Dissolution-precipitation Process Research Articles

Molecular mechanism of elemental sulfur dissolution in H2S under stratal conditions.

Resulting from the solubility reduction of elemental sulfur during the development of high sulfur gas formations, sulfur deposition often occurs to reduce the gas production and threaten the safety of gas wells. Understanding the dissolution mechanism of elemental sulfur in natural gas is essential to reduce the risk caused by sulfur deposition. Because of the harsh conditions in the high-sulfur formations, it remains challenging to in situ characterize the dissolution-precipitation processes, making deficient the knowledge of sulfur dissolution mechanism. The dissolution of sulfur allotropes (SN, N = 2, 4, 6 and 8) in H2S, the main solvent of sulfur in natural gas, is studied in this work by means of first-principles calculations and molecular dynamics simulations. While S6 and S8 undergo physical interaction with H2S under the conditions corresponding to those at 1-6 km stratigraphic depths, S2 and S4 react with H2S and form stable polysulfides. Unravelling the mechanism would be helpful for understanding and controlling the sulfur deposition in high-sulfur gas development.

Influence of coupled dissolution-precipitation processes on the pore structure, characteristics, and evolution of tight sandstone: A case study in the upper Paleozoic reservoir of Bohai Bay Basin, eastern China

Due to the limitations of pore throat characterization techniques, in-depth studies on the evolution and influencing variables of tight sandstone reservoirs remain lacking, despite the importance of pore structure in evaluating their storage and seepage capacities. In this study, the effect of coupled dissolution–precipitation on the heterogeneity of the pore structure of tight sandstone was investigated using advanced techniques in conjunction with traditional geochemical analyses. The primary reasons for the variability in tight sandstone pore structure were different diagenetic processes and tectonic evolution. In tight sandstones, numerous burial phases led to a significant loss of porosity. However, tight sandstones that have been successively leached by meteoric water and deep burial organic acid have improved secondary pore space due to Yanshan tectonic uplift and Himalayan tectonic burial. The redistribution or blockage of pore space can occur as a result of dissolved material migrating and re-precipitating in tight sandstones that have been deeply buried and altered by organic acidic fluids. Furthermore, nuclear magnetic resonance cryoporometry and nuclear magnetic resonance experiments were used to provide precise and accurate quantitative analysis for discussing the evolution of pore structure by complex dissolution–precipitation process within the pore scale. The formation of good pore structure was mainly dependent on the increase in pore volume generated by dissolution in the submicron and micron range (less than 10 μm). Due to interfacial energy effects, authigenic minerals precipitated preferentially in macropores, resulting in a preponderance of microporosity and small changes in porosity but at least an order of magnitude reduction in permeability. This study provides a reliable reference for genesis analysis and evaluation of tight sandstones as well as a new perspective for understanding the formation and evolution of complex pore structures.

Ecological restoration affects the dynamic response of alkaline minerals dissolution in bauxite residue

Regulating alkalinity is the key process to eliminating environmental risk and implementing sustainable management of bauxite residue. Nevertheless, continuous release of free alkali from the solid phase (mainly sodalite and cancrinite) is a major challenge for long-term stability of alkalinity in amended bauxite residue. In order to understand the dissolution behavior of sodalite and cancrinite, their dissolution kinetics under simulated pH conditions of 8, 9 and 10 were investigated. Additionally, PHREEQC software and shrinking core model (SCM) were employed to analyze the release pattern of saline ions. The results revealed that the ratio of Na/Si and Na/Al values exhibited greater stability in sodalite than in cancrinite. The dissolution of elemental Na, Si, and Al in sodalite and cancrinite was matched with non-chemometric characteristics. The kinetic calculations by the shrinking core model (SCM) suggested that both sodalite and cancrinite exhibited slow dissolution kinetics, and their dissolution processes belong to internal diffusion control and external diffusion control, respectively. pH controlled the dissolution kinetic rates of sodalite and cancrinite mainly by changing their coupled dissolution-precipitation processes. More importantly, these findings can predict the change of alkaline components accurately, thus facilitating the implementation of efficient alkalinity regulation strategies for the ecological restoration of bauxite residue disposal areas.

Evolution of H2O content in deforming quartz aggregates: An experimental study

Deformation experiments were carried out on pure quartzite samples (>99% quartz) with a grain size of ∼200 μm from Tana, Northern Norway. Deformation conditions were 900 °C, 0.1 wt% H2O added, strain rate ∼1 × 10−6 s−1 at variable confining pressures from 600 to 2000 MPa. Detailed FTIR measurements of H2O indicate that the H2O content in the grain boundary region is higher than that inside quartz grains. Hydrostatic treatment and deformation at the chosen temperature and pressure conditions lead to further H2O loss from grain interiors and H2O increase in the grain boundary region. Varying the confining pressure does not have an observable effect on the H2O transfer from grains to the grain boundary region. The 3585 cm−1 absorption band increases systematically with increasing confining pressure. As this band is associated with OH in dislocations, the increase may indicate an increased dislocation density with increasing pressure. The triplet of 3317, 3375 and 3438 cm−1 associated with Al-content in quartz increases in the grain boundary region indicating an exchange of H+ together with Al3+ for Si4+. The Al and H exchange suggest dissolution-precipitation processes in the grain boundary region facilitating the movement of the quartz grain boundaries (grain boundary migration). The H2O in the grain boundary region will be important for enhancing grain boundary migration and thus recrystallization processes during deformation.

Tracing short-lived hydrothermal circulation systems and water–rock interactions around small-scale intrusions

Hydrothermal circulation around magmatic intrusions affects hazards, critical metal deposition, and heat transfer, however it is often difficult to directly observe. We combine stable isotope and thermochronologic measurements, hydrothermal circulation modeling, and forward thermal history modeling to understand the short-lived hydrothermal circulation system that developed around the Little Devils Postpile, a small-scale mafic intrusion in the eastern Sierra Nevada Mountains of western North America. Bedrock samples collected in transects orthogonal to the intrusion reveal reset and partially reset apatite (U-Th-Sm)/He and zircon (U-Th)/He ages up to ∼13m from the contact. Measurements of hydrogen isotopes in apatite crystals from the same samples show deuterium depletion near the contact; δD values vary between −120‰ and −132‰ within 3m of the contact, −112‰ to −104‰ at 4–6m from the contact, and −85‰ to −95‰ at distances of 12m to 40m from the contact. In contrast, oxygen isotopes do not vary spatially with a δ18O of +6.4 ± 0.4‰. This depletion of δD and consistency of δ18O suggests that short-lived water–rock interaction occurred following the intrusion emplacement, facilitating the exchange of hydrogen isotopes via diffusion rather than dissolution-precipitation processes. Conductive cooling calculations predict an alteration aureole ten times larger than is observed by the low-temperature thermochronometric ages. Numerical models of hydrothermal circulation, for a range of host bedrock permeabilities and magmatic emplacement temperatures, reveal that the geometry of alteration is most consistent with buoyancy-driven hydrothermal circulation and a relatively high crustal permeability. With this case study, we show that combining thermochronology and hydrothermal modeling allows for the opportunity to model hydrogen isotope exchange and predict plausible apatite-water hydrogen fractionation. These new constraints on the geometry of water–rock interactions coupled with hydrothermal circulation modeling provide (1) a rare window into the pressure–temperature evolution of a small magmatic intrusion, (2) constraints on crustal permeability, and (3) a useful tool for interpreting low-temperature thermochronometric data in volcanic settings.

Precipitation of Polypropylene and Polyethylene Terephthalate Powders Using Green Solvents via Temperature and Antisolvent-Induced Phase Separation

Polymer dissolution and precipitation are two common processes for the production of polymer powders, especially for cases where usual means of comminution are not applicable. I investigated six dissolution–precipitation processes based on high-boiling sustainable green organic solvents and antisolvents for the polypropylene and polyethylene terephthalate with respect to apparent particle morphology for a closed loop production scheme. Of the investigated processes two are considered antisolvent-induced precipitations whereas the other four can be considered temperature induced. The applied solvents included p-cymene, dibutoxymethane, ethylbenzoate, γ-valerolactone, ethanol, and hexanol. All processes yielded powders consisting of agglomerated primary particles at a powder dry substance of less than 25% by weight. The produced powders consist in all cases of agglomerates of smaller primary particles.

Cold sintering assisted processing of Mn-Zn ferrites

Typically, commercial Mn-Zn ferrites are sintered at high temperatures with prolong times. In this work, commercial Fe2O3-rich ferrite powders with the composition of 0.21Mn0.8Zn0.2Fe2O4-0.79Fe2O3 (wt%) are densified by cold sintering at 300 °C with the assistance of organic salts, including MnC2O4·2H2O, FeC2O4·2H2O, and Zn(C2H3O2)2·2H2O. Excessive Fe2O3 enters into spinel structure forming a solid solution through annealing in low pO2 at 1350 °C. The sintering behaviors, microstructures, magnetic properties and impedances are investigated. The dehydration of organic salts provides mediate liquid phase to trigger the dissolution-precipitation process, which assists the densification of ceramics. The grains grow from 0.15 µm to 0.52 µm and 7.67 µm after cold sintering at 300 °C and annealing at 1350 °C, respectively. The initial permeability of cold sintered sample is improved to 11000 with a Curie temperature of 125 °C. This work provides a feasible route for cold sintering assisted processing of commercial soft magnetic ferrites.

Montbrayite from the Svetlinsk Gold–Telluride Deposit (South Urals, Russia): Composition Variability and Decomposition

A rare gold–telluride montbrayite from the large Svetlinsk gold–telluride deposit (South Urals, Russia) was comprehensively studied using optical microscopy, scanning electron microscopy, electron microprobe analysis, reflectance measurements, electron backscatter diffraction, and Raman spectroscopy. Significant variations in the composition of the mineral were revealed (in wt%): Au 36.98–48.66, Te 43.35–56.53, Sb 2.49–8.10, Ag up to 4.56, Pb up to 2.04, Bi up to 0.33, Cu up to 1.42. There are two distinct groups with much more-limited variation within the observed compositional interval (in wt%): (1) Au 36.98–41.22, Te 49.35–56.53, Sb 2.49–5.57; (2) Au 47.86–48.66, Te 43.35–44.92, Sb 7.15–8.10. The empirical formula calculated on the basis of 61 apfu is Au16.43–23.28Sb1.79–6.09Te32.01–38.89Ag0–3.69Bi0–0.14Pb0–0.90Cu0–1.96. Two substitution mechanisms for antimony are proposed in the studied montbrayite grains: Sb→Au (2.5–5.6 wt% Sb) and Sb→Te (7–8 wt% Sb). The dependence of the reflection spectra and Raman spectra on the antimony content and its substitution mechanism, respectively, was found in the mineral. The slope of the reflectance spectra decreases and the curve in the blue–green region of the spectrum disappears with increasing Sb content in montbrayite. Raman spectra are reported for the first time for this mineral. The average positions of the peak with high-intensity are ~64 cm−1 and ~90 cm−1 for montbrayite with Sb→Te and Sb→Au, respectively. Two grains of montbrayite demonstrate decomposition according to two schemes: (1) montbrayite (7 wt% Sb) → native gold + calaverite ± altaite, and (2) montbrayite (5 wt% Sb) → native gold + tellurantimony ± altaite. A combination of melting and dissolution–precipitation processes may be responsible for the formation of these decomposition textures.

Phase transformations during the dissolution-precipitation synthesis of magnesium whitlockite nanopowders from gypsum

In the present work, magnesium whitlockite (Mg-WH) powders were synthesized via a low-temperature dissolution-precipitation process using gypsum as a starting material. The suggested synthetic approach is cost-effective and environmentally friendly solution, promoting sustainable manufacturing practises. The phase evolution and formation of Mg-WH in an aqueous medium in the presence of magnesium and phosphate ions under static and rotating conditions were investigated. Powder XRD patterns, FTIR spectra and SEM images were obtained for samples synthesized for different times to monitor the gradual phase transformation. It was found that single-phase Mg-WH can be obtained using both synthetic approaches, however, the reaction under rotating conditions favors faster formation of Mg-WH crystals. Samples obtained under static conditions had larger crystallite size and higher crystallinity, while those prepared under rotating conditions had smaller crystallites and lower crystallinity. The Rietveld refinement confirmed the structural parameters of the synthesized samples, indicating a slight change in the lattice parameters and magnesium occupancy with an extended synthesis time. We state that the phase composition, crystallite size, crystallinity, and powder morphology can be facilely controlled by regulating the synthesis time and selecting the synthesis setup.

Low-temperature sintering and microwave dielectric properties of CaMoO4 ceramics for LTCC and ULTCC applications

Low-temperature co-fired ceramic (LTCC) technology can meet the requirements of device miniaturization and integration. In this work, a novel series of CaMoO4 + x wt.% Li2MoO4 (CMO+ xLMO, x = 0.0–2.5) microwave dielectric ceramics were prepared. The sintering temperature of CMO ceramic significantly declines from 1050 °C to 600 °C by adding a small amount of LMO. A dissolution-precipitation process at the grain boundary has been demonstrated to be the mechanism for low-temperature sintering through transmission electron microscopy analysis. The low-temperature sintered CMO ceramics present excellent microwave dielectric properties, e.g. CMO+ 1.0 wt.% LMO ceramics sintered at 600 °C, εr ∼ 14.4, Q×f ∼ 13,060 GHz, τƒ ∼ − 41.0 ppm/°C; CMO+ 2.5 wt.% LMO ceramics sintered at 700 °C, εr ∼ 15.1, Q×f ∼ 16,122 GHz, τƒ ∼ − 43.8 ppm/°C, which show great potentials in both LTCC and ULTCC applications.

Preparation of ultrafine (W,Mo)B, (W,Mo)B2.5 and (Mo,W)AlB solid solution composite powders

In this study, ultrafine borides powders including (W,Mo)B, (W,Mo)B2.5 and (Mo,W)AlB were successfully fabricated via boronizing ultrafine W-Mo solid solution composite powder with B4C as the boron source under the assistance of Ca melt or Al melt. Ultrafine W-Mo solid solution powder was obtained by using a two-stage reduction route to reduce the precursor powder synthesized by spray drying. Meanwhile, the effects of Mo/W ratio on the phase composition, morphological characteristics and particle size distribution of boride solid solution composite powder were thoroughly investigated. The shift of diffraction peak in the XRD spectrum, the linear change of lattice constant and the homogeneous distributions of W, Mo, B and Al in the EDS energy spectrum comprehensively confirmed that the boride solid solution with different Mo/W ratios could be prepared. Due to the essentially insolubilities of W and Mo in Ca melt, the (W, Mo)B grains grew following a template growth mechanism, and inherited the nearly spherical morphology feature of ultrafine W-Mo solid solution composite powder with a particle size of approximately 200 nm. Nonetheless, as a result of the high solubilities of W, Mo, and B in Al melt, the process of dissolution-precipitation led to the formations of flaky (W, Mo)B2.5 and short rod-shaped (Mo, W)AlB.

Cd isotope fractionation in a soil-rice system: Roles of pH and mineral transformation during Cd immobilization and migration processes

Cd speciation in soil and its transport to rice roots are influenced by the soil pH, oxidation-reduction potential, and mineral transformation; however, the immobilization and migration of Cd in soil-rice systems with different pH values under distinct water regimes remain unclear. This study used Cd isotope fractionation, soil physical analysis, and root gene quantification to elucidate the immobilization and transport of Cd in different soil-rice systems. In drainage soils, the high soil pH enhanced the transformation and magnitude of negative fractionation of Cd from MgCl2 extract to FeMn oxide-bound pool; however, it favored Cd uptake and root-to-grain transport. Compared with drainage regimes, the flooding regimes shifted fractionation toward heavy isotopes from MgCl2-extracted Cd to FeMn oxide-bound Cd in acidic soils (∆114/110CdMgCl2 extract – FeMn oxide-bound Cd = −0.09 ± 0.03 ‰) and to light isotopes from MgCl2-extracted Cd to carbonate-bound Cd in neutral and alkaline soils (∆114/110CdMgCl2 extract – carbonate-bound Cd = 0.29–0.40 ‰). The submerged soils facilitated the forming of carbonate and poorly crystalline minerals (such as ferrihydrite), which were transformed into highly crystalline forms (such as goethite). These results demonstrated that the dissolution-precipitation process of iron oxides was essential for controlling soil Cd availability under flooding regimes, and the relative contribution of carbonate minerals to Cd immobilization was promoted by a high soil pH. Flooding regimes induced lower expressions of OsNRAMP1 and OsNRAMP5 to limit the uptake of light Cd isotopes from MgCl2-extract pool, whereas a teeter-totter effect on gene expression patterns in roots (including those of OsHMA3 and OsHMA2) limited the transport of heavy Cd isotopes from root to grain. These findings demonstrate that flooding regimes could exert multiple effects on soil Cd immobilization and Cd transport to grain. Moreover, alkaline soil was conducive to forming carbonate minerals to sequester Cd.

Densification mechanism of ZnO ceramics prepared by cold sintering with molten zinc acetate dihydrate as the transient liquid medium

The transportation of Zn2+ in acetic acid (HOAc) or Zn(OAc)2 water solution was considered crucial for the successful cold sintering of ZnO ceramics. However, our work shows that ZnO ceramics can even be densified by cold sintering with the aid of solid Zn(OAc)2·2 H2O without introducing extra free water. DSC-TG analysis reveals that pure Zn(OAc)2·2 H2O is dehydrated completely into solid Zn(OAc)2 during heating in an open environment, while it melts in ZnO-Zn(OAc)2·2 H2O mixture or a high-pressure and semi-closed circumstance due to the strongly suppressed dehydration. Consequently, molten Zn(OAc)2·2 H2O acts as the transient liquid medium for the dissolution-precipitation process at over 100 °C, and plays a dominant role in the densification, microstructural evolution, and mechanical robustness of the cold-sintered ZnO ceramics. The densification mechanism is confirmed by the pressure-time curves, and reveals a novel strategy for cold sintering of water-insoluble ceramics by introducing molten hydrated salt or alkali as the transient liquid medium.

Antimony contamination sources and alteration pathways of Sb mineral phases in an abandoned mining area: The role of secondary mopungite [NaSb(OH)6

Antimony pollution caused by mining activities is a current environmental concern. This study investigates the processes involved in the Sb release and mobility in the abandoned Sb mine of Su Suergiu (SE Sardinia, Italy). Analyses of outcropping rocks, mine wastes and smelting slags by means of X-Ray Powder Diffraction, Scanning Electron Microscopy - Energy Dispersive Spectroscopy and Electron Microprobe – Wavelength Dispersive Spectroscopy provided mineralogical and compositional data which contributed to the discussion about the oxidation pathways of Sb phases. The main Sb sources are metallic Sb and Sb2O3 (valentinite/senarmontite), dumped in the smelting slag heaps as residues of metallurgical processes, and primary stibnite (Sb2S3) found in natural outcrops and mine wastes. These minerals, subjected to weathering processes, release Sb in solution where it is oxidized and remains as dissolved Sb(OH)6−. Carbonates and Na phases, like hydrate NaAl-silicate derived from metallurgical processes, influence the geochemical equilibria of the smelting slag heaps, where the precipitation of the rare mopungite, Na[Sb(OH)6], has been observed. At Su Suergiu, mopungite originates from a dissolution-precipitation process as the last forming mineral of the oxidation pathways, limiting the Sb mobility by bonding the Sb(OH)6− in solution. Among the detected Sb secondary phases (e.g., Sb-oxides, FeSb-oxides, etc.), mopungite is the prevalent Sb binder although it acts as a temporary sink because its stability is influenced by the hydrological regime, its solubility, and the water physicochemical parameters. Secondary Sb-bearing minerals can control the dispersion of Sb in contaminated area. At Su Suergiu the role of Fe-bearing compounds on Sb mobility is subordinate to that of mopungite due to the specific geochemical conditions related to the metallurgical activities. The relevance of this study arises from the known toxicity of Sb and from its worldwide diffuse mining, that results in the widespread occurrence of Na–Sb-rich residues produced by Sb smelting plants.

Removing carbon-black pigments from acrylonitrile-butadiene-styrene (ABS) using collector solvents

As we continue using plastics, the quantity of plastic waste also continues to pollute our land and oceans. To mitigate the plastic waste crisis, various manufacturing firms are trying to produce goods from recycled polymers. However, plastics often contain many additives and colorants, adding additional challenges to recycling. Removing these contaminates is necessary to increase the polymer’s recyclability and ensure that the recovered polymer still has economic value by restoring thermal and mechanical properties. One of the most popular, recyclable polymers is acrylonitrile butadiene styrene (ABS). A widely used colorant in ABS is carbon black (CB) pigment, an insoluble inorganic pigment well dispersed throughout the polymer. Solvent-extraction methods have shown to be successful in restoring properties but also involve energy-intensive filtration steps to separate insoluble contaminants. This work uses a dissolution-precipitation process to dissolve ABS filament in ethyl acetate and polymerize it with methanol. A separation step was conducted to remove CB before precipitation by using a polar collector solvent to attract the hydroxyl group of the CB particles. Both ethylene glycol and distilled water were tested as collector solvents. The difference in density and miscibility between solvents allows for the CB pigment to be easily removed from the dissolved solution. Ethylene glycol was able to complete the separation method in less time than distilled water, thus more time efficient. The Fourier-Transform Infrared Spectroscopy (FTIR) results showed that the recovered samples remained ABS after completing the process. The Thermal Gravimetric Analysis (TGA) results indicated that there was no significant difference in the thermal decomposition behavior of the virgin ABS and the recovered samples when collector solvents were used to remove CB. This separation process helps purify the recycled polymer by eliminating contaminants such as pigments. As a result, the recycled material is suitable for a wider range of applications and meets industry standards, making them more attractive to consumers and manufacturers.

Constructing and validating ternary phase diagrams as basis for polymer dissolution recycling

One of the recycling methods for polymer waste is the dissolution-precipitation process, which is based on dissolving the polymer in a suitable solvent followed by contaminant removal by, optionally filtration, and polymer precipitation through the addition of a nonsolvent. As showcased for poly(vinyl chloride) (PVC), a polymer used in the construction sector and for packaging, the current work makes clear that the less studied ternary phase diagrams are a very promising tool for the ideal solvent-nonsolvent selection. Such ternary phase diagrams provide compositional information concerning the phase separation process pushing forward the dissolution-precipitation recycling technology. It is demonstrated that these diagrams can be constructed by connecting the Flory-Huggins theory, Hansen solubility parameters and UNIQUAC activity coefficients. Model validation is performed via cloud point measurements for which one can utilize labour-intensive visual inspection or, as demonstrated in this work, one can also apply dynamic light scattering and turbidimetry, with the latter as the preferred method that is cheaper and faster. Ternary phase diagrams for multiple solvent-nonsolvent systems are theoretically constructed and experimentally validated, considering cyclohexanone-ethanol and THF-ethanol as solvent-nonsolvent pairs. It follows that PVC phase diagrams are inherently different compared to other, more commonly studied polymers, such as polyethersulfone (PES) and that for PVC the addition of a ternary interaction parameter might be required.

Cathodoluminescence as a tracing technique for quartz precipitation in low velocity shear experiments

Two simulated gouges (a pure quartz and a quartz-muscovite mixture) were experimentally deformed in a ring shear apparatus at a constant low velocity under hydrothermal conditions favourable for dissolution–precipitation processes. Microstructural analysis using scanning electron microscope cathodoluminescence imaging and cathodoluminescence spectroscopy combined with chemical analysis showed that quartz dissolution and precipitation occurred in both experiments. The starting materials and deformation conditions were chosen so that dissolution–precipitation microstructures could be unambiguously identified from their cathodoluminescence signal. Precipitated quartz was observed as blue luminescent fracture fills and overgrowths with increased Al content relative to the original quartz. In the pure quartz gouge, most of the shear deformation was localized on a boundary-parallel slip surface. Sealing of fractures in a pulverized zone directly adjacent to the slip surface may have helped keeping the deformation localized. In the quartz-muscovite mixture, some evidence was observed of shear-accommodating precipitation of quartz in strain shadows, but predominantly in fractures, elongating the original grains. Precipitation of quartz in fractures implies that the length scale of diffusive mass transfer in frictional-viscous flow is shorter than the length of the quartz domains. Additionally, fracturing might play a more important role than generally assumed. Our results show that cathodoluminescence, especially combined with chemical analysis, is a powerful tool in microstructural analyses of experimentally deformed quartz-bearing material and visualizing quartz precipitation.

Material recycling of Acrylonitrile Butadiene Styrene (ABS) from toy waste using density separation and safer solvents

Toy waste is an issue for municipal plastic recycling programs. In particular, toy waste typically is composed of different plastics and some metals. Separation of different parts of toy waste is necessary before recycling. In this study, a dissolution-precipitation process coupled with density separation was developed to extract acrylonitrile butadiene styrene (ABS) from toy waste using safer solvents and antisolvents. The polymer solubility of ABS was measured using Hansen solubility parameters, which were then used to down-select proper safer solvents and antisolvents. The acetone-water with a volumetric ratio of 3:1 was determined to be the most effective safer solvents and antisolvents for extracting 81 wt.% of ABS at room temperature. The recovered ABS has comparable mechanical behavior to the feedstock material with a similar glass transition temperature and molecular weight distribution. Compared to producing virgin ABS material, the dissolution-precipitation process reduces embodied energy by 58%.

Rheological behavior of amphibolite facies migmatites during orogenesis: A case study from the North Qinling Belt, China

The rheological behavior of amphibolite-facies migmatites are key to understanding the evolution of middle–lower crust during orogenesis. The amphibolite-facies metamorphosed migmatites from the North Qinling Terrane are investigated to elucidate high temperature melt-present deformation and shear localization. The metatexite (plagioclase amphibolite and biotite plagiogneiss), diatexites, and deformed residuum (mylonitic amphibolite and layered amphibolite) are well-preserved in outcrops. The SW dipping and E-W striking foliation, and ptygmatic, asymmetrical folds indicate compressional deformation with top-to-the-WNW shearing. Zircon UPb geochronology indicates that crustal anatexis mainly occurred at ca. 400–386 Ma, associated with the collision between the North and South China Blocks. The occurrence of peritectic amphibole, the estimated anatectic conditions of 2.32–4.29 kbar and 595–691 °C and variation of mineral major compositions jointly demonstrate incongruent water-present melting reactions, which involved biotite- or amphibole-breakdown, while the deformation temperature is constrained at 605–644 °C. In the plagioclase amphibolite, the amphibole is dominated by (100)[001] dislocation slip, while plagioclase doesn't display a clear fabric. In the biotite plagiogneiss, plagioclase is dominated by strain-induced (010)[100] slip and quartz shows prism <a > slip. Rheological processes (brittle fracturing, melt(fluid)-assisted partial mylonitization and layering process) indicate that melt migration has an effect on the residuum. The formation of amphibole type-II fabric is controlled by cataclastic flow and rigid rotation during progressive deformation process and dissolution-precipitation processes lead to further weakening and strain localization.

Hierarchical synchrotron diffraction and imaging study of the calcium sulfate hemihydrate-gypsum transformation.

The mechanism of hydration of calcium sulfate hemihydrate (CaSO4·0.5H2O) to form gypsum (CaSO4·2H2O) was studied by combining scanning 3D X-ray diffraction (s3DXRD) and phase contrast tomography (PCT) to determine in situ the spatial and crystallographic relationship between these two phases. From s3DXRD measurements, the crystallographic structure, orientation and position of the crystalline grains in the sample during the hydration reaction were obtained, while the PCT reconstructions allowed visualization of the 3D shapes of the crystals during the reaction. This multi-scale study unfolds structural and morphological evidence of the dissolution-precipitation process of the gypsum plaster system, providing insights into the reactivity of specific crystallographic facets of the hemihydrate. In this work, epitaxial growth of gypsum crystals on the hemihydrate grains was not observed.