Bassanite Research Articles

Modification mechanism, heavy metal coupling and ecological security risk assessment of phosphogypsum utilization in self-leveling mortar

Few researches on high efficiency modified phosphogypsum (MPG) and its resource utilization in bulding materials. This article investigated the effects of different lower temperatures and drying times on the thermodynamic modification mechanism of macroscopic performance and microscopic structure of MPG, and investigates its application in phosphogypsum-based self-leveling mortars (PBSLM). Then, the coupling mechanism of characteristic heavy metals in the modification process (original-modification-hydration) was discussed, and the safety evaluation was conducted on the content of heavy metal elements in the sample. Data from microscopic analysis showed that with the increase of temperature and drying time, the strength of MPG blocks and the decomposition rate of dihydrate gypsum crystal both increased, while the particle size decreased. The degree of crystal decomposition becomes more complete as the temperature rises if the holding time remains constant. As well as, the MPG at 180 °C/7 h, 195 °C/7 h/10 h met the Chinese standard of “Calcined gypsum” (GB/T9776). The heavy metal elements in MPG decreased obviously, caused by the substitution solid solution formed by Ca2+ and Fe3+ and heavy metal ions and the adsorption of calcium sulfate hemihydrate crystals. After hydration of MPG, As and Cd increased slightly because dicalcium phosphate was insoluble in water and soluble in acid, and iron oxide reduced and dissolved Cd. Then, the ecological hazards of heavy metals in hydrated MPG after hydration were evaluated. The results showed that there was no environmental safety problem in the hydrated MPG, but the As and Cr elements in it had an acceptable carcinogenic risk through oral intake. Based on ensuring the safety of MPG, MPG powder was used in PBSLM. The research demonstrates that the basic mechanical properties of the PBSLM produced, when the MPG powder content is 330 g, and cement is 40 g are the best. The heavy metal aqueous solution's leaching amount is lower than China's national standard limit value. (30min fluidity, 24 h-flexural and compressive strength were 154 mm, 5.7 MPa and 10.6 MPa). Finally, based on this research, a set of general evaluation system for safe utilization of solid waste was established according to national standards. This provides theoretical support for the research of heavy metal in PG at low temperature and the ways of harmless and resource utilization.

Enhancing cartilage regeneration and repair through bioactive and biomechanical modification of 3D acellular dermal matrix.

Acellular dermal matrix (ADM) shows promise for cartilage regeneration and repair. However, an effective decellularization technique that removes cellular components while preserving the extracellular matrix, the transformation of 2D-ADM into a suitable 3D scaffold with porosity and the enhancement of bioactive and biomechanical properties in the 3D-ADM scaffold are yet to be fully addressed. In this study, we present an innovative decellularization method involving 0.125% trypsin and 0.5% SDS and a 1% Triton X-100 solution for preparing ADM and converting 2D-ADM into 3D-ADM scaffolds. These scaffolds exhibit favorable physicochemical properties, exceptional biocompatibility and significant potential for driving cartilage regeneration in vitro and in vivo. To further enhance the cartilage regeneration potential of 3D-ADM scaffolds, we incorporated porcine-derived small intestinal submucosa (SIS) for bioactivity and calcium sulfate hemihydrate (CSH) for biomechanical reinforcement. The resulting 3D-ADM+SIS scaffolds displayed heightened biological activity, while the 3D-ADM+CSH scaffolds notably bolstered biomechanical strength. Both scaffold types showed promise for cartilage regeneration and repair in vitro and in vivo, with considerable improvements observed in repairing cartilage defects within a rabbit articular cartilage model. In summary, this research introduces a versatile 3D-ADM scaffold with customizable bioactive and biomechanical properties, poised to revolutionize the field of cartilage regeneration.

Pregelatinized hydroxypropyl distarch phosphate-reinforced calcium sulfate bone cement for bleeding bone treatment.

Considering the shortcomings of known medical hemostatic materials such as bone wax for bleeding bone management, it is essential to develop alternative bone materials capable of efficient hemostasis and bone regeneration and adaptable to clinical surgical needs. Thus, in the current work, a calcium sulfate hemihydrate and starch-based composite paste was developed and optimized. Firstly, it was found that the use of hydroxypropyl distarch phosphate (HDP) coupled with pregelatinization could generate an injectable, malleable and self-hardening paste with impressive anti-collapse ability in a dynamic aqueous environment, suggesting its potential applicability in both open and minimally invasive clinical practice. The as-hardened matrix exhibited a compressive strength of up to 61.68 ± 5.13 MPa compared to calcium sulfate cement with a compressive strength of 15.16 ± 2.42 MPa, making it a promising candidate for the temporary mechanical stabilization of bone defects. Secondly, the as-prepared paste revealed superior hemostasis and bone regenerative capabilities compared to calcium sulfate cement and bone wax, with greatly enhanced bleeding management and bone healing outcomes when subjected to testing in in vitro and in vivo models. In summary, our results confirmed that calcium sulfate bone cement reinforced with the selected starch can act as a reliable platform for bleeding bone treatment, overcoming the limitations of traditional bone hemostatic agents.

Simultaneous effect of Na2EDTA on the phase transformation and morphology evolution during the transformation of gypsum into α-calcium sulfate hemihydrate

The complexation between EDTA2− and Ca2+ inhibits phase transformation, and the selective adsorption of EDTA2− contributes to morphology evolution.

Comparative analysis of sticky bone and demineralized bone matrix with calcium sulfate hemihydrate on alveolar bone and papillary levels in immediate two-stage dental implant placement: A clinico-radiographic evaluation

Comparative analysis of sticky bone and demineralized bone matrix with calcium sulfate hemihydrate on alveolar bone and papillary levels in immediate two-stage dental implant placement: A clinico-radiographic evaluation

Development and Analysis of Biomaterial Based on Calcium Sulfate Hemihydrate and Epoxy Resin

Bone deformation and the degradation of the joint are one of the most common problems faced around the world, especially after the age of 50. Materials like Allograft and Polymethyl-Methacrylate (PMMA) are used in traditional orthotics and prosthetics, and for bone grafting/filling procedures, however, these materials can be expensive. This research proposes, the fabrication of a novel material by utilizing Calcium-Sulfate Hemihydrate (CaSO4. 1/2H2O), and epoxy resin, which can be used as a cost-effective orthotic and prosthetic material. The materials are already used as bone adhesives and bone grafts, hence, are compatible and non-toxic. The fabricated composite material possesses physical properties closest to the natural human bone and is also hydrophilic. Samples with different ratios of the constituents were fabricated and tested for their hardness, compression, and contact angle values using a Hardness tester, PASCO compression tester, and Image J software. The hardness test results indicate that sample 1 has the hardness value i.e., 29.5 ± 2.50 HV in contrast the hardness value of a human bone is found to be 33.3

Organic solvent-free synthesis of calcium sulfate hemihydrate at room temperature.

Calcium sulfate hemihydrate, also known as bassanite or Plaster of Paris, is one of the most extensively produced inorganic materials worldwide. Nowadays, bassanite is mainly obtained by thermal dehydration of calcium sulfate dihydrate (gypsum) - a process that consumes considerable amounts of energy and thus leaves a significant carbon footprint. Towards a more sustainable future, alternative technologies for bassanite production at low temperatures are therefore urgently required. While successful approaches involving organic solvents have been reported, we chose precipitation from aqueous solutions as a potentially even "greener" way of synthesis. In a previous work, we have shown that spontaneous formation of bassanite in water (in competition with thermodynamically favoured gypsum) can be achieved at 40 °C by the use of additives that maintain specific interactions with calcium sulfate precursors and modulate the local hydration household during crystallisation. The results of the present study demonstrate that bassanite can be obtained via simple precipitation from aqueous solutions at room temperature by the combination of additives acting through orthogonal mechanisms.

Development of paste-like organic/inorganic artificial bones compatible with bone remodeling cycles, consisting of β-tricalcium phosphate, calcium sulfate hemihydrate, and poly(lactic-co-glycolic acid) particles

Schematic illustration of organic/inorganic hybrid cement with the simultaneous addition of CSH and PLGA particles.

Study of phosphoric acid slurry rheological behavior in the attack reactor and development of a model to control its viscosity using artificial intelligence

This work aims to determine the rheological properties of the industrial phosphoric acid slurry and its behavior under the operating conditions of the phosphoric acid production process. For that, several experimental tests on the slurry were carried out, using a Rheometer (Anton Paar), which testing the effect of temperature and solid content. The results show that, for a fixed solids rate, the viscosity of the slurry decreases with temperatures from 75°C to 82°C and increases for temperatures above 82°C considered as the maximum temperature required by the process. This phenomenon is due to the morphological change of the gypsum which corresponds to the range of calcium sulfate hemihydrate formation. For a fixed temperature, the viscosity increases with increasing slurry solid content (31% to 37%). The viscosity increases with the shear gradient. Increasing the solid charge in the slurry increases its resistance to flow and movement. Thus, the slurry has a higher tendency to settle. A comparative study of four rheological models, Casson, Bingham, Ostwald and Herschel-Buckley, led to the selection of the Herschel-Bulkley model. This predicts the behavior of the phosphate slurry with a correlation coefficient of 99.9% and a MAE less than 4%. Overall, the results show that the threshold flow of the slurry is negligible, and its behavior is nonlinear. Thus, the slurry is a non-Newtonian fluid, with a dilatant rheological behavior. The various tests carried out enabled us to measure the viscosity of the phosphoric acid suspension for different solids contents and at different temperatures. The results obtained enabled us to study the rheological behavior and develop an artificial neural network model to control the viscosity of the slurry at the phosphoric acid attack tank.

Nano apatite growth on demineralized bone matrix capped with curcumin and silver nanoparticles: Dental implant mechanical stability and optimal cell growth analysis

ObjectivesThe prevention of implant-associated infections is becoming increasingly clinically important in the field of dentistry. Extensive investigations into the development of innovative antibacterial materials that interact effectively to reinforce their functionality are currently being conducted in the biomedical sector. In the present study, a novel dental nano putty (D-nP) has been developed using demineralized bone matrix (DBM), calcium sulfate hemihydrate (CSH), curcumin nanoparticles (CU-NPs), and silver nanoparticles (AgNPs). MethodsThe produced D-nP was evaluated using physicochemical, mechanical, and in vitro analyses. Surface characterization, particularly the analysis of calcium and phosphorus content, was performed before and after immersion in the simulated body fluid (SBF). In addition, the impact of surface treatment on biological activity was studied. ResultsThe results showed that the mechanical properties of the D-nP were outstanding and its performance is promising. D-nP exhibited excellent antibacterial activity against Actinomyces naeslundii (5.22 ± 0.07 mm) and Streptococcus oralis (5.41 ± 0.1 mm). The 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay was conducted using MG-63 osteoblast cells, which exhibited 95 % viability in D-nP. ConclusionsBased on these characterization results, the D-nP developed in this study exhibited excellent performance for tooth tissue in bone repair.

Unraveling the influence of solvent composition on Drop-on-Demand binder jet 3D printed tablets containing calcium sulfate hemihydrate

Recently, binder jet printed modular tablets were loaded with three anti-viral drugs via Drop on Demand (DoD) technology where drug solutions prepared in ethanol showed faster release than those prepared in water. During printing, water is used as a binding agent, whereas ethanol is added to maintain the porous structure of the tablets. Thus, the hypothesis is that the porosity would be controlled by manipulating the percentage of water and ethanol. In this study, Rhodamine 6G (R6G) was selected as a model drug due to its high solubility in water and ethanol, visualization function as a fluorescent dye, and potential therapeutic effects for cancer treatment. Approximately, 10 mg/ml R6G solutions were prepared with five different water–ethanol ratios (0–100, 75–25, 50–50, 75–25, 100–0). The ink solutions were printed onto blank binder jet 3D-printed tablets containing calcium sulphate hemihydrate using DoD technology. The tablets were dried at room temperature and then characterized using SEM-EDX, fluorescent microscope, TGA, XRD, FTIR, and DSC as well as in vitro release studies to investigate the impact of water–ethanol ratio on the release profile of R6G. Results indicated that the solution with higher ethanol ratio penetrated the tablets faster than the lower ethanol ratio, while the solution prepared with pure water was first accumulated onto the tablets' surface and then absorbed by the tablets. Moreover, tablets with more water content gained more weight and thickness. The EDX analysis and fluorescent microscope showed the uniform surface distribution of the drug. The SEM images revealed the difference in the tablet surface among the five formulations. Furthermore, the TGA data presents a notable increase in water loss, with XRD analysis suggesting the formation of gypsum in tablets containing elevated water content. The release study exhibited that the fastest release was from WE0-100, whereas the release rate decreases as the content of water increases. The WE0-100 releases more than 40 % drug within the first hour which is almost twice as high of the WE100-0 formulation. This DoD technology could distribute drugs onto the tablet's surface uniformly. The calcium sulfate would transform from hemihydrate to dihydrate form in the presence of water and therefore, those tablets treated with higher water content led to slower release. In conclusion, this study underscores the substantial impact of the water–ethanol ratio on drug release from binder jet printed tablets and highlights the potential of DoD technology for uniform drug distribution and controlled release.

Effect of glycerin as a plasticizer on flexural strength in the fabrication of gypsum-based chip

Background: Ceramic-based drug delivery systems has received significant attention in both medical and material domains. This study used gypsum as a base material for drug delivery chips, which has the potential to replace existing materials such as collagen and gelatin. The choice of gypsum as a material was based on a unique combination of osteoconductive, bioresorbable, and biodegradable characteristics. Methods: In this study, glycerin was added to distilled water at different concentrations (5%, 10%, 15%, 20%, and 25%) to increase the flexibility of gypsum. Calcium Sulfate Hemihydrate powder was then combined with a mixed solution of water and glycerin and stirred. The mixture was then placed in an acrylic mold measuring 25 x 3 x 1.5 mm and allowed to dry for 24 hours at room temperature. After that, the specimen was analyzed to determine flexural strength using the Universal Testing Machine with a three-point bending method at a crosshead speed of 0.5 mm/min. Results: Statistical analysis revealed that the inclusion of glycerin led to an increase in the percentage of strain. However, it has been observed that the mechanical strength of gypsum chips shows a proportional decrease with increasing glycerin concentration. Conclusions: It can be concluded that the addition of glycerin into the gypsum chip can increase the elasticity of the chip even though the flexural strength is reduced.

Design and Manufacture of Bone Cements Based on Calcium Sulfate Hemihydrate and Mg, Sr-Doped Bioactive Glass.

In the present study, a novel composite bone cement based on calcium sulfate hemihydrate (CSH) and Mg, Sr-containing bioactive glass (BG) as solid phase, and solution of chitosan as liquid phase were developed. The phase composition, morphology, setting time, injectability, viscosity, and cellular responses of the composites with various contents of BG (0, 10, 20, and 30 wt.%) were investigated. The pure calcium sulfate cement was set at approximately 180 min, whereas the setting time was drastically decreased to 6 min by replacing 30 wt.% glass powder for CSH in the cement solid phase. BG changed the microscopic morphology of the set cement and decreased the size and compaction of the precipitated gypsum phase. Replacing the CSH phase with BG increased injection force of the produced cement; however, all the cements were injected at a nearly constant force, lower than 20 N. The viscosity measurements in oscillatory mode determined the shear-thinning behavior of the pastes. Although the viscosity of the pastes increased with increasing BG content, it was influenced by the frequency extent. Pure calcium sulfate cement exhibited some transient cytotoxicity on human-derived bone mesenchymal stem cells and it was compensated by introducing BG phase. Moreover, BG improved the cell proliferation and mineralization of extracellular matrix as shown by calcein measurements. The results indicate the injectable composite cement comprising 70 wt.% CSH and 30 wt.% Mg, Sr-doped BG has better setting, mechanical and cellular behaviors and hence, is a potential candidate for bone repair, however more animal and human clinical evaluations are essential.

One Pot Synthesis of Calcium Sulfate Hemihydrate from Fishbone-derived Carbon

Calcium Sulfate Hemihydrate (CSH) with uniform morphology and high crystallinity were successfully prepared by a precipitation-hydrolysis method in a concentrated sulfuric acid solution containing fishbone-derived carbon. The CSH was produced by carbonization of fishbone powder at 500 °C for 2 h, followed by sulfonation with concentrated sulfuric acid for 3 h. The solid mixture was washed until the pH of 2, then left at room temperature for 3 days. Physical properties of synthesized CSH were characterized using Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), wavelength dispersive X-ray fluorescence (WDXRF), Scanning Electron Microscope (SEM), nitrogen adsorption-desorption isotherm, and melting point test. It is concluded that the CSH were formed due to hydrolysis of fishbone-derived carbon in a moderately concentrated sulfuric acid solution of carbon-derived fishbone and crystallization into a fibrous octa calcium phosphate (OCP) form. In this research, effect of crystal growth time, effect of pH during the crystal growth, and effect of volume of the solution were also investigated. Copyright © 2023 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0).

Accidental Ingestion of Plaster of Paris Causing Thermal Injury of the Esophagus and Stomach in a Toddler

Background: Plaster of Paris (POP) or calcium sulfate hemihydrate is commonly used in regular construction activities and medical appliances. Due to its easy availability, young children can be at risk of exposure. Mixing of POP with water results in exothermic reaction and production of heat. We report the acute endoscopic findings of thermal burn of the gastrointestinal mucosa, following accidental ingestion. Clinical Description: A 21-month-old boy presented with acute hematemesis in our emergency department with his mother giving a history of having noticed his fist full of POP. The child was otherwise stable, afebrile with swollen cheeks, lips, and oral mucosa with some crusting. Management and Outcome: The child was provided supportive care, and an early endoscopy was carried out, which revealed POP causing thermal injury of the mucosa of Zargar 2A grade. Conclusion: Our purpose of reporting this case is to highlight the less known deleterious effects of POP on the gastrointestinal mucosa and the importance of early endoscopic diagnosis, management along the lines of corrosive poisoning. Warning labels over the packets of POP and making them inaccessible to children are absolutely essential.

Novel preparation method and fire performance study of EPS composites based on calcium sulphate hemihydrate

A novel approach was used to prepare a new expanded polystyrene (EPS) composite based on calcium sulphate hemihydrate that significantly improves its fire performance. Negative pressure was applied to open cavities between the EPS beads and promoted the absorption of flame retardant slurry. Three fire retardant EPS (FR-EPS) composites with different densities were obtained. Although, a large number of inorganic additives were added, causing the increase in thermal conductivity to 0.043–0.045 W/(m∙K) and water absorption to 4.7–5.8%, the properties remained within an acceptable range. The results of limiting oxygen index (LOI), UL-94 vertical burning and Cone Calorimeter tests revealed that the FR-EPS1 increased LOI from 18.1% to 35.8%, achieved UL94 V-0 grade, decreased PHRR from 384.12 to 81.39 kW/m2, and reduced PSPR from 0.159 to 0.014 m2/s. With the continued increase of sample density, the measured LOI was further improved, while heat release and smoke production were better suppressed. TG results, and carbon residue after burning indicate that the endothermic dehydration reaction of calcium sulphate dihydrate and the physical barrier effect of the carbonaceous layer contribute to the extraordinary flame retardancy and smoke suppression of the FR-EPS composites.

Tunicate cellulose nanocrystals reinforced modified calcium sulfate bone cement with enhanced mechanical properties for bone repair

Considering the poor mechanical properties of bone cement, its practical application has always been limited. In this study, we introduced tunicate cellulose nanocrystals (TCNCs) into calcium sulfate bone cement for the first time, and multiple enhanced composite bone cement was prepared by the condensation reflux method. Firstly, high-strength modified calcium sulfate hemihydrate (CSH) bone cement was successfully prepared by using tartaric acid, a crystal modifier with a chiral structure. Secondly, the inclusion of TCNCs not only exhibited significant reinforcement and toughening effects but also stimulated the adhesion, proliferation, and differentiation of related osteoblasts. Furthermore, TCNCs encapsulated the CSH particles, overcoming the limitations of excessive degradation rates in bone cement and enabling sustained release of Ca2+, promoting the healing of bone defects. Overall, this study presents novel ideas and methodologies for designing bone cement with exceptional performance. It also provides a new platform for the development of bone tissue engineering and is expected to become a new type of bone regeneration material. The utilization of oceanic resources in this context holds high-value potential, alleviating environmental burdens and providing clinically applicable bone tissue repair materials with broad application prospects.

Fabrication and Characterisation of Calcium Sulphate Hemihydrate Enhanced with Zn- or B-Doped Hydroxyapatite Nanoparticles for Hard Tissue Restoration.

A composite based on calcium sulphate hemihydrate enhanced with Zn- or B-doped hydroxyapatite nanoparticles was fabricated and evaluated for bone graft applications. The investigations of their structural and morphological properties were performed by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), and energy dispersive X-ray (EDX) spectroscopy techniques. To study the bioactive properties of the obtained composites, soaking tests in simulated body fluid (SBF) were performed. The results showed that the addition of 2% Zn results in an increase of 2.27% in crystallinity, while the addition of boron causes an increase of 5.61% compared to the undoped HAp sample. The crystallite size was found to be 10.69 ± 1.59 nm for HAp@B, and in the case of HAp@Zn, the size reaches 16.63 ± 1.83 nm, compared to HAp, whose crystallite size value was 19.44 ± 3.13 nm. The mechanical resistance of the samples doped with zinc was the highest and decreased by about 6% after immersion in SBF. Mixing HAp nanoparticles with gypsum improved cell viability compared to HAp for all concentrations (except for 200 µg/mL). Cell density decreased with increasing nanoparticle concentration, compared to gypsum, where the cell density was not significantly affected. The degree of cellular differentiation of osteoblast-type cells was more accentuated in the case of samples treated with G+HAp@B nanoparticles compared to HAp@B. Cell viability in these samples decreased inversely proportionally to the concentration of administered nanoparticles. From the point of view of cell density, this confirmed the quantitative data.

Improvement of Plasterboard Properties by the Control of Polymethylhydrosiloxane Dosage, Stirring Time, and Drying Temperature Applied to the Calcium Sulfate Hemihydrate and Water Mixture.

Plasterboard is an important building material in the construction industry because it allows for quick installation of walls, partitions, and ceilings. Although a common material, knowledge about its performance related to modern polymers and fabrication conditions is still lacking. The present work analyzes how some manufacturing factors applied during the plaster board fabrication impact on some plasterboard properties, including water absorption, flexural strength, and thermal conductivity. The manufacturing variables evaluated are the dose (D) of polymethylhydrosiloxane (PMHS), the agitation time of the mixture (H), and the drying temperature of the plaster boards after setting (T). The results suggest that factors D, H, and T induce changes in the porosity and the morphological structure of the calcium sulfate dihydrate crystals formed. Performance is evaluated at two levels of each factor following a statistical method of factorial experimental design centered on a cube. Morphological changes in the crystals of the resulting boards were evaluated with scanning electron microscopy (SEM) and the IMAGEJ image analysis program. Porosity changes were evaluated with X-ray microcomputed tomography (XMT) and 3D image analysis tools. The length-to-width ratio of the crystals decreases as it goes from low PMHS dosage to high dosage, favoring a better compaction of the plasterboard under the right stirring time and drying temperature. In contrast, the porosity generated by the incorporation of PMHS increases when going from low-level to high-level conditions and affects the maximum size of the pores being generated, with a maximum value achieved at 0.6% dosage, 40 s, and 140 °C conditions. The presence of an optimal PMHS dosage value that is approximately 0.6-1.0% is evidenced. In fact, when comparing trails without and with PMHS addition, a 10% decrease in thermal conductivity is achieved at high H (60 s) and high T (150 °C) level conditions. Water absorption decreases by more than 90% when PMHS is added, mainly due to the hydrophobic action of the PMHS. Minimum water absorption levels can be obtained at high drying temperatures. Finally, the resistance to flexion is not affected by the addition of PMHS because apparently there are two opposing forces acting: on one hand is the decrease in the length-width ratio giving more compactness, and on the other hand is the generation of pores. The maximum resistance to flexion was found around a dosage of 0.6% PMHS. In conclusion, the results suggest that the addition of PMHS, the correct agitation time of the mixture, and the drying temperature reduce the water absorption and the thermal conductivity of the gypsum boards, with no significant changes in the flexural resistance.

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.