A biogeochemical study of an abandoned Pb-Zn mine in the Aran Valley, Spain; applications of natural attenuation of heavy metals via secondary hydrozincite precipitation

[eng] The Aran Valley in Catalonia (Spain), was the site of large-scale Zn, Pb, Cu, Fe, and Ag mining from the late 19th century until approximately 1950. Although mining activities ceased over 70 years ago, some of the abandoned mining relics exhibit elevated concentrations of metals in the associated water systems, thus posing a health risk to the neighboring ecosystem. In this study, the largest underground mine in the Aran Valley, the Victoria Mine, was chosen as a field site to showcase the processes affecting metal mobility in the environment. The mine is composed of 15 km of tunnel galleries and is situated beneath a steep mountain slope. Moreover, the lowermost gallery exhibits a continuous output of water, whose composition reflects a flow path through overlying host rock and mine. Three sampling campaigns (October 2019, July 2020, and June 2021) provide a spaciotemporal dataset showing the evolution of solute concentrations through the system. Rainwater from the upper catchment flows into the host rock and dissolves ore materials (primarily Zn (sphalerite) and Fe (pyrite) sulfides with Ni and Cd impurities) causing elevated Zn, Ni, and Cd concentrations in the mine tunnels. Subsequently, precipitation of hydrozincite (Zn5(CO3)2(OH)6) in the tunnel gallery where water flows acts as a metal polishing mechanism (e.g. Zn from 155 to 10 ppm, Ni from 377 to 32 ppb, and Cd from 105 to 22 ppb). Hydrozincite has been shown to be product of biomineralization in other sites. However, by way of DNA sequencing of local bacterial communities, bioreactor experiments, morphological comparisons to biomineralized samples and geochemical modeling, it is confirmed that the mineral forms abiotically at the Victoria Mine. Characterization of the solid samples taken from the mine reveal several different morphologies, Zn zonations (i.e. purity changes), and small amounts of smithsonite (ZnCO3) and calcite (CaCO3). In general, all solids show layering, which is likely a result of variable solute concentrations and precipitation rates. The cause of these changes is hypothesized to be rain events, which change the water residence time in the host rock. Solubility experiments and speciation calculations done using the CrunchFlow code demonstrate that hydrozincite here does not have a constant Keq value, but exhibits a range of values (30.0 < log[Keq] <37.68). This behavior is presumed to be a result of precursor effects, such that amorphous solids with higher solubilities may form before hydrozincite. Notably, all analyzed solids from the collected mine samples show significant amounts of amorphous material (i.e. broad XRD peaks). A CrunchFlow reactive transport model constructed to capture the processes occurring in the system (i.e. rainwater infiltration of host rock → mixing of gallery source waters → flow through gallery). The model successfully reproduces the measured concentrations and mineral reactions. Sensitivity analyses of the most relevant parameter values (e.g. hydrozincite solubility, flow velocity, mineral reactivities) is performed to capture the range of behaviors expected to occur, and thereby predict future changes to metal mobility. The model confirms that changes to flow velocity (i.e. rain events), could be the cause of mineral layering and elemental zonation in hydrozincite. The model also confirms that the natural metal attenuation process is expected to occur through a wide range of system perturbations. Thus, the abandoned mine poses little risk to the neighboring ecosystem.[cat] A Catalunya, la Vall d'Aran va ser el lloc d'explotació a gran escala de Zn, Pb, Cu, Fe i Ag des de finals del segle XIX fins aproximadament l'any 1950. Tot i que les activitats mineres van cessar fa més de 70 anys, els sistemes d'aigua associats a les relíquies d’algunes de les mines abandonades (per exemple, galeries, instal·lacions de processament i abocadors de residus) presenten concentracions elevades de metalls, la qual cosa suposa un risc per a la salut dels ecosistemes associats. En aquest treball, s'ha escollit la mina Victòria (la mina subterrània de zinc més gran de la Vall d'Aran) com a àrea d’estudi per mostrar els processos que afecten la mobilitat dels metalls en el seu entorn. La mina està situada a sota d’un vessant escarpat de la muntanya i està formada per 15 km de galeries, moltes inundades actualment. A la galeria més baixa hi ha una sortida d’aigua contínua, la composició de la qual reflecteix el camí del flux a través de la mina i de la roca mare. S’han realitzat tres campanyes de mostreig a la mina (octubre 2019, juliol 2020 i juny 2021). Les dades espacio-temporal obtingudes mostren l'evolució de les concentracions dels soluts a través del sistema seguint el camí del flux. L'aigua de pluja que s’infiltra per la part superior (zona de captació) dissol els minerals sulfurs que formen la roca mare (principalment sulfurs de Zn (esfalerita) i de Fe (pirita) amb impureses de Ni i Cd), augmentant així les concentracions de Zn, Ni i Cd de l’aigua que circula per la mina. En aquestes condicions s’afavoreix la precipitació d’hidrozincita (Zn5(CO3)2(OH)6) al llarg de la galeria. Aquest mecanisme comporta una disminució significativa de les concentrations dels metalls en els fluxos d'aigua. Per exemple, la concentració de Zn disminueix de 155 a 10 ppm, la de Ni de 377 a 32 ppb, i la de Cd de 105 a 22 ppb. S’ha demostrat que en altres llocs la hidrozincita és un producte biomineral. Tanmateix, a partir de la seqüenciació d'ADN de les comunitats microbianes de la galeria, dels resultats experimentals biòtics, de les comparacions morfològiques amb mostres conegudes com a producte de la biomineralització i de la modelització geoquímica, es confirma que en la mina Victoria la formació del mineral és abiòtica. La caracterització de les mostres sòlides recollides a la mina evidencia morfologies diferents, zonacions de Zn en la hidrozincita (és a dir, canvis de puresa) i l’existència de petites quantitats de smithsonita (ZnCO3) i de calcita (CaCO3). En general, tots els sòlids presenten unes bandes com a conseqüència de la precipitació intermitent de diferents productes sòlids. Aquests patrons de precipitació deuen resultar de canvis en les concentracions de soluts i de les velocitats de precipitació. Com a hipòtesi, es planteja que la causa d'aquests canvis són diferents esdeveniments de pluja que modifiquen el temps de residència de l'aigua tant a la roca mare com a la galeria, produint una alteració de la composició de l'aigua. Els resultats dels experiments de solubilitat i els càlculs d'especiació fets amb el codi CrunchFlow demostren que el producte de solubilitat de la hidrozincita no té un valor constant, sinó un rang de valors (30,0 < log[Keq] < 37,7 a 7 °C). Se suposa que aquest comportament és degut a la formació de precursors amorfs amb solubilitats més elevades prèvia a la formació de la hidrozincita estructurada. De fet, els pics amplis en els difractogrames de DRX de totes les mostres sòlides recollides a la mina evidencien quantitats significatives de material amorf. Fent servir el codi CrunchFlow, s’ha elaborat un model de transport reactiu que captura els processos que ocorren al llarg del recorregut del flux a través de la captació: infiltració d'aigua de pluja i flux a través de la roca mare → barreja de diferents orígens d’aigua (goteig) de la galeria → flux d'aigua a través de la galeria. El model reprodueix satisfactòriament les concentracions mesurades i alhora prediu la formació d'hidrozincita, calcita i smithsonita mantenint les proporcions relatives observades a les mostres. S’ha realitzat una anàlisi de sensibilitat variant els valors dels paràmetres geoquímics i hidrodinàmics més rellevants (la solubilitat de la hidrozincita, la velocitat del flux, la dispersivitat i les reactivitats minerals) per avaluar el comportament de la mobilitat dels metalls i possible canvis futurs. El model confirma que els canvis en la velocitat del flux, és a dir, els canvis en la descàrrega volumètrica a través del sistema causats per esdeveniments de pluja, serien la causa de les bandes de minerals i de la zonació metàl·lica en la hidrozincita. El model també confirma que l'atenuació natural dels metalls és un procés factible en un ampli rang de pertorbacions del sistema. Per tant, la mina abandonada estudiada suposa poc risc per a l'ecosistema associat

La carne e iI sangue. Appunli sui vincoli di parentela in Sardegna.

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Low temperature vortex phase diagram of Bi2Sr2CaCu2O8 : a magnetic penetration depth study

We report measurements of the magnetic penetration depth \lambda_m(T) in the presence of a DC magnetic field in optimally doped BSCCO-2212 single crystals. Warming, after magnetic field is applied to a zero-field cooled sample, results in a non-monotonic \lambda_m(T), which does not coincide with a curve obtained upon field cooling, thus exhibiting a hysteretic behaviour. We discuss the possible relation of our results to the vortex decoupling, unbinding, and dimensional crossover.Comment: M2S-HTSC-V

Magnetic penetration depth in electron-doped cuprates - evidence for gap nodes

The in-plane penetration depth \lambda(T) is measured in electron-doped single crystals Nd1.85Ce0.15CuO4-x (NCCO) and Pr1.85Ce0.15CuO4-x (PCCO) using a 11 MHz LC resonator. In NCCO, \lambda(T) exhibits a minimum at 3.8 K and a pronounced upturn down to 0.4 K due to the paramagnetic contribution of Nd3+ ions. The London penetration depth contribution is linear in T. The paramagnetic contribution is absent in PCCO, where \lambda(T)~T^2 at low temperatures. Our results indicate the presence of nodes in the superconducting gap, i.e., non s-wave symmetry of the order parameter in electron-doped cuprates.Comment: 2 pages Acrobat-3 optimized PDF. To be presented at M2S-HTSC-V

Conductance quantization in etched Si/SiGe quantum point contacts

We fabricated strongly confined Schottky-gated quantum point contacts by etching Si/SiGe heterostructures and observed intriguing conductance quantization in units of approximately 1e2/h. Non-linear conductance measurements were performed depleting the quantum point contacts at fixed mode-energy separation. We report evidences of the formation of a half 1e2/h plateau, supporting the speculation that adiabatic transmission occurs through 1D modes with complete removal of valley and spin degeneracies.Comment: to appear in Physical Review

TEMPORAL EVOLUTION OF THERMAL STRUCTURES AND WINTER HEAT CONTENT CHANGE FROM VOS-XBT DATA IN THE CENTRAL MEDITERRANEAN SEA

Seasonal and year-to-year time evolution of the thermal structure, including the heat content change in the upper water column and its relationship with the surface net heat fluxes, have been studied at five locations in the central Mediterranean Sea. The study is based on temperature profiles collected during XBT surveys (eXpendable Bathy- Thermograph) carried out on ships of opportunity, in the framework of the MFSPP (Mediterranean Forecasting System Pilot Project), between September 1999 and May 2001. The five investigated zones are located in the southern Adriatic, NW Ionian, southern and northern Tyrrhenian, and Ligurian Sea. Gradual erosion of the thermocline in autumn, formation of a mixed layer in winter, and the onset of the stratification in spring, are common properties of the temporal evolution of thermal structures at all five locations. Moreover, in the southern Adriatic, a deep convection took place down to about 600m in winter 1999/2000. On the other hand, mild climatic conditions and small surface heat loss in autumn and winter 2000/2001 drastically reduced a mixing/ convection depth which hardly reached 200 m. Simultaneously, the NW Ionian remained slightly stratified throughout the winter period. The heat storage rate in the upper portion of the water column (down to 450 m) is compared with the air-sea net heat flux at a monthly scale. A heat content decrease is determined by the surface heat loss, and the processes such as lateral advection, or upwelling of the colder waters through the base of the water column (for example, in the southern Adriatic and Ionian Seas). Elsewhere (for example, in the northern Tyrrhenian and Ligurian Seas), the upwelling does not contribute significantly to the heat balance within the water column, since the vertical temperature gradients in deeper layers are negligible

Measurements of the absolute value of the penetration depth in high-Tc T_c superconductors using a tunnel diode resonator

A method is presented to measure the absolute value of the London penetration depth, $\lambda$, from the frequency shift of a resonator. The technique involves coating a high-$T_c$ superconductor (HTSC) with film of low - Tc material of known thickness and penetration depth. The method is applied to measure London penetration depth in YBa2Cu3O{7-\delta} (YBCO) Bi2Sr2CaCu2O{8+\delta} (BSCCO) and Pr{1.85}Ce{0.15}CuO{4-\delta}$(PCCO). For YBCO and BSCCO, the values of$\lambda (0)$are in agreement with the literature values. For PCCO$\lambda \approx 2790$ \AA, reported for the first time.Comment: RevTex 4 (beta 4). 4 pages, 4 EPS figures. Submitted to Appl. Phys. Let