195 research outputs found
Synthesis, characterization and thermochemistry of synthetic PbâAs, PbâCu and PbâZn jarosites
The enthalpy of formation from the elements of well characterized Pb-As, Pb-Cu, and Pb-Zn synthetic jarosites, corresponding to chemical formulas (H3O)0.68±0.03Pb0.32±0.002Fe2.86±0.14(SO4)1.69±0.08(AsO4)0.31±0.02(OH)5.59±0.28(H2O)0.41±0.02, (H3O)0.67±0.03Pb0.33±0.02Fe2.71±0.14Cu0.25±0.01(SO4)2±0.00(OH)5.96±0.30(H2O)0.04±0.002 and (H3O)0.57±0.03Pb0.43±0.02Fe2.70±0.14Zn0.21±0.01(SO4)2±0.00(OH)5.95±0.30(H2O)0.05±0.002, was measured by high temperature oxide melt solution calorimetry and gave ÎH°f = -3691.2 ± 8.6 kJ/mol, ÎH°f = -3653.6 ± 8.2 kJ/mol, and ÎH°f = -3669.4 ± 8.4 kJ/mol, respectively. Using estimated entropies, the standard Gibbs free energy of formation from elements at 298 K ÎG°f of the three compounds were calculated to be -3164.8 ± 9.1 kJ/mol, -3131.4 ± 8.7 kJ/mol, and -3153.6 ± 8.9 kJ/mol, respectively. Based on these free energies, their logKsp values are -13.94 ± 1.89, -4.38 ± 1.81 and -3.75 ± 1.80, respectively. For this compounds, a log10{Pb2+} - pH diagram is presented. The diagram shows that the formation of Pb-As jarosite may decrease aqueous arsenic and lead concentrations to meet drinking water standards. The new thermodynamic data confirm that transformation of Pb-As jarosite to plumbojarosite is thermodynamically possible
The environmental and geomorphological impacts of historical gold mining in the Ohinemuri and Waihou river catchments, Coromandel, New Zealand
Between 1875 and 1955 approximately 250,000 Mg yrâ 1 of mercury-, arsenic-, and cyanide-contaminated mine tailings were discharged directly into the Ohinemuri River and its tributaries, in the Coromandel Region, North Island, New Zealand. A devastating flood on 14 January 1907 deposited large amounts of mine waste across the floodplain of the Ohinemuri and Waihou rivers in the vicinity of the township of Paeroa. The 1907 mine-waste flood deposit was located as a dirty yellow silt in cores and floodplain profiles, with a thickness ranging from 0.15â0.50 m. Geochemical analysis of the mine waste shows elevated concentrations of Pb (~ 200â570 mg kgâ 1) and As (~ 30â80 mg kgâ 1), compared to early Holocene background concentrations (Pb < 30 mg kgâ 1; As < 17 mg kgâ 1). Bulk sediment samples recovered from the river channel and overbank deposits also show elevated concentrations of Pb (~ 110 mg kgâ 1), Zn (~ 140â320 mg kgâ 1), Ag (~ 3 mg kgâ 1), and Hg (~ 0.4 mg kgâ 1). Using the mine-waste deposit as a chronological marker shows that sedimentation rates increased from ~ 0.2 mm yrâ 1 in the early Holocene, to 5.5â26.8 mm yrâ 1 following the 1907 flood. Downstream trends in the thickness of the flood deposit show that local-scale geomorphic factors are a significant influence on the deposition of mine waste in such events. Storage of mine waste is greatest in the upstream reaches of the floodplain. The volume of mine waste estimated to be stored in the Ohinemuri floodplain is ~ 1.13 M m3, an order of magnitude larger than recent well-publicised tailings-dam failures, such as the 1996 South America Porco, 2000 Romanian Baia Mare and Baia Borsa accidents, and constituted, and was recognised at the time, a significant geomorphological and environmental event. The mine-waste material remains in the floodplain today, representing a sizable legacy store of contaminant metals and metalloids that pose a long-term risk to the Ohinemuri and Waihou ecosystems
New results from DAMA/LIBRA
DAMA/LIBRA is running at the Gran Sasso National Laboratory of the I.N.F.N..
Here the results obtained with a further exposure of 0.34 ton x yr are
presented. They refer to two further annual cycles collected one before and one
after the first DAMA/LIBRA upgrade occurred on September/October 2008. The
cumulative exposure with those previously released by the former DAMA/NaI and
by DAMA/LIBRA is now 1.17 ton x yr, corresponding to 13 annual cycles. The data
further confirm the model independent evidence of the presence of Dark Matter
(DM) particles in the galactic halo on the basis of the DM annual modulation
signature (8.9 sigma C.L. for the cumulative exposure). In particular, with the
cumulative exposure the modulation amplitude of the single-hit events in the (2
-- 6) keV energy interval measured in NaI(Tl) target is (0.0116 +- 0.0013)
cpd/kg/keV; the measured phase is (146 +- 7) days and the measured period is
(0.999 +- 0.002) yr, values well in agreement with those expected for the DM
particles.Comment: presented at the Int. Conf. Beyond the Standard Models of Particle
Physics, Cosmology and Astrophysics (BEYOND 2010), 1-6 February 2010, Cape
Town, South Afric
On the Nature and Genesis of EUV Waves: A Synthesis of Observations from SOHO, STEREO, SDO, and Hinode
A major, albeit serendipitous, discovery of the SOlar and Heliospheric
Observatory mission was the observation by the Extreme Ultraviolet Telescope
(EIT) of large-scale Extreme Ultraviolet (EUV) intensity fronts propagating
over a significant fraction of the Sun's surface. These so-called EIT or EUV
waves are associated with eruptive phenomena and have been studied intensely.
However, their wave nature has been challenged by non-wave (or pseudo-wave)
interpretations and the subject remains under debate. A string of recent solar
missions has provided a wealth of detailed EUV observations of these waves
bringing us closer to resolving their nature. With this review, we gather the
current state-of-art knowledge in the field and synthesize it into a picture of
an EUV wave driven by the lateral expansion of the CME. This picture can
account for both wave and pseudo-wave interpretations of the observations, thus
resolving the controversy over the nature of EUV waves to a large degree but
not completely. We close with a discussion of several remaining open questions
in the field of EUV waves research.Comment: Solar Physics, Special Issue "The Sun in 360",2012, accepted for
publicatio
Probing exotic phenomena at the interface of nuclear and particle physics with the electric dipole moments of diamagnetic atoms: A unique window to hadronic and semi-leptonic CP violation
The current status of electric dipole moments of diamagnetic atoms which
involves the synergy between atomic experiments and three different theoretical
areas -- particle, nuclear and atomic is reviewed. Various models of particle
physics that predict CP violation, which is necessary for the existence of such
electric dipole moments, are presented. These include the standard model of
particle physics and various extensions of it. Effective hadron level combined
charge conjugation (C) and parity (P) symmetry violating interactions are
derived taking into consideration different ways in which a nucleon interacts
with other nucleons as well as with electrons. Nuclear structure calculations
of the CP-odd nuclear Schiff moment are discussed using the shell model and
other theoretical approaches. Results of the calculations of atomic electric
dipole moments due to the interaction of the nuclear Schiff moment with the
electrons and the P and time-reversal (T) symmetry violating
tensor-pseudotensor electron-nucleus are elucidated using different
relativistic many-body theories. The principles of the measurement of the
electric dipole moments of diamagnetic atoms are outlined. Upper limits for the
nuclear Schiff moment and tensor-pseudotensor coupling constant are obtained
combining the results of atomic experiments and relativistic many-body
theories. The coefficients for the different sources of CP violation have been
estimated at the elementary particle level for all the diamagnetic atoms of
current experimental interest and their implications for physics beyond the
standard model is discussed. Possible improvements of the current results of
the measurements as well as quantum chromodynamics, nuclear and atomic
calculations are suggested.Comment: 46 pages, 19 tables and 16 figures. A review article accepted for
EPJ
Microflares and the Statistics of X-ray Flares
This review surveys the statistics of solar X-ray flares, emphasising the new
views that RHESSI has given us of the weaker events (the microflares). The new
data reveal that these microflares strongly resemble more energetic events in
most respects; they occur solely within active regions and exhibit
high-temperature/nonthermal emissions in approximately the same proportion as
major events. We discuss the distributions of flare parameters (e.g., peak
flux) and how these parameters correlate, for instance via the Neupert effect.
We also highlight the systematic biases involved in intercomparing data
representing many decades of event magnitude. The intermittency of the
flare/microflare occurrence, both in space and in time, argues that these
discrete events do not explain general coronal heating, either in active
regions or in the quiet Sun.Comment: To be published in Space Science Reviews (2011
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