Characterization of surface functional groups present on laboratory-generated and ambient aerosol particles by means of heterogeneous titration reactions

Michel Guillemin, Michel Rossi

2009