Sulfate Phases Research Articles

Effect of steel slag on rheological and mechanical properties of sulfoaluminate cement-based sustainable 3D printing concrete

The low utilisation of steel slag has led to a worsening of environmental problems. This study aims to use tri-potassium citrate (TPC) to activate the cementitious properties of steel slag and further apply sulfoaluminate cement (SAC) as supplement to design low-carbon composites. 3D printing technology can help to reduce materials consumption as well as labour cost; therefore, the advent of SS-SAC-3D printing concrete has the potential to enhance the utilisation of low-carbon composites and reduce process emissions. This study investigates the effects of steel slag and its activation on the properties of 3D-printed concrete. Workability, rheology, setting time and buildability tests were conducted. The strength differences and anisotropy between the printed and molded specimens were compared. The results demonstrate that adding aluminium-rich steel slag altered the ratios between aluminate and sulfate phases, shortened the setting time, and improved the fluidity and rheological properties of the mixture. The addition of 25 %–50 % steel slag can effectively promote the occurrence of composite hydration reactions, improve the strength to reach over 42.5 MPa (standard strength of SAC) at late ages, and significantly reduce carbon emissions. In conclusion, the SS-SAC-3DPC has the potential to become a significant building material owing to its cost-effectiveness and printability, which can meet the requirements of general building structures. More importantly, its application could contribute to a reduction in the carbon footprint of the construction industry.

Pre-ADMET studies of 5-(3',4'-dihydroxyphenyl)-γ-valerolactone, the bioactive intestinal metabolite of proanthocyanidins.

5-(3',4'-Dihydroxyphenyl)-γ-valerolactone (VL) is a bioactive metabolite resulting from the gut microbial metabolism of proanthocyanidins and flavonoids, known for its health-promoting effects, including antidiabetic and anti-inflammatory activities. Although VL has been observed in different in vivo studies, its pre-absorption, distribution, metabolism, excretion, toxicity (ADMET)properties have rarely been investigated. This study aims to address this gap by evaluating the pre-ADMET properties of VL for the first time. Also, the understanding of these properties is significant for correlating the encountered activities to this metabolite. In vitro absorption studies revealed that VL is rapidly metabolized and absorbed as its sulfate phase II conjugate (valerolactone sulfate), which enters systemic circulation and mildly activates the Breast Cancer Resistance Protein efflux transporter. In human S9 liver fraction, a mixture of liver enzymes used to simulate in vivo liver metabolism, VL is metabolized into glucuronic phase II conjugates (valerolactone glucuronide 1 [VLG1] and 2 [VLG2]) with a half-life of 8.72 min and an 80% conversion rate. In human liver microsomes, VL is metabolized at a slower rate (half-life of 23.08 min), suggesting that oxidative metabolism is secondary. Additionally, VL did not activate the pregnane X receptor or inhibit Cytochrome P3A4 (CYP3A4) and Cytochrome P1A2(CYP1A2) enzymes, indicating no risk of herb-drug interactions with coadministered prescription drugs.

Bio-Inspired Fluorescent Calcium Sulfate for the Conservation of Gypsum Plasterwork.

In this work, the potential of bio-inspired strategies for the synthesis of calcium sulfate (CaSO4·nH2O) materials for heritage conservation is explored. For this, a nonclassical multi-step crystallization mechanism to understand the effect of calcein- a fluorescent chelating agent with a high affinity for divalent cations- on the nucleation and growth of calcium sulfate phases is proposed. Moving from the nano- to the macro-scale, this strategy sets the basis for the design and production of fluorescent nano-bassanite (NB-C; CaSO4·0.5H2O), with application as a fully compatible consolidant for the conservation of historic plasterwork. Once applied to gypsum (CaSO4·2H2O) plaster specimens, cementation upon hydration of nano-bassanite results in a significant increase in mechanical strength, while intracrystalline occlusion of calcein in newly-formed gypsum cement improves its weathering resistance. Furthermore, under UV irradiation, the luminescence produced by calcein molecules occluded in gypsum crystals formed upon nano-bassanite hydration allows the easy identification of the newly deposited consolidant within the treated gypsum plaster without altering the substrate's appearance.

Microwave digestion method for sulfide analysis of Çanakkale region coal

ABSTRACT Quantitative analysis of sulfide content in coal is a necessary step for complete analysis. Conventional analysis methods take several days, whereas it takes a few hours in microwave digestion method. In the present study, a new wet chemical analysis technique was developed and applied to quantify the sulfide content in Turkish coal samples. In the initial step, 5 M HCl solution is employed to dissolve the sulfate phases present in the coal. Subsequently, pyrite is separated from the residue obtained in stage 1 through the utilization of 2 M HNO3 solution. The final stage involves the determination of organic sulfur, wherein concentrated HNO3, HCl, HF, and boric acid are utilized to completely decompose the remaining residue from stage 2. The extracted solutions from each stage are promptly analyzed for sulfur content using ICP-OES. The cumulative values of the three sulfur forms consistently correspond with certified total sulfur data for the majority of the examined coals. Among several advantages, the analysis duration is the most distinctive feature. Chemical analysis of sulfide in coal with microwave analysis method completed three times rapid than with conventional analysis.

Sorption retards remediation of clayey sulfuric soils with straw‐derived dissolved organic matter

AbstractWhen sulfidic soils become drained, oxidation of pyrite can cause acidification and formation of iron (Fe) oxyhydroxy sulfate phases such as jarosite. Remediation via re‐establishment of reducing conditions requires submergence and addition of biodegradable organic carbon (OC) to stimulate activity of reducing bacteria. Addition of straw‐derived dissolved organic carbon (DOC) has been shown to induce rapid microbial reduction in sandy sulfuric (pH <4) soils. In clayey sulfuric soil, DOC may be less efficient because of limited availability for microbes due to its sorption to reactive minerals. We tested the possible effect of sorption on the remediative potential of straw‐derived DOC using a set of incubation and sorption experiments, and used solid‐state 13C‐NMR spectroscopy for the chemical characterization of OC. The tested materials were a clayey, jarosite‐containing sulfuric soil (pH 3), and artificial model soils composed of synthesized jarosite either mixed with quartz powder or quartz powder + clay minerals. The results showed that addition of DOC from wheat straw induces reduction conditions varying with soil sorptivity. For the model soils, DOC sorption was little, and DOC additions of 0.8 mg OC g−1 were sufficient to achieve permanently reducing conditions and an increase in pH to >6.0. In the natural sulfuric soil, much higher DOC additions were needed (1.8 mg OC g−1) to facilitate continuous reducing conditions, but pH increased only to values no higher than 5.0–5.5. The natural soil revealed strong sorption of added DOC. Sorption preferentially reduced the proportion of proteins, while the proportion of lignin components, which can hardly be used by microorganisms under reducing conditions, remained relatively high in solution. Thus, high DOC additions were required to overcome the sorption‐induced limitations in OC availability. The results suggest that wheat straw‐derived DOC is a promising approach also for remediation of clayey sulfuric soils; however, OC additions need to be adjusted to compensate for possible sorption.

Effect of alumina source on the retention of rhenium during low-activity waste feed conversion to glass

Volatility of technetium poses a challenge during the vitrification of low-activity waste (LAW) feed to glass. Although this is typically resolved through recycle loops, this can lead to other problems, such as sulfate phase formation. Thus, ensuring high single-pass retention of Tc (or Re, its non-radioactive surrogate) is required for enabling high waste-loading formulations. In our previous study, we observed significantly higher Re retention in final waste glass produced from a LAW melter feed containing gibbsite as the alumina source compared to a compositionally similar feed containing kyanite. To investigate this effect, we prepared representative LAW melter feeds with kyanite and gibbsite as alumina sources and measured the Re retention in the produced glasses. We found that the Re retention is consistently higher in glasses produced with gibbsite, by up to 20 %. We attribute this result to the formation of nanocrystalline alumina in melter feeds containing gibbsite. Possessing a high surface area, nanocrystalline alumina can adsorb the perrhenate-containing molten salt, increasing the rate at which Re is incorporated into the alkali-alumino-boro-silicate glass-forming melt. In addition, we demonstrate that replacing kyanite with gibbsite in LAW melter feeds has no adverse effects on their processing during vitrification.

Enhancing iron biogeochemical cycling for canga ecosystem restoration: insights from microbial stimuli.

The microbial-induced restoration of ferruginous crusts (canga), which partially cover iron deposits and host unique ecosystems, is a promising alternative for reducing the environmental impacts of the iron mining industry. To investigate the potential of microbial action to accelerate the reduction and oxidation of iron in substrates rich in hematite and goethite, four different microbial treatments (water only as a control - W; culture medium only - MO; medium + microbial consortium - MI; medium + microbial consortium + soluble iron - MIC) were periodically applied to induce iron dissolution and subsequent precipitation. Except for W, all the treatments resulted in the formation of biocemented blocks. MO and MI treatments resulted in significant goethite dissolution, followed by precipitation of iron oxyhydroxides and an iron sulfate phase, due to iron oxidation, in addition to the preservation of microfossils. In the MIC treatment, biofilms were identified, but with few mineralogical changes in the iron-rich particles, indicating less iron cycling compared to the MO or MI treatment. Regarding microbial diversity, iron-reducing families, such as Enterobacteriaceae, were found in all microbially treated substrates. However, the presence of Bacillaceae indicates the importance of fermentative bacteria in accelerating the dissolution of iron minerals. The acceleration of iron cycling was also promoted by microorganisms that couple nitrate reduction with Fe(II) oxidation. These findings demonstrate a sustainable and streamlined opportunity for restoration in mining areas.

Black Crust from Historic Buildings as a Natural Indicator of Air Pollution: A Case Study of the Lipowiec Castle, Babice, Southern Poland

The study is focused on the analysis of black crust and soiling on the building materials of the medieval Lipowiec Castle in southern Poland. The castle was constructed using local, partly dolomitic limestones and dolomites, supplemented with other limestones and bricks, during 20th-century renovations of the castle ruins. The crust and soiling components, secondary mineral phases, and particulate matter of anthropogenic origin were analysed using Raman micro-spectroscopy (RS) and scanning electron microscopy coupled with energy-dispersive spectrometry (SEM-EDS). The crust, mostly composed of gypsum and other sulphate phases, was found to contain carbonaceous matter, spherical Si-Al glass particles, and iron oxides, with admixtures of other elements, including heavy metals, as well as irregularly shaped particles containing various metals. These components reflect the air pollution in the region, related to the combustion of solid fuels in both industrial power plants and local domestic furnaces, Zn-Pb ore mining (operational until 2021), and smelting in the neighbouring industrial centre. Despite its location in a rural area, the castle has been exposed to pollution for an extended period due to its proximity to large industrial centres. Therefore, the crust analysed may serve as an environmental indicator of the nature of the air pollution in the region.

FeS-assisted restructuring of zinc-bearing phases into sulfated compounds for efficient zinc extraction from hazardous electric furnace dust

Electric arc furnace dust (EAFD) is a hazardous solid waste generated as a byproduct in the steelmaking process, containing significant amounts of zinc and iron, making it a primary secondary source of zinc. The separation of zinc and iron in an environmentally-friendly and efficient manner poses a crucial technological challenge for the safe disposal and resource utilization of EAFD, facilitating the recovery of valuable zinc and the direct reuse of iron as raw materials for ironmaking. In this study, a novel method for restructuring zinc-bearing phases into sulfated compounds through low-temperature roasting by introducing FeS in EAFD were proposed. Simultaneously, the iron-containing phases undergo a transformation into Fe2O3. Subsequently, efficient separation of zinc and iron is achieved through a leaching process using dilute sulfuric acid. The conditions for the theoretical transformation of zinc-containing phases into ZnSO4 and iron-containing phases into Fe2O3 in EAFD were determined by thermodynamic calculations incorporating FeS. The temperature range for sulfation calcination was determined to be within 550–700 °C based on TG-DSC analysis and the evaluation of SO2 release during the decomposition of FeS. The optimal conditions for the roasting process were determined as an E/F ratio of 1:3, a temperature of 650 °C, and a duration of 3 h. In addition, the optimal conditions for the leaching process were determined as the addition of 1 mL of 1 M H2SO4 and a liquid–solid ratio of 25 mL/g. Under these conditions, the extractions of Zn and Fe reached 95.33 % and 0.17 %, respectively. The mechanism of phase reconstruction from zinc-containing phases to sulfate phases in EAFD was thoroughly analyzed, revealing that the Zn species in EAFD were transformed into Zn3O(SO4)2 through solid–solid and gas–solid reactions, while the majority of Fe species in EAFD and FeS were converted into Fe2O3. Effective separation of zinc and iron was achieved by dissolving Zn3O(SO4)2 in diluted sulfuric acid while retaining Fe2O3 in the residue. This study provides a fresh perspective on the recovery of zinc from zinc-containing solid waste resources, offering significant potential for the sustainable management and utilization of EAFD.

Depositional and Diagenetic Sulfates of Hogwallow Flats and Yori Pass, Jezero Crater: Evaluating Preservation Potential of Environmental Indicators and Possible Biosignatures From Past Martian Surface Waters and Groundwaters

AbstractThe Mars 2020 Perseverance rover has examined and sampled sulfate‐rich clastic rocks from the Hogwallow Flats member at Hawksbill Gap and the Yori Pass member at Cape Nukshak. Both strata are located on the Jezero crater western fan front, are lithologically and stratigraphically similar, and have been assigned to the Shenandoah formation. In situ analyses demonstrate that these are fine‐grained sandstones composed of phyllosilicates, hematite, Ca‐sulfates, Fe‐Mg‐sulfates, ferric sulfates, and possibly chloride salts. Sulfate minerals are found both as depositional grains and diagenetic features, including intergranular cement and vein‐ and vug‐cements. Here, we describe the possibility of various sulfate phases to preserve potential biosignatures and the record of paleoenvironmental conditions in fluid and solid inclusions, based on findings from analog sulfate‐rich rocks on Earth. The samples collected from these outcrops, Hazeltop and Bearwallow from Hogwallow Flats, and Kukaklek from Yori Pass, should be examined for such potential biosignatures and environmental indicators upon return to Earth.

Solution-driven processing of calcium sulfate: The mechanism of the reversible transformation of gypsum to bassanite in brines

Here, we show that calcium sulfate dihydrate (gypsum) can be directly, rapidly and reversibly converted to calcium sulfate hemihydrate (bassanite) in high salinity solutions (brines). The optimum conditions for the efficient production of bassanite in a short time (<5 min) involve the use of brines with c(NaCl) > 4 M and maintaining a temperature, T > 80 °C. When the solution containing bassanite crystals is cooled down to around room temperature, eventually gypsum is formed. When the temperature is raised again to T > 80 °C, bassanite is rapidly re-precipitated. This contrasts with the better-known behaviour of the bassanite phase in low-salt environments. In low-salinity aqueous solutions, bassanite is considered to be metastable with respect to gypsum and anhydrite, and therefore gypsum-to-bassanite conversion does not occur in pure water. Interestingly, the high-salinity transformation of gypsum-to-bassanite has been reported by many authors and used in practice for several decades, although its very occurrence actually contradicts numerical thermodynamic predictions regarding solubility of calcium sulfate phases. By following the evolution of crystalline phases with in situ and time-resolved X-ray diffraction/scattering and Raman spectroscopy, we demonstrated that the phase stability in brines at elevated temperatures was inaccurately represented in the thermodynamic databases. Most notably for c(NaCl) > 4 M, and T > 80 °C gypsum becomes readily more soluble than bassanite, which induces the direct precipitation of the latter from gypsum. The fact that these transformations are controlled by the solution provides extensive opportunities for precise manipulation of crystal formation. Our experiments confirmed that bassanite remained the sole crystalline phase for many hours before reverting into gypsum. This property is extremely advantageous for practical processing and efficient crystal extraction in industrial scenarios.

Evidence of Sulfate‐Rich Fluid Alteration in Jezero Crater Floor, Mars

AbstractSulfur plays a major role in martian geochemistry and sulfate minerals are important repositories of water. However, their hydration states on Mars are poorly constrained. Therefore, understanding the hydration and distribution of sulfate minerals on Mars is important for understanding its geologic, hydrologic, and atmospheric evolution as well as its habitability potential. NASA's Perseverance rover is currently exploring the Noachian‐age Jezero crater, which hosts a fan‐delta system associated with a paleolake. The crater floor includes two igneous units (the Séítah and Máaz formations), both of which contain evidence of later alteration by fluids including sulfate minerals. Results from the rover instruments Scanning Habitable Environments with Raman and Luminescence for Organics and Chemistry and Planetary Instrument for X‐ray Lithochemistry reveal the presence of a mix of crystalline and amorphous hydrated Mg‐sulfate minerals (both MgSO4·[3–5]H2O and possible MgSO4·H2O), and anhydrous Ca‐sulfate minerals. The sulfate phases within each outcrop may have formed from single or multiple episodes of water activity, although several depositional events seem likely for the different units in the crater floor. Textural and chemical evidence suggest that the sulfate minerals most likely precipitated from a low temperature sulfate‐rich fluid of moderate pH. The identification of approximately four waters puts a lower constraint on the hydration state of sulfate minerals in the shallow subsurface, which has implications for the martian hydrological budget. These sulfate minerals are key samples for future Mars sample return.

Nonmetal doped TiO2 nanostructures: preparation, chemical states of dopants, properties

In this work, hydrofluoric acid and ammonium hydrofluoride were used as fluorine precursors, and thiourea and sulfuric acid - as sulfur precursors, and the phase composition, morphology, texture, and electronic structure of non-metals doped TiO2 nanostructures compared, the chemical state of dopants in the obtained materials was examined, and the influence of the specified factors on photocatalytic activity in the processes of photodegradation of complex organic compounds, for example on antibiotic of the tetracycline series – doxycycline, was stadied. It is shown that hydrofluoric acid and thiourea lead to the formation of anatase, while at low ratios of ammonium hydrofluoride to titanium butoxide, anatase heterostructures with brukite are formed, and at high ratios of sulfuric acid to titanium butoxide, the formation of the crystalline phase of titanyl sulfate is observed. It was determined that hydrofluoric acid causes the formation Sheet-like morphology, and the presence of sulfuric acid in the sol-gel reaction mixture leads to the formation of spheroidal particles, which at small ratios of sulfuric acid to titanium butoxide form loosely agglomerated particles of spheroidal morphology, which are formed from anatase crystallites. The photocatalytic activity of codoped TiO2 nanostructures in the doxycycline photodegradation process under UV and visible light irradiation was investigated and it was established that under UV light irradiation the activity mainly depends on the phase composition and crystallite sizes, while under visible light irradiation the activity depends from the interstitual dopants content that increase the materials sensitivity to visible light. It was established that nitrogen, carbon and fluorine co-doped TiO2 nanostructures obtained in the presence of ammonium hydrofluoride are characterized by the presence of surface Ti-F groups and interstitual carbon and surface carbonate, while carbon and sulfur co-doped TiO2 nanostructures obtained in the presence of thiourea after hydrothermal treatment contain Ti-SH groups, which are oxidized as a result of calcination at 450 °C are oxidized with the formation of interstitual sulfur (S6+) and surface sulfate.

Sulfide-sulfate metasomatism and nickel release in the suprasubduction mantle

Metasomatic replacement of olivine by orthopyroxene under the influence of SiO2-rich melts is a widespread process in mantle conditions responsible for the formation of pyroxenite from mantle peridotite. However, the behavior of nickel in this process remains unclear. The reaction of Ni-containing olivine with silica- and sulfur-rich metasomatic agents in the suprasubduction mantle may release nickel from olivine and subsequently form a rock containing orthopyroxene and nickeliferous sulfides. Xenoliths of mantle wedge harzburgite from the Shiveluch volcano (Kamchatka continental arc) contain abundant globules of Ni-rich MSS, pentlandite and smaller amount of copper sulfides, totaling up to 0.75 wt.% (∼2600 ppm S2–), in association with Ca-sulfates (up to 7900 ppm S6+). The process accounting for the observed mineral association can be described via simplified reactions (the coefficients are approximate): (Mg,Fe,Ni)2SiO4 + 2xH+ +SiO2 = 2(Mg,Fe)SiO3 + xNi2+ + xH2O; Ni2+ + S2– = NiS. The influx of both oxidized and reduced sulfur may account for the coexistence of sulfide and sulfate phases. The presence of low-Ti chrome spinel with high Fe(II)/Fe(III) ratios, low Al, Ca and Ti in olivine, and no evidence of deserpentinization confirms the mantle origin of the sulfide/sulfate-bearing xenoliths. The mean isotopic composition of sulfur in the sulfide-sulfate assemblage, δ34S = +4.5‰, supports the contribution of slab-derived sulfur. The accumulations of Ni-(Cu)-rich sulfides and Ca-sulfate in metasomatized peridotites can serve as an intermediate host for sulfur and chalcophile metals, thereby generating magmas containing sulfur at the level of sulfide saturation and simultaneously enriched in Ni and Cu during the subsequent partial melting of the mantle.

A mineralogical and geochemical assessment of the As-, Cu-, In-, Pb-, Sb-, and Zn-rich mine wastes at the Pefka epithermal deposit, Greece

Mining waste residues from the abandoned Pefka polymetallic epithermal deposit (northeastern Greece) were studied to document the products of sulfide oxidation and to evaluate the mobility of the wide range of trace metals and metalloids in these environments. Acidic to circumneutral waste rock and sediment samples (pH 3.3 to 6.7) are characterized by elevated As (up to 640 mg/kg), Cu (up to 1900 mg/kg), In (up to 11 mg/kg), Pb (up to 2300 mg/kg), Sb (up to 480 mg/kg) and Zn (up to 1500 mg/kg). The primary sulfide and sulfosalt minerals are almost completely transformed to gypsum as well as into different (hydr)oxide and (hydroxy)sulfate phases. Mineralogical investigation (powder X-ray diffraction, electron microprobe, Raman spectrometry) and sequential extraction revealed that As and Sb are principally stored in Fe(III) (hydr)oxides (especially goethite) and Pb hydroxysulfates (especially beudantite and hidalgoite). Fe (hydr)oxides also appear to be the main reservoirs of Cu and In. Lead is primarily bound to minerals of the beudantite group (especially beudantite, hidalgoite, and hinsdalite); while Zn is preferentially associated with Mn (hydr)oxides and minerals of the woodwardite group. The leaching test indicates that the Fe(III) (hydr)oxides and Fe(III)/Al(III) hydroxysulfate minerals retain the trace metal(loid)s efficiently but not completely (especially Cu and Zn). However, the mobility of most elements (especially As, In, Pb, and Sb) is very low because of the low solubility of hydroxysulfate minerals and the effective sorption of anionic metalloids under acidic to near-neutral conditions of the waste rocks and sediment.

EVALUATION OF THE EFFECTIVENESS OF INFLUENCE CAUSED BY ULTRA AND NANO-DISPERSE ADDITIVES FOR MODIFICATION OF SULFATE PHASES AND SULFOALUMINATE PHASES

Problem statement. We offer stabilization of ettringite with the help of nanocomponents introduced. When conducting these studies, the problem of developing compositions of new construction materials based on gypsum and cement binder was solved by means of introducing nano-additives. Nanotechnology is a tool that allows you to reliably understand the processes that occur during hydration of composite materials, interaction of chemical and mineral additives with newly formed hydrated structures, formation and development of macro- and microstructure. The next stage in the effective application of nanotechnologies and techniques used in nanotechnologies for studying hydration processes and structure formation of gypsum- and cement-containing binding materials consists in the development of molecular models of hydration of Portland cement products. Creation of a high-strength cement frame is possible by adjusting the size of the solid phase and crystallization centers, as well as by modifying the gypsum- and cement-containing binder with ultra and nanodisperse additives. Purpose is to investigate effectiveness of ultra- and nanodisperse additives for modification of sulfate phases and sulfoaluminate phases. Conclusions. Modification of the compositions of radiation protection solutions of sulfate phases and sulfoaluminate phases with nanodisperse additives led to a decrease in the coefficient of linear expansion to 0.8 %. Herewith, an increase in solid indicators occurred by 8−12 %, which was caused by a change in the structure of neoplasms and the mineralogical composition. Thus, modification of the solution of sulfate and sulfoaluminate phases with carbon nanotubes (CNTs) leads to a decrease in the coefficient of linear expansion and an increase in the scattering coefficient of gamma rays by 30−40 % due to a high specific surface area of CNTs (80−120 m2/g). An optimal solution with the following composition has been experimentally developed: alumina cement, gypsum, BaSO4, nanotubes. It has been established that this solution has a 10−15 % higher water content, which is associated with the formation of ettringite during the process of setting and hardening. As a result, the arithmetic average amount of chemically bound moisture increased, which affected the change in the linear attenuation coefficient of ionizing radiation of the coating by 0.0088−0.009 cm-1. The total coefficient can reach 0,354 cm-1. Such results lead to reduced equivalent thickness (14,6 mm) of the radiation protective layer by 1−1,5 mm.

Effect of biocomposite production factors on the development of an eco-friendly chitosan/alginate-based adsorbent with enhanced copper removal efficiency

Nowadays, wastewater treatment is a critical concern, particularly regarding the removal of heavy metals through adsorption methods. Extensive research has been conducted on obtaining high-yield and environmentally friendly adsorbents. Natural polymer adsorbents especially have shown promise in ion and organic molecule adsorption. To enhance the practical applicability of adsorbents, the combination of biopolymers to form biocomposites is a promising alternative. In this study, adsorbents based on a 1:1 wt./wt. of chitosan (CS) and alginate (SA) were prepared. The influence of the regeneration route and drying conditions on the copper adsorption capacity was investigated, along with reaction parameters such as contact time, adsorbent particle size, and pH. The highest adsorption capacity was observed in the composite material obtained through a one-pot regeneration process and freeze-dried. The CSAR3L sample exhibited a remarkable adsorption capacity of 288 mg Cu(II)/g after 360 min at 25 °C. The synergistic effect between the CS and SA precursors was confirmed by analyzing the individual precursors and their mechanical mixture. The initial adsorption rates at pH 6 followed the order: CSAR3-L > Bk-CSR3L > Bk-SAR3L + Bk-CSR3L > Bk-SAR3L. The physicochemical and morphological properties of the materials were studied by FTIR, XRD, DLS, XPS, optical microscopy, EDS-SEM, elemental chemical analysis, and TGA-DTG. The utilization of different drying methods resulted in the formation of calcium carbonate crystalline phases in the as-prepared materials, thus creating substantial adsorption active sites. After the adsorption process, hydroxylated copper sulfate phases and a significant decrease in calcium concentration were observed, indicating that an ion exchange adsorption mechanism occurred. The analysis of adsorption kinetics and the shape of the adsorption isotherms, in agreement with the characterization results, suggested the presence of multiple active sites and the formation of a chemisorption monolayer.

Optimization of the Microscopic Method of Observing of the Oleogel Structure

Abstract The subject of the research was the oleogel structure of the OraMAF oral suspension, containing a mixture of active substances in which the oleogel environment is formed by purified olive oil in combination with soy lecithin (SL) and sorbitan tristearate (STS). The objective of the research was the development of an optimal methodology for the work process, enabling microscopic observation of the structure of the oleogel suspension. Purified olive oil structured with a combination of gelators SL and STS with the addition of a solid phase of fucoidan (F) and chondroitin sulfate (CS) powders was used for the study as an alternative to OraMAF suspension. The sedimentation method of separation of the medium and staining of solid phases of the suspension brought the expected results, allowing the observation of the network structure of the gel, which consisted of interlaced gelator fibers assembling into star formations. The most interesting structures were clearly the star-like structures created from the star-shaped microtubules trapping the CS and F solid particles, colored blue.

Calcium Sulfate Nanoparticles in Surface Sediments of Lingding Bay of the Pearl River Estuary, China: Implications for the Nonclassical Crystallization Pathway of Gypsum in the Natural Estuary Environment

The mechanism of the nonclassical crystallization pathway of calcium sulfate dihydrate (gypsum) with calcium sulfate hemihydrate (bassanite) as a precursor has been considered in many studies. However, studies on the crystallization of gypsum in natural environments have rarely been reported, especially with regard to natural estuaries, which are one of the most important precipitation environments for calcium sulfate. Here, surface sediments (0–5 cm) of Lingding Bay of the Pearl River Estuary in China were sampled and analyzed. X-ray powder diffraction (XRD) analysis showed that calcium sulfate in the surface sediments mainly existed in the form of gypsum. In high-resolution transmission electron microscopy (HR-TEM) analysis, calcium sulfate nanoparticles were observed in the surface sediments. These particles mainly included spherical calcium sulfate nanoparticles (diameter ranging from 10–50 nm) and bassanite nanorod clusters (sizes ranging from 30 nm × 150 nm to 100 nm × 650 nm), and their main elements included O, S and Ca, with small amounts of N, Si, Na and Mg. The bassanite nanorods self-assembled into aggregates primarily co-oriented along the c axis (i.e., [001] direction). In epitaxial growth into larger bassanite nanorods (100 nm × 650 nm), the crystal form of gypsum could be observed. Based on the observations and analyses, we proposed that the crystallization of gypsum in surface sediments of the natural estuary environment could occur through the nonclassical crystallization pathway. In this pathway, bassanite nanoparticles and nanorods appear as precursors (nanoscale precursors), grow via self-assembly, and are finally transformed into gypsum. This work provided evidence supporting and enhancing the understanding of the crystallization pathway of calcium sulfate phases in the natural estuary environment. Furthermore, the interactions between calcium sulfate nanoparticles and the natural estuary environment were examined.

Oxidation of dimethylsulfoxide in the presence of uranyl salts

We report here the oxidation of dimethyl sulfoxide in the presence of uranyl salts at temperatures typically considered ‘safe’ for its handling. Uranyl salts, even in the absence of light, appear to accelerate the well-known oxidative decomposition of DMSO in air. Sulfate, a product of the decomposition, was captured in the crystalline state as the uranyl sulfate phase, UO2(DMSO)2(SO4).