Structure Of Gypsum Research Articles

Manufacturing and mechanical performance of lightened gypsum reinforced by hemp/epoxy composites

In recent years, the construction industry has increasingly focused on reducing its environmental impact, addressing research efforts towards innovative materials and technological solutions. In this context, gypsum-based materials and natural fibers represent some of the most promising alternatives in terms of sustainability. This paper aims to propose a new gypsum structure reinforced with a composite hemp fabric impregnated with epoxy resin, investigating its manufacturing process and the mechanical properties, specifically in terms of flexural, impact and bearing strength. To achieve lightweight structures, lightened gypsum was also considered in addition to conventional gypsum. Both the lightened gypsum matrix and the hemp/epoxy reinforcement were produced using specific techniques able to obtain lightweight gypsum composites. Beneficial effects in the use of lightened gypsum matrix were found indeed, the reinforced lightweight samples exhibited higher values of flexural strength coupled with a density reduction of about 18%. Additionally, a significant change in post-cracking behavior was observed, with a gradual failure rather than a brittle one. The same trend was observed for the impact, while for bearing strength, the presence of porosity affected negatively the resistance of the composites, prevailing over the benefits of density reduction. Experimental results demonstrated the presence of a good interaction between the hemp fabric and the gypsum matrix, which was further confirmed by the microstructure analysis. The interesting mechanical properties showed by these lightweight gypsum/hemp composites, suggested their possible use for different and unconventional applications of gypsum-based walls and components.

Association of rare earth elements with secondary mineral phases formed during alkalinization of acid mine drainage

Rare Earth Elements (REE) are present in acid mine drainage (AMD) in micromolar concentrations and AMD discharge may lead to an environmental risk. Alkaline Passive Treatment Systems (PTS) are often used to treat AMD and trap toxic trace elements. This study was set up to identify mechanisms by which REE are trapped in or on secondary phases formed in a PTS. Batch alkalinization experiments were performed to simulate PTS by sequentially increasing the pH of AMD collected from the Tharsis mining area inside the Iberian Pyrite Belt and synthetic AMD water samples via CaCO3 addition. The solids that precipitated up to pH ~4 and between pH 4–6 were collected and characterized by Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) in combination with Scanning Electron Microscope/Energy Dispersive X-ray spectroscopy (SEM/EDX) and synchrotron-based X-ray Absorption Spectroscopy (XAS) and synchrotron-based Micro-X-ray Fluorescence (μ-XRF). Results reveal that REE are mostly scavenged between pH 4–6 in association with Al and Fe phases, whereas a smaller fraction is scavenged at pH ~4 by association with gypsum. Synchrotron-based analysis evidences the incorporation of La3+ into the gypsum structure by substituting Ca2+, indicating a co-precipitation mechanism with gypsum occurring mainly at low pH. Results from parallel adsorption and co-precipitation tests suggest that the REE scavenging between pH 4–6 could be due to a combination of adsorption and co-precipitation on Al(OH)3 and ferrihydrite. This implies that in PTS, REE would be mainly found in Al- (and Fe-) oxyhydroxides occurring in deeper layers of the PTS, i.e., where higher pH-values occur, though a small fraction, especially the light REE, could also be found incorporated into gypsum in the upper layers.

LITHOLOGICAL-STRATIGRAPHIC CRITERIA OF KARST ZONING OF THE MIOCENE SULFATE LAYER OF WESTERN UKRAINE

The proposed karst regionalization (zoning) is a novel approach to identifying the unique characteristics of karst processes in specific areas. The sulphate karst of western Ukraine, linked to the Miocene evaporite basin at the junction of the East European Platform and the Pre-Carpathian Foredeep, is a prime example. The previous karst zoning schemes of the East European Plain classified the entire area of sulphate rocks distribution in the west of Ukraine as the Podilsko-Bukovinsky karst Area, with the West Podilsky and Pokutsko-Bukovinsky karst Regions within it. However, with the emergence of numerous detailed stratigraphy works on the evaporite formation of this territory, a new approach to karst zoning in evaporites is necessary. This paper presents a systematic approach to upgrading the mentioned regions to the rank of sub-areas and distinguishing the regions within them based on lithologic-stratigraphic differences. The authors studied six localities as examples. In the first one, the gypsum layer is characterized by the stromatolite, grass-like and sabre-like facies. The last two contain thin carbonate-clay layers, leading to the collapse of large rock blocks inside the Kadubivska Cave. On the second site, the gypsum is composed of stromatolite, coarse-crystalline, and sabre-shaped facies. Only one small Tovtry Cave, which has a hypogene morphology, is known here. The third site has grass-like gypsum facies, and intensive modern karst occurs, with numerous sinkholes, underground rivers, and sinkholes. The influence of facies variability on the development of the mesomorphology of underground galleries is traced here in Pionerka Cave. The fourth area is built of nodular gypsum facies. There are no insoluble layers here, but the facies have many thin mineral films between the grains. Therefore, the entrance parts of the caves are unstable for physical weathering. The fifth section is highlighted as a section of the spread of metasomatic limestone, which replaces sulphate deposits here. They contain a significant cave labyrinth, but whether karstification occurred before or after metasomatization remains unclear. The sixth section is completely composed of stromatolite gypsum facies. It is characterized by stability to collapse due to the monolithic structure of gypsum, which is noticeable in the example of the Cave of Popeliushka (Zolushka) on the border of Ukraine and Moldova. The selected areas are proposed to be considered as examples of karst zoning based on lithologic and stratigraphic features. Key words: karst regionalization; gypsum, limestone; caves, breakdown; relief, landscape.

Morphogenesis of Hollow Bulbous Gypsum Structures Along a Brine Spring in Northeast Alberta

Abstract The stromatolite tufa mound at La Saline Lake developed along the Athabasca River Valley in northeast Alberta consists of a 30 m-high structure with a multi-meter thick caprock of stratified gypsum. The gypsum caprock developed when the meteoric-charged groundwater channeled along shallowly buried Upper Devonian limestone was redirected deeper and encountered anhydrite beds of the Middle Devonian Prairie Evaporite Formation, only 175–200 m below. Discharge of the sulfate-saturated brine from the central vent of the gypsum caprock eventually ceased and the flow was redirected to the western lakefront bank of the tufa mound. This active brine spring, characterized by total dissolved solids level of ∼79,000 mg/L, is channeled along a 25 m gully toward La Saline Lake. The bottom sediment in each of the interconnected brine pools along the gully consists of a 2–4 cm-thick calcite-gypsum thrombolite and an overlying gypsum crust. This sulfate crust developed as densely packed arrays of hollow botryoidal to hemispheroidal and bulbous gypsum protuberances, each 0.5–1.5 cm long, that extend upward into the brine. This is the first documented example of bulbous protuberances of gypsum that developed within brine pools with hollow interiors. The unusual hollowness of these bulbous gypsum protuberances resulted from the rapid encasement of gas bubbles that ascended from the underlying thrombolite ooze and were trapped within the overlying microbial mats and meshwork of gypsum crystallites on the surface of the bottom pool sediment. Nanoscale biomineralization of gypsum developed along the parallel arrays of microbial stalks within the enveloping mat, resulting in a meshwork of parallel aligned crystallites that encased the surfaces of the trapped bubbles. Continued abiotic gypsum precipitation transitioned the abiotic crystallites into enlarged needle-form crystallites distributed as parallel arrays along curvilinear growth surface laminae. Sufficient rigidity on the bubble surfaces precluded implosion-collapse or detachment. Strontium adsorption widely stabilized the acicular crystals, inhibiting complete coalescence as gypsum spar.

Research on Pore Structure of Foam Gypsum Modified by Portland–Sulphoaluminate Composite Cement (PSACC)

Research on Pore Structure of Foam Gypsum Modified by Portland–Sulphoaluminate Composite Cement (PSACC)

Coordinated disposal of FGD gypsum and power plant concentrated brine via preparation of α-hemihydrate gypsum

α-hemihydrate (α-HH), known for its exceptional mechanical properties, is a widely used building material. Despite its advantages, the traditional method of producing α-HH through regular pressure brine poses significant drawbacks. These include substantial industrial salt demands, high production costs, and water pollution. A more environmentally friendly α-HH preparation process has been developed to counteract these issues, combining FGD gypsum and concentrated brine. This study delves into the effects of the principal ions present in concentrated brine on the phase transition process and the microstructure of the final product. Our findings reveal that the reaction rate accelerates with increased concentrations of Ca2+, Mg2+, K+, and Na+ in concentrated brine. However, excessive Na+ concentration can alter the phase transition process, converting the product to β-HH. Additionally, an overly high concentration of KCl may prompt a part of the K+ to engage in the reaction, leading to the formation of isomeric potassium gypsum. This process can disrupt the original structure of hemihydrate gypsum. The addition of maleic acid to the salt solution was found to foster anhydrous gypsum formation. In contrast, succinic acid can decrease the crystals' aspect ratio, resulting in the growth of short columns, thereby enhancing the product's strength performance. Our research also identified that the reaction rate elevates as the pH value declines. However, an acidic environment diminishes the size of the crystal and counteracts the crystal modifier's effects. Lastly, incorporating CaCl2 and MgCl2 into concentrated brine with a low Na+ concentration can convert FGD gypsum into high-strength α-HH. This transformation results in a product boasting a 1-day compressive strength of 40.5 MPa.

Performance and mechanism of amino acids (AAs) on the gypsum setting-time control

Protein retarders can not only prolong the setting time of gypsum in application, but also lower the reduction in strength. The chemical activity of proteins is determined by the basic unit of amino acids (AAs). To enhance the understanding of protein retarding action mechanism, this paper focuses on the AAs-adsorbed gypsum structure, and investigated the retarding effects, crystal morphologies, and nanoscale interactions. Results indicate that the AAs had varying retarding effects on gypsum, and the effects from greatest to smallest were L-arginine, L-glutamic, and L-leucine acid. The rate of initial hydration heat release was reduced, and the peak of hydration release was delayed. Retardation of AAs on gypsum involves chemical adsorption on the surface of dihydrate gypsum crystals, which mainly occurs on the (1 2 0) face and affect gypsum morphology. The mechanism of AAs adsorption involves electrostatic interactions between charged functional groups of AAs and gypsum particles, as well as hydrogen bonding at additional carboxyl and amino groups. The adsorption strength depends on longer chained structure and number of functional groups of the AAs. And intrinsic strength of AAs-adsorbed gypsum nanocrystals contributes to the strength reduction on the macroscale. This paper provides basic data for designing and tailoring enhanced protein retarders for gypsum.

Evaluation and mechanism of ultrasound-assisted electrochemical desulfurization using citric acid as the electrolyte solution

ABSTRACT Achieving the clean utilization of coal is the priority of the coal industries. This paper proposed an efficient electrochemical technology for coal desulfurization before combustion. It was explored that citric acid can chemically provide enough acidic conditions for desulfurization reactions, and the ultrasonic-enhanced treatment physically helps to remove sulfur from coal due to its cavitation effect and mechanical effect. So the experiments of ultrasound-assisted electrochemical desulfurization using citric acid as the electrolyte solution were conducted. They combined physical and chemical methods to effectively remove sulfur from coal. The optimal operating parameters of the desulfurization effect were achieved by qualitative and quantitative analysis of coal samples(coal slurry concentration of 66 g/L, electrolysis time of 8 h, electrolyte concentration of 1.5 mol/L, electrolysis voltage of 4 V, electrolysis temperature of 30°C, ultrasonic strengthening time of 1 h and ultrasonic intensity of 320 W.). The total sulfur removal efficiency reached 45.09%. The electrolytic desulfurization experiments removed samples’ sulfur contents, ash contents, and water. The crystal structures of gypsum, white iron ore, zinc sulfide, and the molybdenite mineral composition were also destroyed for purification. Gaussian simulations showed that C-S bonds and S-S bonds contained in non-thiophene organic sulfur are easier to remove, and S-S bonds are more likely to break than C-S bonds. This study realized the promotion of desulfurization with the ultrasonic wave and citric acid solution. It provides a new idea of synergistic desulfurization and is beneficial to reduce atmospheric sulfur pollution.

Performance enhancement and mechanism of pregelatinized starch–binding gypsum at high water–gypsum ratios

Minimizing gypsum powder usage by increasing water to gypsum (w/c) ratios has both economic and environmental benefits. However, gypsum is limited in application by its poor mechanical strength at high w/c ratios. To enhance the strength of hardened gypsum at high w/c ratios, this paper proposes a pregelatinized starch–binding gypsum structure. The mechanical strength, working abilities, and microstructure of pregelatinized starch–binding gypsum samples at high w/c ratios were evaluated. And the micro-nano structure and enhancement mechanism of pregelatinized starch–modified gypsum was investigated. The results show that at high w/c ratios from 0.8 to 1.0, pregelatinized starch significantly improved the mechanical properties of gypsum, where the flexural and compressive strength of 3 d modified drying sample were 3.3 MPa and 6.6 MPa in comparison to pure gypsum samples tending to 0 MPa. Pregelatinized starch participates in the overlapping structure of gypsum crystals and bind to them without affecting the crystal structure and morphology of single particles. The nanostructure of modified contact points involved strong adsorption of pregelatinized starch onto the (120) face by hydrogen bonding, which enhanced binding adhesion at contact points. And pregelatinized starch effectively reduced separation of the (120) face under x– and z– tensile stretching, and slipping along the (010) face under y– tensile stretching. This paper presents a modification that enhances mechanical properties of gypsum at high w/c ratios, and provides deeper understanding of crystal overlapping mechanisms at the nanoscale.

Original visual imaging in Marsili’s (1658–1730) geology and mapping

Bologna was the birth place of the word Geology by Aldrovandi (1522–1605) in 1603, and of visual imaging of geologic outcrops and landscape by Marsili’s (1658–1730) works, having forerunner in Leonardo (1452–1519). Wide use of visual graphics and imaging characterizes Marsili’s geologic production, under the influence of a tradition beginning with Aldrovandi and peaking with Malpighi’s (1628–1694) teaching and anatomical works, ending in detailed drawings, as done also by Malpighi’s friend Steno (1638–1686), a (re)founder of geology. Marsili’s early visual geologic representations, such as the gypsum structures in the quarries and caves of the Bologna hills (1698), the profiles across the Swiss Alps (1705), the subterranean bedding and an early geological map in the Romagna sulphur mines (1717–1718) show his intent to. dissect geological bodies observed through Europe, as he was thought by Malpighi to do with human bodies. Such original aesthetic scientific design in geology grew in Marsili’s maturity far beyond Steno’s teaching, as shown in Marsili’s major treatises on Danube and oceanography and in his monumental archive, at the Bologna Institute.Marsili’s cartographic skill is highlighted by his manuscript Oreographic Map of Europe, which is the first example of structural map at continental level, as shown by physical connections across seas and alluvial plains of major European mountain belts: Donets through Volga Heights to Karelid chains and Cola Peninsula, Harz Mountains to Norvegian chain, Pyrenees to Provencal chain, Balkan chain to Crimea and Caucasus chain, Bethic to Rif chain (Gibraltar arc), Sicily Apennine to Maghrebian chain, Apulia to Hellenic belt. Relevance of the selected case histories demonstrate that this is not a geographic but a geological map by which Marsili aimed at unravel subsurface structures and trends.

Properties of Gypsum Boards Made with Cedrus Tree (Cedrus libani) Components. Part 2. Chemical and Technological Properties

In this study, the variation of cedrus tree parts and gypsum during experimental panel manufacturing have been evaluated. The burning pattern on the surface of all test boards produced by adding cedrus’s tree components (wood, bark, cone and needle) as reinforcement fillers to the gypsum structure did not reach the threshold limit of 150 mm that specified in the standard value as ISO 11925-2 standard but only limi-ted spreading of char was observed. It was also found that cone looks like create better barrier against heat compare to needle, wood and bark in similar proportions with gypsum. In contrary, although bark could be absorbed and barrier to heat better than others but it may not support flammability that are not support to mass lost when subject to burning. Some chemical changes occurred in main constituents of lignocellu-losic substances in water/gypsum mixture as evidence with FTIR spectrums. It has also realized that bark (SKa6), cone (Sko6), and needle (SI6) in gypsum negative impact on thermal degradation that higher tempe-rature for decomposition compare to wood-based board (Ska1) at similar experimental manufacturing conditions. It has clearly seen that content of fillers dramatically effects thermal stability of gypsum based boards.

Influence of phosphorus impurities on the structure and performance of cellulose-ether-modified gypsum

This study examined the influence mechanism of phosphorus impurities in phosphogypsum on the structure and properties of gypsum. The influence of four phosphorus impurities, namely Ca3(PO4)2, CaHPO4, H3PO4, and Ca(H2PO4)2 on the hydration process, water retention, and mechanical properties of hydroxypropyl methyl cellulose ether (HPMC)-modified gypsum was examined through inductive coupled plasma emission spectrometer, scanning electron microscopy, and nanoparticle size testing. The soluble phosphorus impurities exert a significant retarding effect on HPMC-modified gypsum, which decreases the heat of hydration in the early stage. Moreover, soluble phosphorus impurities significantly decrease the water retention and compressive and flexural strengths of modified gypsum. Although slightly soluble CaHPO4 exerts a similar adverse influence on the structure and properties of modified gypsum, the effect is weaker than that of soluble phosphorus impurities. Insoluble Ca3(PO4)2 does not affect the properties of modified gypsum. Soluble phosphorus in the liquid phase decreases the supersaturation of the gypsum solution and metathesises with the Ca2+ in the solution to produce insoluble calcium phosphate. This product covers the surface of the crystal nucleus, delays the hydration reaction of gypsum, and decreases the amount of heat released in the early hydration process. Moreover, a coarse overlap of the crystal growth and loose structure of the hardened body is observed, and the flexural and compressive strengths decrease. Increase in the amount of soluble phosphorus in the solution decreases the polarity of the hydroxyl group in the HPMC molecule and strength of the hydrogen bond within the association complex. This phenomenon leads to the disintegration of the large colloidal association and the less swelling, owing to which the HPMC molecule cannot effectively block the water transmission channel in the mixture, resulting in decreased water retention of the HPMC-modified gypsum.

Gypsum Precipitating From Volcanic Effluent as an Archive of Volcanic Activity

Records of volcanic activity are a key resource in volcano monitoring and hazard mitigation. The time period for which such records are available and the level of detail vary widely among volcanic centers and there is, therefore, a need for supplementary sources of this information. Here, we use growth-zoned gypsum as a mineral archive of the activity of Kawah Ijen volcano in East-Java, Indonesia. Gypsum precipitates where water seeps from the crater lake and hydrothermal system, and it has formed a 100 m long cascading plateau. A 19 cm plateau cross-section was analysed for minor and trace elements using laser-ablation ICP-MS. Absolute ages were assigned to this transect based on 210Pb dating. This 210Pb age model was corrected for variations in the 210Pb0 resulting from fluctuations in the volcanic radon flux by using 84Kr/36Ar and 132Xe/36Ar. The age model indicates that the transect covers a period from 1919 ± 12 to 2008 ± 0.2. Gypsum-fluid partition coefficients (D) permit the gypsum compositions to be converted to the concentrations in the fluid from which each growth zone grew. The D-values also show the compatibility of the elements in the gypsum structure, and identify the LREE, Sr, Pb, Tl, Ni, Co, Cu, Zn, Cd, Sb, Th, and Mo as least susceptible to contamination from rock fragment and mineral inclusions, and therefore as most reliable elements of the gypsum record. Compositional variability in the timeseries correlates with known element behavior in the Kawah Ijen system and shows three element groups: the LREE, Sr, and Pb that represent rock-leaching; Cu, Zn, and Cd, which have previously been linked to immiscible sulfide destabilization in a deep-seated basalt; and Sb, Tl, and As which point to a contribution from the shallow system and evolved magma. Moreover, the gypsum record shows that episodes of unrest and quiescence have a distinct compositional signature in Kawah Ijen seepage fluids, and can be distinguished. Thus, we show that gypsum is a sensitive recorder of volcanic activity and can provide detailed information on the state of the magmatic-hydrothermal system in the past.

Hydrological and thermodynamic controls on late Holocene gypsum formation by mixing saline groundwater and Dead Sea brine

The rapid retreat of the Dead Sea during the past four decades led to the exposure of unique structures of massive gypsum along the shores. Many of these structures (having the shape of mounds) are associated with the activity of Ein Qedem-type saline springs that currently discharge Ca-chloride brine to the lake. Field observations, radiocarbon dating of aragonite (within the gypsum mounds) that yield ancient ages, and the narrow range of δ34S and δ18O values (δ34Sgyp: 14.1–16.9‰; δ18Ogyp: 14.4–16.5‰) indicates that the formation of the gypsum structures is related to the mixing of brines: the Dead Sea brine and ancient (last glacial) Ein Qedem type brine. These are Ca-chloride brines having different salinities and sulfur concentrations that satisfy conditions of an outsalting process whereby supersaturation of gypsum is attained by the mixing of these two brines in the offshore shallow water environment.Thermodynamic calculations (using the PHREEQC software) show that gypsum outsalting occurred when both brines were enriched with sulfate as compared to the present. The Ein-Qedem brine had higher sulfate when subjected to less intensive bacterial sulfate reduction. The Dead Sea was characterized by higher sulfate concentrations during intervals of low lake stands. The conditions of higher sulfate concentrations and enhanced discharge of the saline springs occurred repeatedly in the Dead Sea between ∼6.6 to 0.6 ka and were intermittent with periods of enhanced supply of sulfate to the lake by freshwaters.

Comparison of Mechanical Properties of Gypsum with and without Polypropylene Fibers

Gypsum is a mineral belonging to the group of sulfates, i.e., sulfuric acid, which is often found in Earth's crust. In this paper, two main types of gypsum, gypsum α and gypsum β, with different water content were prepared. Samples with and without polypropylene fibers, with different fiber content and different fiber lengths during preparation, produced in a gypsum factory located in the Debar region, North Macedonia, were studied. Physical properties such as density, porosity, water absorption capability and their kinetics, packing factor, hardening and others were examined using different methods. The main goal of this paper was the determination of mechanical properties of gypsum such as the compressive and flexure strength and the module of elasticity of the gypsum prisms. For the determination of elastic properties, the nondestructive method of ultrasound testing was used. In this test, the strength and quality of a prism is assessed by measuring the velocity of an ultrasonic pulse passing through a gypsum structure. This test is conducted by passing a pulse of ultrasonic wave through a prism and by measuring the time taken by the pulse to get through the structure. Higher velocities indicate good quality and continuity of the material, while slower velocities may indicate gypsum with many cracks or voids. The comparison of the obtained results from these two types of gypsum shows different mechanical and other physical properties.

Structural characteristic and formation mechanism of hemihydrate calcium sulfate whiskers prepared using FGD gypsum

Hemihydrate calcium sulfate whiskers (HH-CSWs) were hydrothermally synthesized in a sulfuric acid solution at 120°C for different holding times (20, 40, and 60min). The phase structures and morphologies were characterized by XRD and SEM, respectively. The XRD pattern of the sample under 60min was refined via the Rietveld fitting method. The structure models of the HH-CSW sample under a 60-min holding time was established based on Rietveld fitting results. No difference in the positions of diffraction peaks was determined. The as-prepared holding time increased the intensity and aspect ratio of the diffraction peaks of both samples. In the prepared HH-CSW structure, Ca–O polyhedron is a 12-sided polyhedron similar to that in the gypsum structure; the Ca atom is located in two positions in the one-unit cell; the H2O channel along the c-axis similar is O-shaped and bigger than that in hexagonal and monoclinic CaSO4·0.5H2O structures. Therefore, although the prepared HH-CSW crystals’ structure are similar to that of the reported hexagonal and monoclinic CaSO4·0.5H2O structures, they are not the same. The formation mechanism of HH-CSW from flue gas desulfurization (FGD) gypsum is discussed based on the analysis of gypsum structure.

Effect of nano-silica and silicone oil paraffin emulsion composite waterproofing agent on the water resistance of flue gas desulfurization gypsum

This paper indicates the influence of nano-silica and silicone oil paraffin emulsion mixed with flue gas desulfurization (FGD) gypsum on its water resistance. Nano-silica was mixed with FGD gypsum to explore the influence of nano-silica particle size and content on the waterproofing and mechanical properties of FGD gypsum while also analyzing its waterproofing mechanism. In addition, silicone oil paraffin emulsion was mixed along with nano-silica into FGD gypsum to study its effect on FGD gypsum. The results show that nano-silica can improve the water resistance of FGD gypsum. When the particle size of nano-silica is 50 nm and the mass fraction is 0.4%, the softening coefficient of FGD gypsum reaches 0.92. Nano-silica and organic composite emulsion can play a synergistic role and further enhance the performance of FGD gypsum. The water resistance and mechanical properties of gypsum further increased when mixed with nano-silica and silicone oil paraffin emulsion. The water absorption rate decreased to 13.62%, and the compressive strength reached 13.71 MPa. Combined with the microscopic morphology analysis of the gypsum sample, the appropriate size of nano-silica fills the crystal pores, reduces porosity, and, to a certain extent, changes the structure and morphology of gypsum crystals. Silicone oil paraffin emulsion can be wrapped on the surface of gypsum crystals forming a dense oil hydrophobic membrane. It produces a compact gypsum structure together with nano-silica, hindering the entry of water molecules into gypsum, thereby improving the performance of FGD gypsum.

Gypsum Deltas at the Holocene Dead Sea Linked to Grand Solar Minima

AbstractUnique gypsum structures: large capes (termed “gypsum deltas”) and small pitted gypsum mounds are exposed along the western shores of the currently retreating Dead Sea, the hypersaline terminal lake in the Dead Sea Basin. The gypsum deltas were formed during time intervals of low lake stands (∼420 ± 10 m below mean sea level), when sulfate‐rich Ca chloride brines discharged from the coastal aquifer via saline springs, mixed with the Dead Sea brine and precipitated the gypsum (outsalting process). The ages of formation of the gypsum structures coincide with times of North Atlantic cooling events and grand solar minima suggesting a direct impact of the latter on the Dead Sea hydrology and high sensitivity of the regional hydrology (controlling lake level) to global solar‐related events. The temporal occurrence and numbers of the gypsum structures appear to follow the Hallstatt Cycle that approaches minima at ∼3,000–2,000 years before present.

Efficient removal of phosphate impurities in waste phosphogypsum for the production of cement

Phosphogypsum (PG) is an industry solid waste produced from phosphoric acid manufacture. To reduce environmental pollution of the PG, H2C2O4 was employed to purify it, which then can be used for cement production. The optimal concentration of H2C2O4 for PG purification was determined. In addition, differential thermal analysis (DTA), X-ray photoelectron spectroscopy (XPS) and X-ray fluorescence (XRF) were used to determine the removal of phosphate impurity in PG. The effects of purified PG on cement hydration and the environmental implications were also investigated. The results demonstrate that H2C2O4 can remove the intercrystalline phosphate impurities by destroying the part of the crystal structure of gypsum. With the best treatment concentration of 1% H2C2O4, 77.7% of phosphate impurity (as P2O5) was removed from PG, which subsequently shortened the final setting time down to 220min and successfully met the national standard (GB 175-1999). Portland cement prepared by the 1% H2C2O4 treated PG possessed a comparable 3d compressive strength of 20.8MPa and a 28d compressive strength of 44.6MPa. It is concluded that PG purified by 1% H2C2O4 treatment can be used for cement production. Meanwhile, this H2C2O4 treatment can effectively reduce the environmental pollution from PG and offer a sustainable method for the utilization of PG.

Evolution of the Astonishing Naica Giant Crystals in Chihuahua, Mexico

Calcium sulfate (CaSO4) is one of the most common evaporites found in the earth’s crust. It can be found as four main variations: gypsum (CaSO4∙2H2O), bassanite (CaSO4∙0.5H2O), soluble anhydrite, and insoluble anhydrite (CaSO4), being the key difference the hydration state of the sulfate mineral. Naica giant crystals’ growth starts from a supersaturated solution in a delicate thermodynamic balance close to equilibrium, where gypsum can form nanocrystals able to grow up to 11–12 m long. The growth rates are reported to be as slow as (1.4 ± 0.2) × 10−5 nm/s, taking thousands of years to form crystals with a unique smoothness and diaphaneity, which may or may not include solid or liquid inclusions. Conservation efforts can be traced back to other gypsum structures found prior to Naica’s. Furthermore, in the last two decades, several authors have explored the unique requirements in which these crystals grow, the characterization of their environment and microclimatic conditions, and the prediction of deterioration scenarios. We present a state-of-the-art review on the mentioned topics. Beyond the findings on the origin, in this work we present the current state and the foreseeable future of these astounding crystals.