Search Results (37)

This study investigates efficient dehydration and solidification techniques for waste mud generated from loess pile foundations during highway construction in Lanzhou, Northwest China. The waste mud, characterized by high viscosity (85% moisture content) and alkalinity (pH 11.2), poses environmental risks if untreated. Dehydration experiments identified an optimal composite flocculant mixture of 3.5 g polyaluminum chloride (PAC) and 22 mL anionic polyacrylamide (APAM) per 500 mL waste mud, accelerating sedimentation and reducing the supernatant pH to 8.65, compliant with discharge standards. Solidification tests employed a composite curing agent (CG-T1+cement), demonstrating enhanced mechanical properties. The California Bearing Ratio (CBR) of the solidified sediment reached 286%, and the unconfined compressive strength (UCS, 7-day) exceeded 2.0 MPa, meeting roadbed specifications. The combined use of PAC-APAM for dehydration and CG-T1–cement for solidification offers an eco-friendly and economically viable solution for reusing treated waste mud in construction applications, addressing regional challenges in mud disposal and resource recovery. Full article

Germanium (Ge) has been recognized as a critical strategic metal due to its high-technology implications. It is predominantly found in sphalerite within the Pb-Zn deposits, whose genesis is closely related to chloride-bearing hydrothermal activities. However, the dissolution and complexation of Ge in chloride-bearing fluids have not yet been well understood. To address this issue, this study investigates the dissolution behavior of Ge and corresponding species in HCl and NaCl aqueous solutions at 150 °C using the solubility method. The results show that the solubility of Ge in HCl solutions reaches 300 ppm and decreases with increasing HCl concentration. In contrast, the solubility of Ge in NaCl solutions is up to 1500 ppm and exhibits no significant dependence on NaCl concentration. The new findings demonstrate that the solubility of Ge in chloride-bearing solutions is primarily controlled by the solution’s pH. As the pH increases, the concentration of Ge dissolved in solutions rises substantially, suggesting that alkaline fluid environments facilitate Ge dissolution and transport. Further analysis of the experimental data indicates that the dominant species of Ge is Ge(OH${)}_4^0$ in acidic chloride-bearing solutions and Ge(OH${)}_5^{-}$ in neutral-basic chloride-bearing solutions, in which the species Ge(OH${)}_5^{-}$ promotes higher Ge solubility compared to Ge(OH${)}_4^0$. On account of high solubility in both HCl and NaCl solutions, it is proposed that Ge mineralization is not controlled by the co-precipitation process with Pb and Zn but by subsequent solid–liquid reaction between sphalerite and fluids. These experimental data and computational results not only provide new insights into the dissolution, transport, and precipitation processes of Ge in Earth’s material cycling but also offer novel perspectives for the understanding of Ge mineralization and industrial extraction and recovery of Ge. Full article

Highly alkaline hydrogels are gaining increasing attention in building materials research. Specifically, cationic alkaline hydrogels based on diallyldimethylammonium hydroxide (DADMAOH) as the monomer have been effectively used to seal water-bearing cracks or serve as coupling media for electrochemical chloride extraction. However, the residual halogen content and challenges in scaling up monomer production have hindered broader application. Attempts to use a commercially available cation-selective membrane for ion exchange achieved up to 90% chloride-to-hydroxide switch, but the approach proved ineffective due to significant monomer decomposition during the process. By contrast, neutral gels and gel particles can be readily prepared from diallyldimethylammonium chloride (DADMAC) in large quantities and with a wide range of compositions. It is demonstrated here that these neutral gel particles undergo inverse static anion exchange when suspended in NaOH solution, generating DADMAOH particles with residual halide contents of <0.3%, without the need for ion-selective or dialysis membranes. This corresponds to an up to 100-fold reduction in residual chloride content compared to particles produced directly from alkaline monomer solutions, thereby significantly enhancing the efficiency of hydroxide ion release. The swelling behaviour of the particles is primarily influenced by the initial monomer concentration, while conductivity remains largely unaffected, indicating that charge transport occurs mainly along the particle surface. Despite the pronounced increase in swelling with decreasing particle radii, the specific conductivity of 2.8 Ω⁻¹ m⁻¹ is still sufficient for their use as coupling media in concrete applications. In summary, the alkaline particles prepared via inverse static anion exchange meet all necessary requirements for building materials applications, offering a broader range of tuneable properties and greater ease of production compared to gels or particles derived from DADMAOH. Full article

The activation product chlorine-36 (³⁶Cl) is an important radionuclide within the context of the disposal of nuclear wastes, due to its long half-life and environmental mobility. Its behaviour in a range of potential cementitious encapsulants and backfill materials was studied by evaluating its uptake by pure cement hydration phases and hardened cement pastes (HCP). Limited uptake of chloride was observed on calcium silicate hydrates (C-S-H) by electrostatic sorption and by calcium monosulphoferroaluminate hydrate (AFm) phases, due to anion exchange/solid solution formation. Diffusion of ³⁶Cl through cured monolithic HCP samples, representative of cementitious materials considered for use in deep geological repositories across Europe, revealed a markedly diverse migration behaviour. Two of the matrices, a ground granulated blast furnace slag/ordinary Portland cement blend (GGBS–OPC) and an ordinary Portland cement (CEM I) effectively retarded ³⁶Cl migration, retaining the radionuclide in narrow, reactive zones. The migration behaviour of ³⁶Cl within the cementitious matrices is not strictly correlated to the measured sorption distribution ratios (R_d-values), suggesting that physical factors related to the microstructure can also have a distinct effect on diffusion behaviour. The findings have implications when selecting cementitious grouts and/or backfill materials for ³⁶Cl-bearing radioactive wastes. Full article

The non-equiatomic Al_0.32CrFeTi_0.73(Ni_1.50−xMo_x) (x = 0, 0.23) high-entropy alloy (HEA) coatings were prepared by the high-velocity oxygen fuel (HVOF) method. The microstructures and corrosion behaviors of the HVOF-prepared coatings were investigated. The corrosion behaviors were characterized by polarization, EIS and Mott-Schottky tests under a 3.5 wt.% sodium chloride aqueous solution open to air at room temperature. The Al_0.32CrFeTi_0.73Ni_1.50 coating is a simple BCC single-phase solid solution structure compared with the corresponding poly-phase composite bulk. The structure of the Al_0.32CrFeTi_0.73Ni_1.27Mo_0.23 coating, combined with the introduction of the Mo element, means that the (Cr,Mo)-rich sigma phase precipitates out of the BCC solid solution matrix phase, thus forming Cr-depleted regions around the sigma phases. The solid solution of large atomic-size Mo element causes the lattice expansion of the BCC solid solution matrix phase. Micro-hole and micro-crack defects are formed on the surface of both coatings. The growth of both coatings’ passivation films is spontaneous. Both passivation films are stable and Cr₂O₃-rich, P-type, single-layer structures. The Al_0.32CrFeTi_0.73Ni_1.50 coating has better corrosion resistance and much less pitting susceptibility than the corresponding bulk. The corrosion type of the Mo-free coating is mainly pitting, occurring in the coating’s surface defects. The Al_0.32CrFeTi_0.73Ni_1.27Mo_0.23 coating with the introduction of Mo element increases pitting susceptibility and deteriorates corrosion resistance compared with the Mo-free Al_0.32CrFeTi_0.73Ni_1.50 coating. The corrosion type of the Mo-bearing coating is mainly pitting, occurring in the coating’s surface defects and Cr-depleted regions. Full article

A study of the liquid–liquid extraction of ReO₄⁻ anions from hydrochloric acid solutions using the ionic liquid Aliquat 336 (QCl: trialkyl(C₈–C₁₀)methylammonium chloride) via the well-known method of slope analysis along with the determination of the process parameters is presented. This study employs CCl₄, CHCl₃ and C₆H₁₂ as diluents. This study was carried out at room temperature (22 ± 2) °C and an aqueous/organic volumetric ratio of unity. The ligand effect on the complexation properties of ReO₄⁻ is quantitatively assessed in different organic media. The organic extract in chloroform media is examined through ¹H, ¹³C and ¹⁵N NMR analysis as well as the HRMS technique and UV-Vis spectroscopy in order to view the anion exchange and ligand coordination in the organic phase solution. Final conclusions are given highlighting the role of the molecular diluent in complexation processes and selectivity involving ionic liquid ligands and various metal s-, p-, d- and f-cations. ReO₄⁻ ions have shown one of the best solvent extraction behaviors compared to other ions. For instance, the Aliquat 336 derivative bearing Cl⁻ functions shows strongly enhanced extraction as well as pronounced separation abilities towards ReO₄⁻. Full article

Coastal regions, home to a significant portion of the world’s population, confront a formidable challenge: the corrosive impact of chloride-rich environments on vital infrastructure. These areas often host essential transportation systems, such as trains and metros, reliant on pre-existing electrical infrastructure. Unfortunately, complete isolation of this infrastructure is rarely feasible, resulting in the emergence of stray currents and electrical potentials that expedite corrosion processes. When coupled with conducive mediums facilitating chemical electrocell formation, the corrosion of reinforced concrete elements accelerates significantly. To combat this issue, international standards have been established, primarily focusing on augmenting the thickness of reinforcement bar covers and restricting stray voltage between rails and the ground. Nevertheless, these measures only provide partial solutions. When subjected to service loads, these elements develop cracks, especially when exposed to stray currents and chlorides, dramatically increasing corrosion rates. Corrosion products, which expand in volume compared to steel, exert internal forces that widen cracks, hastening the deterioration of structural elements. The study deals with the degradation of reinforced concrete columns under the combined action of loads, chloride-rich environments, and electrical voltage-simulating stray currents. In these conditions, degradation and reduction of load-bearing capacity accelerate compared to unloaded conditions, significantly amplifying the corrosion rate. Astonishingly, even in the absence of mechanical loads, stray currents alone induce tensile stresses in elements due to corrosion product formation, leading to longitudinal cracks parallel to the reinforcement bars. Full article

The mineralogical, fluid inclusion, and stable isotope (C, O) study was conducted on a Late Variscan Zn-Pb vein Bt23C, Příbram uranium and base-metal district, Bohemian Massif, Czech Republic. The vein is hosted by folded Proterozoic clastic sediments in exo-contact of a Devonian-to-Lower-Carboniferous granitic pluton. Siderite, dolomite-ankerite, calcite, quartz, baryte, galena, sphalerite, V-rich mica (roscoelite to an unnamed V-analogue of illite), and chlorite (chamosite) form the studied vein samples. The banded texture of the vein was modified by the episodic dissolution of earlier carbonates and/or sphalerite. Petrographic, microthermometric, and Raman studies of fluid inclusions proved a complicated fluid evolution, related to the activity of aqueous fluids and to an episode involving an aqueous–carbonic fluid mixture. Homogenization temperatures of aqueous inclusions decreased from ~210 to ~50 °C during the evolution of the vein, and salinity varied significantly from pure water up to 27 wt.% NaCl eq. The aqueous–carbonic fluid inclusions hosted by late quartz show highly variable phase compositions caused by the entrapment of accidental mixtures of a carbonic and an aqueous phase. Carbonic fluid is dominated by CO₂ with minor CH₄ and N₂, and the associated aqueous solution has a medium salinity (6–14 wt.% NaCl eq.). The low calculated fluid δ¹⁸O values (−4.7 to +3.6‰ V-SMOW) suggest a predominance of surface waters during the crystallization of dolomite-ankerite and calcite, combined with a well-mixed source of carbon with δ¹³C values ranging between −8.2 and −10.5‰ V-PDB. The participation of three fluid endmembers is probable: (i) early high-temperature high-salinity Na>Ca-Cl fluids from an unspecified “deep” source; (ii) late low-salinity low-temperature waters, likely infiltrating from overlying Permian freshwater partly evaporated piedmont basins; (iii) late high-salinity chloridic solutions with both high and low Ca/Na ratios, which can represent externally derived marine brines, and/or local shield brines. The source of volatiles can be (i) in deep crust, (ii) from interactions of fluids with sedimentary wall rocks and/or (iii) in overlying Permian piedmont basins containing, in places, coal seams. The event dealing with heterogeneous CO₂-bearing fluids yielded constraints on pressure conditions of ore formation (100–270 bar) as well as on the clarification of some additional genetic aspects of the Příbram’s ores, including the reasons for the widespread dissolution of older vein fill, the possible re-cycling of some ore-forming components, pH changes, and occasionally observed carbon isotope shift due to CO₂ degassing. Full article

The degradation patterns of bacterial poly-3-hydroxybutyrate (PHB) in chloroform solution under the action of thionyl chloride in the presence of zinc chloride were studied. When 2.5.mol of zinc chloride and 100 mmol of thionyl chloride were introduced into the solution of 25 mmol PHB, a decrease in the molecular weight of the polymer was observed. During the reaction, a relatively rapid decrease in the molecular weight of the polymer was noted in the first hour of the experiment; thus, the values of the weight-average molecular weight decreased from 840 kDa to 483, 167, 58.6, and 16.7 kDa after 1, 5, 24, and 96 h of the experiment, respectively. The polydispersity also gradually decreased from 2.69 at the beginning to 1.92 at the end of the experiment. Oligomers of PHB containing 3-chlorobutyric acid and 3-hydroxybutyryl chloride residues at the O and C ends of the polymer chain, respectively, were obtained. The results confirm the ability of thionyl chloride to interact with aliphatic esters in the presence of zinc compounds, and demonstrate the possibility of using this reaction to produce oligomeric derivatives of polyesters bearing chloralkyl and acid chloride functional groups. Full article

Interaction of [VO(OiPr)₃] with 6-bis(o-hydroxyaryl)pyridine, 2,6-{HOC(Ph)₂CH₂}₂(NC₅H₃), LH₂, afforded [VO(OiPr)L] (1) in good yield. The reaction of LNa₂, generated in-situ from LH₂ and NaH, with [VCl₃(THF)₃] led to the isolation of [VL₂] (2) in which the pyridyl nitrogen atoms are cis; a regioisomer 3∙2THF, in which the pyridyl nitrogen atoms are trans, was isolated when using [VCl₂(TMEDA)₂]. The reaction of the 2,6-bis(o-hydroxyalkyl)pyridine {HOC(iPr)₂CH₂}₂(NC₅H₃), L¹H₂, with [VO(OR)₃] (R = nPr, iPr) led, following work-up, to [VO(OR)L¹] (R = nPr (4), iPr (5)). Use of the bis(methylpyridine)-substituted alcohol (tBu)C(OH)[CH₂(C₅H₃Me-5)]₂, L²H, with [VO(OR)₃] (R = Et, iPr) led to the isolation of [VO(μ-O)(L²)]₂ (6). Complexes 1 to 6 have been screened for their ability to act as pre-catalysts for the ring opening polymerization (ROP) of ε-caprolactone (ε-CL), δ-valerolactone (δ-VL), and rac-lactide (r-LA) and compared against the known catalyst [Ti(OiPr)₂L] (I). Complexes 1, 4–6 were also screened as catalysts for the polymerization of ethylene (in the presence of dimethylaluminium chloride/ethyltrichloroacetate). For the ROP of ε-CL, in toluene solution, conversions were low to moderate, affording low molecular weight products, whilst as melts, the systems were more active and afforded higher molecular weight polymers. For δ-VL, the systems run as melts afforded good conversions, but in the case of r-LA, all systems as melts exhibited low conversions (<10%) except for 6 (<54%) and I (<39%). In the case of ethylene polymerization, the highest activity (8600 Kg·mol·V⁻¹bar⁻¹h⁻¹) was exhibited by 1 in dichloromethane, affording high molecular weight, linear polyethylene at 70 °C. In the case of 4 and 5, which contain the propyl-bearing chelates, the activities were somewhat lower (≤1500 Kg·mol·V⁻¹bar⁻¹h⁻¹), whilst 6 was found to be inactive. Full article

Experimental studies were conducted to identify the physical and chemical features of gold’s behaviour in hydrothermal processes linked to ore formation and involving CO₂ in oxidized deposits. With the aid of the autoclave method, in a temperature range of between 200 and 400 °C, the isochoric dependences of the PVT parameters of concentrated sulphate chloride fluids were plotted, both in the presence and absence of CO₂. Our experiments established that concentrated sulphate–chloride fluids (22 wt % Na₂SO₄ + 2.2 wt % NaCl) that lack CO₂ are characterized by a wide supercritical temperature range, with homogenization temperatures of between 250 and 325 °C. In the presence of CO₂, the same type of fluids showed heterogenization at a molar fraction of X_CO2 = 0.18 (t = 192 °C, P = 176 bar). The process of homogenization for these low-density and high-salinity fluids was impossible at temperatures between 375 and 400 °C and at pressures between 600 and 700 bar. The behaviour of gold was studied during its interaction with a basic composition fluid of sulphate–chloride. We applied the autoclave method under the conditions of a simultaneous synthesis of pyrite and gold dissolution (metallic Au), at a temperature of 340 °C and at a pressure of 440 bar. High Au concentrations (up to 4410 ppm of Au in CO₂-bearing fluids) were attained at high gold solubilities (up to 13.5 ppm in the presence of CO₂), owing to the process of Au reprecipitation within the pyrite phase. We did not detect Au in the pyrite when we used the XRD or SEM methods, which suggested that it might be present as invisible gold. High values of the distribution coefficient (K_D = C_Au(solid)/C_Au(solution)) in the fluids lacking (K_D = 62) and bearing CO₂ (K_D = 327) empirically confirmed the possibility that gold concentrates in pyrite in structurally non-binding forms. Full article

Calcareous sand is a special soil formed by the accumulation of carbonate fragments. Its compressibility is caused by a high void ratio and breakable particles. Because of its high carbonate content and weak cementation, its load-bearing capacity is limited. In this study, the optimal stimulation solution was obtained with response surface methodology. Then, the effect of reinforcing calcareous sand was analysed with unconfined compressive strength (UCS) tests, calcium carbonate content tests, microscopy and microbial community analyses. The components and concentrations of the optimal stimulation solution were as follows: sodium acetate (38.00 mM), ammonium chloride (124.24 mM), yeast extract (0.46 g/L), urea (333 mM), and nickel chloride (0.01 mM), and the pH was 8.75. After the calcareous sand was treated with the optimal stimulation scheme, the urease activity was 6.1891 mM urea/min, the calcium carbonate production was 8.40%, and the UCS was 770 kPa, which constituted increases of 71.41%, 35.40%, and 83.33%, respectively, compared with the initial scheme. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) analyses showed that calcium carbonate crystals were formed between the particles of the calcareous sand after the reaction, and the calcium carbonate crystals were mainly calcite. Urease-producing microorganisms became the dominant species in calcareous sand after treatment. This study showed that biostimulation-induced mineralization is feasible for reinforcing calcareous sand. Full article

The effect of a Cu addition on the corrosion behavior of 304 austenitic stainless steel in a solution was elaborately investigated through salt spray tests, FeCl₃ immersion tests and characterization analyses. The corrosion behavior was further analyzed by optical microscopy, scanning electron microscopy, inductively coupled plasma mass spectrometry and an X-ray photoelectron spectroscopy analysis. 304Cu showed a higher corrosion resistance than 304 after the salt spray tests in a 5 wt.% NaCl solution for 168 h; the beneficial effect of Cu was not obvious after exposure for 480 h. Penetrating (stripped morphology in 304 and fishbone morphology in 304Cu) and non-penetrating dish-shaped pits were both observed on 304 and 304Cu after immersion in a 6 wt.% FeCl₃ solution for 72 h; the corrosion rates of 304Cu were much higher than 304. Cu and Cu²⁺ were the main existing forms in the as-received 304Cu and Cu⁺ formed with the corrosion in chloride solutions. The results indicated a good corrosion resistance of 304Cu in service. The use of steel in an aggressive environment for a long exposure time should be cautiously considered. Full article

A series of new symmetrical 2,5-dialkyl-1,3,4-oxadiazoles containing substituted alkyl groups at the terminal positions with substituents, such as bromine, isopropyloxycarbonylmethylamino, and carboxymethylamino, were successfully synthesized. The developed multistep method employed commercially available acid chlorides differing in alkyl chain length and terminal substituent, hydrazine hydrate, and phosphorus oxychloride. The intermediate bromine-containing 2,5-dialkyl-1,3,4-oxadiazoles were easily substituted with diisopropyl iminodiacetate, followed by hydrolysis in aqueous methanol solution giving the corresponding 1,3,4-oxadiazoles bearing carboxymethylamino substituents. The structure of all products was confirmed by conventional spectroscopic methods including ¹H NMR, ¹³C NMR, and HRMS. Full article

The primary objective of this study is to report the initial efficacy data observed with the use of cryopreserved human umbilical tissue allografts for supplementation in patients with symptomatic degeneration of load-bearing articular cartilage in the knee joint. Our primary endpoints were pain, stiffness, and functional recovery scores. In this ongoing study, 55 participants (age 56–93 years) received a single Wharton’s jelly tissue allograft application. The study dose consisted of 150 mg of Wharton’s jelly allograft suspended in approximately 2 mL of sterile sodium chloride 0.9% solution (normal saline). Each study knee application was performed under ultrasound guidance in a physician’s office. The research methodology consisted of Numeric Pain Rating Scale (NPRS) scores and Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) subsection scores including pain, stiffness, and physical function. Study enrollment consisted of 55 patients followed for a post-application duration of 90 days. No adverse events or adverse reactions were reported. The results demonstrated statistically significant improvements of NPRS and WOMAC in initial versus 90-day examination. The data represent Wharton’s jelly tissue allograft applications are safe, non-surgical, and efficacious for patients with symptomatic osteoarthritis of the knee. Full article