CaSO4 Research Articles

Process Optimization and Mechanism Study for Sulfur Recovery from High-Silica Phosphogypsum via Carbothermal Reduction Smelting.

Phosphogypsum produced from wet-processed phosphoric acid mainly consists of calcium sulfate dihydrate, which is an important sulfur resource. The traditional sulfuric acid and cement process based on phosphogypsum suffers from unstable cement quality owing to impurities such as phosphorus and fluorine and kiln ringing caused by the low-melting phase. This study investigated sulfur recovery and value-added utilization of liquid slag from high-silica phosphogypsum via carbothermal reduction smelting. A phosphogypsum ingredient (PGI) system was constructed by adding appropriate amounts of silica, alumina, magnesium oxides, and iron oxides to meet the production requirements of slag wool. Carbothermal reduction smelting experiments suggested that the temperature and C/S molar ratio significantly affected the desulfurization rate and phase structure of the slag. More than 97.44 wt % of sulfur could be recovered with a C/S molar ratio of 0.5-0.8 at 1300 °C or above in the molten state, and the molten slag was an amorphous magnesium-calcium-aluminosilicate. The PGI desulfurization mechanism is discussed based on the phase transformation and slag microstructure evolution.

Enhancing Concrete Mechanical Properties through Basalt Fibers and Calcium Sulfate Whiskers: Optimizing Compressive Strength, Elasticity, and Pore Structure.

To study the effects of basalt fibers (BFs), calcium sulfate whiskers (CSWs), and modified calcium sulfate whiskers (MCSWs) on the compressive strength and dynamic modulus of elasticity of concrete, this paper utilizes Mercury Intrusion Porosimetry (MIP) to measure the microstructure of concrete and calculate the fractal dimension of pore surface area. The results indicate that both CSWs and BFs can increase the compressive strength of concrete. CSWs can enhance the dynamic modulus of elasticity of concrete, while the effect of BFs on the dynamic modulus of elasticity is not significant. The improvement in compressive strength and dynamic modulus of elasticity provided by MCSWs is significantly greater than that provided by CSWs. Both CSWs and BFs can effectively improve the pore structure of concrete and have a significant impact on the surface fractal dimension. CSWs inhibit the formation of ink-bottle pores, while BFs increase the number of ink-bottle pores. Due to the ink-bottle pore effect, the fractal dimension of the capillary pore surface is generally greater than three, lacking fractal characteristics. The compressive strength and dynamic modulus of elasticity of concrete have a good correlation with the fractal dimensions of large pores and transition pores.

Alleviating effect of calcium sulfate on aluminum stress through enhanced malate release with increased gene expression of malate transporter and sulfate transporter

ABSTRACT Gypsum (calcium sulfate) are commonly used to improve subsoil acidity. Aluminum (Al) toxicity in acid soil reduces crop yields worldwide, especially in the tropical regions. In soil, sulfate decrease Al toxicity and improves plant growth and yield. Here, we aimed to investigate the effects of CaSO4 on Al stress of Al-tolerant accession Col-0 as well as the Al-sensitive accessions, Wei-0 and Ts-5, of in Arabidopsis thaliana using hydroponics. Our research indicates that CaSO4 supply has a significant effect on root growth and malate release compared to CaCl2 under Al stress, especially in Al-sensitive accessions. In response to Al stress, CaSO4 supply enhanced the expression of malate transporter gene AtALMT1 and sulfate transporter gene SULTR3;5, which were regulated by the Al-resistant transcription factor STOP1. Furthermore, knockout lines of SULTR3;5 and SULTR2;1, which are involved in sulfate uptake and translocation, were more Al-sensitive than the wild type under Al stress without CaSO4, and malate release was reduced with decreased AtALMT1 expression. In conclusion, one of the alleviative effects of gypsum application on Al rhizotoxicity is promoted by sulfate through organic acid release mechanism enhancing AtALMT1 expression, alongside the Ca2+ reduction Al3+ activity on the plasma membrane.

Integration of seeding-induced crystallization with microbubble aeration for membrane fouling and wetting control in vacuum membrane distillation

In this work, a bench-scale vacuum membrane distillation crystallization (VMDC) system coupled with microbubble aeration (MBA) was developed for treating high-salinity feed brine. Herein, the effect of seeding dose on membrane fouling and wetting control in the VMDC system was studied by using synthetic saturated calcium sulfate solution. The results showed that introducing gypsum seeds at a dose of 0.5 g/L effectively restricted membrane fouling and wetting. Subsequently, seeding-induced crystallization coupled with MBA was employed to investigate the control effect on membrane fouling and wetting during VMDC with simulated high-salinity feed brine treatment. As 0.5 g/L gypsum seeds were directly added at 7 h in the VMDC experiment while employing MBA, membrane fouling and wetting were effectively controlled. Finally, the mechanism behind the control of membrane fouling and wetting was elucidated during VMDC operation by integrating seeding-induced crystallization with MBA. This could be ascribed to the synergic effect of gypsum seeds and microbubbles in bulk solution. In brief, this work offers a promising approach to control membrane fouling and wetting during concentrating high-salinity wastewater by VMD.

Precipitation behavior of calcium sulfate in leach solution of ion-adsorption rare earth ore after reverse osmosis

Ion-adsorption rare earth ore (IAREO) is a crucial source of mid-heavy rare earths elements (M-HRE). Reverse osmosis technology is a promising technique for the pre-concentration of the leach solution from in-situ leaching of IAREO. However, calcium sulfate scaling is inevitably formed in sulfate system, causing decreases in the flux and life time of membrane. Herein, to simulate the precipitation behavior of calcium sulfate in the leach solution of IAREO during reverse osmosis, a series of experiments was conducted in binary and quaternary supersaturated calcium sulfate solution systems. Experimental data show that the concentration of Ca2+ decreases with the increase of the concentration of Mg2+, and increases with the increase of the concentration of RE3+ in both binary and quaternary systems. Whereas, the influence of Al3+ on the concentration of Ca2+ is different. This variation of the Ca2+ concentration is explained by thermodynamic analysis. The difference of association concentration for Mg2+, Al3+ and RE3+ with SO42− in binary or quaternary system is the main reason. Finally, the influence and mechanisms of antiscalant on the precipitation behavior of calcium sulfate are discussed. X-ray diffraction (XRD), Zeta potential and scanning electron microscopy (SEM) analyses reveal that polyacrylic acid (PAA) effectively inhibits the crystal growth of calcium sulfate, and the precipitation time of calcium sulfate is prolonged, indicating that PPA is a potential inhibitor for calcium sulfate scaling during the process of reverse osmosis.

Effect of phosphoric acid on leaching of monazite during low-temperature sulfuric acid cyclic leaching process

To completely recover valuable elements and reduce the amount of waste, the impact of phosphoric acid on the decomposition of rare earth, fluorine and phosphorus during cyclic leaching was studied based on the characteristics of low-temperature sulfuric acid decomposition. When a single monazite was leached using 75 wt% H2SO4 solution with phosphoric acid, the size and number of monazite particles in the washing slag gradually decrease with the increase in phosphoric acid content in the leaching solution. The monazite phase can hardly be found in the slag when the phosphoric acid content reaches 70 g/L, which indicates that phosphoric acid is favorable for monazite decomposition. The mixed rare earth concentrate was leached by 75 wt% H2SO4 containing 70 g/L phosphoric acid, the mineral compositions of the washing slag are only gypsum and unwashed rare earth sulfuric acid. After cyclic leaching of 75 wt% H2SO4, the mineral compositions of the primary leaching washing slag are mainly undecomposed monazite, rare earth sulfate and calcium sulfate. However, monazite is not found in the mineral phase of the second and third leaching washing slag. The leaching rates of rare earth and phosphorus gradually increase with the increase in cyclic leaching times. In addition, the phosphoric acid content in the leaching solution increases with the increase in the number of cyclic leaching time. However, the rising trend decreases when the phosphoric acid content reaches 50 g/L by adsorption and crystallization of phosphoric acid. A small amount of water can be used to clean the leaching residue before washing to recover the more soluble phosphorus acid according to the difference of dissolution between phosphoric acid and rare earth sulfuric acid.

Use of spent fluid catalytic cracking catalyst (FCC) in Limestone Calcined Clay Cement (LC3) systems: Studies in pastes and mortars

This study evaluates the substitution of calcined clay for a waste from the petrochemical industry, spent fluid catalytic cracking catalyst (FCC), as a source of reactive aluminosilicates in Limestone Calcined Clay Cements (LC3) systems. Three carbonate types were used to make cement-type LC3: a high-purity calcium carbonate, waste from the marble industry, and another from a dolomite soil source. LC3 blends were prepared by mixing 50 wt% OPC, 5 wt% calcium sulfate dihydrate, 30 wt% FCC and 15 wt% from each carbonate source. A mixture than substituting the carbonate source for a siliceous source was prepared to analyse the influence of carbonate phases in LC3 systems. The hydration process of the LC3 blends was studied by X-ray diffraction, thermogravimetric analyses, isothermal calorimetry and FESEM. Mechanical properties were studied by measuring compressive strength at 7, 28 and 90 days. The obtained results corroborated that the mortars prepared with LC3 cements using the FCC obtained higher compressive strength than the control mortar prepared with ordinary Portland cement (OPC) at 28 and 90 curing days. It has been demonstrated that FCC is a by-product that can substitute calcined clay, and the different sources of carbonates such as high purity, waste or contaminated with magnesium do not interfere with the performance of this type of cement.

65 Testing the effects of rigid encapsulations on bovine primordial follicle quiescence versus growth

OBJECTIVES/GOALS: There is an interest in developing a bioprosthetic ovary for ovarian tissue transplantation. The properties of the ovarian extracellular matrix need to be better understood in order to replicate the human ovary. We tested the effects of an encapsulating hydrogel at different rigidities on bovine primordial follicle activation, growth, and survival. METHODS/STUDY POPULATION: Bovine primordial follicles were isolated from ovarian cortex. A mean of 9.9 follicles (range 3-24) were encapsulated per bead in either 1% or 5 % alginate across 4 experiments. The encapsulated follicles were subsequently crosslinked in a calcium sulfate solution. Follicles were then cultured for 8 days with light microscopy imaging taken every other day along with media exchanges. Follicles were then examined using immunofluorescence. Growth and survival curves were constructed and all statistical analyses were performed using Graph Pad Prism 9. RESULTS/ANTICIPATED RESULTS: A total of 372 follicles were encapsulated across 32 beads (16 in 1% alginate and 16 in 5% alginate). There were no differences in initial follicle size between the two conditions (33.53 µm vs. 32.45 µm, p=0.47). At the end of 8 days, there was no difference between follicle size (59.55 vs. 56.06, p=0.48). Additionally, there was no difference in survival between 1% and 5% alginate encapsulation (57.75% vs. 52.43%. p=0.40). Immunofluorescence is being performed on encapsulated follicles to confirm the presence of DDX4, a molecular marker of oocytes, after 8 days in culture. Additional encapsulated follicles have also been submitted for histologic sectioning and hematoxylin and eosin staining to better characterize the viability and health of these follicles after 8 days in culture. DISCUSSION/SIGNIFICANCE: There was no significant difference in growth or survival between primordial follicles cultured in 1% or 5% alginate gels. Immunofluorescent analysis confirmed the presence of viable follicles at the end of 8 days of culture. Future work needs to further explore how factors in the ovarian extracellular matrix impact follicle maintenance and growth.

CLINICAL AND RADIOGRAPHIC ASSESSMENT OF BOND APATITE IN HORIZONTAL BONE AUGMENTATION AROUND DENTAL IMPLANTS: A RANDOMIZED CONTROLLED TRIAL

Background:Bond apatite is a composite graft, composed of two-thirds biphasic calcium sulfate and one-third hydroxyapatite granules of various sizes and shapes. Oral implants are used to secure dental prostheses in cases of partial or total edentulism. The outcomes of correctly completed dental-implant procedures result in high rates of success and survival of dental prostheses. Objective:The aim of this study was to assess Bond Apatite use in horizontal bone augmentation around dental implants, clinically and radiographically. Materials and Methods:This research included sixteen patients, six men and ten women, with an average age of thirty years having missing maxillary anterior or premolar teeth with insufficient horizontal bone. The patients were divided into two groups: group I patients (N=8) received dental implants with Bond apatite, while group II patients (N=8) received dental implants with Bio-Oss bone graft material and pericardium bioresorbable membranes. All patients were evaluated clinically usingthe modified plaque index (MPI), modified gingival index (MGI) and probing depth (PD) and radiographically to assess bone width dimensions. Results: There was a statistically significant difference between groups regarding MGI(p = 0.038)andperi-implant buccal PD [mm](p = 0.026). There was no statistically significant difference between the tested groups regarding age(p = 0.608), sex(p = 0.123), MPI(p = 0.608),orperi-implant palatalPD [mm](p = 0.118). There was no statistically significant difference between the two groups regarding postoperative bone width (p = 0.187). Conclusion:Bond apatitemay be used as one of the materials of choice for horizontal bone augmentation around dental implants with similar promising results compared to Bio-Oss. Finally, the use of Bond apatite preparation is a straightforward, affordable, and considered successful bone graft material that could be used in osseous defect reconstruction procedure. Trial registration:The study is listed on www.clinicaltrials.gov with registration number (NCT06043258) 22/09/2023. The study was conducted in accordance with the seventh revision of the Helsinki Declaration in 2013 and approved by the Institutional Review Board (IRB) (M07061119) of the Faculty of Dentistry, Mansoura University, Egypt.

Effects of Tb3+ on properties of luminescent calcium sulfate cement

Calcium sulfate powder materials containing terbium ions at 0, 1.0, or 2.0 mol.% were obtained. They are characterized by the presence of a CaSO4 × 0.5H2O phase, while Tb3+ is incorporated into the lattice at ≤1.0 mol.%. Specific surface area enlarged from 2.1 to 22.5 m2/g as crystallite size decreased from 68 to 31 nm. Thermal analysis showed that terbium slightly raises the temperature of CaSO4 × 2H2O-to-CaSO4 transition. Studies of solubility in SBF solution showed the presence of a calcium phosphate layer in terbium-containing cements on the 7th day. Luminescent properties were studied by excitation at 266 nm and 489 nm corresponding to absorption bands of the host and Tb3+ (7F6 - 5D4 absorption band). The recorded emission peaks of the materials showed that the luminescence of the samples was green, with the luminescence intensity increasing when Tb3+ was introduced. The developed materials can find applications in medicine as bioimplants with a possibility of noninvasive visualization of the bone restoration process.

Перспективы исследований фосфогипса как материала для строительства

Objective: analytical investigation of the potential use of hemihydrate (CaSO4 · 0.5H2O) and dihydrate (CaSO4 · 2H2O) calcium sulfate — phosphogypsum — a waste in the production of mineral fertilizers, as a construction material for the construction of roads, soil structures, material for the restoration of roads in the areas of repair of utility networks, as well as unloading of developed landfills for the storage of waste from processing phosphorus ores of chemical enterprises operating in the Russian Federation. Methods: analysis of the current situation at landfills of industrial enterprises, analysis of the knowledge of the issue of utilization and processing of phosphogypsum, as well as analytical (calculation) assessment of the possibility of replacing bulk materials (sand, crushed stone) with phosphogypsum common in construction. Results: this article discusses issues related to the assessment of the possibility of using phosphogypsum with a decrease in its local concentration in the zones of its application, as well as with the use of waste stored at landfills for many years. The considered options for prospective use of the material, which make it possible not only to preserve, but also to increase the operational characteristics of roads and other soil structures, while eliminating the potentially harmful effect of the material during operation associated with its dusting during storage. Practical significance: analysis of the current situation indicates that due to the active production in the Russian Federation, a huge amount of waste from such production — phosphogypsum — accumulates on the territory of industrial enterprises engaged in the processing of phosphorus ores and landfills assigned to these enterprises. The annual utilization of phosphogypsum at such enterprises is estimated at hundreds of thousands and millions of tons — huge dumps are formed, which pose a danger both from the point of view of groundwater pollution and from the point of view of man-made safety. With such large volumes of concentrated storage, the volumes of substances entering the soil and groundwater may repeatedly exceed the permissible values, but at the same time, with a lower concentration, the ingress of these substances into the soil may not only not harm the environment, but also have a positive effect in terms of increasing yield. The use of waste from such production facilities in road construction will solve the problems associated with the disposal of phosphogypsum.

Effect of crystal-water on the optical and dielectric characteristics of calcium sulfate in the THz band

The effect of crystal-water contents on the optical properties and dielectric characteristics of calcium sulfate in the THz band is investigated. The complex dielectric constant and conductivity are analyzed using the Drude-Smith model. The refractive index and absorption coefficient are linearly increased with the content of crystal-water, and the corresponding linear fitting lines of R2 over 0.97 are obtained. The dielectric properties of calcium sulfate are significantly affected by the crystal-water content. These results indicate that a new method to quantitative measurement of the crystal-water content in hydrous minerals is provided.

Effects of Matrix Structure on Protein Digestibility and Antioxidant Property of Different Soybean Curds During In Vitro Digestion.

This study compared the three most common types of tofu (soybean curd), which were prepared by using magnesium chloride (MgCl2 tofu), calcium sulfate (CaSO4 tofu), and glucono-δ-lactone (GDL tofu) coagulants. The results showed that GDL tofu had a higher water holding capacity than MgCl2 tofu and CaSO4 tofu, which was attributed to its high surface hydrophobicity and disulfide bond content. GDL tofu possessed the lowest firmness, gumminess, and chewiness, along with a uniform network structure and a thin protein matrix. In contrast, MgCl2 tofu exhibited an inhomogeneous network structure with a thick protein matrix. Combining the results of protein hydrolysis degree, SDS-PAGE, and free amino acids during in vitro digestion, it was indicated that the degree of protein digestion in GDL tofu was the highest. After intestinal digestion, GDL tofu had the highest total phenolic content, ferric reducing antioxidant power, and DPPH value. These results demonstrated the superior protein digestibility and antioxidant property of GDL tofu during in vitro digestion due to its structural characteristics that facilitate enzyme diffusion in the matrix. The findings offer insight into the protein digestibility and antioxidant properties of different types of tofu during digestion from structural characteristic perspective and valuable reference information for consumer dietary nutrition.

High-strength gypsum binder with improved water-resistance coefficient derived from industrial wastes.

The article presents the possibility of increasing the water resistance of gypsum binders (GBs) obtained based on synthetic gypsum by introducing additives derived from industrial wastes. Regularities were obtained for the influence of the type and amount of additives on the water/gypsum ratio (W/G), strength indicators and water resistance of high-strength GB. The introduction of a single-component additive to improve water resistance does not have a significant effect. Complex additives based on Portland cement, granulated blast-furnace slag, electric steel-smelting slag, expanded clay dust and granite screenings of various fractions have been developed that make the maximum contribution to improving the water resistance of a high-strength GB based on synthetic calcium sulphate dihydrate, which made it possible to increase the water-resistance coefficient from 0.39 to 0.82.

Evaluation of compatibility between formation and Injection water into the Reservoir Rock

Scale deposition represents a critical challenge encountered in water injection systems. The objective of this study is to assess the compatibility between the candidate smart water and the formation water in an oil reservoir rock sample. To achieve this, water samples were collected and analyzed to evaluate the extent of deposit formation under varying temperature and pressure conditions. Additionally, the study also examined the combined influence of temperature and pressure on deposit formation. The results indicated that as the temperature increased, there was a decrease in the concentration of sulfate in the seawater. Taking into account the low concentration of barium (zero) in seawater and the unchanged strontium concentration, the decrease in sulfate concentration can be attributed to the deposition of calcium sulfate. Contrarily, in various ratios of smart water, the sulfate concentration has shown an increase with rising temperatures. This can be attributed to the transformation of sulfite present in the formation water into sulfate due to the influence of temperature. The presence of a low concentration of barium in the formation water resulted in insignificant changes in sulfate concentration due to the precipitation of barium sulfate. Additionally, despite the high concentration of strontium, strontium sulfate deposition did not occur, possibly due to the solubility product constant. The analysis of different smart water ratios under various pressures at ambient temperature revealed that pressure had a minimal effect on the solubility of sulfate and calcium salts. During the sediment analysis, no evidence of strontium sulfate sediment formation was observed. However, the analysis indicated a high possibility of iron sulfide and iron oxide deposits forming. Ultimately, under the experimental conditions, significant sediment formation was not observed.

Influence of Al/Fe ratio on the hydration of brownmillerite in the presence of calcium sulfate

The brownmillerite, as an indispensable mineral phase in Portland cement, is actually a series of solid solution of Ca2(AlyFe(2–y))O5 (0 ≥ y ≤ 1.33). The varying values of y would significantly influence the hydration characteristic of brownmillerite. The hydration performance of brownmillerite where y = 0.9, 1.1 and 1.3 in Ca2(AlyFe(2–y))O5 in the presence of calcium sulfate, is deeply researched in this work. The brownmillerite Ca2(Al1.1Fe0.9)O5 and Ca2(Al1.3Fe0.7)O5 show a doublet of heat flow curve corresponding to formation of different amounts of ettringite while a single exothermic peak appears in Ca2(Al0.9Fe1.1)O5 due to generation of a layer of gel-like phases. Combining with density functional theory (DFT) calculations, it is concluded that the hydration reactivity of brownmillerite increases with reducing Al/Fe ratio. Fe is inclined to occupy octahedral sites as augment of Fe content in brownmillerite. Due to highly hydraulic activity of these sites, the lowest Al/Fe ratio of brownmillerite corresponds to highest hydration rate in first few hours. However, more iron hydroxide radicals aggregate in the surface of unhydrated brownmillerite and form a layer of iron-rich hydration products which would dramatically slow down the following hydration progress. In addition, this postponement to hydration will gradually recede with reduction of Fe content in brownmillerite. This finding provides a novel perspective on the understanding of Al/Fe ratio to the hydration performance of brownmillerite.

Gypsum slurries to apply in oil well: An insight into thickening time

Gypsum is widely used in the construction industry, especially as a hydraulic binder. Studies have indicated the use of α-HH gypsum as an alternative material to Portland Cement in oilwell cementing operations, highlighting the reduction in environmental impacts from the reduction of Portland Cement. Calcium Sulphate α-Hemihydrate (CaSO4 . ½ H2O) has been shown to be a promising material to replace Portland Cement in some applications. The hydration of gypsum pastes goes through the process of saturation of the medium with Ca+2 and SO4-2 ions, then the physical phenomenon of crystallization, and finally the phenomenon of hardening, where the crystals formed precipitate producing Dihydrate (CaSO4 . 2H2O). Gypsum pastes harden very quickly, and their pumpability is impaired with thickening times of less than 20 minutes. For applications requiring longer pumpability times, the use of retarding additives is necessary. This research studied the effects of retarding additives in α-HH gypsum paste systems by varying the water-gypsum factor (FAG 0.4; 0.5 and 0.6) using a pressurized consistometer, under conditions of 54 °C and 9500 psi, with the aim of obtaining formulations with admissible thickening times for oil well cementing applications. The results showed that it was possible to develop paste systems with varying thickening times, with intervals of more than 120 minutes. The 0.5 FAG system proved to be more stable at the same retarder concentrations when compared to the 0.4 and 0.6 FAG systems.

Hydrogeochemical characterization of groundwater in mountainous catchment and its suitability for drinking purposes in Irob, Tigray, Northern Ethiopia

Abstract The primary source of drinking water in Ethiopia's semi-arid mountainous regions is groundwater. The present study aims to assess the hydrogeochemical characteristics of low-grade basement rocks dominated by mountainous catchments. Moreover, it examines the suitability of the groundwater quality for drinking purposes in Irob, Tigray, northern Ethiopia. However, relatively little is known about the water chemistry and groundwater quality of the resources in the area. Fifteen samples of groundwater were collected and examined for ions according to standard procedures. The outcomes were assessed against the World Health Organization (WHO) drinking water quality criteria. To identify the source of dissolved ions and the process involved, graphic interpretations were applied. The results show that Ca–Mg–SO4–HCO3 and Ca–SO4–HCO3 were the dominant water types. Gibbs plots and ionic ratios reveal that silicate weathering, carbonate dissolution and ion exchange control water chemistry. Furthermore, the findings reveal that 60, 80, 46.67, 46.67, 60, 6.67, 60 and 53.33% of samples are above the safe limits of the WHO for hardness, alkalinity, total dissolved solids, electrical conductivity, calcium (Ca2+), potassium (K+), bicarbonate (HCO3-) and sulfate (SO42-), respectively. Consequently, the groundwater quality assessment demonstrates that the water sources in lower parts of the catchment are unsuitable for drinking.

Alternative hydraulic concretes based on calcium sulfate-granulated blast furnace slag composites

Two series of hydraulic concretes were prepared with alternative and sustainable composite binders of mineral calcium sulfate hemihydrate or waste anhydrite fluorgypsum, both supplemented with granulated blast-furnace slag, and fly ash or silica fume. The mixtures with 300 and 400 kg m−3 of binder cured for up to 360 days showed strengths of up to 30 MPa and hydraulic character. The microstructural configuration, characterized by SEM, EDS and XRD, indicated that the precipitated framework of gypsum crystals was stable under water after being engulfed by C–S–H like products formed by the reactions of the slag, pozzolanas and Portland cement. Ettringite was identified and assumed in moderate amounts in some samples, indicating the sulphatic activation for the slag and fly ash. The environmental impact assessed by a simple LCA indicated that the studied concretes release GHG in average 64.6 or 81.3 kgCO2eq·m−3 depending on the binder content, which is up to 5.3 times lower relative to conventional Portland cement mixtures. Depending on the distances travelled, freight was an important factor of GHG, while grinding and sieving were very low.

Sulfur enhances iron plaque formation and stress resistance to reduce the transfer of Cd and As in the soil-rice system

Sulfur plays an essential role in agricultural production, but few studies have been reported on how sulfur simultaneously impacts the transformation of cadmium (Cd) and arsenic (As) in the soil-rice system. This research selected two soils co-contaminated with both Cd and As, varying in acidity and alkalinity levels, to study the impacts of elemental sulfur (S) and calcium sulfate (CaSO4) on the migration and accumulation of Cd and As by rice. Results indicated that two types of sulfur had a substantial (P < 0.05) impact on decreasing the contents of Cd (28.3–50.4 %) and As (20.1–38.6 %) in brown rice in acidic and alkaline soils. They also increased rice biomass (29.3–112.8 %) and reduced Cd transport coefficient (27.2–45.6 %) significantly (P < 0.05). Notably, sulfur augmented the generation of iron plaque on rice root surfaces, which increased the fixation of Cd (17.6–61.0 %) and As (14.0–45.9 %). SEM-EDS results also indicated that the rice root surface exhibited significant enrichment of Fe, Cd, and As. The mechanism of simultaneous Cd and As immobilization by sulfur application was mainly ascribed to the contribution of iron plaque. Additionally, sulfur reduced the contents of Cd and As in soil porewater and promoted the transformation of As(III) to As(V) to reduce the toxicity of As. The K-edge XAFS of As in iron plaque also confirmed that sulfur application significantly promoted As(III) oxidation. Sulfur also promoted the activities of antioxidant enzymes and the contents of NPT, GSH, and PCs in rice plants. In general, this study establishes a foundation for sulfur to lower As and Cd bioavailability in paddy soils, enhance iron plaque and rice resistance, and reduce heavy metal accumulation.