Sulfate Ion Concentration Research Articles

Pore structure evolution and sulfate attack of high-volume slag blended mortars under standard curing and steam curing

Partial replacement of cement with high-volume slag reduces the amount of cement in concrete and thereby lessens the environmental pressure caused by cement production. This paper investigates the pore structure evolution and sulfate attack of high-volume slag blended mortars under standard curing and steam curing, discusses the effects of slag content and pore structure on sulfate attack, and evaluates the methods for determining the sulfate resistance performance. The pore structure results show that the hydration of cement and/or slag reduces the porosity and most probable pore diameter (MPPD) and refines the pore structure of mortars. Steam curing primarily affects the pore size distribution but not the porosity for the mortars within 3 d. Increasing slag replacement increases the porosity for standard-cured and steam-cured mortars at the age of 28 d; however, it significantly reduces the air voids that are detrimental to sulfate resistance. Sulfate attack results show that the combination of the flexural strength test with the sulfate-ion content can evaluate the sulfate resistance well. The sulfate resistance improves with increasing slag content, and 70% of slag improves the sulfate resistance significantly for both standard-cured and steam-cured mortars. In addition, the MPPD, gel pores, and mesopores do not seem to determine the sulfate resistance. Reducing the volume fractions of large capillary pores, especially air voids, can improve sulfate resistance.

EVALUATION OF THE PHYSICAL AND CHEMICAL QUALITY OF THE WATERS OF THE IVORIAN COASTLINE

Water pollution remains an issue that concerns the whole world. That of the coasts is evoked but remains less mediatized compared to that of the consumable fresh water. Therefore, in view of the increasing question of the availability of drinking water resources, this study was initiated with a view to resorting to coastal waters in case of need. After characterization, it appears that the waters of the coast are loaded with salts. They have an average content of sulfate ions ranging from 400 to 1000 mg/L. They are also turbid and have a high biochemical oxygen demand ranging from 100 to 700 mg/L. On the whole, the waters of the Ivorian coastline are not polluted enough to be used for consumption after treatment. But they cannot be consumed without prior treatment.

Effect of Layered Double Hydroxides on the Deterioration Process of Cement Paste under Sulfate Attack

This study investigated the effect of layered double hydroxides (LDHs) on the deterioration process of cement paste in the sulfate environment. Cement pastes with the addition of original and calcined LDHs at 2.5 wt.% and 5.0 wt.% of cement were exposed to Na2SO4 solution for 360 days. The macroscopic performance of the cement paste was assessed based on mass variation, porosity, compressive strength, and content of sulfate ions. Furthermore, the microhardness, microstructures, and composition of the degraded pastes were examined using Vickers hardness (HV), mercury intrusion porosimetry (MIP), scanning electron microscope (SEM), X-ray diffraction (XRD), and thermogravimetric analysis (TGA). The results indicate that cement paste incorporated with LDHs can mitigate the corrosion caused by sulfate effectively, especially in the case of calcined LDHs (C-LDHs), which primarily increase the adsorption of sulfate. Compared with the control specimen, the 180 d compressive strength loss ratio of specimens with 2.5 wt.% and 5.0 wt.% of C-LDHs decreased by 63.66% and 80.51%, respectively. Moreover, LDHs can reduce the amount of ettringite crystals, densify the microstructure, and refine the pore structure to mitigate the cement paste's sulfate corrosion significantly. Compared with the control specimen, the 180 d harmful pore volume fraction of specimens laced with 2.5 wt.% and 5.0 wt.% C-LDHs decreased by 43.77% and 54.51%, respectively. In terms of the content of C-LDHs, an optimal content of C-LDHs could ensure the dominant effect of adsorption, while excessive C-LDHs could refine pores. In addition, Vickers hardness has an excellent correlation with compressive strength, which could precisely predict the compressive strength. Moreover, by combining the Vickers hardness distribution and content distribution of sulfate ions, the cross-section of the paste could be classified into four regions to evaluate the deterioration process accurately: the degraded zone, the strengthened zone, the invaded zone, and the intact zone.

Localized corrosion of steel in alkaline solution with low-level chloride and elevated sulfate concentrations

Localized corrosion developed on post-tensioned steel strand in deficient grout, relating to elevated concentrations of sulfate ions. The deficient grout can also have low-level chloride ion concentrations below threshold values originating from the base materials. Open-circuit potential, linear polarization resistance (LPR), and electrochemical noise (EN) measurements were made on steel specimens exposed in saturated calcium hydroxide solution with 0.012 M Cl−, 0.04 M SO42−, or combined. Results showed that the combined presence of sulfates in low-level chloride alkaline solutions elevated the corrosion rate and the extent of corrosion pitting. The EN technique was shown to provide corrosion rate estimates consistent with LPR and was able to identify pitting characteristics. The outcomes of the research provides supporting evidence that analysis of deficient grout for chlorides alone may not capture the risk for corrosion and that corrosion associated with elevated sulfate concentrations can be exacerbated in presence of low-level chlorides.

Enhanced sulfide oxidation by monsoon rainfall in a small typical karstic catchment of Southwest China

CO2 is released to the atmosphere via sulfuric acid weathering of carbonate rocks, affecting the flux of CO2 drawdown via silicate weathering. Precisely quantifying the proportion of oxidative weathering of sulfide minerals to riverine sulfate is critical to improving the estimation of the global carbon budge. Sulfur and oxygen isotopic compositions of sulfate and major ion concentrations in river water samples collected monthly at 12 sampling sites from a small typical karstic catchment of Southwest China were analyzed, in order to quantify the relative contribution of sulfide oxidation to riverine sulfate and elucidate the factors affecting its changes. Results show that the sulfate concentration and δ34Ssulfate and δ18Osulfate values at most sampling sites have obvious seasonal changes, with low values in the monsoon season and high values in the non-monsoon season, suggesting that the relative contributions of different sulfur sources to riverine sulfate are seasonally variable throughout of the year. Results from the Beyesian isotope mixing model show that overall, the fraction of sulfide-derived sulfate to riverine sulfate ranges from 44.3 ± 13.7% to 53.3 ± 10.5%, although it has a wide range for different sampling sites. In addition, the relative contribution of sulfide weathering displays a seasonal variation and is higher in the monsoon season, which is mainly attributed to the influence of high rainfall in wet season. This study indicates that an increase in rainfall intensity under climate change may lead to a raised sulfide oxidation rate in the karstic catchment, which is important for assessment of global carbonate and silicate weathering in future.

Experimental study of effective compounds in a smart water injection process

The process of smart water injection into carbonate reservoirs has always faced many challenges. This study attempted to investigate this issue by examining two effective factors active ionic compounds in brine and active compounds in the oil phase. The potential for the reaction among three phases’ oil, rock, and brine in changing wettability requires the presence of active ionic compounds in the brine water and active compounds in the oil. These compounds in optimal concentrations are the driving force of the wettability alteration process. In the first step, the contact angle and the spontaneous imbibition process were performed on the outcrop samples and the limestone core to investigate the effect of the active compounds of smart water. The efficiency of calcium and divalent magnesium cations mainly depends on the sulfate ion concentration. However, reservoir physical condition and the presence of other effective compounds in the reactions network can be helpful in the determination of the essential active ions in the reaction. Finally, the optimal concentrations of these three ions lead to the formation of a stable water film and a change in the wettability of the rock, which leads to an increase in oil recovery. In this regard, cations in the presence of sulfate ions as much as the minimum concentration in seawater can have a positive function and have an acceptable efficiency compared to increased concentrations of sulfate ions in seawater. The cores were saturated with two oil samples for further investigation, and again, two tests of measuring contact angle and spontaneous imbibition were performed. The difference between imbibition rate and ultimate recovery illustrates that the carboxylic acid functional group in the original crude oil structure can facilitate displacement compared to oil-free acid components. Therefore, acidic components in crude oil affect the wettability alteration through electrostatic interaction with surface minerals and brine. Active components can act as a critical indicator in smart water injection processes.

Thermal decomposition and oxidation of cation exchange resins with and without Na2CO3–K2CO3 salt

Owing to the capability of trapping sulfur and reducing the formation of sulfur bridges, the addition of carbonate salt is one of the ideal destruction technologies for the treatment of cation exchange resins (CERs). The oxidation processes of CERs with and without Na 2 CO 3 –K 2 CO 3 salt were investigated using TG, FT-IR and XPS. The results of these analyses indicate that in addition to the evaporation process, the oxidation process of CERs can be described as: during the thermal decomposition of the sulfonic acid groups, there are direct destruction of functional groups and the dehydration of functional groups. In addition to the destruction of styrene-divinylbenzene copolymer, the continuous oxidation process includes the direct thermal decomposition of sulfonyl bridges and the formation of sulfur bridges, which decompose at high temperature. The elemental analysis results confirmed that the presence of carbonate salt reduced the formation of sulfur bridges in residue. The SO 2 can be effectively adsorbed by carbonate salt to form sulfate in the salt. Moreover, the content of sulfate ions in waste salt were determined by ICP-MS, which proves that oxidation with Na 2 CO 3 –K 2 CO 3 at 550 °C for 1 h is the optimal oxidation condition to form the sulfate in carbonate salt. • The Na 2 CO 3 –K 2 CO 3 salt can effectively promote the oxidation of resins. • Carbonates can convert the sulfur bridge structure in residue into sulfate. • Four oxidation processes of resin are described by quantifying S content.

INVESTIGATION OF THE SALT FORMATION ISSUE IN THE OIL FIELD OF THE PRECASPIAN REGION

This article analyzes complex laboratory and simulation studies of salt deposition during oil production in conditions of low permeability with falling reservoir pressure. The object of research is Jurassic deposits of horizons with a depth of up to 3000 m. The study of salt formation problems pursues the following objectives: to determine the type of salts (within and using the resources available for research), to conduct modeling to understand longterm trends in salt formation (during water injection projects) or short-term trends (during hydraulic fracturing or cattle), as well as to make recommendations based on tests and the Schlumberger database. The formation waters of the Jurassic deposition of the field have similar hydrochemical parameters along the horizons and are chlorocalcium brines, the total mineralization of which ranges from 147.1 g/l to 186.6 g/l. According to the available data, there is no clear dependence of mineralization on the depth of occurrence. The density in surface conditions is 1097-1131 kg/m3. In terms of concentration, chlorides predominate over alkali metals (sodium, potassium), and the waters are also noticeably enriched with calcium, the content of which significantly prevails over magnesium. A characteristic feature is the low content of sulfate and bicarbonate ions. The research and scientific nature of this work is confirmed by the fact that a new scientific software for the analysis of salt deposition was used for the Kazakhstani industry of intensification of hydrocarbon production. Modeling of critical thermobaric points covers the range of predicted parameters of reservoir pressure and temperature, as well as the resulting temperature in the bottomhole zone, taking into account the operation of the installation of an electric centrifugal pump. The sensitivity analysis was carried out taking into account the percentage ratio of injected and reservoir water, the parameters of the water used during hydraulic fracturing were calculated separately. The result of the study is a quantitative assessment of the permeability from salt deposition and preventive measures to preserve the productivity coefficient of wells.

Assessment and Removal of Heavy Metals and Other Ions from the Industrial Wastewater of Faisalabad, Pakistan

The contamination of surface and groundwater is of major concern around the globe due to the fast industrialization and urbanization. The groundwater and water quality of rivers, Ravi and Chenab in Faisalabad, Pakistan are contaminated due to the industrial wastewater. The aim of this study was the assessment of the physiochemical contaminants of Faisalabad’s industrial wastewater area and the adsorptive removal of ions present in high concentrations following the National Environmental Quality Standards (NEQS) for the municipal and industrial liquid effluents of Pakistan. One of the two samples was collected from a drain carrying wastewater from different industries and other from the outlet of a drain discharging wastewater into river Chenab. The analysis results obtained indicate that most of the contaminants were below the acceptable limit of industrial wastewater NEQS, Pakistan. However, contaminants like sulfate ions (714 mg/L), total dissolved solids (33,951–34,620 mg/L) and barium ions (11–15 mg/L) were found to be higher than the allowable level of NEQS for the municipal and industrial liquid effluents for Pakistan. A novel biosorbent synthesized indigenously from Monotheca buxifolia seeds was used for the removal of sulfate, barium and TDS from the wastewater effluent samples. This biosorbent successfully reduced the sulfate ion concentration in the wastewater sample from 714 to 420 mg/L at pH 6 in 1 h. Similarly, the concentration of TDS reduced to 33,951 from 6295 mg/L at pH 4, whereas barium ions were removed from 15 to 1 mg/L at pH 10 in 1 h. Treatment of wastewater through the synthesized biosorbent efficiently removed the high concentration ions and could potentially be applied to reduce the toxic effects of these contaminants on local public health.

Highly efficient in-situ purification of Fe(II)-rich high-arsenic groundwater under anoxic conditions: Promotion mechanisms of PMS on oxidation and adsorption

Dissolved Fe(II) widely exists in high-arsenic (high-As) groundwater, whose concentration (12–518 µM) is positively correlated with that of As(III). In order to realize the environmental-friendly and highly efficient in-situ simultaneous oxidation and adsorption of As(III) under anoxic conditions, peroxymonosulfate (PMS) was directly dosed into Fe(II)-rich high-As groundwater. Compared with hydrogen peroxide (88.2%) and peroxydisulfate (66.6%), the involvement of PMS gave the best As(III) removal efficiency of 98.8% after 1 min treatment, owing to the dual aspects of the best oxidation of As(III) and the best adsorption of As(V). During As(III) oxidation process, more SO4•− and 1O2 generated and unactivated PMS in Fe(II)-PMS process were responsible for the most efficient oxidation. During the enhanced As(V) adsorption process, the presence of PMS changed the structure of the in-situ formed Fe(III) colloid to provide more adsorption sites. Besides, the higher PMS concentration caused better As(III) oxidation, As(III) immobilization, and As(V) adsorption efficiencies. A wide range of Fe(II) (125–500 µM) coupled with PMS (244 µM) could immobilize more than 90% of As(III) (C0 = 1000 µg/L), and As(III) ranging from 0.2 mg/L to 2.0 mg/L also could be removed over 90% in Fe(II)-PMS process. The coexistence of HCO3–, Cl−, and humic acid slightly affected As(III) immobilization. Furthermore, after treatment, residual Fe ions concentration, residual total arsenic concentration, sulfate ions concentration, and pH value met the drinking water standard. This study could provide a very promising and attractive technology for a fast and efficient in-situ purification of Fe(II)-rich high-As groundwater.

Electrochemical Assessment of Galvanized Steel Corrosion in Alkaline Sulfate Solution

Corrosion of steel prestressing strand in bonded post-tensioned bridge tendons have been associated with elevated concentrations of sulfate ions in deficient grout that can develop due to grout segregation [1]. Previous research indicated that the early presence of elevated sulfate ion concentration in the deficient grout in contact with the embedded steel can impair steel passivity. Metastable pitting was observed for steel in saturated calcium hydroxide solutions with sulfate ion concentrations greater than 1,300 ppm and pitting was observed in solutions above 20,000 ppm [2-4]. In addition to steel strand corrosion, galvanized steel ducts in direct contact with the deficient grout with elevated sulfate ion concentrations were also observed to have severe localized corrosion [1]. Galvanized steel in alkaline solutions, such as in cement pore water, have been characterized to have greater resistance to chloride-induced corrosion with chloride threshold concentrations as much as 2.5 times greater than carbon steel [5]. Information relating to sulfate concentrations is less available. Electrochemical testing including the electrochemical noise (EN) technique was conducted to identify the role of early sulfate ion presence on corrosion of galvanized steel.EN provides a test method to assess the corrosion modality without the influence of an external excitation that can affect the electrode surface and electrolyte chemistry (such as metal oxidation and oxygen reduction) [6-7]. The testing aims to identify the corrosion mitigation characteristics of the galvanized steel such as zinc activity and protective barrier surface oxide layers in presence of sulfate ions as well as combined cases with chloride ion contamination below reported threshold concentrations for galvanized steel. In the testing here, steel specimen were exposed to alkaline solutions simulating pore solutions with pH 12.6 with varying sodium sulfate levels and sodium chloride. Supplemental electrochemical experiments included the steady-state condition (open circuit potential, linear polarization test, and electrochemical impedance spectroscopy). References K. Lau, and I. Lasa. "Corrosion of prestress and post-tension reinforced-concrete bridges." Corrosion of steel in concrete structures. Woodhead Publishing, 2016. 37-57. DOI: https://doi.org/10.1016/B978-1-78242-381-2.00003-1.S. Permeh, K. K . Krishna Vigneshwaran, K.Lau., and I.Lasa. “Corrosion of Post-Tensioned Tendons with Deficient Grout. Part 3: Segregated Grout with Elevated Sulfate and Vestigial Chloride Content.” Corrosion 75 (2019) pp.848-864.S. Permeh, K. Lau, M. Duncan, and R. Simmons. “Initiation of localized steel corrosion in alkaline sulfate solution.” Materials and Structures, 54 (2021), pp.1-17.S. Permeh, K. Lau, M. Duncan, and R. Simmons. “Identification of steel corrosion in alkaline sulfate solution by electrochemical noise.” Materials and Corrosion, 72(2021), pp.1456-1467.S. Yeomans. Galvanized steel reinforcement in concrete. Elsevier, 2004.S. Permeh, and K. Lau. "Electrochemical Behavior of Steel in Alkaline Sulfate Solutions with Low Level Chloride Concentrations." ECS Meeting s. No. 10. IOP Publishing, 2021.K. Lau, S. Permeh. “Assessment of durability and zinc activity of zinc-rich primer coatings by electrochemical noise technique.” Progress in Organic Coatings, 167(2022): 106840.

Sulfate resistance of ultrahigh-performance concrete with recycled fine aggregate

The effect of sulfate attack (SA) on the strength of ultrahigh-performance concrete (UHPC) made with different replacements (0%, 50% and 100% by weight) of natural fine aggregate with recycled fine aggregate (RFA) was investigated. The UHPC samples were soaked in 10% sodium sulfate solution for 0–180 days (SA duration). The sulfate ion concentration, flexural strength and compressive strength of the UHPCs were investigated. The microstructure of the UHPCs before and after SA was analysed using a multi-technique approach (analysis of interfacial transition zones (ITZs), X-ray diffraction, scanning electron microscopy–energy-dispersive X-ray spectroscopy and mercury intrusion porosimetry). The results showed that, with an increase in SA duration, the compressive strength of the UHPC made with RFA increased. The generated gypsum and ettringite refined the microstructure by converting harmful pores (>20 nm) into harmless pores (<20 nm) in the UHPC matrix. For the same SA duration, the sulfate ion concentration of UHPC increased with an increase in RFA content due to more ITZs, pores and microcracks introduced by the RFA. Strength development models for UHPC with different RFA contents under SA were developed.

Calcium leaching from cement hydrates exposed to sodium sulfate solutions

Calcium leaching from cement hydrates to pore solution increases the porosity and reduces the bonding strength of cement hydrates, accelerating the degradation of concrete. Calcium leaching can be quantified by solid–liquid equilibrium curves, which have been studied in deionized water or ammonium nitrate. The research of solid–liquid equilibrium curve of calcium under sulfate attack is limited and its mechanism is poorly understood. Reported here provide insights into the dissolution process of calcium from cement hydrates exposed to the sodium sulfate solution. The experimental programme examines the effects of sulfate ion concentration and temperature. An external sulfate attack (ESA) model considering the influence of calcium leaching is established and validated. The results show that, compared to deionized water, sulfate ions impact strongly the leaching process. Qualitatively, the dissolution of calcium in cement hydrates is accelerated by increasing the concentration of sulfate ions and decreasing the environmental temperature. Quantitatively, the presence of sulfate ions modifies the equilibrium curve describing calcium leaching in deionized water. In addition, the prediction results of the ESA model considering the influence of calcium leaching are in good agreement with the experimental results.

The interplay between microbial reservoir souring and barite scale formation in hydrocarbon reservoirs

The injection of seawater into a hydrocarbon reservoir (seawater flooding) as a secondary or tertiary oil recovery method is associated with two possibly significant challenges. First, the formation and deposition of various types of scale may happen due to incompatibility between the injection seawater and formation brine. Especially, the addition of sulfate ions may trigger the formation of various types of sulfate scales (e.g., barium sulfate, strontium sulfate, and calcium sulfate). Second, microbial reservoir souring may happen due to the activation of Sulfate Reducing Bacteria (SRBs), which reduce sulfate ions to hydrogen sulfide. This is mainly a result of a drop in temperature in the reservoir, the addition of sulfate from the seawater to the reservoir, and the presence of Dissolved Organic Carbon (DOC) coming from reservoir hydrocarbon. Since both these processes include the consumption of sulfate ions, a competition is expected to happen between them. Especially, there is a concern about whether an efficient mitigation strategy for souring (e.g., nitrate treatment) will result in less consumption of sulfate ions and in turn more formation of sulfate scales. This study tests this theory and investigates the effect of souring intensity and mitigation on the severity of barite scale formation inside the reservoir. In this study, a non-isothermal multi-component bio-chemical model to simultaneously simulate both the processes is developed. Several simulation cases in one and two dimensions are investigated in different conditions in order to study the effect of three influential parameters, namely sulfate ion concentration in the injection sweater, the DOC content of the reservoir hydrocarbon, and injection flow rate on barite scale formation, microbial reservoir souring, nitrate treatment, and the interplay among them. The results show that the effect of barite scale formation on reservoir souring is small (a maximum of 4 percent reduction in the total generated hydrogen sulfide) whereas reservoir souring and nitrate treatment significantly influence barite formation. Depending on the case, the presence of souring can cause a complete removal of barite scale especially around the production well (positive effect) or a maximum of 8 times increase in barite scale amount around the production well (negative effect). Moreover, in all cases, with a more efficient nitrate treatment, although less hydrogen sulfide is generated inside the reservoir (up to a full removal of souring), the generation zone moves closer to the production well. Therefore, an insufficient nitrate treatment may cause an earlier hydrogen sulfide production from the production well (up to twice as early). Several other trends observed in the set of results are also presented in this paper.

Greenhouse Gas Emissions from Salt-Affected Soils: Mechanistic Understanding of Interplay Factors and Reclamation Approaches

Salt-affected soils contain high levels of soluble salts (saline soil) and exchangeable sodium (alkali soil). Globally, about 932 million ha (Mha), including 831 Mha of agricultural land, is salt-affected. Salinity and sodicity adversely affect soil microbial diversity and enzymatic activities, and thereby carbon and nitrogen dynamics and greenhouse gas (GHG) emissions from soils. In this review article, we synthesize published information to understand the impact of salinity and sodicity on GHG production and emissions from salt-affected soils, and how various reclamation amendments (gypsum, phosphogypsum, organic manure, biochar, etc.) affect GHG emissions from reclaimed soils. Nitrous oxide (N2O) and methane (CH4) emissions are of greater concern due to their 298 and 28 times higher global warming potential, respectively, compared to carbon dioxide (CO2), on a 100-year time scale. Therefore, CO2 emissions are given negligible/smaller significance compared to the other two. Generally, nitrous oxide (N2O) emissions are higher at lower salinity and reduced at higher salinity mainly due to: (a) higher ammonification and lower nitrification resulting in a reduced substrate for denitrification; (b) reduced diversity of denitrifying bacteria lowered down microbial-mediated denitrification process; and (c) dissimilatory nitrate reduction to ammonium (DNRA), and denitrification processes compete with each other for common substrate/nitrate. Overall, methane (CH4) emissions from normal soils are higher than those of salt-affected soils. High salinity suppresses the activity of both methanogens (CH4 production) and methanotrophs (CH4 consumption). However, it imposes more inhibitory effects on methanogens than methanotrophs, resulting in lower CH4 production and subsequent emissions from these soils. Therefore, reclamation of these soils may enhance N2O and CH4 emissions. However, gypsum is the best reclamation agent, which significantly mitigates CH4 emissions from paddy cultivation in both sodic and non-sodic soils, and mitigation is higher at the higher rate of its application. Gypsum amendment increases sulfate ion concentrations and reduces CH4 emissions mainly due to the inhibition of the methanogenesis by the sulfate reductase bacteria and the enhancement of soil redox potential. Biochar is also good among the organic amendments mitigating both CH4 and N2O emission from salt-affected soils. The application of fresh organic matter and FYM enhance GHG emissions for these soils. This review suggests the need for systematic investigations for studying the impacts of various amendments and reclamation technologies on GHG emissions in order to develop low carbon emission technologies for salt-affected soil reclamation that can enhance the carbon sequestration potential of these soils.

Systemical investigation on the determination of sulfate in cement-based materials based on a promoted conductometric titrator

The concentration of sulfate ion in cement-based materials is the basic data for the design and evaluation of concrete structures exposed to sulfate lakes and saline soil areas. In this study, a conductivity titrator was developed and used to test the sulfate concentration in concrete corroded by sulfate attack based on the Internet of Things. The theories of conductivity measurement and conductivity titration were described; The main hardware composition and software design of conductometric titrator were introduced; Then, the effects of temperature, concentration, hydroxyl ion and hydrogen ion on the conductivity of solution of sodium sulfate and barium chloride were explored by the titrator; The titration parameters, the influence of hydroxyl and hydrogen ion on sodium sulfate titration were determined by test of sulfate ion titrated by barium chloride with known concentration; Finally, the titrator was used to test the sulfate concentration in cement-based materials after sulfate attack. The results show that the titrator can measure the conductivity of solution with 0.4% accuracy and the concentration of sulfate ion with 0.8% accuracy; During the titration of sulfate ion, the concentration of barium chloride should be twice that of sulfate ion, the titration rate should be less than 0.828 mL/s, and the titration volume should be at least 10 mL; It is found that the influence of hydroxyl ion can be effectively eliminated by adding nitric acid or hydrochloric acid, and the influence of hydrogen ion can be effectively eliminated by adding sodium carbonate. This conductivity meter can accurately test the sulfate concentration in the concrete after corrosion.

Anaerobic oxidation of methane and trace-element geochemistry in microbial mat-covered sediments related to methane seepage, northeastern Japan Sea

We evaluated the spatial variability of geochemical features, including trace-element cycles, associated with methane seepage in a knoll off Sakata (called Sakata Knoll) in the eastern Japan Sea. Seafloor observations from a remotely operated vehicle and environmental visualization around Sakata Knoll by an optical mapping device revealed large patches of white and gray microbial mats covering sediment in the depression on the top of the knoll. Push core samples were collected inside and a few meters outside microbial mats, and outside the gas hydrate-bearing areas. For these cores, the interstitial sulfate ion (SO42−) concentrations, sedimentary total organic carbon, total sulfur (TS), and trace-element contents, and bulk carbonate minerals δ13C were analyzed. In the entire core samples below the microbial mats and in sediments below 10 cm depth outside microbial mats, TS contents were substantially higher than those at the reference site, and bulk carbonate minerals δ13C was strongly negative (−20‰ to −40‰). These results imply that the formations of sulfide minerals and authigenic carbonates occur in the anoxic sediments via microbial anaerobic oxidation of methane (AOM) coupled with sulfate reduction. Although a rapid and linear decrease of interstitial water SO42− concentration in the sediments collected inside microbial mats supports the occurrence of AOM, there is no fall in SO42− concentration outside microbial mats, which may be explained by the higher upward flow of methane gas inside than outside the mats. The AOM-impacted sediments at Sakata Knoll were characterized by enrichments in Mo and As that were well correlated with TS contents and the authigenic iron fraction, and by strong enrichment of authigenic Mo relative to U, indicated by higher Mo/U ratios than those of seawater. These observations suggest that Mo and As are effectively transferred from the water column to AOM-impacted sulfidic sediments at Sakata Knoll via precipitation of particulate iron–manganese oxyhydroxides in the water column that have adsorbed Mo and As.

Microstructural investigation of lithium slag geopolymer pastes containing silica fume and fly ash as additive chemical modifiers

Lithium slag is an industrial by-product obtained after lithium extraction from spodumene ore. The higher concentration of sulfate ions (SO4−2) in the form of gypsum/anhydrite makes it a chemically unviable binder. This research investigates the dilution of the sulphatic component in pore solution by additive incorporation of silica fume and fly ash as chemical modifiers in the lithium slag geopolymer. The setting behavior, detailed microstructural properties, mineral phase quantitative analysis, and compressive strength of lithium slag geopolymer containing fly ash and silica fume were studied. The increasing silica to alumina ratios (Si/Al) by incorporating silica fume in sodium tetraborate added geopolymer resulted in the set retardation after the setting accelerated at Si/Al ratio of 3.5. Similarly, the set retardation was observed for all fly ash replaced lithium slag geopolymers marked by the lower dissolution of SO4−2 ions in pore solution. The fragmented and porous N-(C)-A-S-H gel in lithium slag geopolymer densified by additive incorporation of silica fume and fly ash due to suppressed formation of SO4−2 in pore solution, thus increasing the compressive strength. The main binding zeolite phases quantified in mineral and crystal phase analysis of fly ash replaced geopolymer were mordenite, anorthite, analcime, and calcium chabazite, whereas for silica fume incorporated geopolymer were mordenite, anorthite, analcime, and sodium clinoptilolite. Thus, the lithium slag can be a promising geopolymer precursor along with other supplementary cementitious materials. However, further research is suggested for its chemical viability as a sole geopolymer binder.

Corrosion of Stainless Steels S31603, S31655, and S32101 in Sulfuric Acid Solutions: Effects of Concentration, Chlorides, and Temperature

This study investigates the corrosion behavior of three stainless steel grades at two H2SO4 concentrations, namely 1 wt% and 10 wt%, with varying NaCl concentrations in the range from 500 mg/L to 10,000 mg/L. Dissociation of sulfuric acid yields the hydrogen (H+) and sulfate () ions, the former of which lowers the pH value of a solution while the latter increases the concentration of sulfate ions that act as a corrosion inhibitor. The equilibrium chemistry of the solutions was defined at the test temperatures of 22°C, 50°C, 90°C, and 130°C, and correlated with the observations on the electrochemical and microstructural examination of the materials. The results showed clear differences in the main corrosion form between the two H2SO4 concentrations. In 1 wt% H2SO4, pitting was the major form of corrosion attack in the presence of chlorides, whereas uniform corrosion dominated in 10 wt% H2SO4. The pitting corrosion tendency for the three stainless steel grades under various test conditions was consistent, but there were differences in their resistance to uniform corrosion. The chloride-to-sulfate activity ratio, , was found to be the key parameter in defining the occurrence of pitting corrosion for all three alloys. In H2SO4-NaCl systems, no pitting occurred at the activity ratio below 10, with higher values inducing pitting attack, particularly in 1 wt% H2SO4. The described novel results are presented and discussed in this paper.

Separation of rare earth elements from a South American ionic clay lixivium by sequential precipitation

Ionic clays, formed by natural weathering of rare earth element (REE)-containing minerals and surface adsorption of liberated ions, are a critical REE resource. Here, the sequential precipitation of impurities and REEs from the desorption of a South American ionic clay is investigated. Selective sequential precipitation profiles are constructed by stepwise addition of 1.3 M ammonium bicarbonate to the lixivium. During sequential precipitation, ammonium bicarbonate first behaves as a pH adjustor to remove co-extracted impurities as hydroxides, and then behaves as both a carbonate ion source and a pH adjustor to precipitate the REEs as carbonates. Impurity precipitation is completed at pH 6.0 and REE precipitation is completed at pH 6–7.5; however, total carbonate concentration during the impurity precipitation step must be kept low to prevent REE loss. To gain a better understanding of the REE precipitation step, thermodynamic calculations using the Davis model are performed. Dysprosium is studied as a model REE and its speciation diagram as a function of pH and total carbonate and sulfate ion concentrations is constructed. It is found that the primary factors controlling REE precipitation are pH, carbonate, and sulfate concentrations. The knowledge gained in this work provides a deeper understanding of the sequential impurity and REE precipitation processes from the desorption lixivium of a unique ionic clay from South America. The results would help guide future work on REE separation from this distinct ionic clay.