Common Secondary Phases Research Articles

Plutonium Co-precipitation with Calcite

The mobility of plutonium (Pu) in the environment is affected by Pu–mineral interactions, such as adsorption–desorption and structural incorporation. Calcite (CaCO3) is a common secondary phase in ...

Advanced Raman spectroscopy of Cs2AgBiBr6 double perovskites and identification of Cs3Bi2Br9 secondary phases

Cs2AgBiBr6 double perovskites are intensely investigated as lead-free, stable alternatives to organic lead halide perovskites. In this contribution, we revise the vibrational modes of Cs2AgBiBr6 and show that Raman spectroscopy is well suited for the detection of common secondary phases such as Cs3Bi2Br9. The combined Raman analysis at pre-, near- and non-resonant conditions allows us to extract the four vibrational modes of Cs2AgBiBr6 to unprecedented detail, the most intense one at 177.3 cm-1. The experimental results are in good agreement with theoretical density functional theory calculations. In addition, we monitor the decomposition of Cs2AgBiBr6 into Cs3Bi2Br9 at temperatures above 255 °C.

Comparative Bioleaching and Mineralogical Characterization of Black Shale-Hosted Ores and Corresponding Flotation Concentrates

In this study, two black shale copper ores from different Mid-European Kupferschiefer-type deposits and their flotation concentrates were used for bioleaching tests. All samples were subjected to stirred tank bioleaching using an acidophilic, moderately thermophilic microbial consortium. The distribution of sulfides and gangue minerals in the ores, copper concentrates and residues of both, bioleaching and sterile chemical control tests were investigated using EDX-based particle analysis. The black shale ores and the extracted copper concentrates varied in their mineralogical composition with respect to the distribution of sulfides and gangue. While the copper-bearing sulfides in the Sangerhausen black shale and concentrate were dominated by bornite and chalcopyrite, the Rudna black shale and its flotation concentrate were rich in chalcocite and bornite. Differences in the portion of gangue minerals were detected in particular for carbonates that represented the dominant mineral group in the Rudna black shale and its copper concentrate. Distinct Cu dissolution kinetics and recovery rates of Co and other associated metals were observed for the various materials processed by bioleaching. Copper sulfides were completely dissolved also in both black shale ores. However, the sulfide distribution in the bioleaching residues of the Sangerhausen concentrate revealed that a significant portion of chalcopyrite was not leached. Even higher recovery rates for copper and other metals were determined for the bioleaching tests on the Rudna concentrate, in which copper sulfides were nearly completely dissolved. Alteration of copper sulfides and the formation of calcium sulfate were in particular observed in the sterile control residue of the Rudna concentrate, due to excessively use of sulfuric acid for pH stabilization. Lead sulfate precipitates increasingly occurred in the bioleaching residues, but represented also a common secondary phase in the sterile leaching residues.

Long-term immobilisation of Cd2+ at the Tulul Al Hammam natural analogue site, central Jordan

The Tulul Al Hammam area in central Jordan is a natural analogue site where to study long-term Cd2+ retention during the weathering of Cd-enriched combustion-metamorphic marbles with clinker-like mineralogy. Natural Cd-rich portlandite (Ca0.67−0.45Cd0.33−0.55)[OH]2 was discovered and characterised by single-crystal XRD, SEM/EDS, and microprobe analyses, and Raman spectroscopy. The Ca[OH]2 – Cd[OH]2 solid solution ((Ca1−xCdx)[OH]2) is isostructural with Ca[OH]2 and β-Cd[OH]2 crystals in the CdI2-type of structure. Cd-rich portlandite is a common secondary phase in slightly altered massive marbles, where it replaces and rims single-crystals of the high-temperature precursor (Ca1−xCdx)O. The Cd:Ca molar ratios of (Ca1−xCdx)[OH]2 are inherited from the precursor phase (Ca1−xCdx)O. Reliable long-term immobilisation of Cd in (Ca1−xCdx)[OH]2 is assumed for pore water pH values from 10.5 up to 12 buffered by C-S-Hs formed mainly during spurrite hydration. The Tulul Al Hammam site may have some bearing on long-term Cd2+ retention in the concrete matrix.

Thermodynamic evaluation of the thixoformability of Al–Si alloys

The goal of this work is to introduce a simple method for evaluating the thixoformability of Al–Si alloys based on semisolid transformation curves obtained by differential thermal analysis (DTA), differential scanning calorimetry (DSC) and Thermo-Calc® simulation. The Al–Si alloys evaluated had a silicon content ranging from 2 to 7wt% Si and were produced by grain refining with the addition of Al5Ti1B master alloy. The semisolid transition for each alloy was analyzed according to classical thermodynamic thixoformability criteria, i.e., by looking at the highest “knee” on the liquid fraction vs. temperature curve, the sensitivity of liquid fraction (dfL/dT0.4–0.6) at 40/60% liquid fraction and the solidification interval of each alloy. The results showed that thermodynamic characterization using DTA, DSC and Thermo-Calc® was effective in predicting semisolid behavior but that use of the commonly adopted criteria reduces the number of alloys considered suitable for semisolid metal (SSM) processing. The criterion proposed here, “The sensitivity of the liquid fraction, dfL/dT, at the desired liquid fraction, fL, exclusively for the primary phase must be as low as possible (<0.03°C−1)”, increases the number of thixoformable alloys by focusing on the control of SSM processing. Thixoforming or Rheocasting must be avoided at temperatures at which the common secondary phase, i.e., usually the eutectic phase present in SSM raw materials, undergoes transformation as this transformation is more complex and less stable than the corresponding one for the primary phase. The paper also demonstrates that kinetics parameters, such as heating (or cooling) rate, have a major effect on semisolid transformation and should be incorporated in the control of SSM processing so that the best processing window can be determined more accurately.

Hematite and Mn oxide (U-Th)/He dates from the Buckskin-Rawhide detachment system, western Arizona: Gaining insights into hematite (U-Th)/He systematics

In this paper, we use several analytical methods in an effort to better understand the systematics of the (U-Th)/He chronometer in hematite and manganese oxides. 4He diffusion data from a polycrystalline hematite sample is consistent with diffusion from hematite crystals with a range of sizes similar to those directly observed in sample material. Combined with a compilation of hematite He diffusion data from previous studies, this supports the interpretation that in general crystal size is a primary control on He retentivity in hematite. 4He/3He diffusion data from a single fragment of a larger hematite crystal imply the presence of multiple diffusion domains smaller than the observed size of the crystal fragment, which may be related to cracks, inclusions, or other internal features, as well as higher concentrations of 4He in smaller domains. We use kinetic values determined in this and other studies and measurements of hematite crystal size in each dated sample to estimate approximate closure temperatures for each sample, most of which range from 140 to 240 °C. Relationships between minor element and parent nuclide concentrations and (U-Th)/He dates measured in aliquots of some analyzed hematite samples suggest that, in some cases, U and Th are concentrated in interstitial phases other than hematite. We identify two processes responsible for much of the dispersion in hematite dates from single samples. Removal of U- and Th-rich interstitial phases from analyzed material during sample preparation or analysis leaves behind unsupported 4He implanted in hematite crystals. This removal results in apparent (U-Th)/He dates artificially older than the time of hematite He closure. A smaller source of dispersion that is likely to still be significant in some samples can be attributed to the high He diffusivities of observed interstitial phases, which do not retain implanted He. (U-Th)/He dating of hematite from upper and lower-plate rocks in the Buckskin and Rawhide detachment fault system of western Arizona yields ages that coincide with the timing of rapid extension along the detachment fault. Comparisons of estimated hematite closure temperatures and hematite sample ages to data from other studies of the Buckskin-Rawhide detachment system lead us to conclude that hematite dates record rapid cooling that followed detachment zone mineralization. Mn oxide (U-Th)/He dates are interpreted as formation ages of minerals formed by hydrothermal fluids that circulated through upper-plate rocks after cessation of extension along the detachment fault. Overall, we find that (U-Th)/He dating of hematite and Mn oxide minerals are promising methods for obtaining temporal information about the formation and cooling of these common secondary phases.

Zn-poor Cu2 ZnSnSe4 thin films and solar cell devices

This work reports the synthesis of photovoltaic-grade Cu2ZnSnSe4 thin films with Zn-poor compositions (Zn/Sn < 1) prepared by selenization of sputter deposited metallic precursors. This contrasts with most other reports where up to now fabrication of photovoltaic-grade Cu2ZnSnSe4 requires Cu-poor and Zn-rich compositions, which often favor the formation the ZnSe secondary phase. Synthesis of Zn-poor or stoichiometric films opens up prospects for preparing device-grade films while minimizing formation of common secondary phases. While the maximum device efficiency is modest (2.5%), it is notable because it falls outside the optimum compositional range. Annealing conditions including temperature, chalcogen source, and system pressure were varied to determine their influence on film and device properties. Phase characterization confirms that Cu2ZnSnSe4 is the main phase present. Reasons for the formation of device-grade films outside the ideal compositional range are discussed, including the fact that initial film growth is under Zn-rich conditions, and that films are Cu-poor in relation to Zn (Cu/Zn < 2), both of which may potentially give rise to the necessary electronic defects for a photovoltaic-grade absorber layer. Finally, the importance reporting other compositional ratios, especially Cu/Zn and Cu/Sn, instead of the more common ratio Cu/(Zn + Sn), is expounded for this class of materials.

Experimental study of phlogopite reaction rim formation on olivine in phonolite melts: Kinetics, reaction rates, and residence times

Experiments were conducted to reproduce reaction rims of phlogopite ± diopside around olivine that have been observed within a wide range of potassic melts, including phonolite. Phlogopite is also a common secondary phase formed at the expense of olivine during metasomatic events involving K2O-and H2O-rich fluids or melts. Piston-cylinder experiments where olivine single crystals were reacted with synthetic phonolite melt at 10.7–14.7 kbar and 950–1000 °C recreate the mineralogy and textures documented in natural samples. Rim growth is parabolic with time, indicating a diffusion-controlled reaction. Fast diffusion in the melt and varying compositions across the phlogopite reaction rims suggest that diffusion through the rims, along grain boundaries is rate limiting. Reaction rates dramatically increase with temperature as well as the bulk water content of the sample charge. This is because of increasing amounts of atomically bound hydrous species along the grain boundaries that increase the rates of diffusion and thereby the rates of rim growth. Atomically bound hydrous species increase the rates of rim growth by lowering the activation energy for diffusion and by increasing the solubility of diffusing species in the grain boundary region. Transmission electron microscopy shows the presence of isolated pores and open grain boundaries. Most of these may have opened during quenching, but there is some evidence to suggest that a free fluid phase may have been locally present in experiments with high melt water contents (>8 wt%). The measured rim growth rates at different conditions are used to estimate residence times of reacting olivine crystals in natural systems.

Microstructural changes induced by low energy heavy ion irradiation in titanium silicon carbide

Low energy ion irradiation was used to investigate the microstructural modifications induced in Ti 3SiC 2 by nuclear collisions. Characterization of the microstructure of the pristine sample by electron back-scatter diffraction (EBSD) shows a strong texturing of TiSi 2, which is a common secondary phase present in Ti 3SiC 2. A methodology based on atomic force microscopy (AFM) was developed to measure the volume swelling induced by ion irradiation, and it was validated on irradiated silicon carbide. The swelling of Ti 3SiC 2 was estimated to 2.2 ± 0.8% for an irradiation dose of 4.3 dpa at room temperature. Results obtained by both EBSD and AFM analyses showed that nuclear collisions induce an anisotropic swelling in Ti 3SiC 2.

Mineralogical control on inorganic contaminant mobility in leachate from lead-zinc metallurgical slag: experimental approach and long-term assessment

AbstractLead, zinc and arsenic mobilization/attenuation processes during interactions between smelter slag and water show differences depending on the origin of the slag. The studied samples, waste from ore and car-battery processing, were submitted to long-term (365 days) batch leaching at two different initial pH values. The leachate analyses were input to the EQ3NR speciation-solubility code to speciate the solutions and determine the degree of saturation with respect to different phases, and a mineralogical investigation was made of the newly formed phases. An ‘oxidizing’ scenario can be proposed for slag waste disposal, considering that cerussite (PbCO3) at pH &gt;6 becomes a major solubility-controlling phase for Pb, and newly formed hydrous ferric oxides (HFO – common secondary phases under oxidizing conditions) efficiently adsorb As. No efficient scavenging mechanism was found for Zn, which was progressively leached from the slag and in particular from the ore-processing slag. Quenched glass-rich slag from old car-battery processing was found to release significant amounts of Pb, especially in acidic environments. Neither slag would therefore be suitable for recycling for civil engineering purposes. Conversely, extremely low releases of Pb, Zn and As were observed for recent car-battery processing slag, which could therefore be considered for road construction.

Low‐temperature alteration of mesozoic oceanic crust, Ocean Drilling Program Leg 185

Basalts drilled from the Mesozoic crust at Ocean Drilling Program (ODP) Sites 801 and 1149 during Leg 185 have been affected by a succession of submarine, variably oxidative alteration processes by cold seawater. The low‐temperature alteration resulted in various combinations of secondary minerals both as replacements of igneous phases, and as void and crack fillings. Mg‐smectite, calcite, celadonite and Fe‐oxyhydroxide are the dominant secondary minerals. Quartz, chalcedony and phillipsite are always very minor phases that fill open spaces. The rocks generally exhibit concentric haloes, 0.5 to 1 cm in thickness, around gray inner cores and usually adjacent to exposed surfaces. Color zonations result from the abundance of various secondary mineral assemblages present in each zone. The green rocks are dominated by celadonitic phyllosilicates, whereas the dusky red haloes are characterized by abundant iddingsite and Fe‐oxyhydroxides replacing the fine clinopyroxene. Finally Mg‐smectite ± calcite, are the most common secondary phases in the inner gray cores. The most unusual effects of the low‐temperature alteration of the study rocks are the pervasive, pale green to gray green color and the relatively abundant dusky red haloes surrounding inner reddish gray cores. Alteration of Mesozoic crust cored during Leg 185 is comparable with low‐temperature alteration of 310 m thick uppermost volcanic section of the 5.9 My old crust of Hole 504B. Except the renewed precipitation of calcite in veins, the aging of oceanic crust does not depend on time probably because it occurs during the first few millions of years after the accretion, and ceases when the crust is sealed off.