Sodium Sulfate Solution Research Articles

External Sulfate Attack of Ambient-Cured One-Part Alkali-Activated Self-Consolidating Concrete

The mechanism of sulfate attack on alkali-activated materials, particularly the alkali-activated self-consolidating concrete (AASCC), is complex and contradictory. This could be due to the wide range of precursor and activator materials used in the production of AASCC mixtures, which has called into question the reliability and validity of existing evaluation procedures and practices. This paper presents a systematic research effort on AASCC mixtures, based on granulated blast-furnace slag, prone to various sulfate attack scenarios that are thought necessary to establish a proposed criterion. The conducted experimental design demonstrated that single-, binary-, and ternary-precursor AASCC samples, activated with 1:1 Na2CO3 and MetaNa2SiO3, partially submerged in sodium, magnesium, and mixed sulfate solutions could experience a dual sulfate attack scheme. Sulfate attack can occur in the immersed section in sulfate solutions, while physical sulfate attack can occur in the portion above the solution level. The influence of physical sulfate attack on the concrete’s characteristics was not significant given that the damage was confined to the outer surface. However, the damage was primarily monitored by the AASCC different systems’ pore structure, which resulted in the leaching of ions from samples to solutions. It was found that maintaining the pH in the sulfate solutions increased the rate of damage of AASCC mixtures. Furthermore, binary, and ternary precursor blends partially replacing slag with SF, or FA resulted in decreased porosity, surface scaling, and AASCC deterioration caused by an expansion in the volume of very small diameter pores. Finally, in all AASCC systems, gypsum and ettringite were the primary degradation products of sulfate attack.

Experimental Study on the Influence of Snow-Melting Agents on Fiber-Reinforced Cemented Soil under Freezing-Thawing Cycles

To explore the effect of snow-melting agents on the glass fiber-reinforced cemented soil under freezing-thawing cycles, three widely used snow-melting agents, including potassium acetate, magnesium chloride, and sodium sulfate, were used in this article. The effects of snow-melting agent types on the apparent damage, mass loss, and mechanical properties of fiber-reinforced cemented soil under freezing-thawing cycles were analyzed through salt freezing and unconfined compressive strength tests. The results show that the snow-melting effect of potassium acetate is the best, the snow-melting effect of magnesium chloride is the second, and the snow-melting effect of sodium sulfate is the worst. Notably, as the number of freezing-thawing cycles increases, the strength of the test block decreases to varying degrees. After the fifth freezing-thawing cycle, the strength of the block without fiber decreased by 61.30%, 70.22%, and 81.58% in clear water, potassium acetate, and magnesium chloride solution, respectively, while the test block in sodium sulfate solution lost its bearing capacity. A series of studies proved that the snow-melting agent with sodium sulfate as the main component has the most apparent erosion effect on the cemented soil, followed by magnesium chloride, and the erosion effect of potassium acetate is the weakest. The incorporation of glass fiber can effectively improve the resistance of the cemented soil under the action of various salt solution erosion and freezing-thawing coupling and has a significant effect on slowing the development of surface cracks, improving peak strength, and reducing the mass loss rate. This research will provide theoretical support for the design of subgrade and the selection of snow-melting agents in cold areas.

Early Strength Evolution of Cement Grouts Adopted in Reinforced Concrete Subjected to Na2SO4 Corrosion

Due to the harsh application environment, sodium sulfate corrosion poses a considerable threat to the performance of reinforced concrete. Considering high fluidization and early strength cement grouts (HECG) are widely adopted in the repair engineering of reinforced concrete, HECG are also subjected to the action of corrosive substances. Even though numerous research results disclosed the effect of sodium sulfate corrosion on the performance and the degradation mechanisms of conventional cement grouts, the degradation mechanisms of HECG under sodium sulfate corrosion are still to be studied because HECG have the exceptional characteristics of high fluidization and early strength that conventional cement grouts do not have. Hence, the compressive and flexural strengths of HECG after corrosion with different sodium sulfate solution concentrations and corrosion times were tested in this study. Moreover, the evolution of the microstructure of HECG in the process of corrosion was analyzed with a Scanning Electron Microscope (SEM) test. The changes in the hydration products were investigated through the X-ray diffraction (XRD) test and the Differential Scanning Calorimeter (DSC) test. Consequently, the degradation mechanisms of HECG in the case of different sodium sulfate solution concentrations and corrosion times were revealed. The results indicate that the corrosion of sodium sulfate and hydration exists simultaneously when the corrosion time is less than 7 days. When the corrosion time is 14 days, the hydration of HECG was complete. The main source of the early strength of HECG is that the C-S-H gel crosses and clings to form a solid and compact whole in three-dimensional space. The effect of Na2SO4 on the early strength formation of HECG is that the corrosion of Na2SO4 can postpone the conversion of CH crystal into C-S-H gel and damage the generated CH crystal. This study on the degradation mechanisms of HECG exposed to sodium sulfate corrosion can provide new ideas for sulfate resistance and durability design of HECG.

Suitability of the Lower Zab River Sediments for Concrete Works / Southwest of Kirkuk - Northern Iraq

An Engineering study was carried out for five stations in the Lower Zab basin, southwest of Kirkuk, to determine the viability of the Quaternary age sediments for concrete works. The geotechnical evaluation results included that the coarse aggregate's grain size analysis is identical to the gradient class (63.0 mm) according to the [1] classification. As for the gradation of fine aggregate for the sediments of the study area, the results of the granular gradient of the samples after matching them with the limits of AASHTO specification showed that they are identical to the specification with slight differences on some sieves. The elongation and flatness tests showed that the highest percentage of the longitudinal shape is (19.2%) and flat-shaped particles is (28.8%), within permissible limits according to British standard [2], the specific gravity for coarse aggregate was between (2.60 - 2.64) and saturated specific gravity (2.61 - 2.65), and the values of specific weight for fine soil ranged from (2.72 - 2.64) which is suitable for use in concrete works. The results of the laboratory test of the durability tests - The Los Angeles test for the samples showed that the highest percentage for weight loss was (20%), which is suitable for use in the concrete according to the Iraqi standard [3], the results of the laboratory test for stability showed that the percentage of weight loss for coarse aggregate (gravel) by the effect of sodium sulfate solution and for the number of 5 cycles of the samples ranged between (8.3% - 4.1%), which is valid for use in concrete works according to the American specification [4]. The results of the resistance tests - the point load test for stations (S1, S3, S4) within the classification range of very strong - extremely strong, and the two stations (S2, S5) within the class strong - very strong - extremely strong compared to the classification of [5], and they are good for concrete works. It was found from the results of the chemical tests the gypsum content, organic matter content, Total soluble salts, and the sulfate content of the samples of the study area are suitable to for concrete works according to British Standard [6], which is suitable for concrete works, testing the compressive strength of concrete cubes ranged between (24.93 - 18.22 MPa) for age seven days and ranged between (33.02 - 29.76 MPa) for 28 days for reference mixture, Which is (4:2:1 by weight). According to the Iraqi standard specification [7], the compressive strength values of the samples are suitable for regular unreinforced concrete, and in comparison with [8] classification, it was apparent that the concrete produced is of moderate endurance. And suitable for concrete works According to [9].

Strength and Microstructure of a Clayey Soil Stabilized with Natural Stone Industry Waste and Lime or Cement

Industrial waste generated by the natural stone industry when working with limestone and dolostone is mainly composed of calcium carbonate and calcium magnesium carbonate. This mineral composition makes soil stabilization a potential use of the natural stone industry waste. However, much research must be carried out to fully understand the aptitude of this waste for soil improvement. In this work, the strength and microstructure of a clayey soil stabilized using limestone powder waste and lime or cement were studied employing the following techniques: unconfined compressive strength tests, mercury intrusion porosimetry, thermogravimetric analysis, X-ray diffraction, and scanning electron microscopy. Moreover, the effects of an aggressive environment were simulated using a sodium sulfate solution. Its effects were investigated from 7 days to 6 months. The results obtained show an increase in the unconfined compressive strength and a more compact structure for the samples with the industrial waste. Therefore, limestone powder waste from the natural stone industry can be used as a ternary element with lime and cement in soil stabilization.

Direct Electro-oxidation of H2S gas in a membrane electrode assembly cell (MEA): A proof of concept

This work focuses on the treatment in gas phase of air polluted with hydrogen sulphide in an electrochemical cell equipped with a MEA and demonstrates that it is a feasible option, in which this pollutant can be efficiently transformed into solid sulphur and sulfuric oxide. This later species can be successfully retained by reactive absorption into a sodium hydroxide solution producing a sodium sulphate solution, while the elemental sulphur obtained is dragged from the electrochemical reactor to a solid trap. This product has a pale-yellow colour and the XRD diffraction analysis shows that it has a S8 crystallization type. An increase in the current density applied produces an increase in the percentages of hydrogen sulphide removal (37.47, 50.67 and 65.33 % at 20, 50 and 100 mA cm−2) from the gas fed and influences on the speciation, favouring the formation of sulphur and the oxidation of water to oxygen over the formation of sulphur trioxide. The gas flowrate increment gives lower H2S elimination percentages (72.73, 50.67 and 51.69 % at 4, 7 and 10 mL min−1) and favours the dragging of sulphur which seems to be very positive to avoid its further oxidation to sulfuric oxide. Electrochemical characterization indicates that direct electro-oxidation of H2S gas takes place in the anode surface and that MEA does not undergo any relevant deterioration during performance of continuous operation tests. The maximum Coulombic efficiency for SO3 production was 60 % at 7 mL min−1 and 20 mA cm−2, while for the S0 production was 9.5 % at 10 mL min−1 at 50 mA cm−2. Energy consumption for H2S removal ranges from 18 to 87 Wh gS-1.

Inulin impacts tumorigenesis promotion by colibactin-producing Escherichia coli in ApcMin/+ mice.

The prebiotic inulin has previously shown both protective and tumor-promoting effects in colorectal cancer (CRC). These inconsistencies may be due to the gut microbial composition as several bacteria have been associated with CRC. Specifically, polyketide synthase-positive (pks+) Escherichia coli promotes carcinogenesis and facilitates CRC progression through the production of colibactin, a genotoxin that induces double-strand DNA breaks (DSBs). We investigated whether colibactin-producing Escherichia coli changed the protection conferred by inulin against tumor growth and progression using the ApcMin/+ mouse model of CRC. Mice received a 2% dextran sodium sulfate (DSS) solution followed by oral gavage with the murine pks + E. coli strain NC101 (EcNC101) and were fed a diet supplemented with 10% cellulose as control or 10% inulin for 4 weeks. Inulin supplementation led to increase EcNC101 colonization compared to mice receiving the control diet. The increased colonization of EcNC101 resulted in more DSBs, tumor burden, and tumor progression in ApcMin/+ mice. The tumorigenic effect of EcN101 in ApcMin/+ mice mediated by inulin was dependent on colibactin production. Pasteurized E. coli Nissle 1917 (EcN), a probiotic, suppressed the inulin-driven EcNC101 expansion and impacted tumor progression. Our results suggest that the presence of pks + E. coli influences the outcome of inulin supplementation in CRC and that microbiota-targeted interventions may mitigate this effect. Given the prevalence of pks + E. coli in both healthy and CRC populations and the importance of a fiber-rich diet, inulin supplementation in individuals colonized with pks + bacteria should be considered with caution.

Bacterial healing of geopolymer concrete exposed to combined sulfate and freeze-thaw effects

In this study, metakaolin-based colemanite and red mud substituted geopolymer concrete were exposed to combined sulfate and freezing-thawing effects to simulate the effects of cold locations with a sulfate environment. Firstly, samples were exposed to a 5% sodium sulfate solution for four days for combined sulfate and freezing-thawing effects. Then, these samples were subjected to freezing-thawing according to TS EN 15177. Finally, cracks formed on the samples exposed to combined sulfate and freeze–thaw effect. Then, the bacterial healing process was applied to heal the cracks. Sporosarcina pasteurii bacteria were used to form CaCO3 in the cracks. The capillary water absorption, weight measurements, splitting tensile strength, ultrasonic pulse velocity, microstructural analyzes, and visual assessment of bacterial-healed geopolymer concrete samples were performed. As a result of this study, the healing ability of Sporosarcina pasteurii was successfully demonstrated by filling cracks caused by the combined durability effect with CaCO3 precipitates. Also, the recovery percentage of splitting tensile strength of the bacterial-healed samples was obtained as 61.71%.

Chromium-Modified Heterogeneous Bipolar Membrane: Structure, Characteristics, and Practical Application in Electrodialysis.

The modification of an MB-2 bipolar ion exchange membrane with chromium (III) hydroxide was carried out by a chemical method, namely, by the sequential treatment of the membrane with a solution of chromium (III) salt and alkali. Data on the morphology, phase, and chemical composition of the modified membrane were obtained using scanning electron microscopy and energy-dispersive analysis. In particular, it was shown that the modifier was distributed in a layer 30-50 microns thick at the boundary of the cation- and anion-exchange layers of the bipolar membrane. The electrochemical behavior of the modified membrane in the process of sodium sulfate conversion was studied by measurements of the following characteristics: the current efficiency of the acid and base, the energy consumption of the process, and the degree of contamination of the target products with salt ions. It was shown that the resulting membrane has an alkali and acid yield of 61% and 57%, respectively. This is higher than the same yields for the industrial unmodified MB-2 membrane (38% and 30%). The results of this study demonstrated that the modified samples allowed obtaining a higher yield of acid and base, reducing the content of salt ions in the target products and also reducing the electricity consumption for obtaining a unit of the target product. The concentration dependences of the electrical conductivity of the MK-40 heterogeneous ion-exchange membrane, which is a cation-exchange layer of MB-2, in sodium sulfate solutions before and after its modification with chromium (III) oxide were obtained. A decrease in the specific electrical conductivity of the membrane with the introduction of a modifier was established. A quantitative assessment of the influence of the modifier on the current flow, volume fraction, and spatial orientation of the conductive phases of MK-40 was carried out using an extended three-wire model for the description of the model parameters of ion-exchange materials. When a modifying additive was introduced into MK-40, the fraction of the current passing through the inner solution and the intergel phase decreased. This was due to the substitution of part of the free solution in the pore volume by the modifier. A variant of the practical application of electrodialysis with the chromium-modified bipolar ion-exchange membranes is recommended.

Optimisation of multi-component inorganic salt composition as draw solute for preparation of concentrated tea extract using forward osmosis process

This work aims to identify an appropriate food-grade multi-component draw solute composition with enhanced permeate flux and reduced reverse solute flux. This study also highlights the role of the membrane in an efficient FO process. The osmotic properties of selected mixed-salt solutions of magnesium chloride, sodium chloride, sodium sulphate, and potassium chloride were investigated. Based on osmotic pressure, three multi-solute draw solute (DS) compositions were selected for preparation of concentrated tea extract using forward osmosis process. The role of membrane in the efficient membrane process was evaluated by comparing two commercially available hollow fibre forward osmosis membrane. Compared to salts with monovalent ions (such as NaCl and KCl), the SSF of the divalent ions salts (such as MgCl2 and Na2SO4) is reduced by 57.42% due to their larger hydrated radius. The optimised multi-component draw solute performance was compared with single-salt draw solute by maintaining almost the same osmotic pressure. The results of the lab-scale experimental studies revealed that compared to single salt DS (Jw = 17.66 L m−2 h−1 and specific salt flux, SSF = 1.53 g L−1), the identified multi-component DS provides an enhanced permeate flux (16.91 L m−2h−1) with significantly reduced SSF (0.86 g L−1).

Experimental investigation of simultaneous hydrogen production and desalination via electrodialysis process

The primary purpose of the electrodialysis (ED) process is to desalinate saline water; besides this, hydrogen, a valuable energy carrier gas, is generated at the cathode side of the ED cell in this study. However, hydrogen gas reacts with oxygen gas and reforms water due to the internal recirculation of the electrolyte solution from the anode to the cathode compartment. This study investigates the potential of hydrogen gas generation in an ED system that desalinates sodium sulfate (Na2SO4) solution. The maximum conductivity removal ratio is 98.1% when ion-exchange resins are placed into the diluate compartment at pH 8, and the ED system's hydrogen production rate is 76.8 mg H2/h·kg Na2SO4. The maximum hydrogen production rate is achieved as 118.8 mg H2/h·kg Na2SO4 solution under 14.06 mA/cm2 current density. The maximum energy and exergy efficiencies are calculated as 25.29% and 28.78%, respectively. The results indicate that the conventional ED process makes hydrogen production possible while desalinating saline water.

Triggering of Polymer-Degrading Enzymes from Layered Double Hydroxides for Recycling Strategies.

The use of degrading enzymes in polymer formulation is a very attractive strategy to manage the end-of-life of plastics. However, high temperatures cause the denaturation of enzymes and the loss of their catalytic activity; therefore, protection strategies are necessary. Once protected, the enzyme needs to be released in appropriate media to exert its catalytic activity. A successful protection strategy involves the use of layered double hydroxides: cutinase, selected as a highly degrading polyester hydrolytic enzyme, is thermally protected by immobilization in Mg/Al layered double hydroxide structures. Different triggering media are here evaluated in order to find the best releasing conditions of cutinase from LDH. In detail, phosphate and citrate-phosphate buffers, potassium carbonate, sodium chloride, and sodium sulfate solutions are studied. After the comparison of all media in terms of protein release and activity retained, phosphate buffer is selected as the best candidate for the release of cutinase from LDH, and the effect of pH and concentration is also evaluated. The amount of the enzyme released is determined with the Lowry method. Activity tests are performed via spectrophotometry.

Durability of Green Concrete in Severe Environment

In this paper, the effects of different mineral admixtures and sulfate solution types on the appearance, mass change rate, relative dynamic elastic modulus, and corrosion resistance coefficient of concrete were systematically studied. X-ray Diffraction (XRD), Mercury Intrusion Porosimetry (MIP), Scanning Electron Microscopy (SEM), and X-ray Computed Tomography (X-CT) were used to explore and analyze the changes in the microstructure and the corrosion products of concrete in the sulfate solution. The results show that the existence of magnesium ions accelerates concrete deterioration. There is a critical dosage of fly ash for magnesium sulfate resistance of concrete. The magnesium sulfate resistance of concrete is improved when the fly ash content is less than 20%. Slag can significantly improve the corrosion resistance of concrete to magnesium sulfate. The diffusion of sulfate ions into concrete is a gradual process. In the early stages of corrosion, sulfate ion content in the concrete immersed in the magnesium sulfate solution is slightly less than that of the concrete immersed in the sodium sulfate solution. However, in the later stage of corrosion, the sulfate ion content in the concrete immersed in the magnesium sulfate solution is significantly higher than that of the concrete immersed in the sodium sulfate solution.

Исследование экологических и агрохимических показателей осадков сточных вод методом фитотестирования

Purpose: to assess environmental and agrochemical indicators of sewage sludge from municipal wastewater treatment plants through phytotesting. Materials and methods. Sewage sludge from municipal wastewater treatment plants with a three-year stay on the sludge map was studied. The examined sludge contains a high amount of sulfate ions (0.720 g/100 g) with a content of calcium ions of 0.350 g/100 g. The remaining salt ions and heavy metals are in small quantities. Phytotesting was carried out by studying the phytoresponse of the test plants seeds in contact with an aqueous extract and directly with precipitation. In the first variant, solutions of various concentrations were prepared: an aqueous extract of sediments, its two-fold dilution and four-and eight-fold dilution. To control the indicators, the distilled water and one-component model solutions of sodium sulfate with concentrations identical to the tested solutions were used. Testing was carried out on the seeds of oats and vetch. In the second variant, under laboratory conditions, seeds of oats, vetch, white mustard, radish and watercress were sown in vegetation vessels with sewage sludge. Results and discussion. Phytotesting allowed revealing the complex effect of precipitation due to their composition. In the variant of undiluted aqueous extract from sewage sludge, the inhibitory effect of sulfates on seed germination and biomass growth is revealed. In the variant with two-fold dilution, the stimulating effect of precipitation components on seed germination and biomass growth was noted. To clarify the effect of the stimulating effect of sewage sludge, an experiment on sowing test plants directly into the sludge was carried out. The best indicators were noted in the variants with oats sowing. Conclusions. The inhibitory effect of sewage sludge from municipal wastewater treatment plants in Novocherkassk is due to the content of sulfates in them. The best comparability of indicators in both variants was noted for oat seeds.

ИССЛЕДОВАНИЕ СТОЙКОСТИ ХЛОРМАГНЕЗИАЛЬНЫХ КОМПОЗИТОВ К НАСЫЩЕННЫМ СУЛЬФАТАМИ СРЕДАМ

This article studies the resistance of composites based on dolomitic magnesian binders mixed with an aqueous solution of magnesium chloride to long-term exposure to liquid media saturated with sulfate ions. We evaluated the effect of the long-term saturation of samples in an aqueous solution of sodium sulfate on the change in their mass, linear dimensions, strength characteristics, and phase composition. Since magnesia binders belong to the group of air-hardening binders, two series of control samples were kept in air-dry conditions and in a state saturated with water. The duration of the experiment was six months. During this period, the change in the physical and mechanical characteristics and phase composition of the samples stored in water and an aqueous solution of sulfates are similar in nature and are caused by a low coefficient of water resistance of magnesia binders. No traces of chemical interaction of magnesium stone minerals with sulfate ions were found. Thus, chloromagnesium composites, provided that they have a high water-resistance coefficient, can be used in aggressive sulfate environments.

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.

Numerical Simulation of Concrete Attacked by Sulfate under Drying–Wetting Cycles Coupled with Alternating Loads

Concrete structures such as rigid pavements, tunnels, and runways at airports are usually subject to fatigue traffic loading during their service life. Research on the aftereffects of drying–wetting cycles coupled with alternating loads on concrete erosion in saline–alkali and coastal areas is of considerable practical importance. For this study, we utilized specimens of dimensions 100 mm × 100 mm × 400 mm with strength ratios of C30, C40, and C50. We incubated the concrete samples in a 24 h/24 h drying–wetting cycle with sodium sulfate solutions of different concentrations as we applied alternating loads. We conducted ultrasonic wave velocity tests every 30 days from the 60th day of the experiment to determine the change in the sound velocity of the concrete over the course of 360 days. In addition, we examined the invasion depth of SO42− with time. Based on the change in sound velocity, we developed the damage degree function, and we modified the diffusion coefficient of SO42− in concrete in accordance with the coupling of drying–wetting cycles and alternating loads. We conducted a simulation on SO42− penetration depth, and the results were in reasonable agreement with those obtained by experimental testing.

Experimental Study of Effects of Efflorescence Control Admixture in Cement Mortar

This research work focuses on the effectiveness of efflorescence control admixture in reducing efflorescence on ordinary Portland cement mortar. Two different exposure conditions were set up to accelerate the development of efflorescence on mortar specimens. Efflorescence was quantified by digital image processing using MATLAB. A total of 132 mortar cubes of six-inch size were cast from 1:6 mortar with and without admixture. 108 specimens were left in waterlogged soil and 24 were partially submerged in sodium sulfate solution for 28, 56, and 90 days, and photographs of these specimens were processed. A comparison of 276 photographs of the specimens shows there is a considerable reduction in efflorescence in the case of specimens in waterlogged soil, whereas in sodium sulphate solution there was not much reduction in efflorescence. However, it is concluded that efflorescence control admixture can effectively prevent efflorescence in normal environmental conditions.

Усовершенствование технологии обессвинцевания обжиговых никелевых пылей акционерного общества «Кольская горно-металлургическая компания»

The article deals with the problem of reducing the loss of silver during the deleading of fine kiln dust from the nickel production of the Kola MMC. It has been shown that an increase in the degree of silver recovery is achieved by using sodium sulfate solutions or filtrates of water leaching of dust purified from selenium and tellurium as sulfate-containing reagents at the stage of lead sulfate precipitation. This ensures the subsequent separation of silver and lead by sulfite leaching and the production of selective concentrates.

Исследование двойного электрического слоя на композиционных материалах «карбид тугоплавкого металла — углеродное волокно» в пероксиде водорода и сульфате натрия

The electric double layer was studied by impedance spectroscopy on the surface of various composite materials: molybdenum, tantalum and niobium carbides in 1 M sodium sulfate solution and concentrated hydrogen peroxide solution. The data on the activation energy of the electrocatalytic decomposition of hydrogen peroxide on the surface of composite materials were compared with the capacity of the electrical double layer in hydrogen peroxide solution.