Concentrated Sulfuric Solutions Research Articles

Fractal Characteristics and Microstructure of Coal with Impact of Starch-Polymerized Aluminum Sulfate Fracturing Fluids

The degree of irregularity and complexity of the pore structure are comprehensively reflected in the fractal dimension. The porosity of coal was determined by its fractal dimension, where a larger dimension indicates a lower porosity. Fractal theory and the Frenkel–Halsey–Hill (FHH) model were applied to explore the variation rules of concentration on functional groups and pore structure in this study. Combined with infrared spectroscopy (FTIR) and low-temperature nitrogen adsorption, a starch-polymerized aluminum sulfate composite fracturing fluid was prepared, which plays an important role in methane adsorption and permeability of coal samples. The test results showed that, compared with the original coal, the pore volume and specific surface area of each group of coal samples were reduced, the average pore diameter was initially enlarged and then declined, and fractal dimension D1 dropped by 5.4% to 15.4%, while fractal dimension D2 gained 1.2% to 7.9%. Moreover, the nitrogen adsorption of each group of coal samples was obviously lower than the original coal, and the concentration of starch-polymerized aluminum sulfate solution existed at a critical optimal concentration for the modification of the coal samples, and the nitrogen adsorption reached a minimum value of 0.6814 cm3/g at a concentration of 10%. The novel composite solution prepared by the combination of starch and flocculant in this paper enhanced the permeability of the coal seam, which is of great significance in improving the efficiency of coalbed methane mining.

Resistance of Chloride and Sulfate of Geopolymer based on fly ash and silica fume as alternative raw materials.

Concrete durability to salt resistance is the main factor affecting the service life of concrete used in acid or salt environment. This project aims to develop the concrete composition for salt resistance of chloride and sulfate at 50,000 mg/L as the simulated salt solution in this project. Geopolymer consisted of 10%wt ordinary Portland cement (OPC type 1) with the other alternative raw materials which were pozzolanic materials and wastes (fly ash, silica fume and rice husk ash). The various parameters which were type and content of the alternative raw materials, plasticizers content, liquid to powder ratio, etc, were studied for developing the compressive strength of geopolymer after soaking in the simulated salt solution for 14 days as comparison with those in the normal water and the ordinary Portland cement. The results found that geopolymer consisted of fly ash and silica fume with the mixture of NaOH (10M): Na2SiO3 in a ratio of 24:16 (wt./wt.) could improve the compressive strength of geopolymer cement after soaking in the simulated sulfate salt solution for 14 days as compared to the ordinary Portland cement type 1 and type 5. Moreover, this geopolymer showed low density which was beneficial for use in the engineering structure in the high salt area. In addition, the change of chemical reaction and phases after setting of geopolymer in high concentrations of chloride and sulfate solution were studied to understand the mechanism of salt resistance of geopolymer and to develop the concrete composition for salt resistance in the future.

Deterioration law and mechanism of autoclaved aerated concrete under sulfate attack

Autoclaved aerated concrete (AAC) is a lightweight porous material, which is widely used as wall material. However, the performance of AAC under sulfate attack is still unclear. Therefore, this experiment investigated the performance changes of AAC with different bulk densities in sodium sulfate solution. Meanwhile, the influence of B05 grade AAC under erosion by sodium sulfate, magnesium sulfate and ammonium sulfate solutions was studied separately, and the degradation degree of its performance in different concentrations of sodium sulfate solution was analyzed. Mass change, relative dynamic modulus of elasticity (E rd) and compressive strength, mineral phase and micromorphologies were investigated. The results revealed that E rd decreased more obviously with a higher bulk density class, but the variety of the compressive strength was inversed. Moreover, the performances of AAC samples degraded more significantly while they were exposed to sodium sulfate solution. With an increase in sulfate solution concentration, the performance of AAC deteriorated more seriously.

Manganese sulfate application promotes berry flavonoid accumulation in Vitis vinifera cv. 'Cabernet Sauvignon' by regulating flavonoid metabolome and transcriptome profiles.

Flavonoids are vital for developing grapes and wine quality, and manganese deficiency decreases grape berry coloration. However, the effects and underlying mechanisms of action of manganese sulfate on grape metabolic profiles have not been well studied. In this study, three concentrations of manganese sulfate solutions: 0.5 μmol·L-1 (low, L), 5 μmol·L-1 (middle, M, the standard manganese concentration of Hoagland nutrient solution, control), and 1000 μmol·L-1 (high, H) were applied to "Cabernet Sauvignon" grapevine (Vitis vinifera L.) to explore the effect on berry composition. Manganese application effectively improved manganese concentration in grape organs. Furthermore, the concentrations of malvidin 3-O-(6-O-acetyl)-glucoside, malvidin 3-O-glucoside, malvidin-trans-3-O-(6-O-p-coumaryl)-glucoside, and peonidin 3-O-(6-O-acetyl)-glucoside were significantly increased under H treatment. More importantly, weighted gene co-expression network analysis (WGCNA) revealed that the structural genes (VvDFR, VvUFGT, and VvOMT) of flavonoid biosynthesis in brown module were upregulated under H treatment, and positively correlated with malvidin- and peonidin-derived anthocyanin concentrations. This study suggested that manganese application regulates berry transcriptional and flavonoid metabolic profiles, providing a theoretical basis for improving the color of red grapes and wines. This article is protected by copyright. All rights reserved.

Investigation of the Impact of Leaching Agent Concentration and pH on the Stability of Agglomeration of Ion-Absorbed Rare Earth Deposits

Ion-absorbed rare earth deposits react with the leaching agent during the in situ leaching process through ion exchange and hydration, which change the stability of ore agglomerates and even result in mining slopes or landslides. Indoor simulated column leaching assays were conducted on ion-absorbed rare earth deposit samples by using magnesium sulfate solution as the leaching solution. Surface zeta potential, double electric layer thickness, particle gradation, and pore structure were analyzed to measure the different concentrations and pHs of leaching solutions’ impact on the stability of ore agglomerates. Results show that the critical magnesium sulfate solution concentration and pH affecting the stability of deposit sample agglomerates are 3.5% and 4, respectively. The chemical replacement reaction between the leaching agent and rare earth ions occurs during column leaching when it reaches its zero-point potential at a pH of 3.5168. This breaks the balance between the van der Waals gravitational force and double-layer repulsion in clay particles and induces the disruption of agglomerates, which causes the difference in the pore radius ratio of the ore samples before and after column leaching. It is of great engineering guidance to solve the problems of slope instability and landslides that may occur in the ore body during the mining process of ionic rare earth ore.

Strength Degradation of Foamed Lightweight Soil Due to Chemical Erosion and Wet-Dry Cycle and Its Empirical Model.

Foamed lightweight soils (FLS) have been extensively used as backfill material in the construction of transportation infrastructures. However, in the regions consisting of salt-rich soft soil, the earth structure made by FLS experiences both fluctuation of groundwater and chemical environment erosion, which would accelerate the deterioration of its long-term performance. This study conducted laboratory tests to explore the deterioration of FLS in strength after being eroded by sulfate attack and/or wet-dry cycling, where the influencing factors of FLS density, concentration of sulfate solution, and cation type (i.e., Na+ and Mg2+) were considered. An unconfined compressive test (UCT) was conducted, and the corrosion-resistant coefficient (CRC) was adopted to evaluate the erosion degree after the specimens experienced sulfate attack and/or dry-wet cycling for a certain period. The research results show that the erosion of the FLS specimen under the coupling effect of sulfate attack and dry-wet cycling was more remarkable than that only under chemical soaking, and Na2SO4 solution had a severe erosion effect as compared with MgSO4 solution when other conditions were kept constant. An empirical model is proposed based on the test results, and its reliability has been verified with other test results from the literature. The proposed model provides an alternative for engineers to estimate the strength deterioration of FLS on real structures in a preliminary design.

Mechanical properties and abrasion resistance of polyurethane mortar subjected to freeze–thaw cycles and sulfate attack

The objective of this paper is to investigate the properties of polyurethane mortar subjected to freeze–thaw cycles in sulfate environment. Na2SO4 solutions with 5% and 10% sulfate concentrations were prepared. The mass loss, compressive strength, flexural strength and abrasion resistance of the polyurethane mortar were investigated. The interface transition zone and pore structure were then analysed. Results revealed that the damage degree of the mass, compressive strength and flexural strength of polyurethane mortar subjected to freeze–thaw cycles in sulfate solution are greater than that in water, and the high concentrations of sulfate solution can cause severe damage. The polyurethane mortar subjected to freeze–thaw cycles and sulfate attack will appear to have more severe surface damage after abrasion. The abrasion resistance of polyurethane mortar decreases as the freeze–thaw cycles and abrasion time increase. The freeze–thaw cycles and sulfate attack can cause the crack width at the interface transition zone of polyurethane mortar to expand, and the abrasion action accelerates this evolution. With the increase in freeze–thaw cycles, the gel and transition pores are gradually transformed into capillary and large polyurethane mortar pores. The volume fraction of capillary and large pores gradually increases, and the fractal dimension tends to decrease. Furthermore, the fractal dimension of the pore structure is positively correlated with mechanical properties and abrasion resistance. The mechanism analysis shows that abrasion can cause the detachment of loose mortar matrix of polyurethane mortar surface and form a weak area.

Towards non-invasive Wilson’s disease progression monitoring based on corneal copper content

Abstract Patients suffering from Wilson’s disease accumulate copper in their body. Copper load may become visible as Kayser-Fleischer (KF) rings - colorful copper-sulfur granules in the base of the cornea. Reoccurrence of KF rings in patients under anti-copper medication may be a sign for ineffective treatment. This work proposes a hand-held sensing system based on infrared reflectivity measurement of the cornea as a potential method for regular at-home progression monitoring. The intensity of the LEDs used is safe for operation on the human eye. As proof of concept, reflectivity was measured when placing the sensor onto samples of white paper that had copper tape of different sizes centered within the sensitive area. Further, reflectivity was determined for different solutions of copper sulfate in saline that were poured into adapter bowels fitting the sensor head, with Cu2+ concentrations of the samples deducted from literature. While the prototype system can be used to differentiate between two copper strips of 6 and 12 mm2 or larger, a different measuring principle would be needed to also determine the concentration of copper sulfate solutions. Since these two in-vitro models cannot fully represent the complex in-vivo molecular conditions of patients’ corneas, additional measurements on patients’ eyes are necessary to evaluate the potential of the proposed sensing system.

Degradation Characteristics and Mechanism of Black Sandy Dolomite with Fluid Added in a Mechanical Test

Sandy dolomite, being a soluble rock, is prone to dissolution and erosion caused by groundwater, leading to the formation of underground caves and fractures. This may result in geological disasters such as ground subsidence and collapse. In this paper, the changes and mechanical properties of black sandy dolomite after hydrochemistry are studied. A semi-immersion test with different concentrations of iron sulfate solution was carried out to simulate the water-rock interaction in different water environments. After that, scanning electron microscope (SEM) results could reflect the dissolution and pore development of rock by the effect of water-rock interaction from the microscopic. Water-rock interaction enlarges cracks in rocks and dissolves pyrite, carbonate minerals, and other components, reducing the cementation between particles. The change in the mechanical properties of black sandy dolomite under water-rock chemical interaction was revealed by uniaxial compression test. The mechanical properties of the samples exhibit varying degrees of deterioration, with strain increased ranging from 4.96 to 29.58%. The brittleness index modified (BIM) values for each sample ranged from 5.20 to 6.20%, all of which are larger than 4.70% in the natural state.

Experimental Study of Sulfate Erosion Resistance of Cementitious Sand with Waste Glass Powder

In order to save natural resources and protect the natural environment, the relevant performance of waste glass powder as a building material must be enhanced. In general, volcanic ash activity is enhanced through grinding the glass powder particles to a specific degree of fineness, thereby improving the overall strength of cementitious sand. Our current need is to study the effects of replacing standard sand with glass powder of varying particle size and dosage range on its resistance to sulfate erosion as well as the corresponding mechanisms. To further examine the durability properties of glass powder cementitious sand, this study uses glass powder of 100–200 mesh and 200–500 mesh to create cementitious sand samples, replacing 10% and 15% of standard sand with equal volume. After curing for 28 days in a standard curing room, the samples are submerged in tap water and a 5% concentration of sodium sulfate solution for 30, 60, 90, 120, and 150 days. Subsequently, the mass loss rate, flexural strength, and compressive strength are measured to reflect the sulfate erosion resistance of the cementitious sand samples containing glass powder. The findings indicate that the flexural and compressive strengths of cementitious sand with waste glass powder experience a swift decline in strength during the pre-erosion stage and a slow decline or even an increase in strength during the post-erosion stage as erosion age progresses. As the glass powder dosage increases, there is a noticeable decrease in the flexural and compressive strengths, in which the doping of 200–500 mesh doped with 15% of glass powder has the worst effect on the resistance to sulfate erosion. As the particle size increases, both flexural and compressive strengths significantly improve, suggesting that sulfate erosion properties are gradually enhanced. The primary reason for this phenomenon is that when glass powder substitutes fine aggregate, the activity develops more slowly in the initial stage, primarily filling the pores and cracks. However, the activity increases rapidly later, more fully integrating with the cement mortar in sodium hydroxide’s hydration product to create dense hydrated calcium silicate crystals. This enhances the overall strength of the sample, filling the pore structure within the system, and is more conducive to resisting the erosion effect of sulfate ions on the sample.

Application of bio-metal-organic framework-based magnetic dispersive solid phase extraction for the extraction of polycyclic aromatic hydrocarbons from pasteurized milk

This work describes the development of a magnetic dispersive solid phase extraction method based on using bio–metal–organic framework (prepared from vitamin B3 and cobalt salt in water medium) as an efficient sorbent for the extraction of polycyclic aromatic hydrocarbons from milk samples. Briefly, the synthesized sorbent at mg–level is added to the supernatant phase after precipitating the proteins of milk sample and the mixture is vortexed. In the presence of magnetic field, the supernatant is removed and the sorbent particles containing the adsorbed analytes are eluted by using an appropriate organic solvent. The eluted analytes are more enriched using a magnetic ionic liquid–based dispersive liquid–liquid microextraction. After back–extraction of the analytes into n–hexane, the analytes are determined using gas chromatography–mass spectrometry. The experimental variables influencing the suggested method efficiency such as zinc sulfate solution concentration and volume, and vortexing time in proteins precipitating step, sorbent amount, adsorption time, ionic strength, elution solvent type and volume, desorption time, extraction solvent type and volume, and back–extraction solvent type, volume and time in extraction procedure were optimized by one parameter at a time strategy. Under the optimum conditions, low limits of detection (38–78 ng L−1) and quantification (130–260 ng L−1), high extraction recoveries (58–82%) and enrichment factors (145–205), and good precision (relative standard deviations ≤6.1%) were obtained. Finally, the developed method was effectively employed for quantification of polycyclic aromatic hydrocarbons in pasteurized milk samples.

Hofmeister effect-based soaking strategy for gelatin hydrogels with adjustable gelation temperature, mechanical properties, and ionic conductivity

As a natural polymer with good biocompatibility, gelatin hydrogel has been widely used in the field of biomedical science for a long time. However, the lack of suitable gelation temperature and mechanical properties often limit the clinical applicability in diverse and complex environments. Here, we proposed a strategy based on the Hofmeister effect that gelatin hydrogels were soaked in the appropriate concentration of sodium sulfate solution, and the change in molecular chain interactions mainly guided by kosmotropic ions resulted in a comprehensive adjustment of multiple properties. A series of gelatin hydrogels treated with different concentrations of the salt solution gave rise to microstructural changes, which brought a decrease in the number and size of pores, a wide range of gelation temperature from 32 °C to 46 °C, a stress enhancement of about 40 times stronger to 0.8345 MPa, a strain increase of about 7 times higher to 238.05 %, and a certain degree of electrical conductivity to be utilized for versatile applications. In this regard, for example, we prepared microneedles and obtained a remarkable compression (punctuation) strength of 0.661 N/needle, which was 55 times greater than those of untreated ones. Overall, by integrating various characterizations and suggesting the corresponding mechanism behind the phenomenon, this method provides a simpler and more convenient performance control procedure. This allowed us to easily modulate the properties of the hydrogel as per the intended purpose, revealing its vast potential applications such as smart sensors, electronic skin, and drug delivery.

Experimental and numerical investigations on damage evolution of concrete under sulfate attack and freeze-thaw cycles

The macro-microstructure tests of concrete under the alternating action of salt freezing (ASF) were conducted to investigate the macro-mechanical properties and microstructure pore evolution patterns of concrete. Combined with CT scanning and 3D pore model reconstructing technologies, we present the evolution equation of concrete porosity and the quantitative relation between the fractal dimension of concrete pores and the macroscopic strength under the ASF. Then, a macro-microscopic damage evolution model of concrete was proposed to study the structural performance evaluation of an aqueduct. The results show that the compressive strength (fc), splitting tensile strength (ft), and relative dynamic modulus (Erd) of concrete specimens under the ASF show a decreasing trend as a whole, and the mechanical properties of concrete gradually decrease with the increase of sulfate solution concentration. With the increase of the cycles of salt freezing alternation, the pore fractal dimension of the concrete gradually decreases and the porosity gradually increases. After the cycle of 8 times, the pore fractal dimension decreases by 6.06%, and the porosity increases by 7.30% compared with the initial state. The porosity of concrete is negatively correlated with the strength, while the fractal dimension of the pore structure is positively correlated with the strength. When the ASF reaches 8 times, the maximum compressive stress and tensile stress of the groove body are 9.48 MPa and 3.13 MPa, respectively, which appear at the ends of the lower chord. The displacements of the bottom and side wall plates are 0.384 mm and 3.289 mm, respectively. The penetrating cracks appear at the junction, and the structure severely deteriorates.

A single dose of lipopolysaccharide elicits autofluorescence in the mouse brain.

One hallmark of aging is autofluorescence (AF) in the brain. However, the underlying mechanism for inducing AF remains unknown. This study aims to determine the cause(s) of this phenomenon. The endogenous expression pattern of AF in mice was examined at differing ages. Intraperitoneal injection of a single dose of lipopolysaccharide (LPS) was performed to induce AF. Copper sulfate was applied to remove AF to allow for further immunofluorescence staining. AF appeared in the mouse brain as early as 3 months of age. In the cortex, AF occurs in the lysosomes of microglia, astrocytes, endothelial cells, and oligodendrocyte lineage cells and its prevalence increases with age. Interestingly, AF never occurs in the pericytes of young or aged brains. LPS administration resulted in a rapid and marked induction of brain AF, similar to the normal aging process. Finally, age-related and induced AF can be eliminated by low concentrations of copper sulfate solution. This pre-treatment is safe for aging and lineage tracing studies. These findings depict that AF in the brain could be associated with the innate immune response against Gram-negative bacteria infection.

Effect of Sulfate Crystallization on Uniaxial Compressive Behavior of Concrete Subjected to Combined Actions of Dry–Wet and Freeze–Thaw Cycles

This study focuses on the influence of salt crystallization from sodium sulfate on uniaxial compressive properties of concrete subjected to the coupling action of dry–wet cycles and freeze–thaw cycles. Eight groups of concrete specimens with different concentrations of sodium sulfate solution (CSSS) and different numbers of drying and wetting cycles (NDWC) were designed. Three groups of specimens with different numbers of freezing and thawing cycles (NFTC) exposed to same dry–wet cycles and same sulfate concentration were prepared to study the effects of combined environmental conditions. Salt crystallization from sodium sulfate was generated under a cyclical dry–wet time ratio of 3:1. Scanning electron microscopy and X-ray diffraction analysis were used to analyze reaction products of sulfate and concrete matrix. The results show that under single sulfate dry–wet cycles, with the increase of CSSS and NDWC, the uniaxial compressive strength of concrete degrades as a parabola and corresponding strain increases as a parabola, except for the linear increase of CSSS strain. Subjected to the combined action of sulfate dry–wet cycles and freeze–thaw cycles, it shows that the uniaxial compressive strength of concrete decreases as a parabola with the increase of NFTC, but corresponding strains have no obvious variation. The sulfate salt attack in advance greatly accelerates the deterioration of specimens after freeze–thaw cycles. The common dimensionless predication model of stress–strain relationship of concrete subjected to the combined action of dry–wet cycles and freeze–thaw cycles has been established.

Sulfate ions diffusion in concrete under coupled effect of compression load and dry-wet circulation.

The diffusion of Sulfate ions in concrete is a complex process and affects the performance of concrete. Experiments on the time-dependent distribution of sulfate ions in concrete under the coupling of pressure load, dry-wet circulation, and sulfate attack, and the diffusion coefficient of sulfate ions with various parameters was tested. The applicability of the cellular automata (CA) theory to simulate the diffusion of sulfate ions was discussed. In this paper, a multiparameter cellular automata (MPCA) model was developed to simulate the impacts of load, immersion ways, and sulfate solution concentration for the diffusion of sulfate ions in concrete. The MPCA model was compared with experimental data, considering compressive stress, sulfate solution concentration, and other parameters. The numerical simulations verify the calculation results based on the MPCA model are in good agreement with the test data. Finally, the applicability of the established MPCA model was also discussed.

ВИЗНАЧЕННЯ ЕФЕКТИВНОСТІ ВИЛУЧЕННЯ СУЛЬФАТІВ НА ЗВОРОТНООСМОТИЧНІЙ МЕМБРАНІ НИЗЬКОГО ТИСКУ

The dependence of the efficiency of the low-pressure reverse osmosis membrane Filmtec TW30-1812-50 on the initial concentrations of sodium sulfate in the range of 10-650 mg/dm3 at permeate recovery rates of 1-90 % using a pressure of 4 atm was determined. The effect of increasing the permeate recovery rate on selectivity, membrane performance, and the in-crease in the sulfate content of concentrates was determined. It is shown that the concentration of sulfates in permeate depends on their initial concentration in solutions and increases both with an increase in the initial concentration and with an increase in the degree of permeate extraction. The latter factor is quite significant at initial sulfate concentrations of 650 mg/dm3. The membrane performance increases with decreasing salt content in water and decreases with increasing permeate removal rate, which leads to an increase in salt concentration in the pre-membrane space. The selectivity of the membrane for sulfates is 94.9-99.3 % and increases with increasing concentration of sodium sulfate solutions in solutions, despite a certain increase in salt concentrations in permeates. It is shown that as the degree of permeate selection increases, the selectivity for solutions with low initial sulfate concentrations increases. A FFP-based process modeling was performed to determine the sulfate con-centration in the permeate and concentrate at any initial sulfate concentration in a certain range. It was found that the con-centrate solutions are stable in the entire range of concentrations used with an increase in the degree of permeate recovery from 10 to 90 %. Based on the research results, a method for determining the capacity of the plant and the osmotic and oper-ating pressures based on the salt concentration and the set pressure in the system was proposed. From the data obtained, it can be concluded that the permissible level of mineralization at which the use of low-pressure reverse osmosis membranes is ad-visable.

Influence of chlorides and salt concentration on salt crystallization damage of cement-based materials

Durability of concrete exposed to physical salt attack (PSA) has primarily been studied on specimens partially submerged in sulfate solution. However, in sulfate-containing soils, chlorides are often present. The aim of this study is to investigate the influence of salt concentration and the presence of chlorides on the deterioration of cement-based materials caused by PSA. Cement mortars partially submerged in three different concentrations of sodium sulfate solutions (5%, 9% and 13%) and two mixed Na2SO4–NaCl solutions (5%–2% and 5%–5%) and exposed to cyclic drying-wetting were investigated. The crystallization behavior of salt solutions and the alteration in the macroscopic properties and microstructure of the specimens were observed to understand the differences in deterioration. The results showed that the presence of chloride ions significantly reduced the surface scaling above the solution level. Microstructural characterization suggested that thenardite tended to precipitate homogeneously in the specimens partially submerged in solutions containing chlorides. Consequently, crystallization pressure is less likely to develop in such a case. On the contrary, for the specimens partially submerged in pure sodium sulfate solutions, a higher concentration of salt solution facilitated more thenardite accumulation in a thin layer beneath the surfaces, which in turn accelerated the damage process. The findings may improve guidance on the evaluation of concrete resistance to PSA when chlorides are detected in sulfate-bearing environments.

Establishing a dependence of the efficiency of low-pressure reverse osmotic membranes on the level of water mineralization

This paper has established the dependence of the effectiveness of the reverse-osmotic low-pressure membranes Filmtec TW30-1812-50 on the initial concentrations of sulfate and sodium chloride in the range of 20–1000 mg/dm3 at the degrees of permeate selection of 1–90 % with the use of pressure of 3.6–10.0 atm. The dynamics of increasing the content of sulfates and chlorides in concentrates with an increase in the degree of permeate selection, selectivity, productivity, and filtration coefficient of the membrane have been determined. The conditions for calculating the membrane performance depending on the working pressure for sodium sulfate and sodium chloride have been defined. It is shown that the concentrations of sulfates and chlorides in permeates depend on their initial concentration in solutions and increase both with an increase in the initial concentration and with an increase in the degree of permeate selection. The latter factor is quite significant at the initial concentrations of chlorides and sulfates at a concentration of 1000 mg/dm3. The productivity of the membrane increases with a decrease in the salt content in water and decreases as the degree of permeate selection increases, which leads to an increase in the concentration of salts in the premembrane space. The selectivity of the membrane increases with increasing concentration of sodium sulfate and sodium chloride solutions in solutions, despite a certain increase in salt concentrations in permeates. For solutions of Na2SO4 and NaCl (20–1000 mg/dm3) at their reverse-osmotic desalting on the membrane, the filtration coefficients have constant values. For these initial concentrations, the filtration coefficient for Na2SO4 is 3.4–3.8 dm3/(m2∙atm), and for NaCl – 2.6–3.2 dm3/(m2∙atm). The data reported here allow us to conclude about the permissible level of mineralization, at which it is advisable to use reverse-osmotic low-pressure membranes. It is shown that an increase in the concentration of salts in concentrates leads to an increase in osmotic and working pressures

Influence of sulfate crystallization on bond-slip behavior between deformed rebar and concrete subjected to combined actions of dry-wet cycle and freeze-thaw cycle

The bond-slip behavior of deformed rebar with medium embedded length and surrounding concrete without stirrup under sulfate salt, dry-wet cycle and freeze–thaw cycle was investigated in this study. Physical crystallization of sulfate was produced by using a 3:1 drying/wetting time ratio in erosion specimens. Different concentrations of sodium sulfate solution (CSSS), different drying and wetting cycles (DWC), and different freeze–thaw cycles (FTC) were considered as environmental variables in central pull-out tests. The bond characteristics of post-yielding rebar and surrounding concrete under combined environmental factors were obtained. Scanning electron microscope and x-ray diffraction analysis were conducted to identify reaction products. The experimental results showed that CSSS and DWC had both beneficial and adverse effects on the bond strength.1% CSSS and 25 DWC were the turning points of increasing and decreasing of bond strength. The expansion force caused by Na2SO4 physical crystals improved the bond strength in the initial stage, but impaired it after the crack of pore wall of concrete in the later stage. After superimposed FTC, the bond strength was greatly reduced. Sulfate crystallization significantly accelerated the deterioration of bond strength under freeze–thaw cycles. The prediction models of the bond strength between deformed rebar and surrounding concrete after yielding in terms of single and multiple environmental factors had been established. The models can be used to predict the bond strength of post-yielding rebar and surrounding concrete in complex environments of sulfate, dry-wet cycle and freeze–thaw cycle.