Crystal modification of calcium sulfate dihydrate in the presence of some surface-active agents

Role of Additives: Modified Hemihydrate Phosphogypsum Morphology and Enhanced Filtration Performance of Wet-Process Phosphoric Acid

The morphology of hemihydrate phosphogypsum crystals is of vital importance in the hemihydrate-dihydrate (HH-DH) wet-process phosphoric acid production for high filtration strength. The morphology of hemihydrate phosphogypsum is commonly needlelike due to the strong acidic crystallization environment, which is unfavorable to the following filtration process. In this study, the crystal habit of hemihydrate phosphogypsum with a large aspect ratio was skillfully modified by additives to achieve a higher filtration strength. d-Glucitol (DG) reduces the theoretical aspect ratio of hemihydrate phosphogypsum crystals from 2.076 to 1.583 by interacting with the (002) face of CaSO4·0.5H2O preferentially, and poly(vinyl alcohol) (PVA) facilitates the aggregation of small grains to gather into a clusterlike structure. The modified morphologies of hemihydrate phosphogypsum have a lower bulk density and a larger porosity of the formed filter cake, which increases the filtration strength up to 45.9% when DG is added. Our work provides an in-depth explanation of the evolution mechanism of hemihydrate phosphogypsum morphology with the additives and its influence on the filtration performance. The improved filtration strength would reduce the water content of hemihydrate phosphogypsum and relieve the storage pressure of the phosphogypsum slag dump, which is meaningful to the clean production and process emission reduction of the phosphorus chemical industry.

Evaluating the Efficiency of Magnetic Treatment for Feed Water in Reverse Osmosis Processes

The paper presents a new methodology for short-term (5-25 min) benchtop tests to evaluate the effectiveness of magnetic treatment of feed water for reducing mineral scaling on a reverse osmosis (RO) membrane. Scale deposition is measured at a controlled level of salt supersaturation in water flowing through an RO unit in once-through mode. A magnetic water conditioner is tested in a transient flow regime when variations of the permeate flux along the flow path are insignificant. Scale formation under these conditions is governed by salt crystallization on the membrane surface. The proposed method was implemented to investigate the influence of magnetic treatment on gypsum deposition on RO membranes in supersaturated aqueous CaSO₄/NaCl solutions. The effects of magnetic water treatment on scale formation under our experimental conditions were found to be statistically insignificant with a confidence level of 95%. However, this outcome should not be considered to negate the potential efficiency of magnetic water treatment in specific applications. The proposed methodology of testing under a controlled level of salt supersaturation will also be useful for evaluating the efficiency of other water treatment technologies.

Mechanical Behavior of Calcium Sulphate Modified with Citric Acid and with Added Carbon Fibers

The study and subsequent analysis of the interaction of calcium sulfate with added citric acid and with two additional proportions of carbon fibers of different lengths has been based on the IMR and D Method for its realization. The purpose of this work is the study of the physical and mechanical behavior of the resulting material between the intimate mixture of calcium sulfate with additives and carbon fibers, justifying said work with a link to the Sustainable Development Goals (SDG) regarding the benefits that the Calcium sulfate has contributed to civil society since times dating back to ancient Egypt. We find ourselves with a material of which the energy used in its manufacture is far from that required by steel or cement, and construction with this new compound is in a much higher stage than construction with adobe. Therefore, this is a compound that can be developed for a wide variety of applications. The novelty of this study is the inclusion of polymeric fibers in a material used over the centuries to improve its mechanical properties. With these improvements we will be able to reduce thicknesses in manufacturing, which implies a reduction in manufacturing energy and weight structures in buildings, which should be studied and analyzed in the future. The kneading of calcium sulfate with long fibers at high percentages complicates not only the results, but also the manufacturing process. As representative results of the study, we can indicate that a composite material with high mechanical capacity has been achieved, with maximum values of flexural strength of 8.12 N/mm² and compression strength of 17.58 N/mm².

Better filterability and reduced radioactivity of phosphogypsum during phosphoric acid production in Morocco using a fly ash waste and pure silica additive

Reactive silica additives, such as clays, can increase the filterability of phosphogypsum (PG) during wet phosphoric acid production from phosphate rock (PR). In this study, the effect of adding inexpensive fly ash waste (34 kg per t PR) together with lower quantities of pure silica (8.5 kg per t PR) on the radioactivity of PG was investigated. The addition of fly ash waste/pure silica reduced the radiological activity of the PG by roughly 30%. The reduction was attributed to decreased activities from 238U (60% reduction) and 226Ra (30% reduction) in PG. Besides, P2O5 losses were slightly decreased.

Continuous, Large-Scale, and High Proportion of Bioinspired Phosphogypsum Composites via Reactive Extrusion

Biological matter evolution provides an idea for the human design and synthesis of new materials. However, biomimetic materials only stay in laboratory-scale models, and their large-scale industrial applications are yet to be realized. Here, inspired by nacre's architecture, we report a continuous, large-scale method to fabricate phosphogypsum composites by reactive extrusion strategy. After curing for seven days, with more than 50 wt% of beta-hemihydrate phosphogypsum (β-HPG), the compressive strength and softening coefficient were 24.98 MPa and 0.78, increasing by 110.0% and 20.0%, respectively, compared to the pouring method. The results show that the screw extrusion process can improve the mechanical strength and waterproof properties of β-HPG hydration specimens without any special chemical admixtures and cements.

Addition of lactoferrin and substance P in a chitin/PLGA-CaSO4 hydrogel for regeneration of calvarial bone defects

Calcium-based injectable hydrogels with various bioactive active molecules possess a great potential for bone regeneration. Herein, we have synthesized a chitin-PLGA-calcium sulfate hydrogel (CSG) containing bioactive molecules - lactoferrin (LF) and substance P (SP). SEM and XRD analysis revealed that CS crystal growth was altered with the addition of LF. Rheological measurements indicated that the injectability of the hydrogels was maintained after the addition of LF, however, there was a reduction in storage modulus after LF addition. The addition of LF increased stem cell proliferation whereas, SP enhanced the cell migration. Osteogenic gene expression revealed that LF concentration at 25 μg/mg of CSG was optimal for a favourable outcome. To this optimized LF containing CSG, SP was incorporated and 0.05 μg/mg was found to be most effective (CSG-L3S2) in vitro studies. Further, the μ-CT and histological studies confirmed that CSG-L3S2 showed enhanced bone regeneration compared to the controls in critical-sized calvarial defect of mice. Thus the results indicate that a combination of the chemotactic agent (SP), pleiotropic growth protein (LF), and CS in the chitin-PLGA hydrogel could be a promising approach for non-load bearing bone defects.

Innovative findings about ferrous oxalate dihydrate crystallization in simulated dihydrate phosphoric acid product

The basic fundamentals of ferrous oxalate dihydrate (FeC₂O₄.2H₂O) crystallization including supersaturation, nucleation and crystal growth in simulated dihydrate phosphoric acid product with and without cetyl pyridinium chloride (CPC) additive were studied. Oxalic acid and ferrous sulfate heptahydrate crystals were mixed with dilute phosphoric acid (28% P₂O₅) at 60 °C and the turbidity of the reaction mixture was measured at different time intervals. Induction time of ferrous oxalate dihydrate crystals was calculated at different supersaturation ratios ranging from 2.5 to 6.7. With increasing the supersaturation ratio, the induction time decreased. The nucleation rates are 46.4 × 10²⁸ nuclei cm^-3 s^-1 and 50.2 × 10²⁸ nuclei cm^-3 s^-1 at supersaturation ratio 6.7 with and without CPC addition, respectively. The surface energy increases with CPC addition compared to the baseline. In addition, the formed crystals are modified from cubic shape to rod-like shape with increasing CPC dose.

Crystallisation of sodium dodecyl sulfate–water micellar solutions with structurally similar additives: counterion variation

Kinetic and morphological insight into the crystallisation of micellar SDS–H₂O solutions using small quantities of structurally similar additives.

Injectable Shear-Thinning CaSO4/FGF-18-Incorporated Chitin-PLGA Hydrogel Enhances Bone Regeneration in Mice Cranial Bone Defect Model

For craniofacial bone regeneration, shear-thinning injectable hydrogels are favored over conventional scaffolds because of their improved defect margin adaptability, easier handling, and ability to be injected manually into deeper tissues. The most accepted method, after autografting, is the use of recombinant human bone morphogenetic protein-2 (BMP-2); however, complications such as interindividual variations, edema, and poor cost-efficiency in supraphysiological doses have been reported. The endogenous synthesis of BMP-2 is desirable, and a molecule which induces this is fibroblast growth factor-18 (FGF-18) because it can upregulate the BMP-2 expression  by supressing noggin. We developed a chitin-poly(lactide-co-glycolide) (PLGA) composite hydrogel by regeneration chemistry and then incorporated CaSO₄ and FGF-18 for this purpose. Rheologically, a 7-fold increase in the elastic modulus was observed in the CaSO₄-incorporated chitin-PLGA hydrogels as compared to the chitin-PLGA hydrogel. Shear-thinning Herschel-Bulkley fluid nature was observed for both hydrogels. Chitin-PLGA/CaSO₄ gel showed sustained release of FGF-18. In vitro osteogenic differentiation showed an enhanced alkaline phosphatase (ALP) expression in the FGF-18-containing chitin-PLGA/CaSO₄ gel when compared to cells alone. Further, it was confirmed by studying the expression of osteogenic genes [RUNX2, ALP, BMP-2, osteocalcin (OCN), and osteopontin (OPN)], immunofluorescence staining of BMP-2, OCN, and OPN, and alizarin red S staining. Incorporation of FGF-18 in the hydrogel increased the endothelial cell migration. Further, the regeneration potential of the prepared hydrogels was tested in vivo, and longitudinal live animal μ-CT was performed. FGF-18-loaded chitin-PLGA/CaSO₄ showed early and almost complete bone healing in comparison with chitin-PLGA/CaSO₄, chitin-PLGA/FGF-18, chitin-PLGA, and sham control systems, as confirmed by hematoxylin and eosin and osteoid tetrachrome stainings. This shows that the CaSO₄ and FGF-18-incorporated hydrogel is a potential candidate for craniofacial bone defect regeneration.

Investigation of the Effects of Sodium Dicarboxylates on the Crystal Habit of Calcium Sulfate α-Hemihydrate

The effects of disodium malonate, disodium succinate, disodium glutarate, and disodium adipate on the crystal habit of calcium sulfate α-hemihydrate (CaSO₄·0.5H₂O, α-CSH) were studied using experimental studies and molecular dynamics simulations. The calculation and experimental results provided insight into the mechanism of the interaction between the additives mentioned above and the different faces of α-CSH that dominate the morphology of α-CSH. The calculation results indicated that the formation of high-aspect-ratio α-CSH, namely, calcium sulfate α-hemihydrate whiskers (α-CSH whiskers), in aqueous solution was due to the interaction between liquid water and side faces of the α-CSH crystal, which inhibits the growth of α-CSH along the radial direction. However, when a trace amount of crystal habit modifier, such as disodium succinate or disodium glutarate, was added to the aqueous solution, the growth rates along the directions normal to the {0 0 1} and {1 1 4} faces were considerably inhibited. Thus, α-CSH crystals with a low aspect ratio were synthesized using a hydrothermal method. In addition, the calculation methodology used in this work could provide a powerful tool for selecting suitable crystal habit modifiers for preparing α-CSH and other inorganic crystals.

Impact of Surfactants on the Efficacy of Iron Oxide Dispersants

Surfactants form a unique class of compounds that are used in a variety of applications including laundry detergents, dish washing liquids, agrochemicals, pharmaceuticals, petroleum processing, mineral ores, personal care, floor cleaners, paints, coatings, fuel additives, and photographic films. In the present work a variety of surfactants containing different functional groups (i.e., anionic, non-ionic, amphoteric, cationic) has been used to study their influence on the performance of polymeric iron oxide dispersants. Effects of dispersant dosage, time, and polymer architecture have been investigated. The polymers tested include homopolymers of acrylic acid, maleic acid, methacrylic acid, 2-acrylamido-2-methylpropane sulfonic, 2-ethyloxazoline, and acrylic acid, maleic acid based copolymers containing different functional groups. It has been found that polymer performance as dispersant depends on dosage and polymer architecture. Results on the evaluation of surfactants suggest that compared to polymers, surfactants are ineffective iron oxide dispersants. Results on the impact of cationic surfactant (e.g., cetyltrimethyl ammonium chloride, CTAC) suggest that CTAC exhibits an antagonistic effect on the performance of polymers. It has also been found that cationic polymer (e.g., polydiallyldimethyl ammonium chloride) shows much stronger antagonistic effect than CTAC on the efficacy of polymers used as iron oxide dispersants in industrial water systems. The antagonistic behavior shown by cationic surfactant and cationic polymer on the performance of polymers has been explained in terms of cationic – anionic interactions.

Influence of Heat Treatment on the Performance of Polymers as Gypsum (CaSO4 · 2H2O) Scale Inhibitors for Industrial Water Applications

The inhibition of gypsum precipitation by homo-, co-, and terpolymers has been examined in aqueous solution. It has been found that polymer performance as gypsum inhibitor depends upon polymer composition, type of comonomer, and functional groups. Results on the evaluation of polymers suggest that compared to co- and terpolymers, homopolymers containing carboxyl group are effective gypsum inhibitors. The impact of heat treatment (150°C to 240°C) on the performance of various homo-, co-, and teropolymers as gypsum inhibitors has also been investigated. It has been observed that all polymers lose performance to a varying degree when exposed to thermal treatment. Performance data on co- and terpolymers containing amido group show improved performance after heat treatment suggesting the formation of carboxyl group. Scanning electron microscopic investigations of gypsum crystals grown in the presence of polymers show that structures of these crystals are highly modified.

Influence of Surfactants on the Performance of Calcium Phosphate Scale Inhibitors

The pH-stat technique was used to study the influence of various types of surfactants on the performance of polymers used as inhibitors for preventing the precipitation of calcium phosphate in industrial water systems. Four types of surfactants were evaluated: 1) anionic, 2) non-ionic, 3) amphoteric, and 4) cationic. The polymeric inhibitors studied include homo-, co-, and terpolymers containing different functional groups such as carboxylic acid, sulfonic acid, ester, and amide. It has been found that polymer dosage and polymer architecture play important roles in inhibiting calcium phosphate precipitation. The results on the evaluation of surfactants reveal that all surfactants are ineffective calcium phosphate inhibitors. Comparative inhibition data collected for various calcium phosphate inhibiting polymers in the presence surfactants containing different ionic charges are presented. Results are also discussed on the influence of cationic polymeric flocculant in preventing the precipitation of calcium phosphate by anionic polymeric inhibitors.

Effects of Organic Additives on Calcium Sulfate Scaling in Pipes

A comprehensive study of the effects of nine organic additives on the formation of calcium sulfate scale in a pipe system was conducted using a multiple pipe flow system. Several factors that influence the inhibitory capability of phosphonic and carboxylic additives such as their chemical structure, their concentration, and the run time were closely scrutinized. Results showed that the organic additives influence the deposition of calcium sulfate on the walls of a pipe flow system at various levels. The superiority of the phosphonic additives, especially N,N,N′,N′-ethylenediaminetetramethylenephosphonic acid (EDTP) and nitrilotrimethylenephosphonic acid (NTMP), to other organic compounds with respect to scale prevention is discussed thoroughly. For the first time, it was demonstrated that a solution with a given concentration of inhibitor that is continuously refreshed in a pipe reactor becomes less effective over time. The morphology of the scales formed in the presence of different additives is also studied, using scanning electron microscopy.

Dual roles of borax in kinetics of calcium sulfate dihydrate formation

An additive is not exclusively retardant or promoter for a crystallization system. The kinetic studies of calcium sulfate dihydrate (CSD) crystal growth demonstrated that borax played dual roles in the reaction, which accelerated CSD formations at the low concentration levels but inhibited the crystal growth at the high ones. In situ atomic force microscopy studies revealed that borax modulated the CSD crystallization via two different pathways: promoted the secondary nucleation to increase the step density on the growing crystal faces but simultaneously retarded the spread of these growth steps by the Langmuir adsorption. These two contradictory factors were incorporated in the crystallization, and their balance was regulated by the borax concentration. Both the macroscopic and microscopic experimental data nicely displayed the crystallization model of birth and spread that was able to account for the behaviors of borax in CSD formations.