Duojun Wang

Characterization of soil dust aerosol in China and its transport and distribution during 2001 ACE-Asia: 1. Network observations

[1] Mass loading, 20 elemental concentrations, and time series of aerosol particles were investigated over the China Dust Storm Research (ChinaDSR) observational network stations from March to May 2001 during the intensive field campaign period of ACE-Asia. Four extensive and several minor dust storm (DS) events were observed. Mass balance calculations showed that 45 - 82% of the observed aerosol mass was attributable to Asian soil dust particles among the sites, in which Ca and Fe contents are enriched to 12% and 6%, respectively, in the Western High-Dust source regions compared with dust aerosols ejected from the Northern High- Dust source regions. For the latter areas, elemental contents exhibited high Si (30%) and low Fe (4%). For all major source areas and depositional regions, aluminium (Al) comprises 7% of Asian dust. Air mass back-trajectory analysis showed that five major transport pathways of Asian dust storms dominated dust transport in China during spring 2001, all of which passed over Beijing. Measurements also suggest that the sand land in northeastern China is a potential source for Asian dust. The size distribution for estimating vertical dust flux was derived from the observed surface dust size distributions in the desert regions. For particle diameters between 0.25 and 16 mum, a lognormal distribution was obtained from averaging observations at various deserts with a mass mean diameter of 4.5 mum and a standard deviation of 1.5. This range of soil dust constitutes about 69% of the total dust loading. The fractions for particles in the size ranges of 16 mum are around 1.7% and 30%, respectively.

The effect of water on the electrical conductivity of olivine

It is well known that water (as a source of hydrogen) affects the physical and chemical properties of minerals—for example, plastic deformation and melting temperature—and accordingly plays an important role in the dynamics and geochemical evolution of the Earth. Estimating the water content of the Earth’s mantle by direct sampling provides only a limited data set from shallow regions (<200 km depth). Geophysical observations such as electrical conductivity are considered to be sensitive to water content, but there has been no experimental study to determine the effect of water on the electrical conductivity of olivine, the most abundant mineral in the Earth’s mantle. Here we report a laboratory study of the dependence of the electrical conductivity of olivine aggregates on water content at high temperature and pressure. The electrical conductivity of synthetic polycrystalline olivine was determined from a.c. impedance measurements at a pressure of 4 GPa for a temperature range of 873–1,273 K for water contents of 0.01–0.08 wt%. The results show that the electrical conductivity is strongly dependent on water content but depends only modestly on temperature. The water content dependence of conductivity is best explained by a model in which electrical conduction is due to the motion of free protons. A comparison of the laboratory data with geophysical observations suggests that the typical oceanic asthenosphere contains ∼10-2 wt% water, whereas the water content in the continental upper mantle is less than ∼10-3 wt%.

High-temperature dehydration of talc: a kinetics study using in situ X-ray powder diffraction

High-temperature in situ X-ray powder diffraction patterns were used to study the dehydration kinetics of natural talc with a size of 10–15 µm. The talc was annealed from 1073 to 1223 K, and the variations in the characteristic peaks corresponding to talc with the time were recorded to determine the reaction progress. The decomposition of talc occurred, and peaks corresponding to talc and peaks corresponding to enstatite and quartz were observed. The enstatite and talc exhibited a topotactic relationship. The dehydration kinetics of talc was studied as a function of temperature between 1073 and 1223 K. The kinetics data could be modeled using an Avrami equation that considers nucleation and growth processes where n varies from 0.4 to 0.8. The rate constant (k) equation for the natural talc is The reaction mechanism for the dehydration of talc is a heterogeneous nucleation and growth mechanism.

Stabilities of heavy metals in soils treated with red mud

Wastewater containing chloride ions is often discharged from landfills, tanning industries, and pickling industries. The high salt content in the wastewater can give rise to corrosion of waste pipes and pose problems to treatment systems, particularly biological units. Chloride induced is a well-known problem, especially where de-icing salts, chloride-containing admixtures or chloride-contaminated aggregate are incorporated into the concrete. Hydrotalcite (HT) is a class of anionic layered clays which can be described as containing brucite-like layers and positively-charged sheets. The general formula is [Mgl-xAlx(OH)2]x+(CO3)x/2x4H20, where x is equal to the ratio of A13+/(Mg2§247 with a value varying in the range of 0.17-0.50. HT calcined (thermally treated) within a certain temperature range (CHT) has been shown to reconstruct their original layered structure in the presence of aqueous solution of appropriate anions. Therefore, the CHT are good adsorbents for removal of toxic anions from wastewater. This work primarily focuses on investigation of the removal of chloride by CHT, taking it into account the effects of calcined temperature, Mg/A1 molar ratio of HT, and temperature on dechlorination. It was found that dechlorination capacity of CHT-500 ~ is higher than that calcined at other temperatures, and CLDH with an Mg/A1 ratio of 4 has marked ability to adsorb anions. The dechlorination capacity of CHT decreased with the rise of temperature, indicating that the process is exothermic in nature. And the data of isotherms fitted well to the linearly transformed Langmuir equation. The thermodynamic parameters were calculated from equilibrium isotherms. The negative AGO value indicates the spontaneity of the dechlorination process. The negative value of AH0 confirms the exothermic nature of uptake of chlorination. The explanations of chloride removal phenomena have been supported by X-ray diffraction and TG-DTA. The results reported here showed that these factors affect the uptake of chloride and are significant towards a better understanding of the potential application of CHT for removal of contaminated chloride water.

The dehydration kinetics of gypsum at high pressure and high temperature

An in situ dehydration kinetics study of gypsum under water-saturated condition was performed in the temperature and pressure ranges of 383–423 K and 343–1085 MPa by using a hydrothermal diamond anvil cell and Raman spectroscopy. Kinetic analysis shows that the dehydration rate k increases with pressure, suggesting a negative pressure dependence on dehydration rate. The elevation of temperature can contribute to the dehydration. The n values increase with pressure, indicating that the nucleation process becomes slower relative to the growth process. According to the n values of ∼1.0, the dehydration of gypsum is dominated by an instantaneous nucleation and diffusion-controlled growth mechanism. The obtained average activation volume ▵V is equal to 5.69 cm3/mol and the calculated activation energy Ea and the pre-exponential factor A are 66.9 kJ/mol and 4.66 × 105 s−1. The activation energy may be dependent upon grain size, shape, temperature and pressure, and surrounding water.

Electrical conductivity anisotropy in alkali feldspar at high temperature and pressure

The electrical conductivity of alkali feldspar along different orientations was determined at 1.0 GPa and at temperatures of 823–1286 K in a cubic anvil apparatus using alternating current impedance spectroscopy. Impedance arcs representing crystal conductivity occur in the frequency range of ∼103–106 Hz. The electrical conductivity of alkali feldspar increases with increasing temperature. The highest electrical conductivities in alkali feldspars were measured along the a-axis, with somewhat lower conductivities along the b-axis, and the lowest conductivities along the c-axis, suggesting minor anisotropy. The activation enthalpies ranged from 100 to 110 kJ/mol. The anisotropic results were combined to yield an isotropic model with an activation enthalpy of 102 kJ/mol. By comparing these results with previous results, we suggest that the dominating charge carriers for alkali feldspars are alkali ions. The minor anisotropy in conductivity for alkali feldspar may not account for the anisotropy of the crust.

Electrical conductivities of two granite samples in southern Tibet and their geophysical implications

There are clear differences in the electrical conductivities of the crustal granites of the Qinghai-Tibet Plateau. Because these granites are among the major rock types on the Qinghai-Tibet Plateau, it is very important to detect the electrical conductivity of granites under high temperatures and pressures to study the electrical conductivity structure of this area. Using impedance spectroscopy at a frequency range of 10−1–106 Hz, the electrical conductivity of the muscovite-granite collected from Yadong was investigated at a confining pressure of 1.0 GPa and temperatures ranging from 577 to 996 K, while the electrical conductivity of the biotite-granite collected from Lhasa was investigated at a pressure of 1.0 GPa and temperatures ranging from 587 to 1382 K. The calculated activation enthalpies of the Yadong muscovite-granite sample is 0.92 eV in the low-temperature range (577–919 K) and 2.16 eV in the high-temperature range (919–996 K). The activation enthalpies of the Lhasa biotite-granite sample is 0.48 eV in the low-temperature range (587–990 K) and 2.06 eV in the high-temperature range (990–1382 K). The change in the activation enthalpies of the granites at different temperature ranges may be associated with the dehydration of the two samples. The electrical conductivities of the granite samples obtained in the laboratory using impedance spectroscopy correspond well with field observations conducted near the sampling points, both in terms of the actual conductivity values and the observed variations between the low-temperature and high-temperature regimes. This correlation of laboratory and field conductivities indicates that the conductivities of the crustal rocks in the two regions closely correspond to granite conductivities. We calculated the electrical conductivities of muscovite-granite and biotite-granite samples using the effective medium and HS boundary models. When applied to the crustal rocks of southern Tibet, the results of the geophysical conductivity profiles lie within the range of laboratory data. Thus, the electrical characteristics of the crustal rocks underlying the southern Qinghai-Tibet Plateau can largely be attributed to granites, with the large changes to high conductivities at increasing depths resulting from the dehydration of crustal rocks with granitic compositions.

Raman spectroscopic study of calcite III to aragonite transformation under high pressure and high temperature

ABSTRACT In our study, a series of Raman experiments on the phase transition of calcite at high pressure and high temperature were investigated using a hydrothermal diamond anvil cell and Raman spectroscopy technique. It was found that calcite I transformed to calcite II and calcite III at pressures of 1.62 and 2.12 GPa and room temperature. With increasing temperature, the phase transition of calcite III to aragonite occurred. Aragonite was retained upon slowly cooling of the system, indicating that the transition of calcite III to aragonite was irreversible. Based on the available data, the phase boundary between calcite III and aragonite was determined by the following relation: P(GPa) = 0.013 × T(°C) + 1.22 (100°C ≤ T ≤ 170°C). It showed that the transition pressure linearly rose with increasing temperature. A better understanding of the stability of calcite III and aragonite is of great importance to further explore the thermodynamic behavior of carbonates and carbon cycling in the mantle.

Kinetic study of phase transformation of n-octane using hydrothermal diamond anvil cell

A kinetic study of phase transformation of n-octane has been performed using a hydrothermal diamond anvil cell. The results show that pressure has a negative effect on the solid–liquid reaction rate. The increase of pressure can accelerate the liquid–solid transformation rate. Upon the liquid–solid transformation, the light transmittance showed a decreased trend with time in the early stage, which was caused by the formation of a large quantity of crystal nuclei. In the later stage, the light transmittance almost remained the same, thus indicating a growth stage of crystal nuclei. The activation volume yields a value of 2.16×10−5 and –1.35×10−5 m3/mol for the solid–liquid and liquid–solid transformations. Based on the obtained activation energy, the solid–liquid transformation is dominated by the interfacial reaction and diffusion, and the liquid–solid transformation is controlled by diffusion. This technique is an effective and powerful tool for the transformation kinetics study of n-octane.

In Situ Raman Spectroscopic Study of Barite as a Pressure Gauge Using a Hydrothermal Diamond Anvil Cell

In situ Raman measurements of barite were performed at temperatures in the range of 298–673 K and pressures in the range of 105–1217 MPa using a hydrothermal diamond anvil cell combined with laser Raman spectroscopy. The Raman frequency and the full width at half maximum (FWHM) of the most intense ν1 Raman peak for barite as a function of pressure and temperature were obtained. In the experimental P–T ranges, the ν1Raman band systematically shifted toward low wavenumbers with increasing pressure and temperature. The positive pressure dependence of ν1Raman frequency indicates stress-induced shortening of the S–O bond, whereas the negative temperature dependence shows temperature-induced expansion of the S–O bond. In contrast, the observed ν1Raman band became broadened, which should be attributed to the reduced ordering of molecular structure. Based on the obtained data, the established relationships among the Raman shift or the FWHM, pressure and temperature can be used to obtain good estimates of the internal pressure in natural barite-bearing fluid inclusions or hydrothermal diamond anvil cell. This is a sensitive and reliable approach to the accurate determination of geological pressure.