Total Dissolution Research Articles

Behaviour of flotation tailings from a rare earth element deposit at high salinity

Various rare earth element (REE) deposits hosted by carbonatite complexes have been identified in southern (Montviel, Niobec) and northern Quebec (Eldor deposit). During the winter in Quebec, the use of road salts to facilitate transportation on the mine site and/or avoid water freezing during mine operation may be necessary. The sources of salinity can be diverse on a mine site: process water, precipitation, alteration of minerals in the soil. Thus, tailings may come in contact with these salts and react. The purpose of the present study was to evaluate the impact of salinity on the behaviour of flotation tailings (Eldor deposit), i.e. the mobility of the elements contained in the tailings under these conditions and the environmental risks involved. For this purpose, leaching column tests were developed. The solutions were deionized water (CW column), NaCl (25 g/L; CS1 column) and CaCl2 (25 g/L; CS2 column). The leachate analysis revealed that the divalent cations (Ba, Cd, Mg, Mn, Sr, and Zn) are more mobile in the presence of CaCl2 (CaCl2 > NaCl > deionized water). The mobility of these elements appears to be governed by the competition with Ca2+ for tailings sorption sites. U and Sc are most mobile in the presence of salts regardless of the applied salt solution, i.e. CaCl2 = NaCl > deionized water. The formation of soluble chloride complexes with these elements could therefore be the cause of this phenomenon. For S, the leaching solution has no impact on its mobility. In conclusion, the presence of salts would tend to increase the mobility of divalent cations present in these residues and enhance their contamination potential. Modeling using PHREEQC software allowed comparison of these results with post-dismantling mineralogical characterization. Both methods showed: (i) total dissolution of fluorite [CaF2], galena [PbS], richterite [Na(CaNa(Mg,Fe2+)5[Si8O22](OH)] and Ba silicate; (ii) precipitation of iron oxides/hydroxides and silicate minerals. However, the modeling was unable to predict the behaviour of carbonate minerals. Further modeling tests involving kinetics should be considered in a future study.

Rapid Extraction Chemistry Using a Single Column for 230Th/U Dating of Quaternary Hydrothermal Sulfides

230Th/U dating can provide high-precision age constraints on Quaternary hydrothermal sulfides. However, low content of U and Th often involves extraction chemistry for the separation and enrichment of U and Th, but these chemical processes are very complex. We developed a simplified procedure consisting of total sample dissolution and single-column extraction chemistry, which can reduce the time and improve the accuracy of the dating. Concentrated HCl-HF followed by HNO3 was added to ensure complete dissolution. A single column filled with 0.4 mL of AG 1-X8 anion resin was used, then 8 M HNO3, 8 M HCl and 0.1 M HNO3 were used to elute most of the matrix metals, Th and U. This process provided more than 95% recoveries for U and Th, and negligible blanks. Meanwhile, Pb and Bi interferences were tested and showed no effect on the U and Th isotope ratio. The 230Th/238U activity of the Geological Survey of Japan geochemical reference material JZn-1 in secular equilibrium was determined and showed a radioactive equilibrium (1.00 ± 0.01, n = 5, all errors 2σ) and an in-house standard QS-1 was consistent to 0.0078 ± 0.0001 (n = 8, ±2σ) with an average age of 705 ± 10 yrs BP (n = 8, ±2σ). The technique greatly shortens the sample preparation time and allows more concise and effective analysis of U-Th isotopes. It is ideally suited for the high-precision 230Th/U dating of Quaternary submarine hydrothermal sulfides and sulfides from other settings.

Rapid determination of twelve bioactive components in rat plasma by UHPLC-MS/MS and its application to pharmacokinetic and in vitro-in vivo correlation study of compound liquorice tablets

Compound liquorice tablets (CLQTs), composed of Licorice Extract (LE), Powered Poppy Capsule Extractive (PPCE), Camphor, Oleum Anisi Stellati and sodium benzoate, is widely used for antitussive and expectorant. A fast, selective and sensitive UHPLC-MS/MS method for determination of seven flavonoids (liquiritin, isoliquiritin, neoisoliquiritin, liquiritigenin, isoliquiritigenin, liquiritin apioside, and isoliquiritin apioside), two triterpene saponins (glycyrrhizic acid and glycyrrhetinic acid), two isoquinoline alkaloid (codeine and morphine), one aromatic (trans-anethole) in rat plasma was developed and validated. Then, the proposed method was used to investigate the pharmacokinetic differences of eleven bioactive components in rats after administration of CLQTs and the single herb (LE or PPCE). The results showed that LE acted synergistically with PPCE by prolonging the efficacy of CLQTs. Subsequently, based on an AUC-weighting approach, the integrated pharmacokinetics of twelve bioactive components was determined, which might provide a more comprehensive understanding of the relationship between the pharmacokinetic behaviors of herbal medicine. Additionally, in view of the synthetic effect of complex chemicals in traditional Chinese medicine, we put forward a flow-injection analysis method to determine the total components dissolution profile of CLQTs. Finally, the integral pharmacokinetic parameter (lnC) and the cumulative dissolution (Pmr(i)) were used to explore the in vitro-in vivo correlations preliminarily and the R2 was above 0.9383. This study provided more insight for further understanding of the compatibility mechanism of CLQTs and improved the safety and rationality of the clinical use of CLQTs.

Calcium carbonate dissolution patterns in the ocean

Calcium carbonate (CaCO3) minerals secreted by marine organisms are abundant in the ocean. These particles settle and the majority dissolves in deeper waters or at the seafloor. Dissolution of carbonates buffers the ocean, but the vertical and regional distribution and magnitude of dissolution are unclear. Here we use seawater chemistry and age data to derive pelagic CaCO3 dissolution rates in major oceanic regions and provide the first data-based, regional profiles of CaCO3 settling fluxes. We find that global CaCO3 export at 300 m depth is 76 ± 12 Tmol yr−1, of which 36 ± 8 Tmol (47%) dissolves in the water column. Dissolution occurs in two distinct depth zones. In shallow waters, metabolic CO2 release and high-magnesium calcites dominate dissolution while increased CaCO3 solubility governs dissolution in deeper waters. Based on reconstructed sinking fluxes, our data indicate a higher CaCO3 transfer efficiency from the surface to the seafloor in high-productivity, upwelling areas than in oligotrophic systems. These results have implications for assessments of future ocean acidification as well as palaeorecord interpretations, as they demonstrate that surface ecosystems, not only interior ocean chemistry, are key to controlling the dissolution of settling CaCO3 particles. About 50% of total dissolution of marine calcium carbonate occurs in the water column below 300 m depth while sinking to the seafloor, according to a reconstruction of settling fluxes of calcium carbonate in major oceanic regions from seawater observations.

Southern Ocean carbonate dissolution paced by Antarctic Ice-Sheet expansion in the early Miocene

The preservation of calcium carbonate deposits on the seafloor is one of the factors that regulates Earth's carbon cycle over longer timescales. Fluctuations in the carbonate compensation depth (CCD), the depth below which calcium carbonate is completely dissolved, can therefore significantly alter the ocean's capacity to sequester or release atmospheric carbon. High-latitude deep oceans are particularly important to the carbon cycle given their large capacity to store carbon dioxide. Here we present carbonate content results from an abyssal Subantarctic record (Site U1514) that spans the early Miocene and the onset of the Miocene Climatic Optimum. We show that carbonate preservation was highly variable from 19.9 to 17 Ma, with multiple episodes of total carbonate dissolution. Carbonate preservation then improved gradually after 17 Ma following the onset of the Miocene Climatic Optimum. Episodes of carbonate dissolution occurred preferentially at long eccentricity minima while periods of long eccentricity maxima improved carbonate preservation. These patterns of carbonate accumulation are in opposite phase to lower latitude Atlantic and Pacific records, which suggests that different mechanisms of carbonate accumulation/preservation were in place in high and low-latitude oceans. Comparison of Site U1514 with Antarctic records indicates an influence of ice sheet oscillations on carbonate preservation at the Subantarctic seafloor. We propose that carbonate dissolution occurred via the northward expansion of southern-derived undersaturated waters during periods of Antarctic ice sheet expansion. These findings indicate that the Subantarctic Southern Ocean was highly sensitive to Antarctic ice sheet fluctuations during the early Miocene, consistent with observations from Antarctica that show intensified polar amplification under a warmer climate.

Bio-oxidation behavior of pyrite, marcasite, pyrrhotite, and arsenopyrite by sulfur- and iron-oxidizing acidophiles

The oxidation of sulfide minerals is of central importance due to the acid mine drainage (AMD) production. The bio-oxidation of pyrrhotite, pyrite, marcasite, and arsenopyrite was carried out with mesophilic bacteria (Acidithiobacillus ferrooxidans, A. thiooxidans, and Leptospirillum ferrooxidans) at 34 °C for 30 days. Bio-oxidation tests showed that marcasite has a high potential in producing AMD compared to pyrrhotite. Arsenopyrite has different behavior in the presence and the absence of additives (i.e., FeSO4·7H2O and sulfur). While the absence of additives increased the nickel and zinc dissolution, their presence increased the total iron dissolution. Sulfur and jarosite were observed on the surfaces of pyrrhotite and arsenopyrite. With the formation of these passivation layers, the continuous iron extraction is effectively suppressed. This study is helpful to comparatively evaluate the AMD production of sulfide minerals in an oxidizing environment and to study the effects of passivation layers on their biooxidation in different conditions.

Tuning the Anodic and Cathodic Dissolution of Gold by Varying the Surface Roughness

AbstractThis work presents the reactivity and dissolution of an as‐polished and electrochemically pre‐treated polycrystalline Au electrode, which is used as a model system. The effect of the electrochemical pre‐treatment in corrosive 0.37 M HCl solutions on the Au surface roughness and dissolution is investigated by varying the number of pre‐treatment steps at 1.16 V against the reversible hydrogen electrode. It is shown that the first 10 s pre‐treatment of the as‐polished Au results in a higher surface roughness and thus higher electrochemically active surface area (ECSA) than that of the as‐polished Au. With the subsequent pre‐treatments, however, the ECSA is gradually decreasing reaching a steady value. The dissolution rate of the pre‐treated Au electrodes upon potential cycling in 0.1 M H2SO4 is determined by in situ inductively coupled plasma mass spectrometry. A non‐linear dependence of Au dissolution amount is found with respect to the number of pre‐treatments. The overall total Au dissolution rate follows a similar trend as ECSA/roughness. However, an important difference in the dissolution behavior is identified with respect to dissolution processes during Au oxidation (anodic dissolution) and Au reduction (cathodic dissolution): the former is more sensitive to the surface roughness. Thus, the ratio between Au anodic and cathodic dissolution amounts decreases substantially with decrease in surface roughness. This finding is explained by the slow and fast dissolution kinetics for anodic and cathodic processes, respectively. Current work further advances our understanding of the complex Au dissolution mechanism.

The enhanced catalytic activity and stability of Fe3O4-S@C Fenton-like catalyst for phenol degradation

Carbon-coated Fe3O4-S (Fe3O4-S@C) Fenton-like catalyst on carbon cloth is successfully prepared by electrodeposition and subsequent ethanol solvothermal treatment. Fe3O4-S@C with amorphous Fe3O4 presents a rough network structure. Besides, the ≡Fe2+/≡Fe3+ ratio on Fe3O4-S@C is higher than that on sulfur-doped Fe3O4 (Fe3O4-S). The Fe3O4-S@C has the enhanced catalytic activity and improved cycle stability under circumneutral pH. 95.4% phenol is degraded in 18 min with 0.204 ppm of total leached iron. 95% phenol removal efficiency is still maintained after Fe3O4-S@C is reused four times, whereas the Fe3O4-S presents the sharply reduced catalytic performance after the first degradation test. The formed carbon layer not only accelerates the redox cycle of ≡Fe3+/≡Fe2+ by reducing ≡Fe3+ to ≡Fe2+ during the degradation, but inhibits the total iron dissolution effectively. Furthermore, the S6+ can form micro-acidic environment on the catalyst; thus, the degradation reaction can take place under circumneutral pH, and the Sn2− can accelerate the transformation from ≡Fe3+ to ≡Fe2+ through reduction effect. Also, the polar groups of the carbon layer can adsorb more phenol to facilitate degradation process.

Modification of bauxite residue with oxalic acid for improved performance in intumescent coatings

Valorization of bauxite residue (BR) enhances the dynamics of its application in intumescent coating for fire retarding systems. This BR, an alumina production waste could contain up to 45% ferrous oxide along with residual aluminous minerals. In an attempt to optimize the fire retardant properties of these minerals in intumescent systems, BR was treated in oxalic acid, varying the heating temperature between 50 °C and 100 °C at a constant pH of 2.65. X-ray florescence spectrometry revealed up to 80% reduction in iron content and total dissolution of desilication products (DSPs). The process temperature was found to affect the efficiency with which iron oxide was removed and with which the dissolved DSPs were precipitated as aluminum hydrates. X-ray diffraction revealed increased crystallinity and a gibbsite-dominated compound. Incorporation of the modified bauxite residues into a control intumescing formulation resulted in improved endothermic cooling, increased char expansion and char reinforcement. An inverse relationship appeared to exist between aluminum hydrates and iron as removal of iron led to enhanced intumescence and increased char expansion while higher iron content led to a compact, less expanded char. A balance of the fire retarding minerals occurred at a leaching temperature of 75 °C in oxalic acid. Best heat shielding performance thus occurred at XBR75-IC5 as char expansion increased by 12% and the substrate temperature reduced by 31% over the control IC system. Thus, BR may act as alternative fire retardant filler for intumescing systems.

Unstable Density‐Driven Convection of CO2 in Homogeneous and Heterogeneous Porous Media With Implications for Deep Saline Aquifers

AbstractDensity‐driven convection mixing has been identified to enhance CO2 trapping in deep saline aquifers storage. In this study, the dynamics of fingering instability and associated mass transfer caused by convection mixing between the movements of miscible analogue fluid pairs are investigated by magnetic resonance imaging (MRI). Two kinds of homogeneous porous media and six kinds of heterogeneous porous media with varying permeability permutations were used at ambient pressure and temperature. In homogeneous porous media, the detail analyses on the data of fingering pattern, finger number and distribution identify that the large finger sizes and high sinking velocities can be developed when the permeability up to 3.3 × 10−11 m2. In heterogeneous porous media, the sand layer first touched by downward fingers plays a dominant role in finger evolution, channeling and fingering convection mechanisms were found among these cases. Moreover, the dissolution rate characterized by Sherwood number (Shm) (enhance or inhibit fluid mixing, depending on the layout of the sand layer) was found to be independent of the local convection dissolution, such as vortex flow and finger splitting at the sand boundary with mutation permeability (enhanced fluid mixing, promoting CO2 dissolution in carbon storage). Finally, the total CO2 dissolution rate Shm in all cases was compared, Shm are at a range of 970–5,079 in homogeneous porous media, while are 190–688 in heterogeneous porous media.

Effect of coating composition on the micro-galvanic dissolution behavior and antifouling performance of plasma-sprayed laminated-structured Cu Ti composite coating

Abstract Marine biofouling is a critical issue significantly deteriorating the service performance of marine infrastructures. Thus, development of an effective and long-lasting antifouling coating is highly desirable. Here, a laminated-structured copper-titanium (Cu Ti) antifouling coating was fabricated by plasma spraying of mechanically blended Cu and Ti powders. The coating was designed to enable controlled release of Cu ions from Cu/Ti micro-galvanic cells and thus to achieve effective and long-term antifouling performance. The effect of Cu Ti coating composition on its micro-galvanic dissolution behavior and antifouling performance was systematically investigated. The coating compositions were changed by varying Cu content from 8.1 to 65.2%. Analysis of scanning Kelvin probe force microscopy and long-term immersion test results indicated that Cu loading within Cu Ti coating exhibited little influence on the formation and mechanism of Cu/Ti micro-galvanic cells. However, the Cu ions release rate and antifouling duration increased with increasing Cu loading. The antifouling efficiency of Cu Ti coating against bacterial survival increased with the increase in the Cu loading from 8.1 to 19.2% and it reached ~100% when Cu loading exceeded 19.2%. Electrochemical test results revealed that with the variation of Cu loading, the amount of micro-galvanic cells rather than the dissolution rate of each single micro-cell played a more prominent role in deciding the total Cu dissolution rate; and consequently, the Cu ions release rate and self-polishing rate. These results may guide the advanced design of versatile Cu Ti antifouling coatings with environment-friendly, durable, and remarkable antifouling capability for different practical requirements in marine engineering through facilely tailoring coating composition.

Measurement of Fluid Phase Equilibria for High Gas Ratio Mixtures of Carbon Dioxide, Methane, and Brazilian Presalt Crude Oil

The phase behavior of petroleum fluids under reservoir conditions provides fundamental information for an adequate crude oil production scheme. Recently, complex phase transitions have been studied for presalt crude oils, involving atypical liquid–liquid–vapor and liquid–liquid–asphalt phase transitions. In this paper, the phase behavior of synthetic mixtures containing carbon dioxide, methane, and a Brazilian presalt crude oil was investigated using PVT, coupled with near-infrared (NIR) transmittance and high-pressure microscopy (HPM) measurements. Crude oil (API 28.0, 0.68 wt % of asphaltenes) was mixed with 25.0 wt % gas (for a CH4/CO2 ratio from 0 to 62.5 wt %), and the phase behavior of the mixture was evaluated at a reservoir temperature of 343.15 K and pressures up to 100 MPa. Black oil phase behavior was detected for systems with a lower CH4/CO2 ratio and lower gas volume fraction, with no asphaltenes precipitation observed. As the CH4/CO2 ratio increased, pressure–volume curves showed a slight phase transition, with a not evident sharp break in the slope because of the minor difference of fluid compressibility. Moreover, a phase insolubility was confirmed by NIR and HPM tests for a high CH4/CO2 ratio that can be associated with the formation of an asphaltic phase. When total molar gas content increases by increasing the CH4/CO2 ratio, the asphaltic phase is formed at higher pressures. However, asphaltenes were detected as an uncommon fine dispersion with no larger fractal aggregates formation, even at pressures far below the asphaltenes onset pressure (AOP). Additionally, a nontypical behavior was observed in HPM tests with a total asphaltene dissolution when pressure reached the bubble pressure point. This atypical redissolution is in accordance with an instantaneous phase dissolving at pressures higher than the AOP, observed for the same oil at high methane ratios.

Effect of the precipitates on the hydrogen desorption kinetics from zirconium-niobium alloys

This study aims at identifying and quantifying the rate-limiting steps of the hydrogen desorption process from unoxidized M5Framatome alloy. Gaseous deuterium charging, Thermal Desorption Spectrometry (TDS), Differential Scanning Calorimetry (DSC) and finite elements simulations of TDS results reveal that hydrogen desorption kinetics from the metal is limited by the surface molecular recombination (similarly to Zircaloy-4) and that part of the hydrogen originated from the elaboration process of M5Framatome and Zr-2.5%Nb is trapped by the Nb-rich precipitates. In the studied conditions and regarding M5Framatome, the desorption flux corresponding to this initially trapped hydrogen reaches its maximum after the total dissolution of the precipitates, which releases hydrogen into solid solution. The kinetic constant corresponding to surface recombination identified on M5Framatome was identical to the one previously determined on Zircaloy-4.

From Fresh Itabirites and Carbonates to Weathered Iron Ore: Mineral Composition, Density and Porosity of Different Fresh and Altered Rocks from the Quadrilátero Ferrífero, Brazil

The weathering of Paleoproterozoic itabirites (metamorphic-banded iron formations) and dolomites from the Cauê and Gandarela Formations in the Quadrilátero Ferrífero (QF), Brazil, produces supergene iron ore with different mineralogical, chemical, and physical properties. In this work, we present a methodology to assess the changes in chemical and physical features of those rocks during weathering, via quantitative analyses of mineral assemblages. These mineral assemblages were calculated from chemical analyses of fresh and weathered samples collected from drill holes drilled in different iron ore deposits in the QF. In general, the number of mineral species found in fresh or/and weathered itabirite is restricted, which helps the quantification of the mass and volumes of minerals by normative calculation in a large dataset of drilling and channel samples. The calculation of the bulk density takes into consideration, besides the mineral phases, the voids and free water in the altered rock matrix. This study shows that the estimated porosity in supergene ore varies from 0% to 20%, for compact materials, and from 15% to 55% for friable rocks, indicating an important process of rock matrix dissolution during the weathering of itabirites. In this process, MgO, CaO, and FeO are leached out from carbonates, talc, and amphiboles. Magnetite is oxidized to hematite, releasing Fe2+, which is oxidized and precipitates as Fe-hydroxide. There is a concentration of Fe2O3, MnO, Al2O3, and SiO2 in the supergene ore (saprolite) by residual enrichment or recrystallization of hematite, goethite, quartz, manganese oxides, and kaolinite. A calculation of weathering effects on the original protoliths allowed for the establishment of a correlation between different types of fresh itabirites and their corresponding weathered materials. The calculation was carried out in several steps, to account for changes in porosity and masses and has taken into consideration differences in the mineralogical composition of the protolith. Within the weathered zones, a strong link is observed between the existence of collapse on the topographic surface and the presence of supergene ore underneath. The partial to total dissolution of quartz and carbonates from the protolith itabirite results in very porous materials and leads to gravitational collapses.

Single-crystalline rutile TiO2 nanorod array on flexible Ti substrates for efficient photoelectrocatalytic degradation of phenol in water

Single-crystalline nanorods are intrinsic highways for charge transfer and hence ideal nanofeatures for efficient photoelectrochemical (PEC) degradations of pollutants in wastewater. Photocatalytic thin films on flexible substrates avoid the nuisance catalysts-recovering procedure and also allow for the flexible design in photocatalytic apparatus. We therefore directly deposited single-crystalline rutile TiO2 nanorod arrays on flexible and conductive Ti substrates through a hydrothermal technique and optimized the synthetic parameters to achieve an extremely high PEC activity towards phenol removal in water under UV light illumination. In the presence of tetrabutyltitanate (TBT) and HCl reactants under a hydrothermal environment, a balance in the erosion of the Ti substrate and the precipitation of TiO2 nanorods is found to be the key to tune the nanofeatures of the TiO2 thin films and in turn the PEC efficiency. The decreasing TBT concentration achieved a more sparsely distributed nanorod array, which significantly contributes to the PEC activity; yet too little TBT resulted in total dissolution of Ti plates. The PEC activity increased with increasing hydrothermal duration because of more loaded TiO2. The maximum reaction rate constant is 2.74 h−1, which is 39 times that of a commercial P25 TiO2 nanoparticulate film. The photocurrent stabilized at 0.9 mA/cm2 under the illumination of AM1.5G simulated solar light, suggesting a high separation efficiency of photogenerated holes and electrons along the single-crystalline rutile TiO2 nanorod arrays.

Role of aposomes and epididymosomes in sperm quality control: A light and transmission electron microscopic study in an experimental rat model.

The epididymis responds to adverse conditions of misshapen spermatozoa resulting from pathological changes or toxic insults by secretion of a dense matrix that segregates the latter for complete disintegration and dissolution. The objective of this study was to find the source of this matrix and the role-player of disintegration and dissolution of misshapen spermatozoa. We chose Wistar strain male rat model to tackle this issue, and the rats were administered with aflatoxin B1 for 55days so as to increase the incidence of misshapen spermatozoa. At the end of the treatment, different segments of epididymis were processed for microscopic observations. We found that parallel with abundant misshapen spermatozoa in the epididymis the principal cells of the initial segment secrete enormous membrane-bound apical blebs called aposomes, which contain epididymosomes. The aposomes were found to coalesce so as for the content to merge and form a dense matrix that entangles the misshapen spermatozoa and segregates them from viable spermatozoa. The epididymosomes associate with the misshapen spermatozoa, and the latter is processed to disintegration and total dissolution. Therefore, we assign the role of segregation of misshapen spermatozoa from viable ones to the dense matrix of aposomes and their disintegration and dissolution to the epididymosomes.

Determination of germanium in plant and soil samples using high-resolution continuum source graphite furnace atomic absorption spectrometry (HR CS GFAAS) with solid sampling

Germanium (Ge) is commonly an unreported trace element in environmental samples due to the lack of reliable analytical methods. Besides atomic mass spectrometric methods (ICP-MS) and atomic emission spectroscopy (OES), graphite furnace atomic absorption spectrometry (GFAAS) offers the sensitivity that is needed in biological and environmental analysis. However, until recently AAS-techniques for the quantification of Ge were solely described for liquid samples and require time consuming sample preparation steps involving total dissolution of the sample matrix. In the present study we modified an existing method for the determination of Ge in liquid samples by high-resolution continuum source graphite furnace atomic absorption spectrometry (HR CS GFAAS) towards its applicability to solid samples.Similar to liquid HR CS AAS, the addition of Pd/Mg(NO3)2 as modifier was necessary to avoid analyte losses. To achieve a homogeneous wetting of the solid sample Triton X-100, a non-ionic surfactant, was added together with the modifier. A biomass weight of 0.1–0.2 mg was appropriate for the solid sampling set-up, to which 20 μL of modifier, including 0.1% surfactant, was added. The furnace temperatures were adjusted to 90–140 °C for the drying process, to 1500 °C for pyrolysis and to 2550 °C for the atomisation step. Various calibration options were also considered realising routine analysis. Considering Ge concentrations in various environmental samples we observed no significant differences between results obtained from HR CS AAS and ICP-MS, respectively. The analytical technique demonstrated a detection limit for Ge down to 500 μg kg−1 Ge by a characteristic mass of 50 pg for selected biomass samples. The novel method can be applied in geochemical laboratories equipped with HR CS GFAAS devices to determine Ge in range of 0.7–360 mg kg−1 Ge in solid environmental samples without any sample preparation steps except of grinding.

Preconcentration of noble metals on alumina prior to analysis by inductively coupled plasma mass spectrometry: Application to geological samples

A preconcentration method for the determination of noble metals (Ag, Au, Ir, Os, Pd, Pt, Re, Rh, Ru) was developed using alumina as a sorbent. The method involves an off-line preconcentration analytical procedure: the formation of chloro-complexes of these elements with HCl, loading of the chloro-complexes on alumina followed by elution of analytes and analysis by inductively coupled plasma mass spectrometry. The effects of HCl/HNO3 concentration in the sample digest, mass of alumina, and concentration of eluents (HCl and HNO3)/thiourea were studied using multivariate experimental designs. Using 2 M HCl as eluent, detection limits were improved by a factor of 10–20 for Ag, Ir, Os, Pd, Pt, and Ru, and 3–5 for Re and Rh compared to those achieved by direct nebulization (i.e. without preconcentration). Accuracy was verified through analysis of CDN-PGMS-19 ore reference material. Using 2 M HCl for elution, the results for Ag, Pd and Pt agreed with the reference values obtained based on aqua regia digestion (which does not achieve total dissolution). For the determination of Au, evaporation of HNO3 and elution with thiourea were required.

DA DISSOLUÇÃO PARCIAL DE SOCIEDADE NO CPC

O Código de Processo Civil passou a disciplinar o procedimento de dissolução parcial da sociedade cujo procedimento era inexistente perante o ordenamento anterior e que exige um traço distintivo com o procedimento da dissolução total com a perspectiva de atendimento ao princípio da preservação da empresa.

Use of DICTRA® simulations to support carbide particle growth study in NbC-Ni cemented carbide

Carbide particle growth observed in a NbC-12%Ni (mass percent) sample sintered at 1420 °C was discussed using DICTRA® simulation of spherical particles immersed in a Ni matrix. It is possible to describe the liquid formation during sintering using a model that assumes a spherical region of NbC, with radius equivalent to the NbC particle distribution, surrounded by nickel. NbC volume fraction was obtained for different simulation times allowing the evaluation of the dissolution behavior in different particle sizes. Small carbides (around 1 μm in diameter) suffered total dissolution, while major carbides (10 μm in diameter) did not dissolve during the simulation. Chemical content evidenced that Nb and C from carbide dissolution segregated to liquid phase reaching levels up to 15 and 2%, respectively, showing the availability of this elements to re-precipitate in non-dissolved carbides during cooling from sintering temperature. The simulations indicate that carbide particle growth observed in NbC-12%Ni sintered sample can be a result of dissolution and re-precipitation mechanism.